diff --git a/CHANGELOG.md b/CHANGELOG.md
index 3e55e6edd..7ae93bd07 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -17,7 +17,7 @@ You can find and compare releases at the [GitHub release page](https://github.co
 - Use native PHP types for properties of `Type` and its subclasses
 - Throw `SerializationError` over client safe `Error` when failing to serialize leaf types
 - Move debug entries in errors under `extensions` key
-- Use native PHP types for `Schema` and `SchemaConfig`
+- Use native PHP types wherever possible
 - Always throw `RequestError` with useful message when clients provide an invalid JSON body
 - Move class `BlockString` from namespace `GraphQL\Utils` to `GraphQL\Language`
 - Return string-keyed arrays from `GraphQL::getStandardDirectives()`, `GraphQL::getStandardTypes()` and `GraphQL::getStandardValidationRules()`
@@ -32,6 +32,11 @@ You can find and compare releases at the [GitHub release page](https://github.co
 - Always convert recursively when calling `Node::toArray()`
 - Make `Directive::$config['args']` use the same definition style as `FieldDefinition::$config['args']`
 - Rename `FieldArgument` to `Argument`
+- Make errors when parsing scalar literals more precise
+- Change expected `QueryPlan` options from `['group-implementor-fields']` to `['groupImplementorFields' => true]` in `ResolveInfo::lookAhead()`
+- Always convert promises through `PromiseAdapter::convertThenable()` before calling `->then()` on them
+- Use `JSON_THROW_ON_ERROR` in `json_encode()`
+- Validate some internal invariants through `assert()`
 
 ### Added
 
@@ -97,6 +102,7 @@ You can find and compare releases at the [GitHub release page](https://github.co
 - Remove `ListOfType::$ofType`, `ListOfType::getOfType()` and `NonNull::getOfType()`
 - Remove option `commentDescriptions` from `BuildSchema::buildAST()`, `BuildSchema::build()` and `Printer::doPrint()`
 - Remove parameter `$options` from `ASTDefinitionBuilder`
+- Remove `FieldDefinition::create()` in favor of `new FieldDefinition()`
 
 ## 14.11.3
 
diff --git a/benchmarks/Utils/SchemaGenerator.php b/benchmarks/Utils/SchemaGenerator.php
index a9ef523b0..629d9d85c 100644
--- a/benchmarks/Utils/SchemaGenerator.php
+++ b/benchmarks/Utils/SchemaGenerator.php
@@ -89,7 +89,7 @@ protected function createType(int $nestingLevel, ?string $typeName = null): Obje
     }
 
     /**
-     * @return array{0: ObjectType, 1: string}
+     * @return array{0: Type, 1: string}
      */
     protected function getFieldTypeAndName(int $nestingLevel, int $fieldIndex): array
     {
diff --git a/composer.json b/composer.json
index 3ef64bc25..997150c7b 100644
--- a/composer.json
+++ b/composer.json
@@ -29,7 +29,8 @@
     "psr/http-message": "^1",
     "react/promise": "^2",
     "symfony/polyfill-php81": "^1.23",
-    "symfony/var-exporter": "^5.3"
+    "symfony/var-exporter": "^5.3",
+    "thecodingmachine/safe": "^1.3"
   },
   "suggest": {
     "psr/http-message": "To use standard GraphQL server",
diff --git a/docs/class-reference.md b/docs/class-reference.md
index 779a7b608..99ee51d0b 100644
--- a/docs/class-reference.md
+++ b/docs/class-reference.md
@@ -2346,7 +2346,7 @@ static function toArray(GraphQL\Language\AST\Node $node): array
  * | null          | NullValue            |
  *
  * @param Type|mixed|null                                     $value
- * @param ScalarType|EnumType|InputObjectType|ListOfType<Type &InputType>|NonNull $type
+ * @param ScalarType|EnumType|InputObjectType|ListOfType<Type&InputType>|NonNull $type
  *
  * @return ObjectValueNode|ListValueNode|BooleanValueNode|IntValueNode|FloatValueNode|EnumValueNode|StringValueNode|NullValueNode|null
  *
diff --git a/examples/00-hello-world/graphql.php b/examples/00-hello-world/graphql.php
index 89bcd82f4..8012d46f9 100644
--- a/examples/00-hello-world/graphql.php
+++ b/examples/00-hello-world/graphql.php
@@ -58,6 +58,10 @@
     ]);
 
     $rawInput = file_get_contents('php://input');
+    if (false === $rawInput) {
+        throw new RuntimeException('Failed to get php://input');
+    }
+
     $input = json_decode($rawInput, true);
     $query = $input['query'];
     $variableValues = $input['variables'] ?? null;
diff --git a/examples/01-blog/Blog/Type/NodeType.php b/examples/01-blog/Blog/Type/NodeType.php
index f1c41854b..b15716ef3 100644
--- a/examples/01-blog/Blog/Type/NodeType.php
+++ b/examples/01-blog/Blog/Type/NodeType.php
@@ -5,13 +5,13 @@
 namespace GraphQL\Examples\Blog\Type;
 
 use Exception;
-use function get_class;
 use GraphQL\Examples\Blog\Data\Image;
 use GraphQL\Examples\Blog\Data\Story;
 use GraphQL\Examples\Blog\Data\User;
 use GraphQL\Examples\Blog\Types;
 use GraphQL\Type\Definition\InterfaceType;
-use GraphQL\Type\Definition\Type;
+use GraphQL\Type\Definition\ObjectType;
+use GraphQL\Utils\Utils;
 
 class NodeType extends InterfaceType
 {
@@ -26,7 +26,12 @@ public function __construct()
         ]);
     }
 
-    public function resolveNodeType(object $object): Type
+    /**
+     * @param mixed $object
+     *
+     * @return callable(): ObjectType
+     */
+    public function resolveNodeType($object)
     {
         if ($object instanceof User) {
             return Types::user();
@@ -40,6 +45,6 @@ public function resolveNodeType(object $object): Type
             return Types::story();
         }
 
-        throw new Exception('Unknown type: ' . get_class($object));
+        throw new Exception('Unknown type: ' . Utils::printSafe($object));
     }
 }
diff --git a/examples/01-blog/Blog/Type/Scalar/UrlType.php b/examples/01-blog/Blog/Type/Scalar/UrlType.php
index 47bb4fe21..e3f7fa716 100644
--- a/examples/01-blog/Blog/Type/Scalar/UrlType.php
+++ b/examples/01-blog/Blog/Type/Scalar/UrlType.php
@@ -57,6 +57,6 @@ public function parseLiteral(Node $valueNode, ?array $variables = null): string
     private function isUrl($value): bool
     {
         return is_string($value)
-            && filter_var($value, FILTER_VALIDATE_URL);
+            && false !== filter_var($value, FILTER_VALIDATE_URL);
     }
 }
diff --git a/examples/01-blog/Blog/Types.php b/examples/01-blog/Blog/Types.php
index eed37fcf3..e356eabd6 100644
--- a/examples/01-blog/Blog/Types.php
+++ b/examples/01-blog/Blog/Types.php
@@ -4,7 +4,6 @@
 
 namespace GraphQL\Examples\Blog;
 
-use function class_exists;
 use Closure;
 use function count;
 use Exception;
@@ -94,6 +93,8 @@ public static function url(): callable
     }
 
     /**
+     * @param class-string<Type> $classname
+     *
      * @return Closure(): Type
      */
     private static function get(string $classname): Closure
@@ -101,28 +102,20 @@ private static function get(string $classname): Closure
         return static fn () => self::byClassName($classname);
     }
 
+    /**
+     * @param class-string<Type> $classname
+     */
     private static function byClassName(string $classname): Type
     {
         $parts = explode('\\', $classname);
 
         $cacheName = strtolower(preg_replace('~Type$~', '', $parts[count($parts) - 1]));
-        $type = null;
 
         if (! isset(self::$types[$cacheName])) {
-            if (class_exists($classname)) {
-                $type = new $classname();
-            }
-
-            self::$types[$cacheName] = $type;
+            return self::$types[$cacheName] = new $classname();
         }
 
-        $type = self::$types[$cacheName];
-
-        if (! $type) {
-            throw new Exception('Unknown graphql type: ' . $classname);
-        }
-
-        return $type;
+        return self::$types[$cacheName];
     }
 
     public static function byTypeName(string $shortName): Type
diff --git a/examples/02-schema-definition-language/graphql.php b/examples/02-schema-definition-language/graphql.php
index 10830e240..fe27e0ce2 100644
--- a/examples/02-schema-definition-language/graphql.php
+++ b/examples/02-schema-definition-language/graphql.php
@@ -33,6 +33,10 @@
     ];
 
     $rawInput = file_get_contents('php://input');
+    if (false === $rawInput) {
+        throw new RuntimeException('Failed to get php://input');
+    }
+
     $input = json_decode($rawInput, true);
     $query = $input['query'];
     $variableValues = $input['variables'] ?? null;
diff --git a/generate-class-reference.php b/generate-class-reference.php
index 390db6c84..121f88663 100644
--- a/generate-class-reference.php
+++ b/generate-class-reference.php
@@ -174,12 +174,9 @@ function renderProp(ReflectionProperty $prop): string
     return unpadDocblock($prop->getDocComment()) . "\n" . $signature;
 }
 
-/**
- * @param string|false $docBlock
- */
-function unwrapDocblock($docBlock): string
+function unwrapDocblock(string $docBlock): string
 {
-    if (! $docBlock) {
+    if ('' === $docBlock) {
         return '';
     }
 
@@ -196,7 +193,7 @@ function unwrapDocblock($docBlock): string
  */
 function unpadDocblock($docBlock): string
 {
-    if (! $docBlock) {
+    if (false === $docBlock) {
         return '';
     }
 
@@ -215,7 +212,7 @@ function unpadDocblock($docBlock): string
 function isApi(Reflector $reflector): bool
 {
     $comment = $reflector->getDocComment();
-    if (! $comment) {
+    if (false === $comment) {
         return false;
     }
 
diff --git a/phpstan-baseline.neon b/phpstan-baseline.neon
index ad0b5f557..c7c327430 100644
--- a/phpstan-baseline.neon
+++ b/phpstan-baseline.neon
@@ -45,11 +45,6 @@ parameters:
 			count: 1
 			path: examples/01-blog/Blog/Types.php
 
-		-
-			message: "#^Strict comparison using \\=\\=\\= between non\\-empty\\-string and null will always evaluate to false\\.$#"
-			count: 1
-			path: src/Error/Error.php
-
 		-
 			message: "#^SplObjectStorage\\<GraphQL\\\\Type\\\\Definition\\\\ObjectType, SplObjectStorage\\<ArrayObject\\<int, GraphQL\\\\Language\\\\AST\\\\FieldNode\\>, ArrayObject\\<string, ArrayObject\\<int, GraphQL\\\\Language\\\\AST\\\\FieldNode\\>\\>\\>\\> does not accept SplObjectStorage\\<ArrayObject\\<int, GraphQL\\\\Language\\\\AST\\\\FieldNode\\>, ArrayObject\\<string, ArrayObject\\<int, GraphQL\\\\Language\\\\AST\\\\FieldNode\\>\\>\\>\\|SplObjectStorage\\<object, mixed\\>\\.$#"
 			count: 1
@@ -76,8 +71,8 @@ parameters:
 			path: src/Language/AST/Node.php
 
 		-
-			message: "#^Array \\(array\\<array\\<string, mixed\\>\\|T of GraphQL\\\\Language\\\\AST\\\\Node\\>\\) does not accept GraphQL\\\\Language\\\\AST\\\\Node\\.$#"
-			count: 2
+			message: "#^Parameter \\#4 \\$replacement of function array_splice expects array\\|string, array\\<T of GraphQL\\\\Language\\\\AST\\\\Node\\>\\|T of GraphQL\\\\Language\\\\AST\\\\Node\\|null given\\.$#"
+			count: 1
 			path: src/Language/AST/NodeList.php
 
 		-
@@ -110,6 +105,16 @@ parameters:
 			count: 1
 			path: src/Language/Visitor.php
 
+		-
+			message: "#^Parameter \\#1 \\$config of class GraphQL\\\\Type\\\\Definition\\\\Argument constructor expects array\\{name\\: string, type\\: \\(callable\\(\\)\\: GraphQL\\\\Type\\\\Definition\\\\InputType&GraphQL\\\\Type\\\\Definition\\\\Type\\)\\|\\(GraphQL\\\\Type\\\\Definition\\\\InputType&GraphQL\\\\Type\\\\Definition\\\\Type\\), defaultValue\\?\\: mixed, description\\?\\: string\\|null, astNode\\?\\: GraphQL\\\\Language\\\\AST\\\\InputValueDefinitionNode\\|null\\}, non\\-empty\\-array given\\.$#"
+			count: 1
+			path: src/Type/Definition/Argument.php
+
+		-
+			message: "#^Parameter \\#1 \\$config of class GraphQL\\\\Type\\\\Definition\\\\EnumValueDefinition constructor expects array\\{name\\: string, value\\?\\: mixed, deprecationReason\\?\\: string\\|null, description\\?\\: string\\|null, astNode\\?\\: GraphQL\\\\Language\\\\AST\\\\EnumValueDefinitionNode\\|null\\}, array given\\.$#"
+			count: 1
+			path: src/Type/Definition/EnumType.php
+
 		-
 			message: "#^Method GraphQL\\\\Type\\\\Definition\\\\FieldDefinition\\:\\:getType\\(\\) should return GraphQL\\\\Type\\\\Definition\\\\OutputType&GraphQL\\\\Type\\\\Definition\\\\Type but returns GraphQL\\\\Type\\\\Definition\\\\Type\\.$#"
 			count: 1
@@ -120,6 +125,11 @@ parameters:
 			count: 1
 			path: src/Type/Definition/FieldDefinition.php
 
+		-
+			message: "#^Method GraphQL\\\\Type\\\\Definition\\\\NonNull\\:\\:getWrappedType\\(\\) should return GraphQL\\\\Type\\\\Definition\\\\NullableType&GraphQL\\\\Type\\\\Definition\\\\Type but returns GraphQL\\\\Type\\\\Definition\\\\Type\\.$#"
+			count: 1
+			path: src/Type/Definition/NonNull.php
+
 		-
 			message: "#^Array \\(array\\<string, GraphQL\\\\Type\\\\Definition\\\\NamedType&GraphQL\\\\Type\\\\Definition\\\\Type\\>\\) does not accept GraphQL\\\\Type\\\\Definition\\\\Type\\.$#"
 			count: 1
@@ -161,19 +171,14 @@ parameters:
 			path: src/Validator/Rules/KnownDirectives.php
 
 		-
-			message: "#^SplObjectStorage\\<GraphQL\\\\Language\\\\AST\\\\SelectionSetNode, array\\{array\\<string, array\\<int, array\\{GraphQL\\\\Type\\\\Definition\\\\Type, GraphQL\\\\Language\\\\AST\\\\FieldNode, GraphQL\\\\Type\\\\Definition\\\\FieldDefinition\\|null\\}\\>\\>, array\\<int, string\\>\\}\\> does not accept array\\<int, mixed\\>\\.$#"
+			message: "#^Method GraphQL\\\\Validator\\\\Rules\\\\OverlappingFieldsCanBeMerged\\:\\:getFieldsAndFragmentNames\\(\\) should return array\\{array\\<string, array\\<int, array\\{GraphQL\\\\Type\\\\Definition\\\\Type, GraphQL\\\\Language\\\\AST\\\\FieldNode, GraphQL\\\\Type\\\\Definition\\\\FieldDefinition\\|null\\}\\>\\>, array\\<int, string\\>\\} but returns array\\{mixed, array\\<int, int\\|string\\>\\}\\.$#"
 			count: 1
 			path: src/Validator/Rules/OverlappingFieldsCanBeMerged.php
 
 		-
-			message: "#^Call to static method PHPUnit\\\\Framework\\\\Assert\\:\\:assertArrayHasKey\\(\\) with int\\|string and GraphQL\\\\Language\\\\AST\\\\NodeList will always evaluate to false\\.$#"
-			count: 1
-			path: tests/Language/VisitorTest.php
-
-		-
-			message: "#^Instanceof between mixed and GraphQL\\\\Language\\\\AST\\\\NodeList will always evaluate to false\\.$#"
+			message: "#^SplObjectStorage\\<GraphQL\\\\Language\\\\AST\\\\SelectionSetNode, array\\{array\\<string, array\\<int, array\\{GraphQL\\\\Type\\\\Definition\\\\Type, GraphQL\\\\Language\\\\AST\\\\FieldNode, GraphQL\\\\Type\\\\Definition\\\\FieldDefinition\\|null\\}\\>\\>, array\\<int, string\\>\\}\\> does not accept array\\<int, mixed\\>\\.$#"
 			count: 1
-			path: tests/Language/VisitorTest.php
+			path: src/Validator/Rules/OverlappingFieldsCanBeMerged.php
 
 		-
 			message: "#^Method GraphQL\\\\Tests\\\\Language\\\\VisitorTest\\:\\:getNodeByPath\\(\\) return type with generic class GraphQL\\\\Language\\\\AST\\\\NodeList does not specify its types\\: T$#"
diff --git a/phpstan.neon.dist b/phpstan.neon.dist
index 4588c7be7..0f5faf216 100644
--- a/phpstan.neon.dist
+++ b/phpstan.neon.dist
@@ -1,9 +1,6 @@
 parameters:
     # TODO increase to max
-    level: 6
-
-    # TODO revert this setting once we arrived at level: max
-    reportUnmatchedIgnoredErrors: false
+    level: 7
 
     paths:
         - benchmarks
@@ -22,7 +19,6 @@ parameters:
         - "~Variable method call on GraphQL\\\\Language\\\\Parser\\.~"
 
         # We utilize lazy initialization of non-nullable properties
-        - "~Property .+? in isset\\(\\) is not nullable~"
         - "~Property .+? on left side of \\?\\?= is not nullable~"
 
         # Useful/necessary in the default field resolver, deals with arbitrary user data
@@ -45,14 +41,18 @@ includes:
 
 services:
     -
-        class: GraphQL\Tests\PhpStan\Type\Definition\Type\IsInputTypeStaticMethodTypeSpecifyingExtension
+        class: GraphQL\Tests\PhpStan\Type\Definition\Type\IsAbstractTypeStaticMethodTypeSpecifyingExtension
         tags:
             - phpstan.typeSpecifier.staticMethodTypeSpecifyingExtension
     -
-        class: GraphQL\Tests\PhpStan\Type\Definition\Type\IsOutputTypeStaticMethodTypeSpecifyingExtension
+        class: GraphQL\Tests\PhpStan\Type\Definition\Type\IsCompositeTypeStaticMethodTypeSpecifyingExtension
         tags:
             - phpstan.typeSpecifier.staticMethodTypeSpecifyingExtension
     -
-        class: GraphQL\Tests\PhpStan\Type\Definition\Type\IsCompositeTypeStaticMethodTypeSpecifyingExtension
+        class: GraphQL\Tests\PhpStan\Type\Definition\Type\IsInputTypeStaticMethodTypeSpecifyingExtension
+        tags:
+            - phpstan.typeSpecifier.staticMethodTypeSpecifyingExtension
+    -
+        class: GraphQL\Tests\PhpStan\Type\Definition\Type\IsOutputTypeStaticMethodTypeSpecifyingExtension
         tags:
             - phpstan.typeSpecifier.staticMethodTypeSpecifyingExtension
diff --git a/src/Deferred.php b/src/Deferred.php
index fe406f6df..b4f812879 100644
--- a/src/Deferred.php
+++ b/src/Deferred.php
@@ -6,10 +6,13 @@
 
 use GraphQL\Executor\Promise\Adapter\SyncPromise;
 
+/**
+ * @phpstan-import-type Executor from SyncPromise
+ */
 class Deferred extends SyncPromise
 {
     /**
-     * @param callable() : mixed $executor
+     * @param Executor $executor
      */
     public static function create(callable $executor): self
     {
@@ -17,7 +20,7 @@ public static function create(callable $executor): self
     }
 
     /**
-     * @param callable() : mixed $executor
+     * @param Executor $executor
      */
     public function __construct(callable $executor)
     {
diff --git a/src/Error/Error.php b/src/Error/Error.php
index ca556875a..61ab12173 100644
--- a/src/Error/Error.php
+++ b/src/Error/Error.php
@@ -71,7 +71,7 @@ class Error extends Exception implements JsonSerializable, ClientAware, Provides
     protected ?array $extensions;
 
     /**
-     * @param iterable<array-key, Node>|Node|null $nodes
+     * @param iterable<array-key, Node|null>|Node|null $nodes
      * @param array<int, int>|null                $positions
      * @param array<int, int|string>|null         $path
      * @param array<string, mixed>|null           $extensions
@@ -89,9 +89,9 @@ public function __construct(
 
         // Compute list of blame nodes.
         if ($nodes instanceof Traversable) {
-            $this->nodes = iterator_to_array($nodes);
+            $this->nodes = array_filter(iterator_to_array($nodes));
         } elseif (is_array($nodes)) {
-            $this->nodes = $nodes;
+            $this->nodes = array_filter($nodes);
         } elseif (null !== $nodes) {
             $this->nodes = [$nodes];
         } else {
@@ -160,7 +160,7 @@ public static function createLocatedError($error, $nodes = null, ?array $path =
             $message = (string) $error;
         }
 
-        $nonEmptyMessage = '' === $message || null === $message
+        $nonEmptyMessage = '' === $message
             ? 'An unknown error occurred.'
             : $message;
 
diff --git a/src/Error/FormattedError.php b/src/Error/FormattedError.php
index 8d3e07dae..9b5e48bb2 100644
--- a/src/Error/FormattedError.php
+++ b/src/Error/FormattedError.php
@@ -6,7 +6,6 @@
 
 use function addcslashes;
 use function array_filter;
-use function array_intersect_key;
 use function array_map;
 use function array_merge;
 use function array_shift;
@@ -16,7 +15,6 @@
 use function get_class;
 use function gettype;
 use GraphQL\Executor\ExecutionResult;
-use GraphQL\Language\AST\Node;
 use GraphQL\Language\Source;
 use GraphQL\Language\SourceLocation;
 use GraphQL\Type\Definition\Type;
@@ -37,12 +35,7 @@
  * It converts PHP exceptions to [spec-compliant errors](https://facebook.github.io/graphql/#sec-Errors)
  * and provides tools for error debugging.
  *
- * @phpstan-type FormattedErrorArray array{
- *   message: string,
- *   locations?: array<int, array{line: int, column: int}>,
- *   path?: array<int, int|string>,
- *   extensions?: array<string, mixed>,
- * }
+ * @phpstan-import-type SerializableError from ExecutionResult
  * @phpstan-import-type ErrorFormatter from ExecutionResult
  */
 class FormattedError
@@ -67,20 +60,19 @@ public static function setInternalErrorMessage(string $msg): void
     public static function printError(Error $error): string
     {
         $printedLocations = [];
-        if (0 !== count($error->nodes ?? [])) {
-            /** @var Node $node */
-            foreach ($error->nodes as $node) {
-                if (null === $node->loc) {
-                    continue;
-                }
 
-                if (null === $node->loc->source) {
+        $nodes = $error->nodes;
+        if (isset($nodes) && count($nodes) > 0) {
+            foreach ($nodes as $node) {
+                if (! isset($node->loc->source)) {
                     continue;
                 }
 
+                $location = $node->loc;
+                $source = $location->source;
                 $printedLocations[] = self::highlightSourceAtLocation(
-                    $node->loc->source,
-                    $node->loc->source->getLocation($node->loc->start)
+                    $source,
+                    $source->getLocation($location->start)
                 );
             }
         } elseif (null !== $error->getSource() && 0 !== count($error->getLocations())) {
@@ -110,7 +102,9 @@ private static function highlightSourceAtLocation(Source $source, SourceLocation
         $lineNum = (string) $contextLine;
         $nextLineNum = (string) ($contextLine + 1);
         $padLen = strlen($nextLineNum);
+
         $lines = preg_split('/\r\n|[\n\r]/', $source->body);
+        assert(is_array($lines), 'given the regex is valid');
 
         $lines[0] = self::whitespace($source->locationOffset->column - 1) . $lines[0];
 
@@ -150,7 +144,7 @@ private static function lpad(int $len, string $str): string
      *
      * For a list of available debug flags @see \GraphQL\Error\DebugFlag constants.
      *
-     * @return FormattedErrorArray
+     * @return SerializableError
      *
      * @api
      */
@@ -195,10 +189,10 @@ public static function createFromException(Throwable $exception, int $debugFlag
     /**
      * Decorates spec-compliant $formattedError with debug entries according to $debug flags.
      *
-     * @param int                 $debugFlag      For available flags @see \GraphQL\Error\DebugFlag
-     * @param FormattedErrorArray $formattedError
+     * @param SerializableError $formattedError
+     * @param int $debugFlag For available flags @see \GraphQL\Error\DebugFlag
      *
-     * @return FormattedErrorArray
+     * @return SerializableError
      */
     public static function addDebugEntries(array $formattedError, Throwable $e, int $debugFlag): array
     {
@@ -264,8 +258,8 @@ public static function prepareFormatter(?callable $formatter, int $debug): calla
      * Returns error trace as serializable array.
      *
      * @return array<int, array{
-     *     file: string,
-     *     line: int,
+     *     file?: string,
+     *     line?: int,
      *     function?: string,
      *     call?: string,
      * }>
@@ -287,26 +281,34 @@ public static function toSafeTrace(Throwable $error): array
             array_shift($trace);
         }
 
-        return array_map(
-            static function (array $err): array {
-                $safeErr = array_intersect_key($err, ['file' => true, 'line' => true]);
+        $formatted = [];
+        foreach ($trace as $err) {
+            $safeErr = [];
+
+            if (isset($err['file'])) {
+                $safeErr['file'] = $err['file'];
+            }
+
+            if (isset($err['line'])) {
+                $safeErr['line'] = $err['line'];
+            }
 
-                if (isset($err['function'])) {
-                    $func = $err['function'];
-                    $args = array_map([self::class, 'printVar'], $err['args'] ?? []);
-                    $funcStr = $func . '(' . implode(', ', $args) . ')';
+            if (isset($err['function'])) {
+                $func = $err['function'];
+                $args = array_map([self::class, 'printVar'], $err['args'] ?? []);
+                $funcStr = $func . '(' . implode(', ', $args) . ')';
 
-                    if (isset($err['class'])) {
-                        $safeErr['call'] = $err['class'] . '::' . $funcStr;
-                    } else {
-                        $safeErr['function'] = $funcStr;
-                    }
+                if (isset($err['class'])) {
+                    $safeErr['call'] = $err['class'] . '::' . $funcStr;
+                } else {
+                    $safeErr['function'] = $funcStr;
                 }
+            }
+
+            $formatted[] = $safeErr;
+        }
 
-                return $safeErr;
-            },
-            $trace
-        );
+        return $formatted;
     }
 
     /**
diff --git a/src/Error/UserError.php b/src/Error/UserError.php
index d9aefbb55..286112531 100644
--- a/src/Error/UserError.php
+++ b/src/Error/UserError.php
@@ -7,7 +7,7 @@
 use RuntimeException;
 
 /**
- * Error caused by actions of GraphQL clients. Can be safely displayed to a client...
+ * Caused by GraphQL clients and can safely be displayed.
  */
 class UserError extends RuntimeException implements ClientAware
 {
diff --git a/src/Executor/ExecutionContext.php b/src/Executor/ExecutionContext.php
index db45bb7a8..658537739 100644
--- a/src/Executor/ExecutionContext.php
+++ b/src/Executor/ExecutionContext.php
@@ -36,7 +36,10 @@ class ExecutionContext
     /** @var array<string, mixed> */
     public array $variableValues;
 
-    /** @var FieldResolver */
+    /**
+     * @var callable
+     * @phpstan-var FieldResolver
+     */
     public $fieldResolver;
 
     /** @var array<int, Error> */
diff --git a/src/Executor/ExecutionResult.php b/src/Executor/ExecutionResult.php
index cd918de08..74039907a 100644
--- a/src/Executor/ExecutionResult.php
+++ b/src/Executor/ExecutionResult.php
@@ -21,7 +21,12 @@
  * Could be converted to [spec-compliant](https://facebook.github.io/graphql/#sec-Response-Format)
  * serializable array using `toArray()`.
  *
- * @phpstan-type SerializableError array<string, mixed>
+ * @phpstan-type SerializableError array{
+ *   message: string,
+ *   locations?: array<int, array{line: int, column: int}>,
+ *   path?: array<int, int|string>,
+ *   extensions?: array<string, mixed>,
+ * }
  * @phpstan-type SerializableErrors array<int, SerializableError>
  * @phpstan-type SerializableResult array{
  *     data?: array<string, mixed>,
diff --git a/src/Executor/Executor.php b/src/Executor/Executor.php
index f1ea8ab96..352b36081 100644
--- a/src/Executor/Executor.php
+++ b/src/Executor/Executor.php
@@ -19,16 +19,22 @@
  * Implements the "Evaluating requests" section of the GraphQL specification.
  *
  * @phpstan-type FieldResolver callable(mixed, array<string, mixed>, mixed, ResolveInfo): mixed
- * @phpstan-type ImplementationFactory callable(PromiseAdapter, Schema, DocumentNode, mixed=, mixed=, ?array<mixed>=, ?string=, ?callable=): ExecutorImplementation
+ * @phpstan-type ImplementationFactory callable(PromiseAdapter, Schema, DocumentNode, mixed, mixed, array<mixed>, ?string, callable): ExecutorImplementation
  */
 class Executor
 {
-    /** @var FieldResolver */
+    /**
+     * @var callable
+     * @phpstan-var FieldResolver
+     */
     private static $defaultFieldResolver = [self::class, 'defaultFieldResolver'];
 
     private static ?PromiseAdapter $defaultPromiseAdapter;
 
-    /** @var ImplementationFactory */
+    /**
+     * @var callable
+     * @phpstan-var ImplementationFactory
+     */
     private static $implementationFactory = [ReferenceExecutor::class, 'create'];
 
     /**
@@ -91,8 +97,6 @@ public static function setImplementationFactory(callable $implementationFactory)
      * @param array<string, mixed>|null $variableValues
      * @phpstan-param FieldResolver|null $fieldResolver
      *
-     * @return ExecutionResult|array<ExecutionResult>
-     *
      * @api
      */
     public static function execute(
@@ -103,7 +107,7 @@ public static function execute(
         ?array $variableValues = null,
         ?string $operationName = null,
         ?callable $fieldResolver = null
-    ) {
+    ): ExecutionResult {
         $promiseAdapter = new SyncPromiseAdapter();
 
         $result = static::promiseToExecute(
@@ -143,7 +147,6 @@ public static function promiseToExecute(
         ?string $operationName = null,
         ?callable $fieldResolver = null
     ): Promise {
-        /** @var ExecutorImplementation $executor */
         $executor = (self::$implementationFactory)(
             $promiseAdapter,
             $schema,
diff --git a/src/Executor/Promise/Adapter/AmpPromiseAdapter.php b/src/Executor/Promise/Adapter/AmpPromiseAdapter.php
index 44f3abd94..6d621e0ec 100644
--- a/src/Executor/Promise/Adapter/AmpPromiseAdapter.php
+++ b/src/Executor/Promise/Adapter/AmpPromiseAdapter.php
@@ -41,8 +41,9 @@ public function then(Promise $promise, ?callable $onFulfilled = null, ?callable
             }
         };
 
-        /** @var AmpPromise<mixed> $adoptedPromise */
         $adoptedPromise = $promise->adoptedPromise;
+        assert($adoptedPromise instanceof AmpPromise);
+
         $adoptedPromise->onResolve($onResolve);
 
         return new Promise($deferred->promise(), $this);
@@ -84,7 +85,9 @@ public function all(array $promisesOrValues): Promise
         $promises = [];
         foreach ($promisesOrValues as $key => $item) {
             if ($item instanceof Promise) {
-                $promises[$key] = $item->adoptedPromise;
+                $ampPromise = $item->adoptedPromise;
+                assert($ampPromise instanceof AmpPromise);
+                $promises[$key] = $ampPromise;
             } elseif ($item instanceof AmpPromise) {
                 $promises[$key] = $item;
             }
@@ -108,12 +111,12 @@ public function all(array $promisesOrValues): Promise
     }
 
     /**
-     * @param Deferred<TResult>            $deferred
-     * @param callable(TArgument): TResult $callback
-     * @param TArgument                    $argument
-     *
      * @template TArgument
      * @template TResult
+     *
+     * @param Deferred<TResult> $deferred
+     * @param callable(TArgument): TResult $callback
+     * @param TArgument $argument
      */
     private static function resolveWithCallable(Deferred $deferred, callable $callback, $argument): void
     {
@@ -126,6 +129,7 @@ private static function resolveWithCallable(Deferred $deferred, callable $callba
         }
 
         if ($result instanceof Promise) {
+            /** @var TResult $result */
             $result = $result->adoptedPromise;
         }
 
diff --git a/src/Executor/Promise/Adapter/ReactPromiseAdapter.php b/src/Executor/Promise/Adapter/ReactPromiseAdapter.php
index 888d9608b..8bdce962b 100644
--- a/src/Executor/Promise/Adapter/ReactPromiseAdapter.php
+++ b/src/Executor/Promise/Adapter/ReactPromiseAdapter.php
@@ -27,8 +27,8 @@ public function convertThenable($thenable): Promise
 
     public function then(Promise $promise, ?callable $onFulfilled = null, ?callable $onRejected = null): Promise
     {
-        /** @var ReactPromiseInterface $adoptedPromise */
         $adoptedPromise = $promise->adoptedPromise;
+        assert($adoptedPromise instanceof ReactPromiseInterface);
 
         return new Promise($adoptedPromise->then($onFulfilled, $onRejected), $this);
     }
diff --git a/src/Executor/Promise/Adapter/SyncPromise.php b/src/Executor/Promise/Adapter/SyncPromise.php
index 5dfd3c131..869171a17 100644
--- a/src/Executor/Promise/Adapter/SyncPromise.php
+++ b/src/Executor/Promise/Adapter/SyncPromise.php
@@ -22,6 +22,8 @@
  * Root SyncPromise without explicit $executor will never resolve (actually throw while trying).
  * The whole point of Deferred is to ensure it never happens and that any resolver creates
  * at least one $executor to start the promise chain.
+ *
+ * @phpstan-type Executor callable(): mixed
  */
 class SyncPromise
 {
@@ -58,7 +60,7 @@ public static function runQueue(): void
     }
 
     /**
-     * @param (callable(): mixed)|null $executor
+     * @param Executor|null $executor
      */
     public function __construct(?callable $executor = null)
     {
@@ -146,7 +148,6 @@ private function enqueueWaitingPromises(): void
 
         foreach ($this->waiting as $descriptor) {
             self::getQueue()->enqueue(function () use ($descriptor): void {
-                /** @var self $promise */
                 [$promise, $onFulfilled, $onRejected] = $descriptor;
 
                 if (self::FULFILLED === $this->state) {
@@ -183,7 +184,7 @@ public static function getQueue(): SplQueue
     }
 
     /**
-     * @param (callable(mixed): mixed)|null     $onFulfilled
+     * @param (callable(mixed): mixed)|null $onFulfilled
      * @param (callable(Throwable): mixed)|null $onRejected
      */
     public function then(?callable $onFulfilled = null, ?callable $onRejected = null): self
@@ -207,7 +208,7 @@ public function then(?callable $onFulfilled = null, ?callable $onRejected = null
     }
 
     /**
-     * @param callable(Throwable) : mixed $onRejected
+     * @param callable(Throwable): mixed $onRejected
      */
     public function catch(callable $onRejected): self
     {
diff --git a/src/Executor/Promise/Adapter/SyncPromiseAdapter.php b/src/Executor/Promise/Adapter/SyncPromiseAdapter.php
index 41d23ed14..33fd5f37f 100644
--- a/src/Executor/Promise/Adapter/SyncPromiseAdapter.php
+++ b/src/Executor/Promise/Adapter/SyncPromiseAdapter.php
@@ -38,8 +38,8 @@ public function convertThenable($thenable): Promise
 
     public function then(Promise $promise, ?callable $onFulfilled = null, ?callable $onRejected = null): Promise
     {
-        /** @var SyncPromise $adoptedPromise */
         $adoptedPromise = $promise->adoptedPromise;
+        assert($adoptedPromise instanceof SyncPromise);
 
         return new Promise($adoptedPromise->then($onFulfilled, $onRejected), $this);
     }
@@ -120,17 +120,17 @@ public function wait(Promise $promise)
         $this->beforeWait($promise);
         $taskQueue = SyncPromise::getQueue();
 
+        $syncPromise = $promise->adoptedPromise;
+        assert($syncPromise instanceof SyncPromise);
+
         while (
-            SyncPromise::PENDING === $promise->adoptedPromise->state
+            SyncPromise::PENDING === $syncPromise->state
             && ! $taskQueue->isEmpty()
         ) {
             SyncPromise::runQueue();
             $this->onWait($promise);
         }
 
-        /** @var SyncPromise $syncPromise */
-        $syncPromise = $promise->adoptedPromise;
-
         if (SyncPromise::FULFILLED === $syncPromise->state) {
             return $syncPromise->result;
         }
diff --git a/src/Executor/Promise/PromiseAdapter.php b/src/Executor/Promise/PromiseAdapter.php
index 76cf789dd..dc0c92cbe 100644
--- a/src/Executor/Promise/PromiseAdapter.php
+++ b/src/Executor/Promise/PromiseAdapter.php
@@ -23,7 +23,7 @@ public function isThenable($value): bool;
     /**
      * Converts thenable of the underlying platform into GraphQL\Executor\Promise\Promise instance.
      *
-     * @param object $thenable
+     * @param mixed $thenable
      *
      * @api
      */
diff --git a/src/Executor/ReferenceExecutor.php b/src/Executor/ReferenceExecutor.php
index 1376c5840..a2f812124 100644
--- a/src/Executor/ReferenceExecutor.php
+++ b/src/Executor/ReferenceExecutor.php
@@ -39,7 +39,6 @@
 use GraphQL\Type\Definition\OutputType;
 use GraphQL\Type\Definition\ResolveInfo;
 use GraphQL\Type\Definition\Type;
-use GraphQL\Type\Definition\UnionType;
 use GraphQL\Type\Introspection;
 use GraphQL\Type\Schema;
 use GraphQL\Utils\TypeInfo;
@@ -56,7 +55,6 @@
 
 /**
  * @phpstan-import-type FieldResolver from Executor
- * @phpstan-import-type AbstractTypeAlias from AbstractType
  * @phpstan-type Fields ArrayObject<string, ArrayObject<int, FieldNode>>
  */
 class ReferenceExecutor implements ExecutorImplementation
@@ -90,8 +88,8 @@ protected function __construct(ExecutionContext $context)
     }
 
     /**
-     * @param mixed                $rootValue
-     * @param mixed                $contextValue
+     * @param mixed $rootValue
+     * @param mixed $contextValue
      * @param array<string, mixed> $variableValues
      * @phpstan-param FieldResolver $fieldResolver
      */
@@ -249,22 +247,30 @@ public function doExecute(): Promise
 
         // Note: we deviate here from the reference implementation a bit by always returning promise
         // But for the "sync" case it is always fulfilled
-        return $this->isPromise($result)
-            ? $result
-            : $this->exeContext->promiseAdapter->createFulfilled($result);
+
+        $promise = $this->getPromise($result);
+        if (null !== $promise) {
+            return $promise;
+        }
+
+        return $this->exeContext->promiseAdapter->createFulfilled($result);
     }
 
     /**
-     * @param mixed|Promise|null $data
+     * @param mixed $data
      *
      * @return ExecutionResult|Promise
      */
     protected function buildResponse($data)
     {
-        if ($this->isPromise($data)) {
-            return $data->then(function ($resolved) {
-                return $this->buildResponse($resolved);
-            });
+        if ($data instanceof Promise) {
+            return $data->then(fn ($resolved) => $this->buildResponse($resolved));
+        }
+
+        $promiseAdapter = $this->exeContext->promiseAdapter;
+        if ($promiseAdapter->isThenable($data)) {
+            return $promiseAdapter->convertThenable($data)
+                ->then(fn ($resolved) => $this->buildResponse($resolved));
         }
 
         if (null !== $data) {
@@ -295,19 +301,10 @@ protected function executeOperation(OperationDefinitionNode $operation, $rootVal
             $result = 'mutation' === $operation->operation
                 ? $this->executeFieldsSerially($type, $rootValue, $path, $fields)
                 : $this->executeFields($type, $rootValue, $path, $fields);
-            if ($this->isPromise($result)) {
-                return $result->then(
-                    null,
-                    function ($error): ?Promise {
-                        if ($error instanceof Error) {
-                            $this->exeContext->addError($error);
-
-                            return $this->exeContext->promiseAdapter->createFulfilled(null);
-                        }
 
-                        return null;
-                    }
-                );
+            $promise = $this->getPromise($result);
+            if (null !== $promise) {
+                return $promise->then(null, [$this, 'onError']);
             }
 
             return $result;
@@ -318,6 +315,20 @@ function ($error): ?Promise {
         }
     }
 
+    /**
+     * @param mixed $error
+     */
+    public function onError($error): ?Promise
+    {
+        if ($error instanceof Error) {
+            $this->exeContext->addError($error);
+
+            return $this->exeContext->promiseAdapter->createFulfilled(null);
+        }
+
+        return null;
+    }
+
     /**
      * Extracts the root type of the operation from the schema.
      *
@@ -543,10 +554,11 @@ function ($results, $responseName) use ($path, $parentType, $rootValue, $fields)
             []
         );
 
-        if ($this->isPromise($result)) {
-            return $result->then(static function ($resolvedResults) {
-                return static::fixResultsIfEmptyArray($resolvedResults);
-            });
+        $promise = $this->getPromise($result);
+        if (null !== $promise) {
+            return $result->then(
+                static fn ($resolvedResults) => static::fixResultsIfEmptyArray($resolvedResults)
+            );
         }
 
         return static::fixResultsIfEmptyArray($result);
@@ -771,7 +783,7 @@ protected function handleFieldError($rawError, ArrayObject $fieldNodes, array $p
      * definition.
      *
      * If the field is an abstract type, determine the runtime type of the value
-     * and then complete based on that type
+     * and then complete based on that type.
      *
      * Otherwise, the field type expects a sub-selection set, and will complete the
      * value by evaluating all sub-selections.
@@ -831,7 +843,7 @@ protected function completeValue(
             return $this->completeListValue($returnType, $fieldNodes, $info, $path, $result);
         }
 
-        /** @var Type&NamedType $returnType wrapping types returned early */
+        assert($returnType instanceof NamedType, 'Wrapping types should return early');
 
         // Account for invalid schema definition when typeLoader returns different
         // instance than `resolveType` or $field->getType() or $arg->getType()
@@ -885,8 +897,9 @@ protected function getPromise($value): ?Promise
             return $value;
         }
 
-        if ($this->exeContext->promiseAdapter->isThenable($value)) {
-            return $this->exeContext->promiseAdapter->convertThenable($value);
+        $promiseAdapter = $this->exeContext->promiseAdapter;
+        if ($promiseAdapter->isThenable($value)) {
+            return $promiseAdapter->convertThenable($value);
         }
 
         return null;
@@ -925,10 +938,10 @@ function ($previous, $value) use ($callback) {
     /**
      * Complete a list value by completing each item in the list with the inner type.
      *
-     * @param ListOfType<Type             &OutputType> $returnType
+     * @param ListOfType<Type&OutputType> $returnType
      * @param ArrayObject<int, FieldNode> $fieldNodes
-     * @param list<string|int>            $path
-     * @param iterable<mixed>             $results
+     * @param list<string|int> $path
+     * @param iterable<mixed> $results
      *
      * @throws Exception
      *
@@ -990,10 +1003,10 @@ protected function completeLeafValue(LeafType $returnType, &$result)
      * Complete a value of an abstract type by determining the runtime object type
      * of that value, then complete the value for that type.
      *
+     * @param AbstractType&Type $returnType
      * @param ArrayObject<int, FieldNode> $fieldNodes
-     * @param array<string|int>           $path
-     * @param array<mixed>                $result
-     * @phpstan-param AbstractTypeAlias $returnType
+     * @param array<string|int> $path
+     * @param array<mixed> $result
      *
      * @throws Error
      *
@@ -1012,7 +1025,7 @@ protected function completeAbstractValue(
         if (null === $typeCandidate) {
             $runtimeType = static::defaultTypeResolver($result, $exeContext->contextValue, $info, $returnType);
         } elseif (is_callable($typeCandidate)) {
-            $runtimeType = Schema::resolveType($typeCandidate);
+            $runtimeType = $typeCandidate();
         } else {
             $runtimeType = $typeCandidate;
         }
@@ -1065,9 +1078,9 @@ protected function completeAbstractValue(
      * Otherwise, test each possible type for the abstract type by calling
      * isTypeOf for the object being coerced, returning the first type that matches.
      *
-     * @param mixed|null        $value
-     * @param mixed|null        $contextValue
-     * @param AbstractTypeAlias $abstractType
+     * @param mixed|null $value
+     * @param mixed|null $contextValue
+     * @param AbstractType&Type $abstractType
      *
      * @return Promise|Type|string|null
      */
@@ -1109,13 +1122,14 @@ protected function defaultTypeResolver($value, $contextValue, ResolveInfo $info,
             $promise = $this->getPromise($isTypeOfResult);
             if (null !== $promise) {
                 $promisedIsTypeOfResults[$index] = $promise;
-            } elseif ($isTypeOfResult) {
+            } elseif (true === $isTypeOfResult) {
                 return $type;
             }
         }
 
         if (count($promisedIsTypeOfResults) > 0) {
-            return $this->exeContext->promiseAdapter->all($promisedIsTypeOfResults)
+            return $this->exeContext->promiseAdapter
+                ->all($promisedIsTypeOfResults)
                 ->then(static function ($isTypeOfResults) use ($possibleTypes): ?ObjectType {
                     foreach ($isTypeOfResults as $index => $result) {
                         if ($result) {
@@ -1174,6 +1188,7 @@ protected function completeObjectValue(
                 });
             }
 
+            assert(is_bool($isTypeOf), 'Promise would return early');
             if (! $isTypeOf) {
                 throw $this->invalidReturnTypeError($returnType, $result, $fieldNodes);
             }
@@ -1338,9 +1353,9 @@ protected function promiseForAssocArray(array $assoc): Promise
     }
 
     /**
-     * @param string|ObjectType|null  $runtimeTypeOrName
-     * @param InterfaceType|UnionType $returnType
-     * @param mixed                   $result
+     * @param mixed $runtimeTypeOrName
+     * @param AbstractType&Type $returnType
+     * @param mixed $result
      */
     protected function ensureValidRuntimeType(
         $runtimeTypeOrName,
@@ -1352,48 +1367,29 @@ protected function ensureValidRuntimeType(
             ? $this->exeContext->schema->getType($runtimeTypeOrName)
             : $runtimeTypeOrName;
         if (! $runtimeType instanceof ObjectType) {
+            $safeResult = Utils::printSafe($result);
+            $notObjectType = Utils::printSafe($runtimeType);
+
             throw new InvariantViolation(
-                sprintf(
-                    'Abstract type %s must resolve to an Object type at '
-                    . 'runtime for field %s.%s with value "%s", received "%s". '
-                    . 'Either the %s type should provide a "resolveType" '
-                    . 'function or each possible type should provide an "isTypeOf" function.',
-                    $returnType,
-                    $info->parentType,
-                    $info->fieldName,
-                    Utils::printSafe($result),
-                    Utils::printSafe($runtimeType),
-                    $returnType
-                )
+                "Abstract type {$returnType} must resolve to an Object type at runtime for field {$info->parentType}.{$info->fieldName} with value \"{$safeResult}\", received \"{$notObjectType}\". Either the {$returnType} type should provide a \"resolveType\" function or each possible type should provide an \"isTypeOf\" function."
             );
         }
 
         if (! $this->exeContext->schema->isSubType($returnType, $runtimeType)) {
             throw new InvariantViolation(
-                sprintf('Runtime Object type "%s" is not a possible type for "%s".', $runtimeType, $returnType)
+                "Runtime Object type \"{$runtimeType}\" is not a possible type for \"{$returnType}\"."
             );
         }
 
         if (null === $this->exeContext->schema->getType($runtimeType->name)) {
             throw new InvariantViolation(
-                'Schema does not contain type "' . $runtimeType->name . '". '
-                . 'This can happen when an object type is only referenced indirectly through '
-                . 'abstract types and never directly through fields.'
-                . 'List the type in the option "types" during schema construction, '
-                . 'see https://webonyx.github.io/graphql-php/type-system/schema/#configuration-options.'
+                "Schema does not contain type \"{$runtimeType}\". This can happen when an object type is only referenced indirectly through abstract types and never directly through fields.List the type in the option \"types\" during schema construction, see https://webonyx.github.io/graphql-php/type-system/schema/#configuration-options."
             );
         }
 
         if ($runtimeType !== $this->exeContext->schema->getType($runtimeType->name)) {
             throw new InvariantViolation(
-                sprintf(
-                    'Schema must contain unique named types but contains multiple types named "%s". '
-                    . 'Make sure that `resolveType` function of abstract type "%s" returns the same '
-                    . 'type instance as referenced anywhere else within the schema '
-                    . '(see https://webonyx.github.io/graphql-php/type-definitions/#type-registry).',
-                    $runtimeType,
-                    $returnType
-                )
+                "Schema must contain unique named types but contains multiple types named \"{$runtimeType}\". Make sure that `resolveType` function of abstract type \"{$returnType}\" returns the same type instance as referenced anywhere else within the schema (see https://webonyx.github.io/graphql-php/type-definitions/#type-registry)."
             );
         }
 
diff --git a/src/Executor/Values.php b/src/Executor/Values.php
index 1ce1a0a63..c3d25c1c5 100644
--- a/src/Executor/Values.php
+++ b/src/Executor/Values.php
@@ -22,7 +22,6 @@
 use GraphQL\Language\Printer;
 use GraphQL\Type\Definition\Directive;
 use GraphQL\Type\Definition\FieldDefinition;
-use GraphQL\Type\Definition\InputType;
 use GraphQL\Type\Definition\NonNull;
 use GraphQL\Type\Definition\Type;
 use GraphQL\Type\Schema;
@@ -45,7 +44,7 @@ class Values
      * to match the variable definitions, an Error will be thrown.
      *
      * @param NodeList<VariableDefinitionNode> $varDefNodes
-     * @param array<string, mixed>             $rawVariableValues
+     * @param array<string, mixed> $rawVariableValues
      *
      * @return array{array<int, Error>, null}|array{null, array<string, mixed>}
      */
@@ -60,16 +59,12 @@ public static function getVariableValues(Schema $schema, NodeList $varDefNodes,
             if (! Type::isInputType($varType)) {
                 // Must use input types for variables. This should be caught during
                 // validation, however is checked again here for safety.
+                $typeStr = Printer::doPrint($varDefNode->type);
                 $errors[] = new Error(
-                    sprintf(
-                        'Variable "$%s" expected value of type "%s" which cannot be used as an input type.',
-                        $varName,
-                        Printer::doPrint($varDefNode->type)
-                    ),
+                    "Variable \"\${$varName}\" expected value of type \"{$typeStr}\" which cannot be used as an input type.",
                     [$varDefNode->type]
                 );
             } else {
-                /** @var InputType&Type $varType */
                 $hasValue = array_key_exists($varName, $rawVariableValues);
                 $value = $hasValue
                     ? $rawVariableValues[$varName]
@@ -140,11 +135,11 @@ public static function getVariableValues(Schema $schema, NodeList $varDefNodes,
      * If the directive does not exist on the node, returns undefined.
      *
      * @param FragmentSpreadNode|FieldNode|InlineFragmentNode|EnumValueDefinitionNode|FieldDefinitionNode $node
-     * @param mixed[]|null                                                                                $variableValues
+     * @param array<string, mixed>|null $variableValues
      *
      * @return array<string, mixed>|null
      */
-    public static function getDirectiveValues(Directive $directiveDef, $node, $variableValues = null): ?array
+    public static function getDirectiveValues(Directive $directiveDef, Node $node, ?array $variableValues = null): ?array
     {
         $directiveNode = Utils::find(
             $node->directives,
@@ -165,23 +160,23 @@ static function (DirectiveNode $directive) use ($directiveDef): bool {
      * definitions and list of argument AST nodes.
      *
      * @param FieldDefinition|Directive $def
-     * @param FieldNode|DirectiveNode   $node
-     * @param mixed[]                   $variableValues
+     * @param FieldNode|DirectiveNode $node
+     * @param array<string, mixed>|null $variableValues
      *
      * @throws Error
      *
      * @return array<string, mixed>
      */
-    public static function getArgumentValues($def, $node, $variableValues = null): array
+    public static function getArgumentValues($def, Node $node, ?array $variableValues = null): array
     {
         if (0 === count($def->args)) {
             return [];
         }
 
-        $argumentNodes = $node->arguments;
         /** @var array<string, ArgumentNodeValue> $argumentValueMap */
         $argumentValueMap = [];
-        foreach ($argumentNodes as $argumentNode) {
+
+        foreach ($node->arguments as $argumentNode) {
             $argumentValueMap[$argumentNode->name->value] = $argumentNode->value;
         }
 
@@ -189,28 +184,27 @@ public static function getArgumentValues($def, $node, $variableValues = null): a
     }
 
     /**
-     * @param FieldDefinition|Directive        $fieldDefinition
+     * @param FieldDefinition|Directive $def
      * @param array<string, ArgumentNodeValue> $argumentValueMap
-     * @param mixed[]                          $variableValues
-     * @param Node|null                        $referenceNode
+     * @param array<string, mixed>|null $variableValues
      *
      * @throws Error
      *
-     * @return mixed[]
+     * @return array<string, mixed>
      */
-    public static function getArgumentValuesForMap($fieldDefinition, array $argumentValueMap, $variableValues = null, $referenceNode = null): array
+    public static function getArgumentValuesForMap($def, array $argumentValueMap, ?array $variableValues = null, ?Node $referenceNode = null): array
     {
-        $argumentDefinitions = $fieldDefinition->args;
+        /** @var array<string, mixed> $coercedValues */
         $coercedValues = [];
 
-        foreach ($argumentDefinitions as $argumentDefinition) {
+        foreach ($def->args as $argumentDefinition) {
             $name = $argumentDefinition->name;
             $argType = $argumentDefinition->getType();
             $argumentValueNode = $argumentValueMap[$name] ?? null;
 
             if ($argumentValueNode instanceof VariableNode) {
                 $variableName = $argumentValueNode->name->value;
-                $hasValue = array_key_exists($variableName, $variableValues ?? []);
+                $hasValue = null !== $variableValues && array_key_exists($variableName, $variableValues);
                 $isNull = $hasValue
                     ? null === $variableValues[$variableName]
                     : false;
@@ -263,14 +257,14 @@ public static function getArgumentValuesForMap($fieldDefinition, array $argument
                     // usage here is of the correct type.
                     $coercedValues[$name] = $variableValues[$variableName] ?? null;
                 } else {
-                    $valueNode = $argumentValueNode;
-                    $coercedValue = AST::valueFromAST($valueNode, $argType, $variableValues);
+                    $coercedValue = AST::valueFromAST($argumentValueNode, $argType, $variableValues);
                     if (Utils::isInvalid($coercedValue)) {
                         // Note: ValuesOfCorrectType validation should catch this before
                         // execution. This is a runtime check to ensure execution does not
                         // continue with an invalid argument value.
+                        $invalidValue = Printer::doPrint($argumentValueNode);
                         throw new Error(
-                            'Argument "' . $name . '" has invalid value ' . Printer::doPrint($valueNode) . '.',
+                            "Argument \"{$name}\" has invalid value {$invalidValue}.",
                             [$argumentValueNode]
                         );
                     }
diff --git a/src/GraphQL.php b/src/GraphQL.php
index f07aee126..9a93f258c 100644
--- a/src/GraphQL.php
+++ b/src/GraphQL.php
@@ -130,10 +130,9 @@ public static function promiseToExecute(
                 ? $source
                 : Parser::parse(new Source($source, 'GraphQL'));
 
-            // TODO this could be more elegant
-            if (0 === count($validationRules ?? [])) {
-                /** @var QueryComplexity $queryComplexity */
+            if (null === $validationRules || 0 === count($validationRules)) {
                 $queryComplexity = DocumentValidator::getRule(QueryComplexity::class);
+                assert($queryComplexity instanceof QueryComplexity, 'should not register a different rule for QueryComplexity');
                 $queryComplexity->setRawVariableValues($variableValues);
             } else {
                 foreach ($validationRules as $rule) {
diff --git a/src/Language/AST/ArgumentNode.php b/src/Language/AST/ArgumentNode.php
index d83870724..7aa245c99 100644
--- a/src/Language/AST/ArgumentNode.php
+++ b/src/Language/AST/ArgumentNode.php
@@ -11,9 +11,8 @@ class ArgumentNode extends Node
 {
     public string $kind = NodeKind::ARGUMENT;
 
-    /** @var ArgumentNodeValue */
-    public $value;
+    /** @phpstan-var ArgumentNodeValue */
+    public ValueNode $value;
 
-    /** @var NameNode */
-    public $name;
+    public NameNode $name;
 }
diff --git a/src/Language/AST/BooleanValueNode.php b/src/Language/AST/BooleanValueNode.php
index 47d7c4475..86c24f261 100644
--- a/src/Language/AST/BooleanValueNode.php
+++ b/src/Language/AST/BooleanValueNode.php
@@ -8,6 +8,5 @@ class BooleanValueNode extends Node implements ValueNode
 {
     public string $kind = NodeKind::BOOLEAN;
 
-    /** @var bool */
-    public $value;
+    public bool $value;
 }
diff --git a/src/Language/AST/DirectiveDefinitionNode.php b/src/Language/AST/DirectiveDefinitionNode.php
index d0cc4f6da..d9e20a7ae 100644
--- a/src/Language/AST/DirectiveDefinitionNode.php
+++ b/src/Language/AST/DirectiveDefinitionNode.php
@@ -8,18 +8,15 @@ class DirectiveDefinitionNode extends Node implements TypeSystemDefinitionNode
 {
     public string $kind = NodeKind::DIRECTIVE_DEFINITION;
 
-    /** @var NameNode */
-    public $name;
+    public NameNode $name;
 
-    /** @var StringValueNode|null */
-    public $description;
+    public ?StringValueNode $description = null;
 
     /** @var NodeList<InputValueDefinitionNode> */
-    public $arguments;
+    public NodeList $arguments;
 
-    /** @var bool */
-    public $repeatable;
+    public bool $repeatable;
 
     /** @var NodeList<NameNode> */
-    public $locations;
+    public NodeList $locations;
 }
diff --git a/src/Language/AST/DirectiveNode.php b/src/Language/AST/DirectiveNode.php
index 19d5235f0..431d463af 100644
--- a/src/Language/AST/DirectiveNode.php
+++ b/src/Language/AST/DirectiveNode.php
@@ -8,9 +8,8 @@ class DirectiveNode extends Node
 {
     public string $kind = NodeKind::DIRECTIVE;
 
-    /** @var NameNode */
-    public $name;
+    public NameNode $name;
 
     /** @var NodeList<ArgumentNode> */
-    public $arguments;
+    public NodeList $arguments;
 }
diff --git a/src/Language/AST/DocumentNode.php b/src/Language/AST/DocumentNode.php
index acecbc453..f974463bf 100644
--- a/src/Language/AST/DocumentNode.php
+++ b/src/Language/AST/DocumentNode.php
@@ -9,5 +9,5 @@ class DocumentNode extends Node
     public string $kind = NodeKind::DOCUMENT;
 
     /** @var NodeList<DefinitionNode&Node> */
-    public $definitions;
+    public NodeList $definitions;
 }
diff --git a/src/Language/AST/EnumTypeDefinitionNode.php b/src/Language/AST/EnumTypeDefinitionNode.php
index ec19fe13b..9c89965c2 100644
--- a/src/Language/AST/EnumTypeDefinitionNode.php
+++ b/src/Language/AST/EnumTypeDefinitionNode.php
@@ -8,15 +8,13 @@ class EnumTypeDefinitionNode extends Node implements TypeDefinitionNode
 {
     public string $kind = NodeKind::ENUM_TYPE_DEFINITION;
 
-    /** @var NameNode */
-    public $name;
+    public NameNode $name;
 
     /** @var NodeList<DirectiveNode> */
-    public $directives;
+    public NodeList $directives;
 
     /** @var NodeList<EnumValueDefinitionNode> */
-    public $values;
+    public NodeList $values;
 
-    /** @var StringValueNode|null */
-    public $description;
+    public ?StringValueNode $description = null;
 }
diff --git a/src/Language/AST/EnumTypeExtensionNode.php b/src/Language/AST/EnumTypeExtensionNode.php
index 55e21a6ed..6f545ba45 100644
--- a/src/Language/AST/EnumTypeExtensionNode.php
+++ b/src/Language/AST/EnumTypeExtensionNode.php
@@ -8,12 +8,11 @@ class EnumTypeExtensionNode extends Node implements TypeExtensionNode
 {
     public string $kind = NodeKind::ENUM_TYPE_EXTENSION;
 
-    /** @var NameNode */
-    public $name;
+    public NameNode $name;
 
     /** @var NodeList<DirectiveNode> */
-    public $directives;
+    public NodeList $directives;
 
     /** @var NodeList<EnumValueDefinitionNode> */
-    public $values;
+    public NodeList $values;
 }
diff --git a/src/Language/AST/EnumValueDefinitionNode.php b/src/Language/AST/EnumValueDefinitionNode.php
index c45184d3c..11c05dada 100644
--- a/src/Language/AST/EnumValueDefinitionNode.php
+++ b/src/Language/AST/EnumValueDefinitionNode.php
@@ -8,12 +8,10 @@ class EnumValueDefinitionNode extends Node
 {
     public string $kind = NodeKind::ENUM_VALUE_DEFINITION;
 
-    /** @var NameNode */
-    public $name;
+    public NameNode $name;
 
     /** @var NodeList<DirectiveNode> */
-    public $directives;
+    public NodeList $directives;
 
-    /** @var StringValueNode|null */
-    public $description;
+    public ?StringValueNode $description = null;
 }
diff --git a/src/Language/AST/EnumValueNode.php b/src/Language/AST/EnumValueNode.php
index db3227145..bac94b182 100644
--- a/src/Language/AST/EnumValueNode.php
+++ b/src/Language/AST/EnumValueNode.php
@@ -8,6 +8,5 @@ class EnumValueNode extends Node implements ValueNode
 {
     public string $kind = NodeKind::ENUM;
 
-    /** @var string */
-    public $value;
+    public string $value;
 }
diff --git a/src/Language/AST/FieldDefinitionNode.php b/src/Language/AST/FieldDefinitionNode.php
index e828bac20..7e082211f 100644
--- a/src/Language/AST/FieldDefinitionNode.php
+++ b/src/Language/AST/FieldDefinitionNode.php
@@ -8,18 +8,16 @@ class FieldDefinitionNode extends Node
 {
     public string $kind = NodeKind::FIELD_DEFINITION;
 
-    /** @var NameNode */
-    public $name;
+    public NameNode $name;
 
     /** @var NodeList<InputValueDefinitionNode> */
-    public $arguments;
+    public NodeList $arguments;
 
     /** @var NamedTypeNode|ListTypeNode|NonNullTypeNode */
-    public $type;
+    public TypeNode $type;
 
     /** @var NodeList<DirectiveNode> */
-    public $directives;
+    public NodeList $directives;
 
-    /** @var StringValueNode|null */
-    public $description;
+    public ?StringValueNode $description = null;
 }
diff --git a/src/Language/AST/FloatValueNode.php b/src/Language/AST/FloatValueNode.php
index 0bacde57b..f65063767 100644
--- a/src/Language/AST/FloatValueNode.php
+++ b/src/Language/AST/FloatValueNode.php
@@ -8,6 +8,5 @@ class FloatValueNode extends Node implements ValueNode
 {
     public string $kind = NodeKind::FLOAT;
 
-    /** @var string */
-    public $value;
+    public string $value;
 }
diff --git a/src/Language/AST/FragmentDefinitionNode.php b/src/Language/AST/FragmentDefinitionNode.php
index 89144946b..41796ce82 100644
--- a/src/Language/AST/FragmentDefinitionNode.php
+++ b/src/Language/AST/FragmentDefinitionNode.php
@@ -8,8 +8,7 @@ class FragmentDefinitionNode extends Node implements ExecutableDefinitionNode, H
 {
     public string $kind = NodeKind::FRAGMENT_DEFINITION;
 
-    /** @var NameNode */
-    public $name;
+    public NameNode $name;
 
     /**
      * Note: fragment variable definitions are experimental and may be changed
@@ -19,14 +18,12 @@ class FragmentDefinitionNode extends Node implements ExecutableDefinitionNode, H
      *
      * @var NodeList<VariableDefinitionNode>|null
      */
-    public $variableDefinitions;
+    public ?NodeList $variableDefinitions = null;
 
-    /** @var NamedTypeNode */
-    public $typeCondition;
+    public NamedTypeNode $typeCondition;
 
     /** @var NodeList<DirectiveNode> */
-    public $directives;
+    public NodeList $directives;
 
-    /** @var SelectionSetNode */
-    public $selectionSet;
+    public SelectionSetNode $selectionSet;
 }
diff --git a/src/Language/AST/FragmentSpreadNode.php b/src/Language/AST/FragmentSpreadNode.php
index 5151d766d..840f5f4d8 100644
--- a/src/Language/AST/FragmentSpreadNode.php
+++ b/src/Language/AST/FragmentSpreadNode.php
@@ -8,9 +8,8 @@ class FragmentSpreadNode extends Node implements SelectionNode
 {
     public string $kind = NodeKind::FRAGMENT_SPREAD;
 
-    /** @var NameNode */
-    public $name;
+    public NameNode $name;
 
     /** @var NodeList<DirectiveNode> */
-    public $directives;
+    public NodeList $directives;
 }
diff --git a/src/Language/AST/InputObjectTypeDefinitionNode.php b/src/Language/AST/InputObjectTypeDefinitionNode.php
index 2592c3a56..26098bdc7 100644
--- a/src/Language/AST/InputObjectTypeDefinitionNode.php
+++ b/src/Language/AST/InputObjectTypeDefinitionNode.php
@@ -8,15 +8,13 @@ class InputObjectTypeDefinitionNode extends Node implements TypeDefinitionNode
 {
     public string $kind = NodeKind::INPUT_OBJECT_TYPE_DEFINITION;
 
-    /** @var NameNode */
-    public $name;
+    public NameNode $name;
 
     /** @var NodeList<DirectiveNode> */
-    public $directives;
+    public NodeList $directives;
 
     /** @var NodeList<InputValueDefinitionNode> */
-    public $fields;
+    public NodeList $fields;
 
-    /** @var StringValueNode|null */
-    public $description;
+    public ?StringValueNode $description = null;
 }
diff --git a/src/Language/AST/InputObjectTypeExtensionNode.php b/src/Language/AST/InputObjectTypeExtensionNode.php
index 406577ae7..15da4d92a 100644
--- a/src/Language/AST/InputObjectTypeExtensionNode.php
+++ b/src/Language/AST/InputObjectTypeExtensionNode.php
@@ -8,12 +8,11 @@ class InputObjectTypeExtensionNode extends Node implements TypeExtensionNode
 {
     public string $kind = NodeKind::INPUT_OBJECT_TYPE_EXTENSION;
 
-    /** @var NameNode */
-    public $name;
+    public NameNode $name;
 
     /** @var NodeList<DirectiveNode> */
-    public $directives;
+    public NodeList $directives;
 
     /** @var NodeList<InputValueDefinitionNode> */
-    public $fields;
+    public NodeList $fields;
 }
diff --git a/src/Language/AST/InputValueDefinitionNode.php b/src/Language/AST/InputValueDefinitionNode.php
index 969b149e4..1b2c68f3f 100644
--- a/src/Language/AST/InputValueDefinitionNode.php
+++ b/src/Language/AST/InputValueDefinitionNode.php
@@ -8,18 +8,16 @@ class InputValueDefinitionNode extends Node
 {
     public string $kind = NodeKind::INPUT_VALUE_DEFINITION;
 
-    /** @var NameNode */
-    public $name;
+    public NameNode $name;
 
     /** @var NamedTypeNode|ListTypeNode|NonNullTypeNode */
-    public $type;
+    public TypeNode $type;
 
     /** @var VariableNode|NullValueNode|IntValueNode|FloatValueNode|StringValueNode|BooleanValueNode|EnumValueNode|ListValueNode|ObjectValueNode|null */
-    public $defaultValue;
+    public ?ValueNode $defaultValue = null;
 
     /** @var NodeList<DirectiveNode> */
-    public $directives;
+    public NodeList $directives;
 
-    /** @var StringValueNode|null */
-    public $description;
+    public ?StringValueNode $description = null;
 }
diff --git a/src/Language/AST/IntValueNode.php b/src/Language/AST/IntValueNode.php
index 9d2003b07..b5d00ec6e 100644
--- a/src/Language/AST/IntValueNode.php
+++ b/src/Language/AST/IntValueNode.php
@@ -8,6 +8,5 @@ class IntValueNode extends Node implements ValueNode
 {
     public string $kind = NodeKind::INT;
 
-    /** @var string */
-    public $value;
+    public string $value;
 }
diff --git a/src/Language/AST/InterfaceTypeDefinitionNode.php b/src/Language/AST/InterfaceTypeDefinitionNode.php
index 8ccb5387d..16d14ff37 100644
--- a/src/Language/AST/InterfaceTypeDefinitionNode.php
+++ b/src/Language/AST/InterfaceTypeDefinitionNode.php
@@ -8,18 +8,16 @@ class InterfaceTypeDefinitionNode extends Node implements TypeDefinitionNode
 {
     public string $kind = NodeKind::INTERFACE_TYPE_DEFINITION;
 
-    /** @var NameNode */
-    public $name;
+    public NameNode $name;
 
     /** @var NodeList<DirectiveNode> */
-    public $directives;
+    public NodeList $directives;
 
     /** @var NodeList<NamedTypeNode> */
-    public $interfaces;
+    public NodeList $interfaces;
 
     /** @var NodeList<FieldDefinitionNode> */
-    public $fields;
+    public NodeList $fields;
 
-    /** @var StringValueNode|null */
-    public $description;
+    public ?StringValueNode $description = null;
 }
diff --git a/src/Language/AST/InterfaceTypeExtensionNode.php b/src/Language/AST/InterfaceTypeExtensionNode.php
index 4b45f68b1..33eb61ce6 100644
--- a/src/Language/AST/InterfaceTypeExtensionNode.php
+++ b/src/Language/AST/InterfaceTypeExtensionNode.php
@@ -8,15 +8,14 @@ class InterfaceTypeExtensionNode extends Node implements TypeExtensionNode
 {
     public string $kind = NodeKind::INTERFACE_TYPE_EXTENSION;
 
-    /** @var NameNode */
-    public $name;
+    public NameNode $name;
 
     /** @var NodeList<DirectiveNode> */
-    public $directives;
+    public NodeList $directives;
 
     /** @var NodeList<NamedTypeNode> */
-    public $interfaces;
+    public NodeList $interfaces;
 
     /** @var NodeList<FieldDefinitionNode> */
-    public $fields;
+    public NodeList $fields;
 }
diff --git a/src/Language/AST/ListTypeNode.php b/src/Language/AST/ListTypeNode.php
index a48e898e8..d619531ee 100644
--- a/src/Language/AST/ListTypeNode.php
+++ b/src/Language/AST/ListTypeNode.php
@@ -9,5 +9,5 @@ class ListTypeNode extends Node implements TypeNode
     public string $kind = NodeKind::LIST_TYPE;
 
     /** @var NamedTypeNode|ListTypeNode|NonNullTypeNode */
-    public $type;
+    public TypeNode $type;
 }
diff --git a/src/Language/AST/ListValueNode.php b/src/Language/AST/ListValueNode.php
index df05df08d..11381166d 100644
--- a/src/Language/AST/ListValueNode.php
+++ b/src/Language/AST/ListValueNode.php
@@ -9,5 +9,5 @@ class ListValueNode extends Node implements ValueNode
     public string $kind = NodeKind::LST;
 
     /** @var NodeList<ValueNode&Node> */
-    public $values;
+    public NodeList $values;
 }
diff --git a/src/Language/AST/Location.php b/src/Language/AST/Location.php
index 2c62d9fc7..f4e3bfd4d 100644
--- a/src/Language/AST/Location.php
+++ b/src/Language/AST/Location.php
@@ -28,17 +28,17 @@ class Location
     /**
      * The Token at which this Node begins.
      */
-    public ?Token $startToken;
+    public ?Token $startToken = null;
 
     /**
      * The Token at which this Node ends.
      */
-    public ?Token $endToken;
+    public ?Token $endToken = null;
 
     /**
      * The Source document the AST represents.
      */
-    public ?Source $source;
+    public ?Source $source = null;
 
     public static function create(int $start, int $end): self
     {
diff --git a/src/Language/AST/NameNode.php b/src/Language/AST/NameNode.php
index 95b2ade78..bc019dc78 100644
--- a/src/Language/AST/NameNode.php
+++ b/src/Language/AST/NameNode.php
@@ -8,6 +8,5 @@ class NameNode extends Node implements TypeNode
 {
     public string $kind = NodeKind::NAME;
 
-    /** @var string */
-    public $value;
+    public string $value;
 }
diff --git a/src/Language/AST/NamedTypeNode.php b/src/Language/AST/NamedTypeNode.php
index 1e77eb8f4..9e5f096d0 100644
--- a/src/Language/AST/NamedTypeNode.php
+++ b/src/Language/AST/NamedTypeNode.php
@@ -8,6 +8,5 @@ class NamedTypeNode extends Node implements TypeNode
 {
     public string $kind = NodeKind::NAMED_TYPE;
 
-    /** @var NameNode */
-    public $name;
+    public NameNode $name;
 }
diff --git a/src/Language/AST/Node.php b/src/Language/AST/Node.php
index 1ed316eed..ea5580c56 100644
--- a/src/Language/AST/Node.php
+++ b/src/Language/AST/Node.php
@@ -63,12 +63,12 @@ public function cloneDeep(): self
     }
 
     /**
+     * @template TNode of Node
+     * @template TCloneable of TNode|NodeList<TNode>|Location|string
+     *
      * @phpstan-param TCloneable $value
      *
      * @phpstan-return TCloneable
-     *
-     * @template TNode of Node
-     * @template TCloneable of TNode|NodeList<TNode>|Location|string
      */
     protected static function cloneValue($value)
     {
@@ -90,7 +90,7 @@ protected static function cloneValue($value)
 
     public function __toString(): string
     {
-        return json_encode($this);
+        return json_encode($this, JSON_THROW_ON_ERROR);
     }
 
     /**
diff --git a/src/Language/AST/NodeList.php b/src/Language/AST/NodeList.php
index 5f6f0d00d..f0a1f3fc3 100644
--- a/src/Language/AST/NodeList.php
+++ b/src/Language/AST/NodeList.php
@@ -137,7 +137,7 @@ public function merge(iterable $list): NodeList
     public function getIterator(): Traversable
     {
         foreach ($this->nodes as $key => $_) {
-            yield $this->offsetGet($key);
+            yield $key => $this->offsetGet($key);
         }
     }
 
@@ -153,8 +153,9 @@ public function count(): int
      */
     public function cloneDeep(): self
     {
-        $cloned = clone $this;
-        foreach ($this->nodes as $key => $node) {
+        /** @var static<T> $cloned */
+        $cloned = new static([]);
+        foreach ($this->getIterator() as $key => $node) {
             $cloned[$key] = $node->cloneDeep();
         }
 
diff --git a/src/Language/AST/NonNullTypeNode.php b/src/Language/AST/NonNullTypeNode.php
index 8f8de7b0c..e8a01e17b 100644
--- a/src/Language/AST/NonNullTypeNode.php
+++ b/src/Language/AST/NonNullTypeNode.php
@@ -9,5 +9,5 @@ class NonNullTypeNode extends Node implements TypeNode
     public string $kind = NodeKind::NON_NULL_TYPE;
 
     /** @var NamedTypeNode|ListTypeNode */
-    public $type;
+    public TypeNode $type;
 }
diff --git a/src/Language/AST/ObjectFieldNode.php b/src/Language/AST/ObjectFieldNode.php
index 7947224bf..abd2592b9 100644
--- a/src/Language/AST/ObjectFieldNode.php
+++ b/src/Language/AST/ObjectFieldNode.php
@@ -8,9 +8,8 @@ class ObjectFieldNode extends Node
 {
     public string $kind = NodeKind::OBJECT_FIELD;
 
-    /** @var NameNode */
-    public $name;
+    public NameNode $name;
 
     /** @var VariableNode|NullValueNode|IntValueNode|FloatValueNode|StringValueNode|BooleanValueNode|EnumValueNode|ListValueNode|ObjectValueNode */
-    public $value;
+    public ValueNode $value;
 }
diff --git a/src/Language/AST/ObjectTypeDefinitionNode.php b/src/Language/AST/ObjectTypeDefinitionNode.php
index 0c0f73752..2cf71a453 100644
--- a/src/Language/AST/ObjectTypeDefinitionNode.php
+++ b/src/Language/AST/ObjectTypeDefinitionNode.php
@@ -8,18 +8,16 @@ class ObjectTypeDefinitionNode extends Node implements TypeDefinitionNode
 {
     public string $kind = NodeKind::OBJECT_TYPE_DEFINITION;
 
-    /** @var NameNode */
-    public $name;
+    public NameNode $name;
 
     /** @var NodeList<NamedTypeNode> */
-    public $interfaces;
+    public NodeList $interfaces;
 
     /** @var NodeList<DirectiveNode> */
-    public $directives;
+    public NodeList $directives;
 
     /** @var NodeList<FieldDefinitionNode> */
-    public $fields;
+    public NodeList $fields;
 
-    /** @var StringValueNode|null */
-    public $description;
+    public ?StringValueNode $description = null;
 }
diff --git a/src/Language/AST/ObjectTypeExtensionNode.php b/src/Language/AST/ObjectTypeExtensionNode.php
index d89092672..13b474307 100644
--- a/src/Language/AST/ObjectTypeExtensionNode.php
+++ b/src/Language/AST/ObjectTypeExtensionNode.php
@@ -8,15 +8,14 @@ class ObjectTypeExtensionNode extends Node implements TypeExtensionNode
 {
     public string $kind = NodeKind::OBJECT_TYPE_EXTENSION;
 
-    /** @var NameNode */
-    public $name;
+    public NameNode $name;
 
     /** @var NodeList<NamedTypeNode> */
-    public $interfaces;
+    public NodeList $interfaces;
 
     /** @var NodeList<DirectiveNode> */
-    public $directives;
+    public NodeList $directives;
 
     /** @var NodeList<FieldDefinitionNode> */
-    public $fields;
+    public NodeList $fields;
 }
diff --git a/src/Language/AST/ObjectValueNode.php b/src/Language/AST/ObjectValueNode.php
index 888557368..f3320fa4e 100644
--- a/src/Language/AST/ObjectValueNode.php
+++ b/src/Language/AST/ObjectValueNode.php
@@ -9,5 +9,5 @@ class ObjectValueNode extends Node implements ValueNode
     public string $kind = NodeKind::OBJECT;
 
     /** @var NodeList<ObjectFieldNode> */
-    public $fields;
+    public NodeList $fields;
 }
diff --git a/src/Language/AST/OperationDefinitionNode.php b/src/Language/AST/OperationDefinitionNode.php
index b95e78cec..1bcc6bb90 100644
--- a/src/Language/AST/OperationDefinitionNode.php
+++ b/src/Language/AST/OperationDefinitionNode.php
@@ -10,7 +10,9 @@ class OperationDefinitionNode extends Node implements ExecutableDefinitionNode,
 
     public ?NameNode $name = null;
 
-    /** @var string (oneOf 'query', 'mutation', 'subscription')) */
+    /**
+     * @var 'query'|'mutation'|'subscription'
+     */
     public string $operation;
 
     /** @var NodeList<VariableDefinitionNode> */
diff --git a/src/Language/AST/OperationTypeDefinitionNode.php b/src/Language/AST/OperationTypeDefinitionNode.php
index 3afd4edaf..8f36b34f2 100644
--- a/src/Language/AST/OperationTypeDefinitionNode.php
+++ b/src/Language/AST/OperationTypeDefinitionNode.php
@@ -9,12 +9,9 @@ class OperationTypeDefinitionNode extends Node
     public string $kind = NodeKind::OPERATION_TYPE_DEFINITION;
 
     /**
-     * One of 'query' | 'mutation' | 'subscription'.
-     *
-     * @var string
+     * @var 'query'|'mutation'|'subscription'
      */
-    public $operation;
+    public string $operation;
 
-    /** @var NamedTypeNode */
-    public $type;
+    public NamedTypeNode $type;
 }
diff --git a/src/Language/AST/ScalarTypeDefinitionNode.php b/src/Language/AST/ScalarTypeDefinitionNode.php
index 20b69a0c9..1dd2c1d9a 100644
--- a/src/Language/AST/ScalarTypeDefinitionNode.php
+++ b/src/Language/AST/ScalarTypeDefinitionNode.php
@@ -8,12 +8,10 @@ class ScalarTypeDefinitionNode extends Node implements TypeDefinitionNode
 {
     public string $kind = NodeKind::SCALAR_TYPE_DEFINITION;
 
-    /** @var NameNode */
-    public $name;
+    public NameNode $name;
 
     /** @var NodeList<DirectiveNode> */
-    public $directives;
+    public NodeList $directives;
 
-    /** @var StringValueNode|null */
-    public $description;
+    public ?StringValueNode $description = null;
 }
diff --git a/src/Language/AST/ScalarTypeExtensionNode.php b/src/Language/AST/ScalarTypeExtensionNode.php
index 7473caca1..79a7b6233 100644
--- a/src/Language/AST/ScalarTypeExtensionNode.php
+++ b/src/Language/AST/ScalarTypeExtensionNode.php
@@ -8,9 +8,8 @@ class ScalarTypeExtensionNode extends Node implements TypeExtensionNode
 {
     public string $kind = NodeKind::SCALAR_TYPE_EXTENSION;
 
-    /** @var NameNode */
-    public $name;
+    public NameNode $name;
 
     /** @var NodeList<DirectiveNode> */
-    public $directives;
+    public NodeList $directives;
 }
diff --git a/src/Language/AST/SchemaDefinitionNode.php b/src/Language/AST/SchemaDefinitionNode.php
index 1bffd7b18..65893756e 100644
--- a/src/Language/AST/SchemaDefinitionNode.php
+++ b/src/Language/AST/SchemaDefinitionNode.php
@@ -9,8 +9,8 @@ class SchemaDefinitionNode extends Node implements TypeSystemDefinitionNode
     public string $kind = NodeKind::SCHEMA_DEFINITION;
 
     /** @var NodeList<DirectiveNode> */
-    public $directives;
+    public NodeList $directives;
 
     /** @var NodeList<OperationTypeDefinitionNode> */
-    public $operationTypes;
+    public NodeList $operationTypes;
 }
diff --git a/src/Language/AST/SchemaTypeExtensionNode.php b/src/Language/AST/SchemaTypeExtensionNode.php
index a8bc46659..bc1313607 100644
--- a/src/Language/AST/SchemaTypeExtensionNode.php
+++ b/src/Language/AST/SchemaTypeExtensionNode.php
@@ -9,8 +9,8 @@ class SchemaTypeExtensionNode extends Node implements TypeExtensionNode
     public string $kind = NodeKind::SCHEMA_EXTENSION;
 
     /** @var NodeList<DirectiveNode> */
-    public $directives;
+    public NodeList $directives;
 
     /** @var NodeList<OperationTypeDefinitionNode> */
-    public $operationTypes;
+    public NodeList $operationTypes;
 }
diff --git a/src/Language/AST/StringValueNode.php b/src/Language/AST/StringValueNode.php
index 060c27724..9ceea0d43 100644
--- a/src/Language/AST/StringValueNode.php
+++ b/src/Language/AST/StringValueNode.php
@@ -8,9 +8,7 @@ class StringValueNode extends Node implements ValueNode
 {
     public string $kind = NodeKind::STRING;
 
-    /** @var string */
-    public $value;
+    public string $value;
 
-    /** @var bool */
-    public $block;
+    public bool $block = false;
 }
diff --git a/src/Language/AST/UnionTypeDefinitionNode.php b/src/Language/AST/UnionTypeDefinitionNode.php
index b9768d8c7..9813a82ce 100644
--- a/src/Language/AST/UnionTypeDefinitionNode.php
+++ b/src/Language/AST/UnionTypeDefinitionNode.php
@@ -8,15 +8,13 @@ class UnionTypeDefinitionNode extends Node implements TypeDefinitionNode
 {
     public string $kind = NodeKind::UNION_TYPE_DEFINITION;
 
-    /** @var NameNode */
-    public $name;
+    public NameNode $name;
 
     /** @var NodeList<DirectiveNode> */
-    public $directives;
+    public NodeList $directives;
 
     /** @var NodeList<NamedTypeNode> */
-    public $types;
+    public NodeList $types;
 
-    /** @var StringValueNode|null */
-    public $description;
+    public ?StringValueNode $description = null;
 }
diff --git a/src/Language/AST/UnionTypeExtensionNode.php b/src/Language/AST/UnionTypeExtensionNode.php
index 1f4981f2e..b0c8705bd 100644
--- a/src/Language/AST/UnionTypeExtensionNode.php
+++ b/src/Language/AST/UnionTypeExtensionNode.php
@@ -8,12 +8,11 @@ class UnionTypeExtensionNode extends Node implements TypeExtensionNode
 {
     public string $kind = NodeKind::UNION_TYPE_EXTENSION;
 
-    /** @var NameNode */
-    public $name;
+    public NameNode $name;
 
     /** @var NodeList<DirectiveNode> */
-    public $directives;
+    public NodeList $directives;
 
     /** @var NodeList<NamedTypeNode> */
-    public $types;
+    public NodeList $types;
 }
diff --git a/src/Language/AST/VariableDefinitionNode.php b/src/Language/AST/VariableDefinitionNode.php
index ad0a06756..aebbc6ce1 100644
--- a/src/Language/AST/VariableDefinitionNode.php
+++ b/src/Language/AST/VariableDefinitionNode.php
@@ -8,15 +8,14 @@ class VariableDefinitionNode extends Node implements DefinitionNode
 {
     public string $kind = NodeKind::VARIABLE_DEFINITION;
 
-    /** @var VariableNode */
-    public $variable;
+    public VariableNode $variable;
 
     /** @var NamedTypeNode|ListTypeNode|NonNullTypeNode */
-    public $type;
+    public TypeNode $type;
 
     /** @var VariableNode|NullValueNode|IntValueNode|FloatValueNode|StringValueNode|BooleanValueNode|EnumValueNode|ListValueNode|ObjectValueNode|null */
-    public $defaultValue;
+    public ?ValueNode $defaultValue = null;
 
     /** @var NodeList<DirectiveNode> */
-    public $directives;
+    public NodeList $directives;
 }
diff --git a/src/Language/AST/VariableNode.php b/src/Language/AST/VariableNode.php
index 895795dfc..4e958091e 100644
--- a/src/Language/AST/VariableNode.php
+++ b/src/Language/AST/VariableNode.php
@@ -8,6 +8,5 @@ class VariableNode extends Node implements ValueNode
 {
     public string $kind = NodeKind::VARIABLE;
 
-    /** @var NameNode */
-    public $name;
+    public NameNode $name;
 }
diff --git a/src/Language/BlockString.php b/src/Language/BlockString.php
index 60b6cb606..b0fbcf951 100644
--- a/src/Language/BlockString.php
+++ b/src/Language/BlockString.php
@@ -26,6 +26,7 @@ public static function dedentValue(string $rawString): string
     {
         // Expand a block string's raw value into independent lines.
         $lines = preg_split('/\\r\\n|[\\n\\r]/', $rawString);
+        assert(is_array($lines), 'given the regex is valid');
 
         // Remove common indentation from all lines but first.
         $commonIndent = self::getIndentation($rawString);
diff --git a/src/Language/Lexer.php b/src/Language/Lexer.php
index b999d072a..c3ab6a2d3 100644
--- a/src/Language/Lexer.php
+++ b/src/Language/Lexer.php
@@ -504,7 +504,7 @@ private function readString(int $line, int $col, Token $prev): Token
                     case 117:
                         $position = $this->position;
                         [$hex] = $this->readChars(4, true);
-                        if (! preg_match('/[0-9a-fA-F]{4}/', $hex)) {
+                        if (1 !== preg_match('/[0-9a-fA-F]{4}/', $hex)) {
                             throw new SyntaxError(
                                 $this->source,
                                 $position - 1,
@@ -513,12 +513,13 @@ private function readString(int $line, int $col, Token $prev): Token
                         }
 
                         $code = hexdec($hex);
+                        assert(is_int($code), 'Since only a single char is read');
 
                         // UTF-16 surrogate pair detection and handling.
                         $highOrderByte = $code >> 8;
                         if (0xD8 <= $highOrderByte && $highOrderByte <= 0xDF) {
                             [$utf16Continuation] = $this->readChars(6, true);
-                            if (! preg_match('/^\\\u[0-9a-fA-F]{4}$/', $utf16Continuation)) {
+                            if (1 !== preg_match('/^\\\u[0-9a-fA-F]{4}$/', $utf16Continuation)) {
                                 throw new SyntaxError(
                                     $this->source,
                                     $this->position - 5,
diff --git a/src/Language/Parser.php b/src/Language/Parser.php
index 7c7228e01..9f6fd2ed4 100644
--- a/src/Language/Parser.php
+++ b/src/Language/Parser.php
@@ -206,9 +206,9 @@ public static function parse($source, array $options = []): DocumentNode
      * Consider providing the results to the utility function: `GraphQL\Utils\AST::valueFromAST()`.
      *
      * @param Source|string $source
-     * @phpstan-param ParserOptions       $options
+     * @phpstan-param ParserOptions $options
      *
-     * @return BooleanValueNode|EnumValueNode|FloatValueNode|IntValueNode|ListValueNode|ObjectValueNode|StringValueNode|VariableNode
+     * @return BooleanValueNode|EnumValueNode|FloatValueNode|IntValueNode|ListValueNode|NullValueNode|ObjectValueNode|StringValueNode|VariableNode
      *
      * @api
      */
@@ -356,8 +356,6 @@ private function skip(string $kind): bool
     /**
      * If the next token is of the given kind, return that token after advancing
      * the parser. Otherwise, do not change the parser state and return false.
-     *
-     * @throws SyntaxError
      */
     private function expect(string $kind): Token
     {
@@ -379,8 +377,6 @@ private function expect(string $kind): Token
     /**
      * If the next token is a keyword with the given value, advance the lexer.
      * Otherwise, throw an error.
-     *
-     * @throws SyntaxError
      */
     private function expectKeyword(string $value): void
     {
@@ -425,8 +421,6 @@ private function unexpected(?Token $atToken = null): SyntaxError
      * and ends with a lex token of closeKind. Advances the parser
      * to the next lex token after the closing token.
      *
-     * @throws SyntaxError
-     *
      * @return NodeList<Node>
      */
     private function any(string $openKind, callable $parseFn, string $closeKind): NodeList
@@ -447,13 +441,11 @@ private function any(string $openKind, callable $parseFn, string $closeKind): No
      * and ends with a lex token of closeKind. Advances the parser
      * to the next lex token after the closing token.
      *
-     * @param callable(self): TNode $parseFn
+     * @template TNode of Node
      *
-     * @throws SyntaxError
+     * @param callable(self): TNode $parseFn
      *
      * @return NodeList<TNode>
-     *
-     * @template TNode of Node
      */
     private function many(string $openKind, callable $parseFn, string $closeKind): NodeList
     {
@@ -469,8 +461,6 @@ private function many(string $openKind, callable $parseFn, string $closeKind): N
 
     /**
      * Converts a name lex token into a name parse node.
-     *
-     * @throws SyntaxError
      */
     private function parseName(): NameNode
     {
@@ -484,8 +474,6 @@ private function parseName(): NameNode
 
     /**
      * Implements the parsing rules in the Document section.
-     *
-     * @throws SyntaxError
      */
     private function parseDocument(): DocumentNode
     {
@@ -502,8 +490,6 @@ private function parseDocument(): DocumentNode
     }
 
     /**
-     * @throws SyntaxError
-     *
      * @return DefinitionNode&Node
      */
     private function parseDefinition(): DefinitionNode
@@ -540,8 +526,6 @@ private function parseDefinition(): DefinitionNode
     }
 
     /**
-     * @throws SyntaxError
-     *
      * @return ExecutableDefinitionNode&Node
      */
     private function parseExecutableDefinition(): ExecutableDefinitionNode
@@ -566,8 +550,6 @@ private function parseExecutableDefinition(): ExecutableDefinitionNode
     // Implements the parsing rules in the Operations section.
 
     /**
-     * @throws SyntaxError
-     *
      * @return OperationDefinitionNode&Node
      */
     private function parseOperationDefinition(): OperationDefinitionNode
@@ -601,9 +583,6 @@ private function parseOperationDefinition(): OperationDefinitionNode
         ]);
     }
 
-    /**
-     * @throws SyntaxError
-     */
     private function parseOperationType(): string
     {
         $operationToken = $this->expect(Token::NAME);
@@ -626,6 +605,7 @@ private function parseOperationType(): string
      */
     private function parseVariableDefinitions(): NodeList
     {
+        // @phpstan-ignore-next-line generic type of empty NodeList is not initialized
         return $this->peek(Token::PAREN_L)
             ? $this->many(
                 Token::PAREN_L,
@@ -635,9 +615,6 @@ private function parseVariableDefinitions(): NodeList
             : new NodeList([]);
     }
 
-    /**
-     * @throws SyntaxError
-     */
     private function parseVariableDefinition(): VariableDefinitionNode
     {
         $start = $this->lexer->token;
@@ -657,9 +634,6 @@ private function parseVariableDefinition(): VariableDefinitionNode
         ]);
     }
 
-    /**
-     * @throws SyntaxError
-     */
     private function parseVariable(): VariableNode
     {
         $start = $this->lexer->token;
@@ -697,9 +671,6 @@ private function parseSelection(): SelectionNode
             : $this->parseField();
     }
 
-    /**
-     * @throws SyntaxError
-     */
     private function parseField(): FieldNode
     {
         $start = $this->lexer->token;
@@ -724,8 +695,6 @@ private function parseField(): FieldNode
     }
 
     /**
-     * @throws SyntaxError
-     *
      * @return NodeList<ArgumentNode>
      */
     private function parseArguments(bool $isConst): NodeList
@@ -734,14 +703,12 @@ private function parseArguments(bool $isConst): NodeList
             ? fn (): ArgumentNode => $this->parseConstArgument()
             : fn (): ArgumentNode => $this->parseArgument();
 
+        // @phpstan-ignore-next-line generic type of empty NodeList is not initialized
         return $this->peek(Token::PAREN_L)
             ? $this->many(Token::PAREN_L, $parseFn, Token::PAREN_R)
             : new NodeList([]);
     }
 
-    /**
-     * @throws SyntaxError
-     */
     private function parseArgument(): ArgumentNode
     {
         $start = $this->lexer->token;
@@ -757,9 +724,6 @@ private function parseArgument(): ArgumentNode
         ]);
     }
 
-    /**
-     * @throws SyntaxError
-     */
     private function parseConstArgument(): ArgumentNode
     {
         $start = $this->lexer->token;
@@ -778,8 +742,6 @@ private function parseConstArgument(): ArgumentNode
     // Implements the parsing rules in the Fragments section.
 
     /**
-     * @throws SyntaxError
-     *
      * @return FragmentSpreadNode|InlineFragmentNode
      */
     private function parseFragment(): SelectionNode
@@ -804,9 +766,6 @@ private function parseFragment(): SelectionNode
         ]);
     }
 
-    /**
-     * @throws SyntaxError
-     */
     private function parseFragmentDefinition(): FragmentDefinitionNode
     {
         $start = $this->lexer->token;
@@ -834,9 +793,6 @@ private function parseFragmentDefinition(): FragmentDefinitionNode
         ]);
     }
 
-    /**
-     * @throws SyntaxError
-     */
     private function parseFragmentName(): NameNode
     {
         if ('on' === $this->lexer->token->value) {
@@ -866,8 +822,6 @@ private function parseFragmentName(): NameNode
      *
      * EnumValue : Name but not `true`, `false` or `null`
      *
-     * @throws SyntaxError
-     *
      * @return BooleanValueNode|EnumValueNode|FloatValueNode|IntValueNode|StringValueNode|VariableNode|ListValueNode|ObjectValueNode|NullValueNode
      */
     private function parseValueLiteral(bool $isConst): ValueNode
@@ -947,19 +901,11 @@ private function parseStringLiteral(): StringValueNode
         ]);
     }
 
-    /**
-     * @throws SyntaxError
-     *
-     * @return BooleanValueNode|EnumValueNode|FloatValueNode|IntValueNode|StringValueNode|VariableNode
-     */
     private function parseConstValue(): ValueNode
     {
         return $this->parseValueLiteral(true);
     }
 
-    /**
-     * @return BooleanValueNode|EnumValueNode|FloatValueNode|IntValueNode|ListValueNode|ObjectValueNode|StringValueNode|VariableNode
-     */
     private function parseVariableValue(): ValueNode
     {
         return $this->parseValueLiteral(false);
@@ -969,19 +915,13 @@ private function parseArray(bool $isConst): ListValueNode
     {
         $start = $this->lexer->token;
         $parseFn = $isConst
-            ? function () {
-                return $this->parseConstValue();
-            }
-        : function () {
-            return $this->parseVariableValue();
-        };
+            ? fn (): ValueNode => $this->parseConstValue()
+            : fn (): ValueNode => $this->parseVariableValue();
 
-        return new ListValueNode(
-            [
-                'values' => $this->any(Token::BRACKET_L, $parseFn, Token::BRACKET_R),
-                'loc' => $this->loc($start),
-            ]
-        );
+        return new ListValueNode([
+            'values' => $this->any(Token::BRACKET_L, $parseFn, Token::BRACKET_R),
+            'loc' => $this->loc($start),
+        ]);
     }
 
     private function parseObject(bool $isConst): ObjectValueNode
@@ -1016,8 +956,6 @@ private function parseObjectField(bool $isConst): ObjectFieldNode
     // Implements the parsing rules in the Directives section.
 
     /**
-     * @throws SyntaxError
-     *
      * @return NodeList<DirectiveNode>
      */
     private function parseDirectives(bool $isConst): NodeList
@@ -1030,9 +968,6 @@ private function parseDirectives(bool $isConst): NodeList
         return new NodeList($directives);
     }
 
-    /**
-     * @throws SyntaxError
-     */
     private function parseDirective(bool $isConst): DirectiveNode
     {
         $start = $this->lexer->token;
@@ -1050,8 +985,6 @@ private function parseDirective(bool $isConst): DirectiveNode
     /**
      * Handles the Type: TypeName, ListType, and NonNullType parsing rules.
      *
-     * @throws SyntaxError
-     *
      * @return ListTypeNode|NamedTypeNode|NonNullTypeNode
      */
     private function parseTypeReference(): TypeNode
@@ -1092,8 +1025,6 @@ private function parseNamedType(): NamedTypeNode
     // Implements the parsing rules in the Type Definition section.
 
     /**
-     * @throws SyntaxError
-     *
      * @return TypeSystemDefinitionNode&Node
      */
     private function parseTypeSystemDefinition(): TypeSystemDefinitionNode
@@ -1151,9 +1082,6 @@ private function parseDescription(): ?StringValueNode
         return null;
     }
 
-    /**
-     * @throws SyntaxError
-     */
     private function parseSchemaDefinition(): SchemaDefinitionNode
     {
         $start = $this->lexer->token;
@@ -1175,9 +1103,6 @@ function (): OperationTypeDefinitionNode {
         ]);
     }
 
-    /**
-     * @throws SyntaxError
-     */
     private function parseOperationTypeDefinition(): OperationTypeDefinitionNode
     {
         $start = $this->lexer->token;
@@ -1192,9 +1117,6 @@ private function parseOperationTypeDefinition(): OperationTypeDefinitionNode
         ]);
     }
 
-    /**
-     * @throws SyntaxError
-     */
     private function parseScalarTypeDefinition(): ScalarTypeDefinitionNode
     {
         $start = $this->lexer->token;
@@ -1211,9 +1133,6 @@ private function parseScalarTypeDefinition(): ScalarTypeDefinitionNode
         ]);
     }
 
-    /**
-     * @throws SyntaxError
-     */
     private function parseObjectTypeDefinition(): ObjectTypeDefinitionNode
     {
         $start = $this->lexer->token;
@@ -1256,8 +1175,6 @@ private function parseImplementsInterfaces(): NodeList
     }
 
     /**
-     * @throws SyntaxError
-     *
      * @return NodeList<FieldDefinitionNode>
      */
     private function parseFieldsDefinition(): NodeList
@@ -1287,9 +1204,6 @@ private function parseFieldsDefinition(): NodeList
         return $nodeList;
     }
 
-    /**
-     * @throws SyntaxError
-     */
     private function parseFieldDefinition(): FieldDefinitionNode
     {
         $start = $this->lexer->token;
@@ -1311,27 +1225,20 @@ private function parseFieldDefinition(): FieldDefinitionNode
     }
 
     /**
-     * @throws SyntaxError
-     *
      * @return NodeList<InputValueDefinitionNode>
      */
     private function parseArgumentsDefinition(): NodeList
     {
-        /** @var NodeList<InputValueDefinitionNode> $nodeList */
-        $nodeList = $this->peek(Token::PAREN_L)
+        // @phpstan-ignore-next-line generic type of empty NodeList is not initialized
+        return $this->peek(Token::PAREN_L)
             ? $this->many(
                 Token::PAREN_L,
                 fn (): InputValueDefinitionNode => $this->parseInputValueDefinition(),
                 Token::PAREN_R
             )
             : new NodeList([]);
-
-        return $nodeList;
     }
 
-    /**
-     * @throws SyntaxError
-     */
     private function parseInputValueDefinition(): InputValueDefinitionNode
     {
         $start = $this->lexer->token;
@@ -1356,9 +1263,6 @@ private function parseInputValueDefinition(): InputValueDefinitionNode
         ]);
     }
 
-    /**
-     * @throws SyntaxError
-     */
     private function parseInterfaceTypeDefinition(): InterfaceTypeDefinitionNode
     {
         $start = $this->lexer->token;
@@ -1382,8 +1286,6 @@ private function parseInterfaceTypeDefinition(): InterfaceTypeDefinitionNode
     /**
      * UnionTypeDefinition :
      *   - Description? union Name Directives[Const]? UnionMemberTypes?
-     *
-     * @throws SyntaxError
      */
     private function parseUnionTypeDefinition(): UnionTypeDefinitionNode
     {
@@ -1420,9 +1322,6 @@ private function parseUnionMemberTypes(): NodeList
         return new NodeList($types);
     }
 
-    /**
-     * @throws SyntaxError
-     */
     private function parseEnumTypeDefinition(): EnumTypeDefinitionNode
     {
         $start = $this->lexer->token;
@@ -1442,27 +1341,20 @@ private function parseEnumTypeDefinition(): EnumTypeDefinitionNode
     }
 
     /**
-     * @throws SyntaxError
-     *
      * @return NodeList<EnumValueDefinitionNode>
      */
     private function parseEnumValuesDefinition(): NodeList
     {
-        /** @var NodeList<EnumValueDefinitionNode> $nodeList */
-        $nodeList = $this->peek(Token::BRACE_L)
+        // @phpstan-ignore-next-line generic type of empty NodeList is not initialized
+        return $this->peek(Token::BRACE_L)
             ? $this->many(
                 Token::BRACE_L,
                 fn (): EnumValueDefinitionNode => $this->parseEnumValueDefinition(),
                 Token::BRACE_R
             )
             : new NodeList([]);
-
-        return $nodeList;
     }
 
-    /**
-     * @throws SyntaxError
-     */
     private function parseEnumValueDefinition(): EnumValueDefinitionNode
     {
         $start = $this->lexer->token;
@@ -1478,9 +1370,6 @@ private function parseEnumValueDefinition(): EnumValueDefinitionNode
         ]);
     }
 
-    /**
-     * @throws SyntaxError
-     */
     private function parseInputObjectTypeDefinition(): InputObjectTypeDefinitionNode
     {
         $start = $this->lexer->token;
@@ -1500,14 +1389,12 @@ private function parseInputObjectTypeDefinition(): InputObjectTypeDefinitionNode
     }
 
     /**
-     * @throws SyntaxError
-     *
      * @return NodeList<InputValueDefinitionNode>
      */
     private function parseInputFieldsDefinition(): NodeList
     {
-        /** @var NodeList<InputValueDefinitionNode> $nodeList */
-        $nodeList = $this->peek(Token::BRACE_L)
+        // @phpstan-ignore-next-line generic type of empty NodeList is not initialized
+        return $this->peek(Token::BRACE_L)
             ? $this->many(
                 Token::BRACE_L,
                 function (): InputValueDefinitionNode {
@@ -1516,13 +1403,9 @@ function (): InputValueDefinitionNode {
                 Token::BRACE_R
             )
             : new NodeList([]);
-
-        return $nodeList;
     }
 
     /**
-     * @throws SyntaxError
-     *
      * @return TypeExtensionNode&Node
      */
     private function parseTypeExtension(): TypeExtensionNode
@@ -1557,9 +1440,6 @@ private function parseTypeExtension(): TypeExtensionNode
         throw $this->unexpected($keywordToken);
     }
 
-    /**
-     * @throws SyntaxError
-     */
     private function parseSchemaTypeExtension(): SchemaTypeExtensionNode
     {
         $start = $this->lexer->token;
@@ -1585,9 +1465,6 @@ private function parseSchemaTypeExtension(): SchemaTypeExtensionNode
         ]);
     }
 
-    /**
-     * @throws SyntaxError
-     */
     private function parseScalarTypeExtension(): ScalarTypeExtensionNode
     {
         $start = $this->lexer->token;
@@ -1606,9 +1483,6 @@ private function parseScalarTypeExtension(): ScalarTypeExtensionNode
         ]);
     }
 
-    /**
-     * @throws SyntaxError
-     */
     private function parseObjectTypeExtension(): ObjectTypeExtensionNode
     {
         $start = $this->lexer->token;
@@ -1636,9 +1510,6 @@ private function parseObjectTypeExtension(): ObjectTypeExtensionNode
         ]);
     }
 
-    /**
-     * @throws SyntaxError
-     */
     private function parseInterfaceTypeExtension(): InterfaceTypeExtensionNode
     {
         $start = $this->lexer->token;
@@ -1669,8 +1540,6 @@ private function parseInterfaceTypeExtension(): InterfaceTypeExtensionNode
      * UnionTypeExtension :
      *   - extend union Name Directives[Const]? UnionMemberTypes
      *   - extend union Name Directives[Const].
-     *
-     * @throws SyntaxError
      */
     private function parseUnionTypeExtension(): UnionTypeExtensionNode
     {
@@ -1692,9 +1561,6 @@ private function parseUnionTypeExtension(): UnionTypeExtensionNode
         ]);
     }
 
-    /**
-     * @throws SyntaxError
-     */
     private function parseEnumTypeExtension(): EnumTypeExtensionNode
     {
         $start = $this->lexer->token;
@@ -1718,9 +1584,6 @@ private function parseEnumTypeExtension(): EnumTypeExtensionNode
         ]);
     }
 
-    /**
-     * @throws SyntaxError
-     */
     private function parseInputObjectTypeExtension(): InputObjectTypeExtensionNode
     {
         $start = $this->lexer->token;
@@ -1747,8 +1610,6 @@ private function parseInputObjectTypeExtension(): InputObjectTypeExtensionNode
     /**
      * DirectiveDefinition :
      *   - Description? directive @ Name ArgumentsDefinition? `repeatable`? on DirectiveLocations.
-     *
-     * @throws SyntaxError
      */
     private function parseDirectiveDefinition(): DirectiveDefinitionNode
     {
@@ -1773,8 +1634,6 @@ private function parseDirectiveDefinition(): DirectiveDefinitionNode
     }
 
     /**
-     * @throws SyntaxError
-     *
      * @return NodeList<NameNode>
      */
     private function parseDirectiveLocations(): NodeList
@@ -1789,9 +1648,6 @@ private function parseDirectiveLocations(): NodeList
         return new NodeList($locations);
     }
 
-    /**
-     * @throws SyntaxError
-     */
     private function parseDirectiveLocation(): NameNode
     {
         $start = $this->lexer->token;
diff --git a/src/Language/Printer.php b/src/Language/Printer.php
index 4692ee916..8fc0a3fe8 100644
--- a/src/Language/Printer.php
+++ b/src/Language/Printer.php
@@ -213,6 +213,7 @@ protected function p(?Node $node, bool $isDescription = false): string
                 return 'fragment ' . $this->p($node->name)
                     . $this->wrap(
                         '(',
+                        // @phpstan-ignore-next-line generic type of empty NodeList is not recognized
                         $this->printList($node->variableDefinitions ?? new NodeList([]), ', '),
                         ')'
                     )
@@ -408,7 +409,7 @@ protected function p(?Node $node, bool $isDescription = false): string
                     return BlockString::print($node->value, $isDescription ? '' : '  ');
                 }
 
-                return json_encode($node->value);
+                return json_encode($node->value, JSON_THROW_ON_ERROR);
 
             case $node instanceof UnionTypeDefinitionNode:
                 $typesStr = $this->printList($node->types, ' | ');
@@ -455,9 +456,9 @@ protected function p(?Node $node, bool $isDescription = false): string
     }
 
     /**
-     * @param NodeList<TNode> $list
-     *
      * @template TNode of Node
+     *
+     * @param NodeList<TNode> $list
      */
     protected function printList(NodeList $list, string $separator = ''): string
     {
@@ -472,9 +473,9 @@ protected function printList(NodeList $list, string $separator = ''): string
     /**
      * Print each item on its own line, wrapped in an indented "{ }" block.
      *
-     * @param NodeList<TNode> $list
-     *
      * @template TNode of Node
+     *
+     * @param NodeList<TNode> $list
      */
     protected function printListBlock(NodeList $list): string
     {
diff --git a/src/Language/Visitor.php b/src/Language/Visitor.php
index 90e81866b..8ede7d2da 100644
--- a/src/Language/Visitor.php
+++ b/src/Language/Visitor.php
@@ -169,16 +169,16 @@ class Visitor
     /**
      * Visit the AST (see class description for details).
      *
-     * @param NodeList<TNode>|Node      $root
-     * @param VisitorArray              $visitor
+     * @template TNode of Node
+     *
+     * @param NodeList<TNode>|Node $root
+     * @param VisitorArray $visitor
      * @param array<string, mixed>|null $keyMap
      *
      * @throws Exception
      *
      * @return Node|mixed
      *
-     * @template TNode of Node
-     *
      * @api
      */
     public static function visit(object $root, array $visitor, ?array $keyMap = null)
@@ -212,12 +212,8 @@ public static function visit(object $root, array $visitor, ?array $keyMap = null
                 $parent = array_pop($ancestors);
 
                 if ($isEdited) {
-                    if ($inArray) {
-                        // $node = $node; // arrays are value types in PHP
-                        if ($node instanceof NodeList) {
-                            $node = clone $node;
-                        }
-                    } else {
+                    if ($node instanceof Node || $node instanceof NodeList) {
+                        // TODO should we use cloneDeep()?
                         $node = clone $node;
                     }
 
@@ -231,6 +227,7 @@ public static function visit(object $root, array $visitor, ?array $keyMap = null
                         }
 
                         if ($inArray && null === $editValue) {
+                            assert($node instanceof NodeList, 'Follows from $inArray');
                             $node->splice($editKey, 1);
                             ++$editOffset;
                         } else {
diff --git a/src/Server/Helper.php b/src/Server/Helper.php
index e52618f06..f5e971c36 100644
--- a/src/Server/Helper.php
+++ b/src/Server/Helper.php
@@ -212,7 +212,7 @@ public function executeOperation(ServerConfig $config, OperationParams $op)
      *
      * @param array<OperationParams> $operations
      *
-     * @return ExecutionResult|array<int, ExecutionResult>|Promise
+     * @return array<int, ExecutionResult>|Promise
      *
      * @api
      */
@@ -610,13 +610,10 @@ public function toPsrResponse($result, ResponseInterface $response, StreamInterf
      */
     private function doConvertToPsrResponse($result, ResponseInterface $response, StreamInterface $writableBodyStream): ResponseInterface
     {
-        $httpStatus = $this->resolveHttpStatus($result);
-
-        $result = json_encode($result);
-        $writableBodyStream->write($result);
+        $writableBodyStream->write(json_encode($result, JSON_THROW_ON_ERROR));
 
         return $response
-            ->withStatus($httpStatus)
+            ->withStatus($this->resolveHttpStatus($result))
             ->withHeader('Content-Type', 'application/json')
             ->withBody($writableBodyStream);
     }
diff --git a/src/Server/ServerConfig.php b/src/Server/ServerConfig.php
index b626942ef..62ca667dd 100644
--- a/src/Server/ServerConfig.php
+++ b/src/Server/ServerConfig.php
@@ -92,7 +92,7 @@ public static function create(array $config = []): self
 
     private ?Schema $schema = null;
 
-    /** @var mixed|callable(self, OperationParams, DocumentNode $doc): mixed|null */
+    /** @var mixed|callable(self, OperationParams, DocumentNode): mixed|null */
     private $context = null;
 
     /**
diff --git a/src/Server/StandardServer.php b/src/Server/StandardServer.php
index 2fe082361..1fab892a0 100644
--- a/src/Server/StandardServer.php
+++ b/src/Server/StandardServer.php
@@ -39,11 +39,9 @@
  */
 class StandardServer
 {
-    /** @var ServerConfig */
-    private $config;
+    private ServerConfig $config;
 
-    /** @var Helper */
-    private $helper;
+    private Helper $helper;
 
     /**
      * Converts and exception to error and sends spec-compliant HTTP 500 error.
diff --git a/src/Type/Definition/AbstractType.php b/src/Type/Definition/AbstractType.php
index 313804e7c..d85fee4c4 100644
--- a/src/Type/Definition/AbstractType.php
+++ b/src/Type/Definition/AbstractType.php
@@ -4,9 +4,10 @@
 
 namespace GraphQL\Type\Definition;
 
+use GraphQL\Deferred;
+
 /**
- * @phpstan-type AbstractTypeAlias InterfaceType|UnionType
- * @phpstan-type ResolveTypeReturn ObjectType|string|callable(): (ObjectType|string|null)|null
+ * @phpstan-type ResolveTypeReturn ObjectType|string|callable(): (ObjectType|string|null)|Deferred|null
  * @phpstan-type ResolveType callable(mixed $objectValue, mixed $context, ResolveInfo $resolveInfo): ResolveTypeReturn
  */
 interface AbstractType
@@ -15,9 +16,9 @@ interface AbstractType
      * Resolves the concrete ObjectType for the given value.
      *
      * @param mixed $objectValue The resolved value for the object type
-     * @param mixed $context     The context that was passed to GraphQL::execute()
+     * @param mixed $context The context that was passed to GraphQL::execute()
      *
-     * @return ObjectType|string|callable|null
+     * @return ObjectType|string|callable|Deferred|null
      * @phpstan-return ResolveTypeReturn
      */
     public function resolveType($objectValue, $context, ResolveInfo $info);
diff --git a/src/Type/Definition/Argument.php b/src/Type/Definition/Argument.php
index 77decf5a1..a3c517621 100644
--- a/src/Type/Definition/Argument.php
+++ b/src/Type/Definition/Argument.php
@@ -12,7 +12,6 @@
 use function is_array;
 
 /**
- * @phpstan-import-type InputTypeAlias from InputType
  * @phpstan-type ArgumentType (Type&InputType)|callable(): (Type&InputType)
  * @phpstan-type UnnamedArgumentConfig array{
  *     name?: string,
@@ -44,7 +43,7 @@ class Argument
 
     public ?InputValueDefinitionNode $astNode;
 
-    /** @var ArgumentConfig */
+    /** @phpstan-var ArgumentConfig */
     public array $config;
 
     /**
@@ -83,7 +82,6 @@ public static function listFromConfig(iterable $config): array
 
     /**
      * @return Type&InputType
-     * @phpstan-return InputTypeAlias
      */
     public function getType(): Type
     {
@@ -107,7 +105,7 @@ public function isRequired(): bool
     }
 
     /**
-     * @param Type &NamedType $parentType
+     * @param Type&NamedType $parentType
      */
     public function assertValid(FieldDefinition $parentField, Type $parentType): void
     {
diff --git a/src/Type/Definition/BooleanType.php b/src/Type/Definition/BooleanType.php
index bdb2945a4..e9eea85d9 100644
--- a/src/Type/Definition/BooleanType.php
+++ b/src/Type/Definition/BooleanType.php
@@ -7,6 +7,7 @@
 use GraphQL\Error\Error;
 use GraphQL\Language\AST\BooleanValueNode;
 use GraphQL\Language\AST\Node;
+use GraphQL\Language\Printer;
 use GraphQL\Utils\Utils;
 use function is_bool;
 
@@ -33,7 +34,8 @@ public function parseValue($value): bool
             return $value;
         }
 
-        throw new Error('Boolean cannot represent a non boolean value: ' . Utils::printSafe($value));
+        $notBoolean = Utils::printSafe($value);
+        throw new Error("Boolean cannot represent a non boolean value: {$notBoolean}");
     }
 
     public function parseLiteral(Node $valueNode, ?array $variables = null): bool
@@ -42,7 +44,7 @@ public function parseLiteral(Node $valueNode, ?array $variables = null): bool
             return $valueNode->value;
         }
 
-        // Intentionally without message, as all information already in wrapped Exception
-        throw new Error();
+        $notBoolean = Printer::doPrint($valueNode);
+        throw new Error("Boolean cannot represent a non boolean value: {$notBoolean}", $valueNode);
     }
 }
diff --git a/src/Type/Definition/CustomScalarType.php b/src/Type/Definition/CustomScalarType.php
index 34cda69ff..ef5a26064 100644
--- a/src/Type/Definition/CustomScalarType.php
+++ b/src/Type/Definition/CustomScalarType.php
@@ -8,20 +8,30 @@
 use GraphQL\Language\AST\Node;
 use GraphQL\Language\AST\ScalarTypeDefinitionNode;
 use GraphQL\Language\AST\ScalarTypeExtensionNode;
+use GraphQL\Language\AST\ValueNode;
 use GraphQL\Utils\AST;
 use function is_callable;
 
 /**
- * @phpstan-import-type LeafValueNode from LeafType
- * @phpstan-type CustomScalarConfig array{
+ * @phpstan-type InputCustomScalarConfig array{
+ *   name?: string|null,
+ *   description?: string|null,
+ *   serialize?: callable(mixed): mixed,
+ *   parseValue: callable(mixed): mixed,
+ *   parseLiteral: callable(ValueNode&Node, array<string, mixed>|null): mixed,
+ *   astNode?: ScalarTypeDefinitionNode|null,
+ *   extensionASTNodes?: array<ScalarTypeExtensionNode>|null,
+ * }
+ * @phpstan-type OutputCustomScalarConfig array{
  *   name?: string|null,
  *   description?: string|null,
  *   serialize: callable(mixed): mixed,
  *   parseValue?: callable(mixed): mixed,
- *   parseLiteral?: callable(LeafValueNode, array<string, mixed>|null): mixed,
+ *   parseLiteral?: callable(ValueNode&Node, array<string, mixed>|null): mixed,
  *   astNode?: ScalarTypeDefinitionNode|null,
  *   extensionASTNodes?: array<ScalarTypeExtensionNode>|null,
  * }
+ * @phpstan-type CustomScalarConfig InputCustomScalarConfig|OutputCustomScalarConfig
  */
 class CustomScalarType extends ScalarType
 {
@@ -40,7 +50,11 @@ public function __construct(array $config)
 
     public function serialize($value)
     {
-        return $this->config['serialize']($value);
+        if (isset($this->config['serialize'])) {
+            return $this->config['serialize']($value);
+        }
+
+        return $value;
     }
 
     public function parseValue($value)
@@ -66,7 +80,7 @@ public function assertValid(): void
         parent::assertValid();
 
         // @phpstan-ignore-next-line should not happen if used correctly
-        if (! isset($this->config['serialize']) || ! is_callable($this->config['serialize'])) {
+        if (isset($this->config['serialize']) && ! is_callable($this->config['serialize'])) {
             throw new InvariantViolation(
                 "{$this->name} must provide \"serialize\" function. If this custom Scalar "
                 . 'is also used as an input type, ensure "parseValue" and "parseLiteral" '
diff --git a/src/Type/Definition/EnumType.php b/src/Type/Definition/EnumType.php
index 8ced10361..f3d1ff4ce 100644
--- a/src/Type/Definition/EnumType.php
+++ b/src/Type/Definition/EnumType.php
@@ -11,6 +11,7 @@
 use GraphQL\Language\AST\EnumTypeExtensionNode;
 use GraphQL\Language\AST\EnumValueNode;
 use GraphQL\Language\AST\Node;
+use GraphQL\Language\Printer;
 use GraphQL\Utils\MixedStore;
 use GraphQL\Utils\Utils;
 use function is_array;
@@ -164,20 +165,26 @@ public function parseValue($value)
 
     public function parseLiteral(Node $valueNode, ?array $variables = null)
     {
-        if ($valueNode instanceof EnumValueNode) {
-            $name = $valueNode->value;
+        if (! $valueNode instanceof EnumValueNode) {
+            $valueStr = Printer::doPrint($valueNode);
+            throw new Error(
+                "Enum \"{$this->name}\" cannot represent non-enum value: {$valueStr}.{$this->didYouMean($valueStr)}",
+                $valueNode
+            );
+        }
 
-            if (! isset($this->nameLookup)) {
-                $this->initializeNameLookup();
-            }
+        $name = $valueNode->value;
 
-            if (isset($this->nameLookup[$name])) {
-                return $this->nameLookup[$name]->value;
-            }
+        if (! isset($this->nameLookup)) {
+            $this->initializeNameLookup();
         }
 
-        // Intentionally without message, as all information already in wrapped Exception
-        throw new Error();
+        if (isset($this->nameLookup[$name])) {
+            return $this->nameLookup[$name]->value;
+        }
+
+        $valueStr = Printer::doPrint($valueNode);
+        throw new Error("Value \"{$valueStr}\" does not exist in \"{$this->name}\" enum.{$this->didYouMean($valueStr)}", $valueNode);
     }
 
     /**
@@ -205,4 +212,19 @@ private function initializeNameLookup(): void
             $this->nameLookup[$value->name] = $value;
         }
     }
+
+    protected function didYouMean(string $unknownValue): ?string
+    {
+        $suggestions = Utils::suggestionList(
+            $unknownValue,
+            array_map(
+                static fn (EnumValueDefinition $value): string => $value->name,
+                $this->getValues()
+            )
+        );
+
+        return [] === $suggestions
+            ? null
+            : ' Did you mean the enum value ' . Utils::quotedOrList($suggestions) . '?';
+    }
 }
diff --git a/src/Type/Definition/EnumValueDefinition.php b/src/Type/Definition/EnumValueDefinition.php
index 28c412319..115aeda27 100644
--- a/src/Type/Definition/EnumValueDefinition.php
+++ b/src/Type/Definition/EnumValueDefinition.php
@@ -28,11 +28,11 @@ class EnumValueDefinition
 
     public ?EnumValueDefinitionNode $astNode;
 
-    /** @var array<string, mixed> */
-    public $config;
+    /** @phpstan-var EnumValueConfig */
+    public array $config;
 
     /**
-     * @param array<string, mixed> $config
+     * @phpstan-param EnumValueConfig $config
      */
     public function __construct(array $config)
     {
diff --git a/src/Type/Definition/FieldDefinition.php b/src/Type/Definition/FieldDefinition.php
index e134f97ad..d6cc5535b 100644
--- a/src/Type/Definition/FieldDefinition.php
+++ b/src/Type/Definition/FieldDefinition.php
@@ -18,7 +18,7 @@
  * @phpstan-import-type FieldResolver from Executor
  * @phpstan-import-type ArgumentListConfig from Argument
  * @phpstan-type FieldType (Type&OutputType)|callable(): (Type&OutputType)
- * @phpstan-type ComplexityFn callable(int, array<string, mixed>): int|null
+ * @phpstan-type ComplexityFn callable(int, array<string, mixed>): (int|null)
  * @phpstan-type FieldDefinitionConfig array{
  *     name: string,
  *     type: FieldType,
@@ -38,7 +38,16 @@
  *     astNode?: FieldDefinitionNode|null,
  *     complexity?: ComplexityFn|null,
  * }
- * @phpstan-type FieldMapConfig (callable(): iterable<mixed>)|iterable<mixed>
+ * @phpstan-type FieldsConfig iterable<mixed>|(callable(): iterable<mixed>)
+ */
+/*
+ * TODO check if newer versions of PHPStan can handle the full definition, it currently crashes when it is used
+ * @phpstan-type EagerListEntry FieldDefinitionConfig|(Type&OutputType)
+ * @phpstan-type EagerMapEntry UnnamedFieldDefinitionConfig|FieldDefinition
+ * @phpstan-type FieldsList iterable<EagerListEntry|(callable(): EagerListEntry)>
+ * @phpstan-type FieldsMap iterable<string, EagerMapEntry|(callable(): EagerMapEntry)>
+ * @phpstan-type FieldsIterable FieldsList|FieldsMap
+ * @phpstan-type FieldsConfig FieldsIterable|(callable(): FieldsIterable)
  */
 class FieldDefinition
 {
@@ -61,13 +70,16 @@ class FieldDefinition
 
     public ?FieldDefinitionNode $astNode;
 
-    /** @var ComplexityFn|null */
+    /**
+     * @var callable|null
+     * @phpstan-var ComplexityFn|null
+     */
     public $complexityFn;
 
     /**
      * Original field definition config.
      *
-     * @var FieldDefinitionConfig
+     * @phpstan-var FieldDefinitionConfig
      */
     public array $config;
 
@@ -77,7 +89,7 @@ class FieldDefinition
     /**
      * @param FieldDefinitionConfig $config
      */
-    protected function __construct(array $config)
+    public function __construct(array $config)
     {
         $this->name = $config['name'];
         $this->resolveFn = $config['resolve'] ?? null;
@@ -94,10 +106,10 @@ protected function __construct(array $config)
 
     /**
      * @param ObjectType|InterfaceType $parentType
-     * @param callable|iterable        $fields
-     * @phpstan-param FieldMapConfig $fields
+     * @param callable|iterable $fields
+     * @phpstan-param FieldsConfig $fields
      *
-     * @return array<string, self>
+     * @return array<string, self|UnresolvedFieldDefinition>
      */
     public static function defineFieldMap(Type $parentType, $fields): array
     {
@@ -125,13 +137,8 @@ public static function defineFieldMap(Type $parentType, $fields): array
                     $field['name'] = $maybeName;
                 }
 
-                if (isset($field['args']) && ! is_array($field['args'])) {
-                    throw new InvariantViolation(
-                        "{$parentType->name}.{$maybeName} args must be an array."
-                    );
-                }
-
-                $fieldDef = self::create($field);
+                // @phpstan-ignore-next-line PHPStan won't let us define the whole type
+                $fieldDef = new self($field);
             } elseif ($field instanceof self) {
                 $fieldDef = $field;
             } elseif (is_callable($field)) {
@@ -141,9 +148,13 @@ public static function defineFieldMap(Type $parentType, $fields): array
                     );
                 }
 
-                $fieldDef = new UnresolvedFieldDefinition($parentType, $maybeName, $field);
+                $fieldDef = new UnresolvedFieldDefinition($maybeName, $field);
             } elseif ($field instanceof Type) {
-                $fieldDef = self::create(['name' => $maybeName, 'type' => $field]);
+                // @phpstan-ignore-next-line PHPStan won't let us define the whole type
+                $fieldDef = new self([
+                    'name' => $maybeName,
+                    'type' => $field,
+                ]);
             } else {
                 $invalidFieldConfig = Utils::printSafe($field);
 
@@ -158,14 +169,6 @@ public static function defineFieldMap(Type $parentType, $fields): array
         return $map;
     }
 
-    /**
-     * @param array<string, mixed> $field
-     */
-    public static function create(array $field): FieldDefinition
-    {
-        return new self($field);
-    }
-
     public function getArg(string $name): ?Argument
     {
         foreach ($this->args as $arg) {
@@ -196,7 +199,7 @@ public function isDeprecated(): bool
     }
 
     /**
-     * @param Type &NamedType $parentType
+     * @param Type&NamedType $parentType
      *
      * @throws InvariantViolation
      */
diff --git a/src/Type/Definition/FloatType.php b/src/Type/Definition/FloatType.php
index c52fb0bb3..6b5f03b8f 100644
--- a/src/Type/Definition/FloatType.php
+++ b/src/Type/Definition/FloatType.php
@@ -9,6 +9,7 @@
 use GraphQL\Language\AST\FloatValueNode;
 use GraphQL\Language\AST\IntValueNode;
 use GraphQL\Language\AST\Node;
+use GraphQL\Language\Printer;
 use GraphQL\Utils\Utils;
 use function is_bool;
 use function is_finite;
@@ -48,10 +49,8 @@ public function parseValue($value): float
             : null;
 
         if (null === $float || ! is_finite($float)) {
-            throw new Error(
-                'Float cannot represent non numeric value: '
-                . Utils::printSafe($value)
-            );
+            $notFloat = Utils::printSafe($value);
+            throw new Error("Float cannot represent non numeric value: {$notFloat}");
         }
 
         return $float;
@@ -63,7 +62,7 @@ public function parseLiteral(Node $valueNode, ?array $variables = null)
             return (float) $valueNode->value;
         }
 
-        // Intentionally without message, as all information already in wrapped Exception
-        throw new Error();
+        $notFloat = Printer::doPrint($valueNode);
+        throw new Error("Float cannot represent non numeric value: {$notFloat}", $valueNode);
     }
 }
diff --git a/src/Type/Definition/HasFieldsTypeImplementation.php b/src/Type/Definition/HasFieldsTypeImplementation.php
index 4d80c58f6..a1019d826 100644
--- a/src/Type/Definition/HasFieldsTypeImplementation.php
+++ b/src/Type/Definition/HasFieldsTypeImplementation.php
@@ -43,11 +43,12 @@ public function findField(string $name): ?FieldDefinition
             return null;
         }
 
-        if ($this->fields[$name] instanceof UnresolvedFieldDefinition) {
-            $this->fields[$name] = $this->fields[$name]->resolve();
+        $field = $this->fields[$name];
+        if ($field instanceof UnresolvedFieldDefinition) {
+            return $this->fields[$name] = $field->resolve();
         }
 
-        return $this->fields[$name];
+        return $field;
     }
 
     public function hasField(string $name): bool
@@ -62,13 +63,12 @@ public function getFields(): array
         $this->initializeFields();
 
         foreach ($this->fields as $name => $field) {
-            if (! ($field instanceof UnresolvedFieldDefinition)) {
-                continue;
+            if ($field instanceof UnresolvedFieldDefinition) {
+                $this->fields[$name] = $field->resolve();
             }
-
-            $this->fields[$name] = $field->resolve();
         }
 
+        // @phpstan-ignore-next-line all field definitions are now resolved
         return $this->fields;
     }
 
diff --git a/src/Type/Definition/IDType.php b/src/Type/Definition/IDType.php
index 5daf010e2..7c85d5134 100644
--- a/src/Type/Definition/IDType.php
+++ b/src/Type/Definition/IDType.php
@@ -9,6 +9,7 @@
 use GraphQL\Language\AST\IntValueNode;
 use GraphQL\Language\AST\Node;
 use GraphQL\Language\AST\StringValueNode;
+use GraphQL\Language\Printer;
 use GraphQL\Utils\Utils;
 use function is_int;
 use function is_object;
@@ -33,7 +34,8 @@ public function serialize($value): string
             || (is_object($value) && method_exists($value, '__toString'));
 
         if (! $canCast) {
-            throw new SerializationError('ID cannot represent value: ' . Utils::printSafe($value));
+            $notID = Utils::printSafe($value);
+            throw new SerializationError("ID cannot represent a non-string and non-integer value: {$notID}");
         }
 
         return (string) $value;
@@ -45,7 +47,8 @@ public function parseValue($value): string
             return (string) $value;
         }
 
-        throw new Error('ID cannot represent value: ' . Utils::printSafe($value));
+        $notID = Utils::printSafe($value);
+        throw new Error("ID cannot represent a non-string and non-integer value: {$notID}");
     }
 
     public function parseLiteral(Node $valueNode, ?array $variables = null): string
@@ -54,7 +57,7 @@ public function parseLiteral(Node $valueNode, ?array $variables = null): string
             return $valueNode->value;
         }
 
-        // Intentionally without message, as the wrapping Exception will have all necessary information
-        throw new Error();
+        $notID = Printer::doPrint($valueNode);
+        throw new Error("ID cannot represent a non-string and non-integer value: {$notID}", $valueNode);
     }
 }
diff --git a/src/Type/Definition/InputObjectField.php b/src/Type/Definition/InputObjectField.php
index 6cd79d322..9bb70c3f9 100644
--- a/src/Type/Definition/InputObjectField.php
+++ b/src/Type/Definition/InputObjectField.php
@@ -11,7 +11,6 @@
 use GraphQL\Utils\Utils;
 
 /**
- * @phpstan-import-type InputTypeAlias from InputType
  * @phpstan-type ArgumentType (Type&InputType)|callable(): (Type&InputType)
  * @phpstan-type InputObjectFieldConfig array{
  *   name: string,
@@ -42,7 +41,7 @@ class InputObjectField
 
     public ?InputValueDefinitionNode $astNode;
 
-    /** @var array<string, mixed> */
+    /** @phpstan-var InputObjectFieldConfig */
     public array $config;
 
     /**
@@ -61,7 +60,6 @@ public function __construct(array $config)
 
     /**
      * @return Type&InputType
-     * @phpstan-return InputTypeAlias
      */
     public function getType(): Type
     {
@@ -85,7 +83,7 @@ public function isRequired(): bool
     }
 
     /**
-     * @param Type &NamedType $parentType
+     * @param Type&NamedType $parentType
      *
      * @throws InvariantViolation
      */
@@ -104,6 +102,7 @@ public function assertValid(Type $parentType): void
             throw new InvariantViolation("{$parentType->name}.{$this->name} field type must be Input Type but got: {$notInputType}");
         }
 
+        // @phpstan-ignore-next-line should not happen if used properly
         if (array_key_exists('resolve', $this->config)) {
             throw new InvariantViolation("{$parentType->name}.{$this->name} field has a resolve property, but Input Types cannot define resolvers.");
         }
diff --git a/src/Type/Definition/InputObjectType.php b/src/Type/Definition/InputObjectType.php
index d78388855..7fb07abeb 100644
--- a/src/Type/Definition/InputObjectType.php
+++ b/src/Type/Definition/InputObjectType.php
@@ -131,9 +131,9 @@ protected function initializeField($nameOrIndex, $field): void
         }
 
         if (is_array($field)) {
-            $name = $field['name'] ??= $nameOrIndex;
+            $field['name'] ??= $nameOrIndex;
 
-            if (! is_string($name)) {
+            if (! is_string($field['name'])) {
                 throw new InvariantViolation(
                     "{$this->name} fields must be an associative array with field names as keys, an array of arrays with a name attribute, or a callable which returns one of those."
                 );
diff --git a/src/Type/Definition/InputType.php b/src/Type/Definition/InputType.php
index 6b10be4f3..d970bff3d 100644
--- a/src/Type/Definition/InputType.php
+++ b/src/Type/Definition/InputType.php
@@ -16,8 +16,6 @@
       | InputObjectType
       | ListOfType<InputType>,
     >;
- *
- * @phpstan-type InputTypeAlias ScalarType|EnumType|InputObjectType|ListOfType<Type&InputType>|NonNull
  */
 interface InputType
 {
diff --git a/src/Type/Definition/IntType.php b/src/Type/Definition/IntType.php
index 96cff30bd..ba138582d 100644
--- a/src/Type/Definition/IntType.php
+++ b/src/Type/Definition/IntType.php
@@ -9,6 +9,7 @@
 use GraphQL\Error\SerializationError;
 use GraphQL\Language\AST\IntValueNode;
 use GraphQL\Language\AST\Node;
+use GraphQL\Language\Printer;
 use GraphQL\Utils\Utils;
 use function is_bool;
 use function is_float;
@@ -43,17 +44,13 @@ public function serialize($value): int
             : null;
 
         if (null === $float || floor($float) !== $float) {
-            throw new SerializationError(
-                'Int cannot represent non-integer value: '
-                . Utils::printSafe($value)
-            );
+            $notInt = Utils::printSafe($value);
+            throw new SerializationError("Int cannot represent non-integer value: {$notInt}");
         }
 
         if ($float > self::MAX_INT || $float < self::MIN_INT) {
-            throw new SerializationError(
-                'Int cannot represent non 32-bit signed integer value: '
-                . Utils::printSafe($value)
-            );
+            $outOfRangeInt = Utils::printSafe($value);
+            throw new SerializationError("Int cannot represent non 32-bit signed integer value: {$outOfRangeInt}");
         }
 
         return (int) $float;
@@ -61,20 +58,17 @@ public function serialize($value): int
 
     public function parseValue($value): int
     {
-        $isInt = is_int($value) || (is_float($value) && floor($value) === $value);
+        $isInt = is_int($value)
+            || (is_float($value) && floor($value) === $value);
 
         if (! $isInt) {
-            throw new Error(
-                'Int cannot represent non-integer value: '
-                . Utils::printSafe($value)
-            );
+            $notInt = Utils::printSafe($value);
+            throw new Error("Int cannot represent non-integer value: {$notInt}");
         }
 
         if ($value > self::MAX_INT || $value < self::MIN_INT) {
-            throw new Error(
-                'Int cannot represent non 32-bit signed integer value: '
-                . Utils::printSafe($value)
-            );
+            $outOfRangeInt = Utils::printSafe($value);
+            throw new Error("Int cannot represent non 32-bit signed integer value: {$outOfRangeInt}");
         }
 
         return (int) $value;
@@ -89,7 +83,7 @@ public function parseLiteral(Node $valueNode, ?array $variables = null): int
             }
         }
 
-        // Intentionally without message, as all information already in wrapped Exception
-        throw new Error();
+        $notInt = Printer::doPrint($valueNode);
+        throw new Error("Int cannot represent non-integer value: {$notInt}", $valueNode);
     }
 }
diff --git a/src/Type/Definition/InterfaceType.php b/src/Type/Definition/InterfaceType.php
index f3700684d..47580ecac 100644
--- a/src/Type/Definition/InterfaceType.php
+++ b/src/Type/Definition/InterfaceType.php
@@ -13,12 +13,12 @@
 
 /**
  * @phpstan-import-type ResolveType from AbstractType
- * @phpstan-import-type FieldMapConfig from FieldDefinition
+ * @phpstan-import-type FieldsConfig from FieldDefinition
  * @phpstan-type InterfaceTypeReference InterfaceType|callable(): InterfaceType
  * @phpstan-type InterfaceConfig array{
  *   name?: string|null,
  *   description?: string|null,
- *   fields: FieldMapConfig,
+ *   fields: FieldsConfig,
  *   interfaces?: iterable<InterfaceTypeReference>|callable(): iterable<InterfaceTypeReference>,
  *   resolveType?: ResolveType|null,
  *   astNode?: InterfaceTypeDefinitionNode|null,
diff --git a/src/Type/Definition/LeafType.php b/src/Type/Definition/LeafType.php
index 6583f701e..d26689a70 100644
--- a/src/Type/Definition/LeafType.php
+++ b/src/Type/Definition/LeafType.php
@@ -4,13 +4,8 @@
 
 namespace GraphQL\Type\Definition;
 
-use GraphQL\Language\AST\BooleanValueNode;
-use GraphQL\Language\AST\EnumValueNode;
-use GraphQL\Language\AST\FloatValueNode;
-use GraphQL\Language\AST\IntValueNode;
 use GraphQL\Language\AST\Node;
-use GraphQL\Language\AST\NullValueNode;
-use GraphQL\Language\AST\StringValueNode;
+use GraphQL\Language\AST\ValueNode;
 
 /*
 export type GraphQLLeafType =
@@ -18,9 +13,6 @@
 GraphQLEnumType;
 */
 
-/**
- * @phpstan-type LeafValueNode IntValueNode|FloatValueNode|StringValueNode|BooleanValueNode|NullValueNode|EnumValueNode
- */
 interface LeafType
 {
     /**
@@ -50,8 +42,8 @@ public function parseValue($value);
      *
      * Should throw an exception with a client friendly message on invalid value nodes, @see ClientAware.
      *
+     * @param ValueNode&Node $valueNode
      * @param array<string, mixed>|null $variables
-     * @phpstan-param LeafValueNode    $valueNode
      *
      * @return mixed
      */
diff --git a/src/Type/Definition/ListOfType.php b/src/Type/Definition/ListOfType.php
index e329ca0e9..78a10b244 100644
--- a/src/Type/Definition/ListOfType.php
+++ b/src/Type/Definition/ListOfType.php
@@ -46,7 +46,8 @@ public function getInnermostType(): NamedType
             $type = $type->getWrappedType();
         }
 
-        /** @var Type&NamedType $type known because we unwrapped all the way down */
+        assert($type instanceof NamedType, 'known because we unwrapped all the way down');
+
         return $type;
     }
 }
diff --git a/src/Type/Definition/NonNull.php b/src/Type/Definition/NonNull.php
index e1c54c618..a0ccdedc0 100644
--- a/src/Type/Definition/NonNull.php
+++ b/src/Type/Definition/NonNull.php
@@ -36,7 +36,6 @@ public function toString(): string
      */
     public function getWrappedType(): Type
     {
-        // @phpstan-ignore-next-line generics in Schema::resolveType() are not recognized correctly
         return Schema::resolveType($this->wrappedType);
     }
 
@@ -47,7 +46,8 @@ public function getInnermostType(): NamedType
             $type = $type->getWrappedType();
         }
 
-        /** @var Type&NamedType $type known because we unwrapped all the way down */
+        assert($type instanceof NamedType, 'known because we unwrapped all the way down');
+
         return $type;
     }
 }
diff --git a/src/Type/Definition/ObjectType.php b/src/Type/Definition/ObjectType.php
index e39d97098..4ae135252 100644
--- a/src/Type/Definition/ObjectType.php
+++ b/src/Type/Definition/ObjectType.php
@@ -57,7 +57,7 @@
  * @phpstan-type ObjectConfig array{
  *   name?: string|null,
  *   description?: string|null,
- *   resolveField?: FieldResolver,
+ *   resolveField?: FieldResolver|null,
  *   fields: (callable(): iterable<mixed>)|iterable<mixed>,
  *   interfaces?: iterable<InterfaceTypeReference>|callable(): iterable<InterfaceTypeReference>,
  *   isTypeOf?: (callable(mixed $objectValue, mixed $context, ResolveInfo $resolveInfo): (bool|Deferred|null))|null,
@@ -76,7 +76,10 @@ class ObjectType extends Type implements OutputType, CompositeType, NullableType
     /** @var array<int, ObjectTypeExtensionNode> */
     public array $extensionASTNodes;
 
-    /** @var callable|null */
+    /**
+     * @var callable|null
+     * @phpstan-var FieldResolver|null
+     */
     public $resolveFieldFn;
 
     /** @phpstan-var ObjectConfig */
diff --git a/src/Type/Definition/QueryPlan.php b/src/Type/Definition/QueryPlan.php
index 5e5c8a3fb..8821c5eb9 100644
--- a/src/Type/Definition/QueryPlan.php
+++ b/src/Type/Definition/QueryPlan.php
@@ -26,6 +26,11 @@
 use function is_array;
 use function is_numeric;
 
+/**
+ * @phpstan-type QueryPlanOptions array{
+ *   groupImplementorFields?: bool,
+ * }
+ */
 class QueryPlan
 {
     /** @var array<string, array<int, string>> */
@@ -45,17 +50,17 @@ class QueryPlan
     private bool $groupImplementorFields;
 
     /**
-     * @param iterable<FieldNode>                   $fieldNodes
-     * @param array<string, mixed>                  $variableValues
+     * @param iterable<FieldNode> $fieldNodes
+     * @param array<string, mixed> $variableValues
      * @param array<string, FragmentDefinitionNode> $fragments
-     * @param array<string>                         $options        TODO move to using key
+     * @param QueryPlanOptions $options
      */
     public function __construct(ObjectType $parentType, Schema $schema, iterable $fieldNodes, array $variableValues, array $fragments, array $options = [])
     {
         $this->schema = $schema;
         $this->variableValues = $variableValues;
         $this->fragments = $fragments;
-        $this->groupImplementorFields = in_array('group-implementor-fields', $options, true);
+        $this->groupImplementorFields = $options['groupImplementorFields'] ?? false;
         $this->analyzeQueryPlan($parentType, $fieldNodes);
     }
 
@@ -113,16 +118,15 @@ private function analyzeQueryPlan(ObjectType $parentType, iterable $fieldNodes):
     {
         $queryPlan = [];
         $implementors = [];
-        /** @var FieldNode $fieldNode */
         foreach ($fieldNodes as $fieldNode) {
             if (null === $fieldNode->selectionSet) {
                 continue;
             }
 
-            /** @var ObjectType|InterfaceType $type proven because it must be a type with fields and was unwrapped */
             $type = Type::getNamedType(
                 $parentType->getField($fieldNode->name->value)->getType()
             );
+            assert($type instanceof ObjectType || $type instanceof InterfaceType, 'proven because it must be a type with fields and was unwrapped');
 
             $subfields = $this->analyzeSelectionSet($fieldNode->selectionSet, $type, $implementors);
 
@@ -149,8 +153,8 @@ private function analyzeQueryPlan(ObjectType $parentType, iterable $fieldNodes):
     }
 
     /**
-     * @param InterfaceType|ObjectType $parentType
-     * @param array<string, mixed>     $implementors
+     * @param Type&NamedType $parentType
+     * @param array<string, mixed> $implementors
      *
      * @throws Error
      *
@@ -162,6 +166,8 @@ private function analyzeSelectionSet(SelectionSetNode $selectionSet, Type $paren
         $implementors = [];
         foreach ($selectionSet->selections as $selectionNode) {
             if ($selectionNode instanceof FieldNode) {
+                assert($parentType instanceof HasFieldsType, 'ensured by query validation');
+
                 $fieldName = $selectionNode->name->value;
 
                 if (Introspection::TYPE_NAME_FIELD_NAME === $fieldName) {
@@ -225,10 +231,10 @@ private function analyzeSubFields(Type $type, SelectionSetNode $selectionSet, ar
     }
 
     /**
-     * @param Type                 &NamedType    $parentType
-     * @param Type                 &NamedType    $type
-     * @param array<mixed>         $fields
-     * @param array<mixed>         $subfields
+     * @param Type&NamedType $parentType
+     * @param Type&NamedType $type
+     * @param array<mixed> $fields
+     * @param array<mixed> $subfields
      * @param array<string, mixed> $implementors
      *
      * @return array<mixed>
diff --git a/src/Type/Definition/ResolveInfo.php b/src/Type/Definition/ResolveInfo.php
index 3bdcfbd86..061a9082d 100644
--- a/src/Type/Definition/ResolveInfo.php
+++ b/src/Type/Definition/ResolveInfo.php
@@ -17,6 +17,8 @@
  * Structure containing information useful for field resolution process.
  *
  * Passed as 4th argument to every field resolver. See [docs on field resolving (data fetching)](data-fetching.md).
+ *
+ * @phpstan-import-type QueryPlanOptions from QueryPlan
  */
 class ResolveInfo
 {
@@ -184,7 +186,6 @@ public function getFieldSelection(int $depth = 0): array
     {
         $fields = [];
 
-        /** @var FieldNode $fieldNode */
         foreach ($this->fieldNodes as $fieldNode) {
             if (null === $fieldNode->selectionSet) {
                 continue;
@@ -200,7 +201,7 @@ public function getFieldSelection(int $depth = 0): array
     }
 
     /**
-     * @param mixed[] $options
+     * @param QueryPlanOptions $options
      */
     public function lookAhead(array $options = []): QueryPlan
     {
@@ -232,7 +233,6 @@ private function foldSelectionSet(SelectionSetNode $selectionSet, int $descend):
             } elseif ($selectionNode instanceof FragmentSpreadNode) {
                 $spreadName = $selectionNode->name->value;
                 if (isset($this->fragments[$spreadName])) {
-                    /** @var FragmentDefinitionNode $fragment */
                     $fragment = $this->fragments[$spreadName];
                     $fields = array_merge_recursive(
                         $this->foldSelectionSet($fragment->selectionSet, $descend),
diff --git a/src/Type/Definition/StringType.php b/src/Type/Definition/StringType.php
index 5ca460360..f45ec6a18 100644
--- a/src/Type/Definition/StringType.php
+++ b/src/Type/Definition/StringType.php
@@ -8,6 +8,7 @@
 use GraphQL\Error\SerializationError;
 use GraphQL\Language\AST\Node;
 use GraphQL\Language\AST\StringValueNode;
+use GraphQL\Language\Printer;
 use GraphQL\Utils\Utils;
 use function is_object;
 use function is_scalar;
@@ -41,9 +42,8 @@ public function serialize($value): string
     public function parseValue($value): string
     {
         if (! is_string($value)) {
-            throw new Error(
-                'String cannot represent a non string value: ' . Utils::printSafe($value)
-            );
+            $notString = Utils::printSafe($value);
+            throw new Error("String cannot represent a non string value: {$notString}");
         }
 
         return $value;
@@ -55,7 +55,7 @@ public function parseLiteral(Node $valueNode, ?array $variables = null): string
             return $valueNode->value;
         }
 
-        // Intentionally without message, as all information already in wrapped Exception
-        throw new Error();
+        $notString = Printer::doPrint($valueNode);
+        throw new Error("String cannot represent a non string value: {$notString}", $valueNode);
     }
 }
diff --git a/src/Type/Definition/Type.php b/src/Type/Definition/Type.php
index 7679ac219..c94bb7ede 100644
--- a/src/Type/Definition/Type.php
+++ b/src/Type/Definition/Type.php
@@ -91,12 +91,12 @@ public static function float(): ScalarType
     }
 
     /**
+     * @template T of Type
+     *
      * @param T|callable():T $type
      *
      * @return ListOfType<T>
      *
-     * @template T of Type
-     *
      * @api
      */
     public static function listOf($type): ListOfType
@@ -190,10 +190,13 @@ public static function isInputType($type): bool
      */
     public static function getNamedType(?Type $type): ?Type
     {
-        /** @var (Type&WrappingType)|(Type&NamedType)|null $type */
-        return $type instanceof WrappingType
-            ? $type->getInnermostType()
-            : $type;
+        if ($type instanceof WrappingType) {
+            return $type->getInnermostType();
+        }
+
+        assert(null === $type || $type instanceof NamedType, 'only other option');
+
+        return $type;
     }
 
     /**
@@ -243,10 +246,13 @@ public static function isAbstractType($type): bool
      */
     public static function getNullableType(Type $type): Type
     {
-        /** @var (Type&NullableType)|(Type&NonNull) $type */
-        return $type instanceof NonNull
-            ? $type->getWrappedType()
-            : $type;
+        if ($type instanceof NonNull) {
+            return $type->getWrappedType();
+        }
+
+        assert($type instanceof NullableType, 'only other option');
+
+        return $type;
     }
 
     abstract public function toString(): string;
diff --git a/src/Type/Definition/UnresolvedFieldDefinition.php b/src/Type/Definition/UnresolvedFieldDefinition.php
index 6e354fbcf..7ebeb2142 100644
--- a/src/Type/Definition/UnresolvedFieldDefinition.php
+++ b/src/Type/Definition/UnresolvedFieldDefinition.php
@@ -4,28 +4,27 @@
 
 namespace GraphQL\Type\Definition;
 
-use GraphQL\Error\InvariantViolation;
-use function is_array;
-
+/**
+ * @phpstan-import-type UnnamedFieldDefinitionConfig from FieldDefinition
+ * @phpstan-type DefinitionResolver callable(): (FieldDefinition|(Type&OutputType)|UnnamedFieldDefinitionConfig)
+ */
 class UnresolvedFieldDefinition
 {
-    /** @var ObjectType|InterfaceType */
-    private Type $parentType;
-
     private string $name;
 
-    /** @var callable(): (FieldDefinition|array<string, mixed>|Type) */
-    private $resolver;
+    /**
+     * @var callable
+     * @phpstan-var DefinitionResolver
+     */
+    private $definitionResolver;
 
     /**
-     * @param ObjectType|InterfaceType                                $parentType
-     * @param callable(): (FieldDefinition|array<string, mixed>|Type) $resolver
+     * @param DefinitionResolver $definitionResolver
      */
-    public function __construct(Type $parentType, string $name, callable $resolver)
+    public function __construct(string $name, callable $definitionResolver)
     {
-        $this->parentType = $parentType;
         $this->name = $name;
-        $this->resolver = $resolver;
+        $this->definitionResolver = $definitionResolver;
     }
 
     public function getName(): string
@@ -35,36 +34,19 @@ public function getName(): string
 
     public function resolve(): FieldDefinition
     {
-        $field = ($this->resolver)();
+        $field = ($this->definitionResolver)();
 
         if ($field instanceof FieldDefinition) {
-            if ($field->name !== $this->name) {
-                throw new InvariantViolation(
-                    "{$this->parentType->name}.{$this->name} should not dynamically change its name when resolved lazily."
-                );
-            }
-
             return $field;
         }
 
-        if (! is_array($field)) {
-            return FieldDefinition::create(['name' => $this->name, 'type' => $field]);
-        }
-
-        if (! isset($field['name'])) {
-            $field['name'] = $this->name;
-        } elseif ($field['name'] !== $this->name) {
-            throw new InvariantViolation(
-                "{$this->parentType->name}.{$this->name} should not dynamically change its name when resolved lazily."
-            );
-        }
-
-        if (isset($field['args']) && ! is_array($field['args'])) {
-            throw new InvariantViolation(
-                "{$this->parentType->name}.{$this->name} args must be an array."
-            );
+        if ($field instanceof Type) {
+            return new FieldDefinition([
+                'name' => $this->name,
+                'type' => $field,
+            ]);
         }
 
-        return FieldDefinition::create($field);
+        return new FieldDefinition($field + ['name' => $this->name]);
     }
 }
diff --git a/src/Type/Introspection.php b/src/Type/Introspection.php
index 4634d9958..d08ff9c5d 100644
--- a/src/Type/Introspection.php
+++ b/src/Type/Introspection.php
@@ -160,7 +160,7 @@ enumValues(includeDeprecated: true) {
     }
 
     /**
-     * @param Type &NamedType $type
+     * @param Type&NamedType $type
      */
     public static function isIntrospectionType(NamedType $type): bool
     {
@@ -676,7 +676,7 @@ public static function _directiveLocation(): EnumType
 
     public static function schemaMetaFieldDef(): FieldDefinition
     {
-        return self::$map[self::SCHEMA_FIELD_NAME] ??= FieldDefinition::create([
+        return self::$map[self::SCHEMA_FIELD_NAME] ??= new FieldDefinition([
             'name' => self::SCHEMA_FIELD_NAME,
             'type' => Type::nonNull(self::_schema()),
             'description' => 'Access the current type schema of this server.',
@@ -687,7 +687,7 @@ public static function schemaMetaFieldDef(): FieldDefinition
 
     public static function typeMetaFieldDef(): FieldDefinition
     {
-        return self::$map[self::TYPE_FIELD_NAME] ??= FieldDefinition::create([
+        return self::$map[self::TYPE_FIELD_NAME] ??= new FieldDefinition([
             'name' => self::TYPE_FIELD_NAME,
             'type' => self::_type(),
             'description' => 'Request the type information of a single type.',
@@ -703,7 +703,7 @@ public static function typeMetaFieldDef(): FieldDefinition
 
     public static function typeNameMetaFieldDef(): FieldDefinition
     {
-        return self::$map[self::TYPE_NAME_FIELD_NAME] ??= FieldDefinition::create([
+        return self::$map[self::TYPE_NAME_FIELD_NAME] ??= new FieldDefinition([
             'name' => self::TYPE_NAME_FIELD_NAME,
             'type' => Type::nonNull(Type::string()),
             'description' => 'The name of the current Object type at runtime.',
diff --git a/src/Type/Schema.php b/src/Type/Schema.php
index c3df54581..cffe10c1e 100644
--- a/src/Type/Schema.php
+++ b/src/Type/Schema.php
@@ -5,7 +5,6 @@
 namespace GraphQL\Type;
 
 use Generator;
-use function get_class;
 use GraphQL\Error\Error;
 use GraphQL\Error\InvariantViolation;
 use GraphQL\GraphQL;
@@ -23,7 +22,6 @@
 use GraphQL\Utils\TypeInfo;
 use GraphQL\Utils\Utils;
 use function implode;
-use InvalidArgumentException;
 use function is_array;
 use function is_callable;
 use function is_iterable;
@@ -189,11 +187,11 @@ public function getTypeMap(): array
     }
 
     /**
-     * @return array<Type&NamedType>
+     * @return array<string, Type&NamedType>
      */
     private function collectAllTypes(): array
     {
-        /** @var array<Type&NamedType> $typeMap */
+        /** @var array<string, Type&NamedType> $typeMap */
         $typeMap = [];
         foreach ($this->resolvedTypes as $type) {
             TypeInfo::extractTypes($type, $typeMap);
@@ -368,12 +366,12 @@ private function defaultTypeLoader(string $typeName): ?Type
     }
 
     /**
+     * @template T of Type
+     *
      * @param Type|callable $type
      * @phpstan-param T|callable():T $type
      *
      * @phpstan-return T
-     *
-     * @template T of Type
      */
     public static function resolveType($type): Type
     {
@@ -390,17 +388,21 @@ public static function resolveType($type): Type
      *
      * This operation requires full schema scan. Do not use in production environment.
      *
-     * @param InterfaceType|UnionType $abstractType
+     * @param AbstractType&Type $abstractType
      *
      * @return array<ObjectType>
      *
      * @api
      */
-    public function getPossibleTypes(Type $abstractType): array
+    public function getPossibleTypes(AbstractType $abstractType): array
     {
-        return $abstractType instanceof UnionType
-            ? $abstractType->getTypes()
-            : $this->getImplementations($abstractType)->objects();
+        if ($abstractType instanceof UnionType) {
+            return $abstractType->getTypes();
+        }
+
+        assert($abstractType instanceof InterfaceType, 'only other option');
+
+        return $this->getImplementations($abstractType)->objects();
     }
 
     /**
@@ -423,7 +425,15 @@ private function collectImplementations(): array
         if (! isset($this->implementationsMap)) {
             $this->implementationsMap = [];
 
-            /** @var array<string, array<string, Type>> $foundImplementations */
+            /**
+             * @var array<
+             *     string,
+             *     array{
+             *         objects: array<int, ObjectType>,
+             *         interfaces: array<int, InterfaceType>,
+             *     }
+             * > $foundImplementations
+             */
             $foundImplementations = [];
             foreach ($this->getTypeMap() as $type) {
                 if ($type instanceof InterfaceType) {
@@ -460,8 +470,8 @@ private function collectImplementations(): array
     /**
      * Returns true if the given type is a sub type of the given abstract type.
      *
-     * @param UnionType|InterfaceType  $abstractType
-     * @param ObjectType|InterfaceType $maybeSubType
+     * @param AbstractType&Type $abstractType
+     * @param ImplementingType&Type $maybeSubType
      *
      * @api
      */
@@ -471,13 +481,9 @@ public function isSubType(AbstractType $abstractType, ImplementingType $maybeSub
             return $maybeSubType->implementsInterface($abstractType);
         }
 
-        // @phpstan-ignore-next-line necessary until function can be type hinted with actual union type
-        if ($abstractType instanceof UnionType) {
-            return $abstractType->isPossibleType($maybeSubType);
-        }
+        assert($abstractType instanceof UnionType, 'only other option');
 
-        // @phpstan-ignore-next-line necessary until function can be type hinted with actual union type
-        throw new InvalidArgumentException('$abstractType must be of type UnionType|InterfaceType got: ' . get_class($abstractType) . '.');
+        return $abstractType->isPossibleType($maybeSubType);
     }
 
     /**
diff --git a/src/Type/SchemaValidationContext.php b/src/Type/SchemaValidationContext.php
index 36d24c9af..aa9f69bd6 100644
--- a/src/Type/SchemaValidationContext.php
+++ b/src/Type/SchemaValidationContext.php
@@ -92,7 +92,7 @@ public function validateRootTypes(): void
     }
 
     /**
-     * @param array<Node>|Node|null $nodes
+     * @param array<Node|null>|Node|null $nodes
      */
     public function reportError(string $message, $nodes = null): void
     {
@@ -165,7 +165,7 @@ public function validateDirectiveDefinitions(): void
                 $argNames[$argName] = true;
 
                 // Ensure the type is an input type.
-                // @phpstan-ignore-next-line the type of $arg->getType() says it is an input type, but it might not always be true
+                // @phpstan-ignore-next-line necessary until PHP supports union types
                 if (Type::isInputType($arg->getType())) {
                     continue;
                 }
@@ -200,7 +200,7 @@ public function validateDirectiveDefinitions(): void
     }
 
     /**
-     * @param Type|Directive|FieldDefinition|EnumValueDefinition|InputObjectField|Argument $object
+     * @param (Type&NamedType)|Directive|FieldDefinition|EnumValueDefinition|InputObjectField|Argument $object
      */
     private function validateName(object $object): void
     {
@@ -208,7 +208,7 @@ private function validateName(object $object): void
         $error = Utils::isValidNameError($object->name, $object->astNode);
         if (
             null === $error
-            || ($object instanceof Type && $object instanceof NamedType && Introspection::isIntrospectionType($object))
+            || ($object instanceof Type && Introspection::isIntrospectionType($object))
         ) {
             return;
         }
@@ -565,13 +565,11 @@ private function getAllFieldArgNodes(Type $type, string $fieldName, string $argN
     {
         $argNodes = [];
         $fieldNode = $this->getFieldNode($type, $fieldName);
-        if (null !== $fieldNode && null !== $fieldNode->arguments) {
+        if (null !== $fieldNode) {
             foreach ($fieldNode->arguments as $node) {
-                if ($node->name->value !== $argName) {
-                    continue;
+                if ($node->name->value === $argName) {
+                    $argNodes[] = $node;
                 }
-
-                $argNodes[] = $node;
             }
         }
 
@@ -643,13 +641,19 @@ private function validateInterfaces(ImplementingType $type): void
     }
 
     /**
-     * @param Schema|Type $object
+     * @param Schema|(Type&NamedType) $object
      *
      * @return NodeList<DirectiveNode>
      */
     private function getDirectives(object $object): NodeList
     {
         $directives = [];
+        /**
+         * Excluding directiveNode, since $object is not Directive.
+         *
+         * @var SchemaDefinitionNode|SchemaTypeExtensionNode|ObjectTypeDefinitionNode|ObjectTypeExtensionNode|InterfaceTypeDefinitionNode|InterfaceTypeExtensionNode|UnionTypeDefinitionNode|UnionTypeExtensionNode|EnumTypeDefinitionNode|EnumTypeExtensionNode|InputObjectTypeDefinitionNode|InputObjectTypeExtensionNode $node
+         */
+        // @phpstan-ignore-next-line union types are not pervasive
         foreach ($this->getAllNodes($object) as $node) {
             foreach ($node->directives as $directive) {
                 $directives[] = $directive;
diff --git a/src/Utils/AST.php b/src/Utils/AST.php
index ba6cf007f..e8e7889b8 100644
--- a/src/Utils/AST.php
+++ b/src/Utils/AST.php
@@ -36,8 +36,10 @@
 use GraphQL\Type\Definition\IDType;
 use GraphQL\Type\Definition\InputObjectType;
 use GraphQL\Type\Definition\InputType;
+use GraphQL\Type\Definition\LeafType;
 use GraphQL\Type\Definition\ListOfType;
 use GraphQL\Type\Definition\NonNull;
+use GraphQL\Type\Definition\NullableType;
 use GraphQL\Type\Definition\ScalarType;
 use GraphQL\Type\Definition\Type;
 use GraphQL\Type\Schema;
@@ -49,7 +51,6 @@
 use function is_string;
 use function property_exists;
 use Throwable;
-use Traversable;
 
 /**
  * Various utilities dealing with AST.
@@ -148,16 +149,17 @@ public static function toArray(Node $node): array
      * | Mixed         | Enum Value           |
      * | null          | NullValue            |
      *
-     * @param Type|mixed|null                                     $value
-     * @param ScalarType|EnumType|InputObjectType|ListOfType<Type &InputType>|NonNull $type
+     * @param mixed $value
+     * @param InputType&Type $type
      *
-     * @return ObjectValueNode|ListValueNode|BooleanValueNode|IntValueNode|FloatValueNode|EnumValueNode|StringValueNode|NullValueNode|null
+     * @return (ValueNode&Node)|null
      *
      * @api
      */
-    public static function astFromValue($value, InputType $type)
+    public static function astFromValue($value, InputType $type): ?ValueNode
     {
         if ($type instanceof NonNull) {
+            // @phpstan-ignore-next-line wrapped type must also be input type
             $astValue = self::astFromValue($value, $type->getWrappedType());
             if ($astValue instanceof NullValueNode) {
                 return null;
@@ -170,11 +172,13 @@ public static function astFromValue($value, InputType $type)
             return new NullValueNode([]);
         }
 
-        // Convert PHP array to GraphQL list. If the GraphQLType is a list, but
+        // Convert PHP iterables to GraphQL list. If the GraphQLType is a list, but
         // the value is not an array, convert the value using the list's item type.
         if ($type instanceof ListOfType) {
             $itemType = $type->getWrappedType();
-            if (is_array($value) || ($value instanceof Traversable)) {
+            assert($itemType instanceof InputType, 'proven by schema validation');
+
+            if (is_iterable($value)) {
                 $valuesNodes = [];
                 foreach ($value as $item) {
                     $itemNode = self::astFromValue($item, $itemType);
@@ -240,6 +244,8 @@ public static function astFromValue($value, InputType $type)
             return new ObjectValueNode(['fields' => new NodeList($fieldNodes)]);
         }
 
+        assert($type instanceof LeafType, 'other options were exhausted');
+
         // Since value is an internally represented value, it must be serialized
         // to an externally represented value before converting into an AST.
         $serialized = $type->serialize($value);
@@ -301,8 +307,8 @@ public static function astFromValue($value, InputType $type)
      * | Enum Value           | Mixed         |
      * | Null Value           | null          |
      *
-     * @param VariableNode|NullValueNode|IntValueNode|FloatValueNode|StringValueNode|BooleanValueNode|EnumValueNode|ListValueNode|ObjectValueNode|null $valueNode
-     * @param array<string, mixed>|null                                                                                                                $variables
+     * @param (ValueNode&Node)|null $valueNode
+     * @param array<string, mixed>|null $variables
      *
      * @throws Exception
      *
@@ -441,26 +447,24 @@ public static function valueFromAST(?ValueNode $valueNode, Type $type, ?array $v
             }
         }
 
-        if ($type instanceof ScalarType) {
-            // Scalars fulfill parsing a literal value via parseLiteral().
-            // Invalid values represent a failure to parse correctly, in which case
-            // no value is returned.
-            try {
-                return $type->parseLiteral($valueNode, $variables);
-            } catch (Throwable $error) {
-                return $undefined;
-            }
-        }
+        assert($type instanceof ScalarType, 'only remaining option');
 
-        throw new Error('Unknown type: ' . Utils::printSafe($type) . '.');
+        // Scalars fulfill parsing a literal value via parseLiteral().
+        // Invalid values represent a failure to parse correctly, in which case
+        // no value is returned.
+        try {
+            return $type->parseLiteral($valueNode, $variables);
+        } catch (Throwable $error) {
+            return $undefined;
+        }
     }
 
     /**
      * Returns true if the provided valueNode is a variable which is not defined
      * in the set of variables.
      *
-     * @param VariableNode|NullValueNode|IntValueNode|FloatValueNode|StringValueNode|BooleanValueNode|EnumValueNode|ListValueNode|ObjectValueNode $valueNode
-     * @param array<string, mixed>|null                                                                                                           $variables
+     * @param ValueNode&Node $valueNode
+     * @param array<string, mixed>|null $variables
      */
     private static function isMissingVariable(ValueNode $valueNode, ?array $variables): bool
     {
@@ -557,10 +561,13 @@ public static function typeFromAST(Schema $schema, Node $inputTypeNode): ?Type
 
         if ($inputTypeNode instanceof NonNullTypeNode) {
             $innerType = self::typeFromAST($schema, $inputTypeNode->type);
+            if (null === $innerType) {
+                return null;
+            }
 
-            return null === $innerType
-                ? null
-                : new NonNull($innerType);
+            assert($innerType instanceof NullableType, 'proven by schema validation');
+
+            return new NonNull($innerType);
         }
 
         return $schema->getType($inputTypeNode->name->value);
diff --git a/src/Utils/ASTDefinitionBuilder.php b/src/Utils/ASTDefinitionBuilder.php
index f4932b9af..658cb2cfe 100644
--- a/src/Utils/ASTDefinitionBuilder.php
+++ b/src/Utils/ASTDefinitionBuilder.php
@@ -27,19 +27,22 @@
 use GraphQL\Type\Definition\Directive;
 use GraphQL\Type\Definition\EnumType;
 use GraphQL\Type\Definition\FieldDefinition;
+use GraphQL\Type\Definition\InputObjectField;
 use GraphQL\Type\Definition\InputObjectType;
+use GraphQL\Type\Definition\InputType;
 use GraphQL\Type\Definition\InterfaceType;
 use GraphQL\Type\Definition\ObjectType;
+use GraphQL\Type\Definition\OutputType;
 use GraphQL\Type\Definition\Type;
 use GraphQL\Type\Definition\UnionType;
 use function is_array;
 use function is_string;
-use function sprintf;
 use Throwable;
 
 /**
- * @phpstan-import-type FieldMapConfig from FieldDefinition
  * @phpstan-import-type UnnamedFieldDefinitionConfig from FieldDefinition
+ * @phpstan-import-type InputObjectFieldConfig from InputObjectField
+ * @phpstan-import-type UnnamedInputObjectFieldConfig from InputObjectField
  * @phpstan-type ResolveType callable(string, Node|null): Type
  * @phpstan-type TypeConfigDecorator callable(array<string, mixed>, Node&TypeDefinitionNode, array<string, Node&TypeDefinitionNode>): array<string, mixed>
  */
@@ -64,7 +67,7 @@ class ASTDefinitionBuilder
     private array $cache;
 
     /**
-     * @param array<string, Node &TypeDefinitionNode> $typeDefinitionsMap
+     * @param array<string, Node&TypeDefinitionNode> $typeDefinitionsMap
      * @phpstan-param ResolveType $resolveType
      * @phpstan-param TypeConfigDecorator|null $typeConfigDecorator
      */
@@ -100,15 +103,17 @@ public function buildDirective(DirectiveDefinitionNode $directiveNode): Directiv
     /**
      * @param NodeList<InputValueDefinitionNode> $values
      *
-     * @return array<string, array<string, mixed>>
+     * @return array<string, UnnamedInputObjectFieldConfig>
      */
     private function makeInputValues(NodeList $values): array
     {
+        /** @var array<string, UnnamedInputObjectFieldConfig> $map */
         $map = [];
         foreach ($values as $value) {
             // Note: While this could make assertions to get the correctly typed
             // value, that would throw immediately while type system validation
             // with validateSchema() will produce more actionable results.
+            /** @var Type&InputType $type */
             $type = $this->buildWrappedType($value->type);
 
             $config = [
@@ -117,7 +122,8 @@ private function makeInputValues(NodeList $values): array
                 'description' => $value->description->value ?? null,
                 'astNode' => $value,
             ];
-            if (isset($value->defaultValue)) {
+
+            if (null !== $value->defaultValue) {
                 $config['defaultValue'] = AST::valueFromAST($value->defaultValue, $type);
             }
 
@@ -137,6 +143,7 @@ private function buildWrappedType(TypeNode $typeNode): Type
         }
 
         if ($typeNode instanceof NonNullTypeNode) {
+            // @phpstan-ignore-next-line contained type is NullableType
             return Type::nonNull($this->buildWrappedType($typeNode->type));
         }
 
@@ -144,7 +151,7 @@ private function buildWrappedType(TypeNode $typeNode): Type
     }
 
     /**
-     * @param string|(Node &NamedTypeNode)|(Node&TypeDefinitionNode) $ref
+     * @param string|(Node&NamedTypeNode)|(Node&TypeDefinitionNode) $ref
      */
     public function buildType($ref): Type
     {
@@ -156,7 +163,7 @@ public function buildType($ref): Type
     }
 
     /**
-     * @param (Node &NamedTypeNode)|(Node&TypeDefinitionNode)|null $typeNode
+     * @param (Node&NamedTypeNode)|(Node&TypeDefinitionNode)|null $typeNode
      *
      * @throws Error
      */
@@ -204,7 +211,7 @@ private function internalBuildType(string $typeName, ?Node $typeNode = null): Ty
     }
 
     /**
-     * @param ObjectTypeDefinitionNode|InterfaceTypeDefinitionNode|EnumTypeDefinitionNode|ScalarTypeDefinitionNode|InputObjectTypeDefinitionNode|UnionTypeDefinitionNode $def
+     * @param TypeDefinitionNode&Node $def
      *
      * @throws Error
      *
@@ -229,6 +236,8 @@ private function makeSchemaDef(Node $def): Type
                 return $this->makeScalarDef($def);
 
             default:
+                assert($def instanceof InputObjectTypeDefinitionNode, 'all implementations are known');
+
                 return $this->makeInputObjectDef($def);
         }
     }
@@ -264,11 +273,14 @@ private function makeFieldDefMap(Node $def): array
      */
     public function buildField(FieldDefinitionNode $field): array
     {
+        // Note: While this could make assertions to get the correctly typed
+        // value, that would throw immediately while type system validation
+        // with validateSchema() will produce more actionable results.
+        /** @var OutputType&Type $type */
+        $type = $this->buildWrappedType($field->type);
+
         return [
-            // Note: While this could make assertions to get the correctly typed
-            // value, that would throw immediately while type system validation
-            // with validateSchema() will produce more actionable results.
-            'type' => $this->buildWrappedType($field->type),
+            'type' => $type,
             'description' => $field->description->value ?? null,
             'args' => $this->makeInputValues($field->arguments),
             'deprecationReason' => $this->getDeprecationReason($field),
@@ -356,6 +368,7 @@ private function makeUnionDef(UnionTypeDefinitionNode $def): UnionType
                     $types[] = $this->buildType($type);
                 }
 
+                /** @var array<int, ObjectType> $types */
                 return $types;
             },
             'astNode' => $def,
@@ -393,34 +406,40 @@ private function makeSchemaDefFromConfig(Node $def, array $config): Type
     {
         switch (true) {
             case $def instanceof ObjectTypeDefinitionNode:
+                // @phpstan-ignore-next-line assume the config matches
                 return new ObjectType($config);
 
             case $def instanceof InterfaceTypeDefinitionNode:
+                // @phpstan-ignore-next-line assume the config matches
                 return new InterfaceType($config);
 
             case $def instanceof EnumTypeDefinitionNode:
+                // @phpstan-ignore-next-line assume the config matches
                 return new EnumType($config);
 
             case $def instanceof UnionTypeDefinitionNode:
+                // @phpstan-ignore-next-line assume the config matches
                 return new UnionType($config);
 
             case $def instanceof ScalarTypeDefinitionNode:
                 return new CustomScalarType($config);
 
             case $def instanceof InputObjectTypeDefinitionNode:
+                // @phpstan-ignore-next-line assume the config matches
                 return new InputObjectType($config);
 
             default:
-                throw new Error(sprintf('Type kind of %s not supported.', $def->kind));
+                throw new Error("Type kind of {$def->kind} not supported.");
         }
     }
 
     /**
-     * @return array<string, mixed>
+     * @return InputObjectFieldConfig
      */
     public function buildInputField(InputValueDefinitionNode $value): array
     {
         $type = $this->buildWrappedType($value->type);
+        assert($type instanceof InputType, 'proven by schema validation');
 
         $config = [
             'name' => $value->name->value,
@@ -430,7 +449,7 @@ public function buildInputField(InputValueDefinitionNode $value): array
         ];
 
         if (null !== $value->defaultValue) {
-            $config['defaultValue'] = $value->defaultValue;
+            $config['defaultValue'] = AST::valueFromAST($value->defaultValue, $type);
         }
 
         return $config;
diff --git a/src/Utils/BreakingChangesFinder.php b/src/Utils/BreakingChangesFinder.php
index eaaea71b4..0f94b98ab 100644
--- a/src/Utils/BreakingChangesFinder.php
+++ b/src/Utils/BreakingChangesFinder.php
@@ -151,7 +151,7 @@ public static function findTypesThatChangedKind(
     }
 
     /**
-     * @param Type &NamedType $type
+     * @param Type&NamedType $type
      */
     private static function typeKindName(NamedType $type): string
     {
diff --git a/src/Utils/BuildClientSchema.php b/src/Utils/BuildClientSchema.php
index f0312b91c..86ff097d2 100644
--- a/src/Utils/BuildClientSchema.php
+++ b/src/Utils/BuildClientSchema.php
@@ -13,13 +13,13 @@
 use GraphQL\Type\Definition\Directive;
 use GraphQL\Type\Definition\EnumType;
 use GraphQL\Type\Definition\FieldDefinition;
+use GraphQL\Type\Definition\InputObjectField;
 use GraphQL\Type\Definition\InputObjectType;
 use GraphQL\Type\Definition\InputType;
 use GraphQL\Type\Definition\InterfaceType;
 use GraphQL\Type\Definition\ListOfType;
 use GraphQL\Type\Definition\NamedType;
 use GraphQL\Type\Definition\NonNull;
-use GraphQL\Type\Definition\NullableType;
 use GraphQL\Type\Definition\ObjectType;
 use GraphQL\Type\Definition\OutputType;
 use GraphQL\Type\Definition\ScalarType;
@@ -33,6 +33,7 @@
 
 /**
  * @phpstan-import-type UnnamedFieldDefinitionConfig from FieldDefinition
+ * @phpstan-import-type UnnamedInputObjectFieldConfig from InputObjectField
  * @phpstan-type Options array{
  *   assumeValid?: bool,
  * }
@@ -168,10 +169,8 @@ private function getType(array $typeRef): Type
                     throw new InvariantViolation('Decorated type deeper than introspection query.');
                 }
 
-                /** @var NullableType $nullableType */
-                $nullableType = $this->getType($typeRef['ofType']);
-
-                return new NonNull($nullableType);
+                // @phpstan-ignore-next-line if the type is not a nullable type, schema validation will catch it
+                return new NonNull($this->getType($typeRef['ofType']));
             }
         }
 
@@ -368,7 +367,7 @@ private function buildInterfaceDef(array $interface): InterfaceType
     }
 
     /**
-     * @param array<string, string|array<string>> $union
+     * @param array<string, mixed> $union
      */
     private function buildUnionDef(array $union): UnionType
     {
@@ -387,7 +386,7 @@ private function buildUnionDef(array $union): UnionType
     }
 
     /**
-     * @param array<string, string|array<string, string>> $enum
+     * @param array<string, mixed> $enum
      */
     private function buildEnumDef(array $enum): EnumType
     {
@@ -439,6 +438,7 @@ private function buildFieldDefMap(array $typeIntrospection): array
             throw new InvariantViolation('Introspection result missing fields: ' . json_encode($typeIntrospection) . '.');
         }
 
+        /** @var array<string, UnnamedFieldDefinitionConfig> $map */
         $map = [];
         foreach ($typeIntrospection['fields'] as $field) {
             if (! array_key_exists('args', $field)) {
@@ -453,28 +453,31 @@ private function buildFieldDefMap(array $typeIntrospection): array
             ];
         }
 
+        // @phpstan-ignore-next-line unless the returned name was numeric, this works
         return $map;
     }
 
     /**
      * @param array<int, array<string, mixed>> $inputValueIntrospections
      *
-     * @return array<string, array<string, mixed>>
+     * @return array<string, UnnamedInputObjectFieldConfig>
      */
     private function buildInputValueDefMap(array $inputValueIntrospections): array
     {
+        /** @var array<string, UnnamedInputObjectFieldConfig> $map */
         $map = [];
         foreach ($inputValueIntrospections as $value) {
             $map[$value['name']] = $this->buildInputValue($value);
         }
 
+        // @phpstan-ignore-next-line unless the returned name was numeric, this works
         return $map;
     }
 
     /**
      * @param array<string, mixed> $inputValueIntrospection
      *
-     * @return array<string, mixed>
+     * @return UnnamedInputObjectFieldConfig
      */
     public function buildInputValue(array $inputValueIntrospection): array
     {
diff --git a/src/Utils/BuildSchema.php b/src/Utils/BuildSchema.php
index c6bf4ac0e..cc2f016cd 100644
--- a/src/Utils/BuildSchema.php
+++ b/src/Utils/BuildSchema.php
@@ -132,8 +132,10 @@ public function buildSchema(): Schema
 
         $schemaDef = null;
         $this->nodeMap = [];
+
         /** @var array<int, DirectiveDefinitionNode> $directiveDefs */
         $directiveDefs = [];
+
         foreach ($this->ast->definitions as $definition) {
             switch (true) {
                 case $definition instanceof SchemaDefinitionNode:
diff --git a/src/Utils/SchemaExtender.php b/src/Utils/SchemaExtender.php
index 1afd7cf54..bf0138d37 100644
--- a/src/Utils/SchemaExtender.php
+++ b/src/Utils/SchemaExtender.php
@@ -16,6 +16,7 @@
 use GraphQL\Language\AST\InterfaceTypeExtensionNode;
 use GraphQL\Language\AST\Node;
 use GraphQL\Language\AST\ObjectTypeExtensionNode;
+use GraphQL\Language\AST\ScalarTypeExtensionNode;
 use GraphQL\Language\AST\SchemaDefinitionNode;
 use GraphQL\Language\AST\SchemaTypeExtensionNode;
 use GraphQL\Language\AST\TypeDefinitionNode;
@@ -26,7 +27,9 @@
 use GraphQL\Type\Definition\Directive;
 use GraphQL\Type\Definition\EnumType;
 use GraphQL\Type\Definition\ImplementingType;
+use GraphQL\Type\Definition\InputObjectField;
 use GraphQL\Type\Definition\InputObjectType;
+use GraphQL\Type\Definition\InputType;
 use GraphQL\Type\Definition\InterfaceType;
 use GraphQL\Type\Definition\ListOfType;
 use GraphQL\Type\Definition\NamedType;
@@ -41,6 +44,8 @@
 
 /**
  * @phpstan-import-type TypeConfigDecorator from ASTDefinitionBuilder
+ * @phpstan-import-type UnnamedArgumentConfig from Argument
+ * @phpstan-import-type UnnamedInputObjectFieldConfig from InputObjectField
  */
 class SchemaExtender
 {
@@ -53,11 +58,11 @@ class SchemaExtender
     protected static ASTDefinitionBuilder $astBuilder;
 
     /**
-     * @param Type &NamedType $type
+     * @param Type&NamedType $type
      *
      * @return array<TypeExtensionNode>|null
      */
-    protected static function getExtensionASTNodes(NamedType $type): ?array
+    protected static function extensionASTNodes(NamedType $type): ?array
     {
         return array_merge(
             $type->extensionASTNodes ?? [],
@@ -66,7 +71,7 @@ protected static function getExtensionASTNodes(NamedType $type): ?array
     }
 
     /**
-     * @param Type &NamedType $type
+     * @param Type&NamedType $type
      *
      * @throws Error
      */
@@ -123,6 +128,9 @@ protected static function assertTypeMatchesExtension(NamedType $type, Node $node
 
     protected static function extendScalarType(ScalarType $type): CustomScalarType
     {
+        /** @var array<int, ScalarTypeExtensionNode> $extensionASTNodes */
+        $extensionASTNodes = static::extensionASTNodes($type);
+
         return new CustomScalarType([
             'name' => $type->name,
             'description' => $type->description,
@@ -130,72 +138,83 @@ protected static function extendScalarType(ScalarType $type): CustomScalarType
             'parseValue' => [$type, 'parseValue'],
             'parseLiteral' => [$type, 'parseLiteral'],
             'astNode' => $type->astNode,
-            'extensionASTNodes' => static::getExtensionASTNodes($type),
+            'extensionASTNodes' => $extensionASTNodes,
         ]);
     }
 
     protected static function extendUnionType(UnionType $type): UnionType
     {
+        /** @var array<int, UnionTypeExtensionNode> $extensionASTNodes */
+        $extensionASTNodes = static::extensionASTNodes($type);
+
         return new UnionType([
             'name' => $type->name,
             'description' => $type->description,
             'types' => static fn (): array => static::extendUnionPossibleTypes($type),
             'resolveType' => [$type, 'resolveType'],
             'astNode' => $type->astNode,
-            'extensionASTNodes' => static::getExtensionASTNodes($type),
+            'extensionASTNodes' => $extensionASTNodes,
         ]);
     }
 
     protected static function extendEnumType(EnumType $type): EnumType
     {
+        /** @var array<int, EnumTypeExtensionNode> $extensionASTNodes */
+        $extensionASTNodes = static::extensionASTNodes($type);
+
         return new EnumType([
             'name' => $type->name,
             'description' => $type->description,
             'values' => static::extendEnumValueMap($type),
             'astNode' => $type->astNode,
-            'extensionASTNodes' => static::getExtensionASTNodes($type),
+            'extensionASTNodes' => $extensionASTNodes,
         ]);
     }
 
     protected static function extendInputObjectType(InputObjectType $type): InputObjectType
     {
+        /** @var array<int, InputObjectTypeExtensionNode> $extensionASTNodes */
+        $extensionASTNodes = static::extensionASTNodes($type);
+
         return new InputObjectType([
             'name' => $type->name,
             'description' => $type->description,
             'fields' => static fn (): array => static::extendInputFieldMap($type),
             'astNode' => $type->astNode,
-            'extensionASTNodes' => static::getExtensionASTNodes($type),
+            'extensionASTNodes' => $extensionASTNodes,
         ]);
     }
 
     /**
-     * @return array<string, array<string, mixed>>
+     * @return array<string, UnnamedInputObjectFieldConfig>
      */
     protected static function extendInputFieldMap(InputObjectType $type): array
     {
+        /** @var array<string, UnnamedInputObjectFieldConfig> $newFieldMap */
         $newFieldMap = [];
+
         $oldFieldMap = $type->getFields();
         foreach ($oldFieldMap as $fieldName => $field) {
-            $newFieldMap[$fieldName] = [
+            $extendedType = static::extendType($field->getType());
+            assert($extendedType instanceof InputType, 'proven by schema validation');
+
+            $newFieldConfig = [
                 'description' => $field->description,
-                'type' => static::extendType($field->getType()),
+                'type' => $extendedType,
                 'astNode' => $field->astNode,
             ];
 
-            if (! $field->defaultValueExists()) {
-                continue;
+            if ($field->defaultValueExists()) {
+                $newFieldConfig['defaultValue'] = $field->defaultValue;
             }
 
-            $newFieldMap[$fieldName]['defaultValue'] = $field->defaultValue;
+            $newFieldMap[$fieldName] = $newFieldConfig;
         }
 
         if (isset(static::$typeExtensionsMap[$type->name])) {
-            /**
-             * Proven by @see assertTypeMatchesExtension().
-             *
-             * @var InputObjectTypeExtensionNode $extension
-             */
             foreach (static::$typeExtensionsMap[$type->name] as $extension) {
+                assert($extension instanceof InputObjectTypeExtensionNode, 'proven by assertTypeMatchesExtension()');
+
                 foreach ($extension->fields as $field) {
                     $fieldName = $field->name->value;
                     if (isset($oldFieldMap[$fieldName])) {
@@ -228,12 +247,9 @@ protected static function extendEnumValueMap(EnumType $type): array
         }
 
         if (isset(static::$typeExtensionsMap[$type->name])) {
-            /**
-             * Proven by @see assertTypeMatchesExtension().
-             *
-             * @var EnumTypeExtensionNode $extension
-             */
             foreach (static::$typeExtensionsMap[$type->name] as $extension) {
+                assert($extension instanceof EnumTypeExtensionNode, 'proven by assertTypeMatchesExtension()');
+
                 foreach ($extension->values as $value) {
                     $newValueMap[$value->name->value] = static::$astBuilder->buildEnumValue($value);
                 }
@@ -244,7 +260,7 @@ protected static function extendEnumValueMap(EnumType $type): array
     }
 
     /**
-     * @return array<int, Type> Should be ObjectType, will be caught in schema validation
+     * @return array<int, Type&ObjectType>
      */
     protected static function extendUnionPossibleTypes(UnionType $type): array
     {
@@ -254,25 +270,23 @@ protected static function extendUnionPossibleTypes(UnionType $type): array
         );
 
         if (isset(static::$typeExtensionsMap[$type->name])) {
-            /**
-             * Proven by @see assertTypeMatchesExtension().
-             *
-             * @var UnionTypeExtensionNode $extension
-             */
             foreach (static::$typeExtensionsMap[$type->name] as $extension) {
+                assert($extension instanceof UnionTypeExtensionNode, 'proven by assertTypeMatchesExtension()');
+
                 foreach ($extension->types as $namedType) {
                     $possibleTypes[] = static::$astBuilder->buildType($namedType);
                 }
             }
         }
 
+        // @phpstan-ignore-next-line proven by schema validation
         return $possibleTypes;
     }
 
     /**
      * @param ObjectType|InterfaceType $type
      *
-     * @return array<int, Type> Should be InterfaceType, will be caught in schema validation
+     * @return array<int, Type&InterfaceType>
      */
     protected static function extendImplementedInterfaces(ImplementingType $type): array
     {
@@ -282,49 +296,62 @@ protected static function extendImplementedInterfaces(ImplementingType $type): a
         );
 
         if (isset(static::$typeExtensionsMap[$type->name])) {
-            /**
-             * Proven by @see assertTypeMatchesExtension().
-             *
-             * @var ObjectTypeExtensionNode|InterfaceTypeExtensionNode $extension
-             */
             foreach (static::$typeExtensionsMap[$type->name] as $extension) {
+                assert(
+                    $extension instanceof ObjectTypeExtensionNode || $extension instanceof InterfaceTypeExtensionNode,
+                    'proven by assertTypeMatchesExtension()'
+                );
+
                 foreach ($extension->interfaces as $namedType) {
-                    /** @var InterfaceType $interface we know this, but PHP templates cannot express it */
                     $interface = static::$astBuilder->buildType($namedType);
+                    assert($interface instanceof InterfaceType, 'we know this, but PHP templates cannot express it');
+
                     $interfaces[] = $interface;
                 }
             }
         }
 
+        // @phpstan-ignore-next-line will be caught in schema validation
         return $interfaces;
     }
 
+    /**
+     * @template T of Type
+     *
+     * @param T $typeDef
+     *
+     * @return T
+     */
     protected static function extendType(Type $typeDef): Type
     {
         if ($typeDef instanceof ListOfType) {
+            // @phpstan-ignore-next-line PHPStan does not understand this is the same generic type as the input
             return Type::listOf(static::extendType($typeDef->getWrappedType()));
         }
 
         if ($typeDef instanceof NonNull) {
+            // @phpstan-ignore-next-line PHPStan does not understand this is the same generic type as the input
             return Type::nonNull(static::extendType($typeDef->getWrappedType()));
         }
 
-        /** @var NamedType&Type $typeDef */
-
+        // @phpstan-ignore-next-line PHPStan does not understand this is the same generic type as the input
         return static::extendNamedType($typeDef);
     }
 
     /**
      * @param array<Argument> $args
      *
-     * @return array<string, array<string, mixed>>
+     * @return array<string, UnnamedArgumentConfig>
      */
     protected static function extendArgs(array $args): array
     {
         $extended = [];
         foreach ($args as $arg) {
+            $extendedType = static::extendType($arg->getType());
+            assert($extendedType instanceof InputType, 'proven by schema validation');
+
             $def = [
-                'type' => static::extendType($arg->getType()),
+                'type' => $extendedType,
                 'description' => $arg->description,
                 'astNode' => $arg->astNode,
             ];
@@ -366,12 +393,12 @@ protected static function extendFieldMap(Type $type): array
         }
 
         if (isset(static::$typeExtensionsMap[$type->name])) {
-            /**
-             * Proven by @see assertTypeMatchesExtension().
-             *
-             * @var ObjectTypeExtensionNode|InputObjectTypeExtensionNode $extension
-             */
             foreach (static::$typeExtensionsMap[$type->name] as $extension) {
+                assert(
+                    $extension instanceof ObjectTypeExtensionNode || $extension instanceof InterfaceTypeExtensionNode,
+                    'proven by assertTypeMatchesExtension()'
+                );
+
                 foreach ($extension->fields as $field) {
                     $fieldName = $field->name->value;
                     if (isset($oldFieldMap[$fieldName])) {
@@ -388,6 +415,9 @@ protected static function extendFieldMap(Type $type): array
 
     protected static function extendObjectType(ObjectType $type): ObjectType
     {
+        /** @var array<int, ObjectTypeExtensionNode> $extensionASTNodes */
+        $extensionASTNodes = static::extensionASTNodes($type);
+
         return new ObjectType([
             'name' => $type->name,
             'description' => $type->description,
@@ -396,12 +426,15 @@ protected static function extendObjectType(ObjectType $type): ObjectType
             'isTypeOf' => [$type, 'isTypeOf'],
             'resolveField' => $type->resolveFieldFn ?? null,
             'astNode' => $type->astNode,
-            'extensionASTNodes' => static::getExtensionASTNodes($type),
+            'extensionASTNodes' => $extensionASTNodes,
         ]);
     }
 
     protected static function extendInterfaceType(InterfaceType $type): InterfaceType
     {
+        /** @var array<int, InterfaceTypeExtensionNode> $extensionASTNodes */
+        $extensionASTNodes = static::extensionASTNodes($type);
+
         return new InterfaceType([
             'name' => $type->name,
             'description' => $type->description,
@@ -409,7 +442,7 @@ protected static function extendInterfaceType(InterfaceType $type): InterfaceTyp
             'fields' => static fn (): array => static::extendFieldMap($type),
             'resolveType' => [$type, 'resolveType'],
             'astNode' => $type->astNode,
-            'extensionASTNodes' => static::getExtensionASTNodes($type),
+            'extensionASTNodes' => $extensionASTNodes,
         ]);
     }
 
@@ -426,11 +459,11 @@ protected static function isSpecifiedScalarType(Type $type): bool
     }
 
     /**
-     * @param T &NamedType $type
+     * @template T of Type
      *
-     * @return T&NamedType
+     * @param T&NamedType $type
      *
-     * @template T of Type
+     * @return T&NamedType
      */
     protected static function extendNamedType(Type $type): Type
     {
@@ -460,11 +493,11 @@ protected static function extendNamedType(Type $type): Type
     }
 
     /**
-     * @param (T &NamedType)|null $type
+     * @template T of Type
      *
-     * @return (T&NamedType)|null
+     * @param (T&NamedType)|null $type
      *
-     * @template T of Type
+     * @return (T&NamedType)|null
      */
     protected static function extendMaybeNamedType(?Type $type = null): ?Type
     {
@@ -527,10 +560,15 @@ public static function extend(
 
         /** @var array<string, Node&TypeDefinitionNode> $typeDefinitionMap */
         $typeDefinitionMap = [];
+
         static::$typeExtensionsMap = [];
+
+        /** @var array<int, DirectiveDefinitionNode> $directiveDefinitions */
         $directiveDefinitions = [];
+
         /** @var SchemaDefinitionNode|null $schemaDef */
         $schemaDef = null;
+
         /** @var array<int, SchemaTypeExtensionNode> $schemaExtensions */
         $schemaExtensions = [];
 
diff --git a/src/Utils/SchemaPrinter.php b/src/Utils/SchemaPrinter.php
index cf572df20..46147b727 100644
--- a/src/Utils/SchemaPrinter.php
+++ b/src/Utils/SchemaPrinter.php
@@ -205,7 +205,7 @@ protected static function printDirective(Directive $directive, array $options):
 
     /**
      * @param array<string, bool>                                                          $options
-     * @param Type|Directive|EnumValueDefinition|Argument|FieldDefinition|InputObjectField $def
+     * @param (Type&NamedType)|Directive|EnumValueDefinition|Argument|FieldDefinition|InputObjectField $def
      */
     protected static function printDescription(array $options, $def, string $indentation = '', bool $firstInBlock = true): string
     {
@@ -252,12 +252,18 @@ protected static function printArgs(array $options, array $args, string $indenta
         if (
             Utils::every(
                 $args,
-                static function ($arg): bool {
-                    return 0 === strlen($arg->description ?? '');
-                }
+                static fn (Argument $arg): bool => 0 === strlen($arg->description ?? '')
             )
         ) {
-            return '(' . implode(', ', array_map('static::printInputValue', $args)) . ')';
+            return '('
+                . implode(
+                    ', ',
+                    array_map(
+                        [static::class, 'printInputValue'],
+                        $args
+                    )
+                )
+                . ')';
         }
 
         return sprintf(
diff --git a/src/Utils/TypeComparators.php b/src/Utils/TypeComparators.php
index 9f37f55ac..3a3544662 100644
--- a/src/Utils/TypeComparators.php
+++ b/src/Utils/TypeComparators.php
@@ -4,16 +4,12 @@
 
 namespace GraphQL\Utils;
 
-use GraphQL\Type\Definition\AbstractType;
 use GraphQL\Type\Definition\ImplementingType;
 use GraphQL\Type\Definition\ListOfType;
 use GraphQL\Type\Definition\NonNull;
 use GraphQL\Type\Definition\Type;
 use GraphQL\Type\Schema;
 
-/**
- * @phpstan-import-type AbstractTypeAlias from AbstractType
- */
 class TypeComparators
 {
     /**
@@ -82,7 +78,6 @@ public static function isTypeSubTypeOf(Schema $schema, Type $maybeSubType, Type
         if (Type::isAbstractType($superType)) {
             // If superType type is an abstract type, maybeSubType type may be a currently
             // possible object or interface type.
-            /** @phpstan-var AbstractTypeAlias $superType proven by Type::isAbstractType() */
 
             return $maybeSubType instanceof ImplementingType
                 && $schema->isSubType($superType, $maybeSubType);
diff --git a/src/Utils/TypeInfo.php b/src/Utils/TypeInfo.php
index 47318828d..7a9e404d3 100644
--- a/src/Utils/TypeInfo.php
+++ b/src/Utils/TypeInfo.php
@@ -43,26 +43,23 @@
 use GraphQL\Type\Introspection;
 use GraphQL\Type\Schema;
 
-/**
- * @phpstan-import-type InputTypeAlias from InputType
- */
 class TypeInfo
 {
     private Schema $schema;
 
-    /** @var array<(OutputType&Type)|null> */
+    /** @var array<int, (OutputType&Type)|null> */
     private array $typeStack = [];
 
-    /** @var array<(CompositeType&Type)|null> */
+    /** @var array<int, (CompositeType&Type)|null> */
     private array $parentTypeStack = [];
 
-    /** @var array<(InputType&Type)|null> */
+    /** @var array<int, (InputType&Type)|null> */
     private array $inputTypeStack = [];
 
-    /** @var array<FieldDefinition> */
+    /** @var array<int, FieldDefinition> */
     private array $fieldDefStack = [];
 
-    /** @var array<mixed> */
+    /** @var array<int, mixed> */
     private array $defaultValueStack = [];
 
     private ?Directive $directive = null;
@@ -90,17 +87,18 @@ public function __construct(Schema $schema)
      *     ...
      * ]
      *
-     * @param array<Type> $typeMap
+     * @param array<string, Type&NamedType> $typeMap
      */
     public static function extractTypes(Type $type, array &$typeMap): void
     {
-        /** @var (Type&WrappingType)|(Type&NamedType) $type */
         if ($type instanceof WrappingType) {
             self::extractTypes($type->getInnermostType(), $typeMap);
 
             return;
         }
 
+        assert($type instanceof NamedType, 'only other option');
+
         $name = $type->name;
 
         if (isset($typeMap[$name])) {
@@ -151,7 +149,7 @@ public static function extractTypes(Type $type, array &$typeMap): void
     }
 
     /**
-     * @param array<Type> $typeMap
+     * @param array<string, Type&NamedType> $typeMap
      */
     public static function extractTypesFromDirectives(Directive $directive, array &$typeMap): void
     {
@@ -221,7 +219,8 @@ public function enter(Node $node): void
                     $type = $schema->getQueryType();
                 } elseif ('mutation' === $node->operation) {
                     $type = $schema->getMutationType();
-                } elseif ('subscription' === $node->operation) {
+                } else {
+                    // Only other option
                     $type = $schema->getSubscriptionType();
                 }
 
@@ -366,7 +365,7 @@ private static function getFieldDefinition(Schema $schema, Type $parentType, Fie
      *
      * @throws InvariantViolation
      */
-    public static function typeFromAST(Schema $schema, $inputTypeNode): ?Type
+    public static function typeFromAST(Schema $schema, Node $inputTypeNode): ?Type
     {
         return AST::typeFromAST($schema, $inputTypeNode);
     }
@@ -390,7 +389,7 @@ public function getDefaultValue()
     }
 
     /**
-     * @phpstan-return InputTypeAlias|null
+     * @return (InputType&Type)|null
      */
     public function getInputType(): ?InputType
     {
diff --git a/src/Utils/Utils.php b/src/Utils/Utils.php
index c460041f7..8eb8940e5 100644
--- a/src/Utils/Utils.php
+++ b/src/Utils/Utils.php
@@ -69,7 +69,7 @@ public static function assign(object $obj, array $vars): object
             if (! property_exists($obj, $key)) {
                 $cls = get_class($obj);
                 Warning::warn(
-                    sprintf("Trying to set non-existing property '%s' on class '%s'", $key, $cls),
+                    "Trying to set non-existing property '{$key}' on class '{$cls}'",
                     Warning::WARNING_ASSIGN
                 );
             }
@@ -81,15 +81,15 @@ public static function assign(object $obj, array $vars): object
     }
 
     /**
+     * @template TKey of array-key
+     * @template TValue
+     *
      * @param iterable<mixed> $iterable
      * @phpstan-param iterable<TKey, TValue> $iterable
      * @phpstan-param callable(TValue, TKey): bool $predicate
      *
      * @return mixed
      * @phpstan-return TValue|null
-     *
-     * @template TKey of array-key
-     * @template TValue
      */
     public static function find(iterable $iterable, callable $predicate)
     {
@@ -159,11 +159,11 @@ public static function invariant($test, $message = ''): void
     public static function printSafeJson($var): string
     {
         if ($var instanceof stdClass) {
-            return json_encode($var);
+            return json_encode($var, JSON_THROW_ON_ERROR);
         }
 
         if (is_array($var)) {
-            return json_encode($var);
+            return json_encode($var, JSON_THROW_ON_ERROR);
         }
 
         if ('' === $var) {
@@ -211,7 +211,7 @@ public static function printSafe($var): string
         }
 
         if (is_array($var)) {
-            return json_encode($var);
+            return json_encode($var, JSON_THROW_ON_ERROR);
         }
 
         if ('' === $var) {
@@ -266,37 +266,30 @@ public static function ord(string $char, string $encoding = 'UTF-8'): int
             $char = mb_convert_encoding($char, 'UCS-4BE', $encoding);
         }
 
+        // @phpstan-ignore-next-line format string is statically known to be correct
         return unpack('N', $char)[1];
     }
 
     /**
      * Returns UTF-8 char code at given $positing of the $string.
-     *
-     * @param string $string
-     * @param int    $position
-     *
-     * @return mixed
      */
-    public static function charCodeAt($string, $position)
+    public static function charCodeAt(string $string, int $position): int
     {
         $char = mb_substr($string, $position, 1, 'UTF-8');
 
         return self::ord($char);
     }
 
-    /**
-     * @param int|null $code
-     */
-    public static function printCharCode($code): string
+    public static function printCharCode(?int $code): string
     {
         if (null === $code) {
             return '<EOF>';
         }
 
         return $code < 0x007F
-            // Trust JSON for ASCII.
-            ? json_encode(self::chr($code))
-            // Otherwise print the escaped form.
+            // Trust JSON for ASCII
+            ? json_encode(self::chr($code), JSON_THROW_ON_ERROR)
+            // Otherwise, print the escaped form
             : '"\\u' . dechex($code) . '"';
     }
 
@@ -325,7 +318,7 @@ public static function isValidNameError(string $name, ?Node $node = null): ?Erro
             );
         }
 
-        if (! preg_match('/^[_a-zA-Z][_a-zA-Z0-9]*$/', $name)) {
+        if (1 !== preg_match('/^[_a-zA-Z][_a-zA-Z0-9]*$/', $name)) {
             return new Error(
                 'Names must match /^[_a-zA-Z][_a-zA-Z0-9]*$/ but "' . $name . '" does not.',
                 $node
diff --git a/src/Utils/Value.php b/src/Utils/Value.php
index d3d33a137..8285bfb28 100644
--- a/src/Utils/Value.php
+++ b/src/Utils/Value.php
@@ -34,15 +34,15 @@
  * @phpstan-type CoercedErrors array{errors: array<int, Error>, value: null}
  *
  * The key prev should actually also be typed as Path, but PHPStan does not support recursive types.
- * @phpstan-type Path array{prev: array<string, mixed>, key: string|int}
+ * @phpstan-type Path array{prev: array<string, mixed>|null, key: string|int}
  */
 class Value
 {
     /**
      * Given a type and any value, return a runtime value coerced to match the type.
      *
-     * @param mixed                                               $value
-     * @param ScalarType|EnumType|InputObjectType|ListOfType<Type &InputType>|NonNull $type
+     * @param mixed $value
+     * @param InputType&Type $type
      * @phpstan-param Path|null $path
      *
      * @phpstan-return CoercedValue|CoercedErrors
@@ -60,6 +60,7 @@ public static function coerceValue($value, InputType $type, ?VariableDefinitionN
                 ]);
             }
 
+            // @phpstan-ignore-next-line wrapped type is known to be input type after schema validation
             return self::coerceValue($value, $type->getWrappedType(), $blameNode, $path);
         }
 
@@ -117,6 +118,8 @@ public static function coerceValue($value, InputType $type, ?VariableDefinitionN
 
         if ($type instanceof ListOfType) {
             $itemType = $type->getWrappedType();
+            assert($itemType instanceof InputType, 'known through schema validation');
+
             if (is_array($value) || $value instanceof Traversable) {
                 $errors = [];
                 $coercedValue = [];
@@ -148,6 +151,8 @@ public static function coerceValue($value, InputType $type, ?VariableDefinitionN
                 : self::ofValue([$coercedItem['value']]);
         }
 
+        assert($type instanceof InputObjectType, 'we handled all other cases at this point');
+
         if ($value instanceof stdClass) {
             // Cast objects to associative array before checking the fields.
             // Note that the coerced value will be an array.
diff --git a/src/Validator/DocumentValidator.php b/src/Validator/DocumentValidator.php
index 34dc81dc0..d184f8764 100644
--- a/src/Validator/DocumentValidator.php
+++ b/src/Validator/DocumentValidator.php
@@ -114,7 +114,7 @@ public static function validate(
     /**
      * Returns all global validation rules.
      *
-     * @return array<class-string<ValidationRule>, ValidationRule>
+     * @return array<string, ValidationRule>
      *
      * @api
      */
@@ -219,22 +219,16 @@ public static function visitUsingRules(Schema $schema, TypeInfo $typeInfo, Docum
     }
 
     /**
-     * Returns global validation rule by name. Standard rules are named by class name, so
-     * example usage for such rules:.
-     *
-     * $rule = DocumentValidator::getRule(GraphQL\Validator\Rules\QueryComplexity::class);
-     *
-     * @param class-string<T> $name
+     * Returns global validation rule by name.
      *
-     * @return T|null
+     * Standard rules are named by class name, so example usage for such rules:
      *
-     * @template T of ValidationRule
+     * @example DocumentValidator::getRule(GraphQL\Validator\Rules\QueryComplexity::class);
      *
      * @api
      */
     public static function getRule(string $name): ?ValidationRule
     {
-        // @phpstan-ignore-next-line class-strings are always mapped to a matching class instance
         return static::allRules()[$name] ?? null;
     }
 
diff --git a/src/Validator/Rules/ExecutableDefinitions.php b/src/Validator/Rules/ExecutableDefinitions.php
index dbd30f4da..3a1595df3 100644
--- a/src/Validator/Rules/ExecutableDefinitions.php
+++ b/src/Validator/Rules/ExecutableDefinitions.php
@@ -25,16 +25,15 @@ public function getVisitor(ValidationContext $context): array
     {
         return [
             NodeKind::DOCUMENT => static function (DocumentNode $node) use ($context): VisitorOperation {
-                /** @var ExecutableDefinitionNode|TypeSystemDefinitionNode $definition */
                 foreach ($node->definitions as $definition) {
-                    if ($definition instanceof ExecutableDefinitionNode) {
-                        continue;
-                    }
+                    if (! $definition instanceof ExecutableDefinitionNode) {
+                        assert($definition instanceof TypeSystemDefinitionNode, 'only other option');
 
-                    $context->reportError(new Error(
-                        static::nonExecutableDefinitionMessage($definition->name->value),
-                        [$definition->name]
-                    ));
+                        $context->reportError(new Error(
+                            static::nonExecutableDefinitionMessage($definition->name->value),
+                            [$definition->name]
+                        ));
+                    }
                 }
 
                 return Visitor::skipNode();
diff --git a/src/Validator/Rules/FieldsOnCorrectType.php b/src/Validator/Rules/FieldsOnCorrectType.php
index aac429d0b..0dabc37bd 100644
--- a/src/Validator/Rules/FieldsOnCorrectType.php
+++ b/src/Validator/Rules/FieldsOnCorrectType.php
@@ -10,7 +10,6 @@
 use GraphQL\Error\Error;
 use GraphQL\Language\AST\FieldNode;
 use GraphQL\Language\AST\NodeKind;
-use GraphQL\Type\Definition\AbstractType;
 use GraphQL\Type\Definition\HasFieldsType;
 use GraphQL\Type\Definition\NamedType;
 use GraphQL\Type\Definition\Type;
@@ -18,9 +17,6 @@
 use GraphQL\Utils\Utils;
 use GraphQL\Validator\ValidationContext;
 
-/**
- * @phpstan-import-type AbstractTypeAlias from AbstractType
- */
 class FieldsOnCorrectType extends ValidationRule
 {
     public function getVisitor(ValidationContext $context): array
@@ -72,7 +68,6 @@ public function getVisitor(ValidationContext $context): array
     protected function getSuggestedTypeNames(Schema $schema, Type $type, string $fieldName): array
     {
         if (Type::isAbstractType($type)) {
-            /** @phpstan-var AbstractTypeAlias $type proven by Type::isAbstractType() */
             $suggestedObjectTypes = [];
             $interfaceUsageCount = [];
 
diff --git a/src/Validator/Rules/KnownArgumentNamesOnDirectives.php b/src/Validator/Rules/KnownArgumentNamesOnDirectives.php
index 195d4a058..5f28f338e 100644
--- a/src/Validator/Rules/KnownArgumentNamesOnDirectives.php
+++ b/src/Validator/Rules/KnownArgumentNamesOnDirectives.php
@@ -74,31 +74,24 @@ public function getASTVisitor(ASTValidationContext $context): array
 
         $astDefinitions = $context->getDocument()->definitions;
         foreach ($astDefinitions as $def) {
-            if (! ($def instanceof DirectiveDefinitionNode)) {
-                continue;
-            }
-
-            $name = $def->name->value;
-            if (null !== $def->arguments) {
+            if ($def instanceof DirectiveDefinitionNode) {
                 $argNames = [];
                 foreach ($def->arguments as $arg) {
                     $argNames[] = $arg->name->value;
                 }
 
-                $directiveArgs[$name] = $argNames;
-            } else {
-                $directiveArgs[$name] = [];
+                $directiveArgs[$def->name->value] = $argNames;
             }
         }
 
         return [
             NodeKind::DIRECTIVE => static function (DirectiveNode $directiveNode) use ($directiveArgs, $context): VisitorOperation {
                 $directiveName = $directiveNode->name->value;
-                $knownArgs = $directiveArgs[$directiveName] ?? null;
 
-                if (null === $directiveNode->arguments || null === $knownArgs) {
+                if (! isset($directiveArgs[$directiveName])) {
                     return Visitor::skipNode();
                 }
+                $knownArgs = $directiveArgs[$directiveName];
 
                 foreach ($directiveNode->arguments as $argNode) {
                     $argName = $argNode->name->value;
diff --git a/src/Validator/Rules/NoUnusedVariables.php b/src/Validator/Rules/NoUnusedVariables.php
index 33cfa740e..823a0626d 100644
--- a/src/Validator/Rules/NoUnusedVariables.php
+++ b/src/Validator/Rules/NoUnusedVariables.php
@@ -12,7 +12,7 @@
 
 class NoUnusedVariables extends ValidationRule
 {
-    /** @var VariableDefinitionNode[] */
+    /** @var array<int, VariableDefinitionNode> */
     protected array $variableDefs;
 
     public function getVisitor(ValidationContext $context): array
diff --git a/src/Validator/Rules/OverlappingFieldsCanBeMerged.php b/src/Validator/Rules/OverlappingFieldsCanBeMerged.php
index 9fce2de3a..878cb72ad 100644
--- a/src/Validator/Rules/OverlappingFieldsCanBeMerged.php
+++ b/src/Validator/Rules/OverlappingFieldsCanBeMerged.php
@@ -7,7 +7,6 @@
 use function array_keys;
 use function array_map;
 use function array_merge;
-use function array_reduce;
 use function count;
 use GraphQL\Error\Error;
 use GraphQL\Language\AST\ArgumentNode;
@@ -34,8 +33,11 @@
 use SplObjectStorage;
 
 /**
- * @phpstan-type ReasonOrReasons string|array<array{string, string|array<array{string, string}>}>
- * @phpstan-type Conflict array{array{string, ReasonOrReasons}, array{FieldNode}, array{FieldNode}}
+ * ReasonOrReasons is recursive, but PHPStan does not support that.
+ *
+ * @phpstan-type ReasonOrReasons string|array<array{string, string|array<mixed>}>
+ *
+ * @phpstan-type Conflict array{array{string, ReasonOrReasons}, array<int, FieldNode>, array<int, FieldNode>}
  * @phpstan-type FieldInfo array{Type, FieldNode, FieldDefinition|null}
  * @phpstan-type FieldMap array<string, array<int, FieldInfo>>
  */
@@ -235,7 +237,7 @@ protected function getFieldsAndFragmentNames(
      * as well as a list of nested fragment names referenced via fragment spreads.
      *
      * @param array<string, bool> $fragmentNames
-     * @phpstan-param FieldMap   $astAndDefs
+     * @phpstan-param FieldMap $astAndDefs
      */
     protected function internalCollectFieldsAndFragmentNames(
         ValidationContext $context,
@@ -336,7 +338,7 @@ protected function collectConflictsWithin(
      * @param array{Type, FieldNode, FieldDefinition|null} $field1
      * @param array{Type, FieldNode, FieldDefinition|null} $field2
      *
-     * @return array{array{string, string}, array{FieldNode}, array{FieldNode}}|null
+     * @phpstan-return Conflict|null
      */
     protected function findConflict(
         ValidationContext $context,
@@ -813,8 +815,7 @@ protected function collectConflictsBetweenFragments(
     }
 
     /**
-     * Given a series of Conflicts which occurred between two sub-fields, generate
-     * a single Conflict.
+     * Merge Conflicts between two sub-fields into a single Conflict.
      *
      * @phpstan-param array<int, Conflict> $conflicts
      *
@@ -830,28 +831,32 @@ protected function subfieldConflicts(
             return null;
         }
 
+        $reasons = [];
+        foreach ($conflicts as $conflict) {
+            $reasons[] = $conflict[0];
+        }
+
+        $fields1 = [$ast1];
+        foreach ($conflicts as $conflict) {
+            foreach ($conflict[1] as $field) {
+                $fields1[] = $field;
+            }
+        }
+
+        $fields2 = [$ast2];
+        foreach ($conflicts as $conflict) {
+            foreach ($conflict[2] as $field) {
+                $fields2[] = $field;
+            }
+        }
+
         return [
             [
                 $responseName,
-                array_map(
-                    static fn (array $conflict) => $conflict[0],
-                    $conflicts
-                ),
+                $reasons,
             ],
-            array_reduce(
-                $conflicts,
-                static function ($allFields, $conflict): array {
-                    return array_merge($allFields, $conflict[1]);
-                },
-                [$ast1]
-            ),
-            array_reduce(
-                $conflicts,
-                static function ($allFields, $conflict): array {
-                    return array_merge($allFields, $conflict[2]);
-                },
-                [$ast2]
-            ),
+            $fields1,
+            $fields2,
         ];
     }
 
diff --git a/src/Validator/Rules/PossibleFragmentSpreads.php b/src/Validator/Rules/PossibleFragmentSpreads.php
index f483ee6e5..678e07dd5 100644
--- a/src/Validator/Rules/PossibleFragmentSpreads.php
+++ b/src/Validator/Rules/PossibleFragmentSpreads.php
@@ -62,8 +62,8 @@ public function getVisitor(ValidationContext $context): array
     }
 
     /**
-     * @param CompositeType &Type $fragType
-     * @param CompositeType &Type $parentType
+     * @param CompositeType&Type $fragType
+     * @param CompositeType&Type $parentType
      */
     protected function doTypesOverlap(Schema $schema, CompositeType $fragType, CompositeType $parentType): bool
     {
diff --git a/src/Validator/Rules/QueryComplexity.php b/src/Validator/Rules/QueryComplexity.php
index 3d544703b..6d2bf8790 100644
--- a/src/Validator/Rules/QueryComplexity.php
+++ b/src/Validator/Rules/QueryComplexity.php
@@ -168,34 +168,34 @@ protected function directiveExcludesField(FieldNode $node): bool
                 $this->variableDefs,
                 $this->getRawVariableValues()
             );
-            if (count($errors ?? []) > 0) {
+            if (null !== $errors && count($errors) > 0) {
                 throw new Error(implode(
                     "\n\n",
                     array_map(
-                        static fn ($error) => $error->getMessage(),
+                        static fn (Error $error): string => $error->getMessage(),
                         $errors
                     )
                 ));
             }
 
             if (Directive::INCLUDE_NAME === $directiveNode->name->value) {
-                /** @var array{if: bool} $includeArguments */
                 $includeArguments = Values::getArgumentValues(
                     Directive::includeDirective(),
                     $directiveNode,
                     $variableValues
                 );
+                assert(is_bool($includeArguments['if']), 'ensured by query validation');
 
                 return ! $includeArguments['if'];
             }
 
             if (Directive::SKIP_NAME === $directiveNode->name->value) {
-                /** @var array{if: bool} $skipArguments */
                 $skipArguments = Values::getArgumentValues(
                     Directive::skipDirective(),
                     $directiveNode,
                     $variableValues
                 );
+                assert(is_bool($skipArguments['if']), 'ensured by query validation');
 
                 return $skipArguments['if'];
             }
diff --git a/src/Validator/Rules/UniqueArgumentNames.php b/src/Validator/Rules/UniqueArgumentNames.php
index 27f93779d..fd676d97c 100644
--- a/src/Validator/Rules/UniqueArgumentNames.php
+++ b/src/Validator/Rules/UniqueArgumentNames.php
@@ -48,7 +48,7 @@ public function getASTVisitor(ASTValidationContext $context): array
             },
             NodeKind::ARGUMENT => function (ArgumentNode $node) use ($context): VisitorOperation {
                 $argName = $node->name->value;
-                if ($this->knownArgNames[$argName] ?? false) {
+                if (isset($this->knownArgNames[$argName])) {
                     $context->reportError(new Error(
                         static::duplicateArgMessage($argName),
                         [$this->knownArgNames[$argName], $node->name]
diff --git a/src/Validator/Rules/UniqueDirectivesPerLocation.php b/src/Validator/Rules/UniqueDirectivesPerLocation.php
index b378f8358..f335b0346 100644
--- a/src/Validator/Rules/UniqueDirectivesPerLocation.php
+++ b/src/Validator/Rules/UniqueDirectivesPerLocation.php
@@ -6,7 +6,6 @@
 
 use GraphQL\Error\Error;
 use GraphQL\Language\AST\DirectiveDefinitionNode;
-use GraphQL\Language\AST\DirectiveNode;
 use GraphQL\Language\AST\Node;
 use GraphQL\Language\Visitor;
 use GraphQL\Type\Definition\Directive;
@@ -66,7 +65,6 @@ public function getASTVisitor(ASTValidationContext $context): array
 
                 $knownDirectives = [];
 
-                /** @var DirectiveNode $directive */
                 foreach ($node->directives as $directive) {
                     $directiveName = $directive->name->value;
 
diff --git a/src/Validator/Rules/UniqueOperationNames.php b/src/Validator/Rules/UniqueOperationNames.php
index e9f17ba9b..24dc26887 100644
--- a/src/Validator/Rules/UniqueOperationNames.php
+++ b/src/Validator/Rules/UniqueOperationNames.php
@@ -14,7 +14,7 @@
 
 class UniqueOperationNames extends ValidationRule
 {
-    /** @var NameNode[] */
+    /** @var array<string, NameNode> */
     protected array $knownOperationNames;
 
     public function getVisitor(ValidationContext $context): array
diff --git a/src/Validator/Rules/ValuesOfCorrectType.php b/src/Validator/Rules/ValuesOfCorrectType.php
index d52fbb3c0..e87c4b0c0 100644
--- a/src/Validator/Rules/ValuesOfCorrectType.php
+++ b/src/Validator/Rules/ValuesOfCorrectType.php
@@ -5,12 +5,10 @@
 namespace GraphQL\Validator\Rules;
 
 use function array_keys;
-use function array_map;
 use function count;
 use GraphQL\Error\Error;
 use GraphQL\Language\AST\BooleanValueNode;
 use GraphQL\Language\AST\EnumValueNode;
-use GraphQL\Language\AST\FieldNode;
 use GraphQL\Language\AST\FloatValueNode;
 use GraphQL\Language\AST\IntValueNode;
 use GraphQL\Language\AST\ListValueNode;
@@ -24,13 +22,10 @@
 use GraphQL\Language\Printer;
 use GraphQL\Language\Visitor;
 use GraphQL\Language\VisitorOperation;
-use GraphQL\Type\Definition\EnumType;
-use GraphQL\Type\Definition\EnumValueDefinition;
 use GraphQL\Type\Definition\InputObjectType;
-use GraphQL\Type\Definition\InputType;
+use GraphQL\Type\Definition\LeafType;
 use GraphQL\Type\Definition\ListOfType;
 use GraphQL\Type\Definition\NonNull;
-use GraphQL\Type\Definition\ScalarType;
 use GraphQL\Type\Definition\Type;
 use GraphQL\Utils\Utils;
 use GraphQL\Validator\ValidationContext;
@@ -46,28 +41,21 @@ class ValuesOfCorrectType extends ValidationRule
 {
     public function getVisitor(ValidationContext $context): array
     {
-        $fieldName = '';
-
         return [
-            NodeKind::FIELD => [
-                'enter' => static function (FieldNode $node) use (&$fieldName): void {
-                    $fieldName = $node->name->value;
-                },
-            ],
-            NodeKind::NULL => static function (NullValueNode $node) use ($context, &$fieldName): void {
+            NodeKind::NULL => static function (NullValueNode $node) use ($context): void {
                 $type = $context->getInputType();
-                if (! ($type instanceof NonNull)) {
-                    return;
+                if ($type instanceof NonNull) {
+                    $typeStr = Utils::printSafe($type);
+                    $nodeStr = Printer::doPrint($node);
+                    $context->reportError(
+                        new Error(
+                            "Expected value of type \"{$typeStr}\", found {$nodeStr}.",
+                            $node
+                        )
+                    );
                 }
-
-                $context->reportError(
-                    new Error(
-                        static::getBadValueMessage((string) $type, Printer::doPrint($node), null, $context, $fieldName),
-                        $node
-                    )
-                );
             },
-            NodeKind::LST => function (ListValueNode $node) use ($context, &$fieldName): ?VisitorOperation {
+            NodeKind::LST => function (ListValueNode $node) use ($context): ?VisitorOperation {
                 // Note: TypeInfo will traverse into a list's item type, so look to the
                 // parent input type to check if it is a list.
                 $parentType = $context->getParentInputType();
@@ -75,19 +63,17 @@ public function getVisitor(ValidationContext $context): array
                     ? null
                     : Type::getNullableType($parentType);
                 if (! $type instanceof ListOfType) {
-                    $this->isValidScalar($context, $node, $fieldName);
+                    $this->isValidValueNode($context, $node);
 
                     return Visitor::skipNode();
                 }
 
                 return null;
             },
-            NodeKind::OBJECT => function (ObjectValueNode $node) use ($context, &$fieldName): ?VisitorOperation {
-                // Note: TypeInfo will traverse into a list's item type, so look to the
-                // parent input type to check if it is a list.
+            NodeKind::OBJECT => function (ObjectValueNode $node) use ($context): ?VisitorOperation {
                 $type = Type::getNamedType($context->getInputType());
                 if (! $type instanceof InputObjectType) {
-                    $this->isValidScalar($context, $node, $fieldName);
+                    $this->isValidValueNode($context, $node);
 
                     return Visitor::skipNode();
                 }
@@ -101,14 +87,14 @@ public function getVisitor(ValidationContext $context): array
                 }
 
                 foreach ($inputFields as $inputFieldName => $fieldDef) {
-                    $fieldType = $fieldDef->getType();
                     if (isset($fieldNodeMap[$inputFieldName]) || ! $fieldDef->isRequired()) {
                         continue;
                     }
+                    $fieldType = Utils::printSafe($fieldDef->getType());
 
                     $context->reportError(
                         new Error(
-                            static::requiredFieldMessage($type->name, $inputFieldName, (string) $fieldType),
+                            "Field {$type->name}.{$inputFieldName} of required type {$fieldType} was not provided.",
                             $node
                         )
                     );
@@ -131,83 +117,53 @@ public function getVisitor(ValidationContext $context): array
                     array_keys($parentType->getFields())
                 );
                 $didYouMean = count($suggestions) > 0
-                    ? 'Did you mean ' . Utils::orList($suggestions) . '?'
+                    ? ' Did you mean ' . Utils::quotedOrList($suggestions) . '?'
                     : null;
 
                 $context->reportError(
                     new Error(
-                        static::unknownFieldMessage($parentType->name, $node->name->value, $didYouMean),
+                        "Field \"{$node->name->value}\" is not defined by type \"{$parentType->name}\".{$didYouMean}",
                         $node
                     )
                 );
             },
-            NodeKind::ENUM => function (EnumValueNode $node) use ($context, &$fieldName): void {
-                $type = Type::getNamedType($context->getInputType());
-                if (! $type instanceof EnumType) {
-                    $this->isValidScalar($context, $node, $fieldName);
-                } elseif (null === $type->getValue($node->value)) {
-                    $context->reportError(
-                        new Error(
-                            static::getBadValueMessage(
-                                $type->name,
-                                Printer::doPrint($node),
-                                $this->enumTypeSuggestion($type, $node),
-                                $context,
-                                $fieldName
-                            ),
-                            $node
-                        )
-                    );
-                }
+            NodeKind::ENUM => function (EnumValueNode $node) use ($context): void {
+                $this->isValidValueNode($context, $node);
             },
-            NodeKind::INT => function (IntValueNode $node) use ($context, &$fieldName): void {
-                $this->isValidScalar($context, $node, $fieldName);
+            NodeKind::INT => function (IntValueNode $node) use ($context): void {
+                $this->isValidValueNode($context, $node);
             },
-            NodeKind::FLOAT => function (FloatValueNode $node) use ($context, &$fieldName): void {
-                $this->isValidScalar($context, $node, $fieldName);
+            NodeKind::FLOAT => function (FloatValueNode $node) use ($context): void {
+                $this->isValidValueNode($context, $node);
             },
-            NodeKind::STRING => function (StringValueNode $node) use ($context, &$fieldName): void {
-                $this->isValidScalar($context, $node, $fieldName);
+            NodeKind::STRING => function (StringValueNode $node) use ($context): void {
+                $this->isValidValueNode($context, $node);
             },
-            NodeKind::BOOLEAN => function (BooleanValueNode $node) use ($context, &$fieldName): void {
-                $this->isValidScalar($context, $node, $fieldName);
+            NodeKind::BOOLEAN => function (BooleanValueNode $node) use ($context): void {
+                $this->isValidValueNode($context, $node);
             },
         ];
     }
 
-    public static function badValueMessage(string $typeName, string $valueName, ?string $message = null): string
-    {
-        return "Expected type {$typeName}, found {$valueName}"
-            . (null !== $message && '' !== $message
-                ? "; ${message}"
-                : '.');
-    }
-
     /**
      * @param VariableNode|NullValueNode|IntValueNode|FloatValueNode|StringValueNode|BooleanValueNode|EnumValueNode|ListValueNode|ObjectValueNode $node
      */
-    protected function isValidScalar(ValidationContext $context, ValueNode $node, string $fieldName): void
+    protected function isValidValueNode(ValidationContext $context, ValueNode $node): void
     {
         // Report any error at the full type expected by the location.
-        /** @var ScalarType|EnumType|InputObjectType|ListOfType<Type&InputType>|NonNull|null $locationType */
         $locationType = $context->getInputType();
-
         if (null === $locationType) {
             return;
         }
 
         $type = Type::getNamedType($locationType);
 
-        if (! $type instanceof ScalarType) {
+        if (! $type instanceof LeafType) {
+            $typeStr = Utils::printSafe($type);
+            $nodeStr = Printer::doPrint($node);
             $context->reportError(
                 new Error(
-                    static::getBadValueMessage(
-                        (string) $locationType,
-                        Printer::doPrint($node),
-                        $this->enumTypeSuggestion($type, $node),
-                        $context,
-                        $fieldName
-                    ),
+                    "Expected value of type \"{$typeStr}\", found {$nodeStr}.",
                     $node
                 )
             );
@@ -220,87 +176,22 @@ protected function isValidScalar(ValidationContext $context, ValueNode $node, st
         try {
             $type->parseLiteral($node);
         } catch (Throwable $error) {
-            // Ensure a reference to the original error is maintained.
-            $context->reportError(
-                new Error(
-                    static::getBadValueMessage(
-                        (string) $locationType,
-                        Printer::doPrint($node),
-                        $error->getMessage(),
-                        $context,
-                        $fieldName
-                    ),
-                    $node,
-                    null,
-                    [],
-                    null,
-                    $error
-                )
-            );
-        }
-    }
-
-    /**
-     * @param VariableNode|NullValueNode|IntValueNode|FloatValueNode|StringValueNode|BooleanValueNode|EnumValueNode|ListValueNode|ObjectValueNode $node
-     */
-    protected function enumTypeSuggestion(Type $type, ValueNode $node): ?string
-    {
-        if ($type instanceof EnumType) {
-            $suggestions = Utils::suggestionList(
-                Printer::doPrint($node),
-                array_map(
-                    static fn (EnumValueDefinition $value): string => $value->name,
-                    $type->getValues()
-                )
-            );
-
-            return [] === $suggestions
-                ? null
-                : 'Did you mean the enum value ' . Utils::orList($suggestions) . '?';
-        }
-
-        return null;
-    }
-
-    public static function badArgumentValueMessage(string $typeName, string $valueName, string $fieldName, string $argName, ?string $message = null): string
-    {
-        return "Field \"{$fieldName}\" argument \"{$argName}\" requires type {$typeName}, found {$valueName}"
-            . (
-                null !== $message && '' !== $message
-                ? "; {$message}"
-                : '.'
-            );
-    }
-
-    public static function requiredFieldMessage(string $typeName, string $fieldName, string $fieldTypeName): string
-    {
-        return "Field {$typeName}.{$fieldName} of required type {$fieldTypeName} was not provided.";
-    }
-
-    public static function unknownFieldMessage(string $typeName, string $fieldName, ?string $message = null): string
-    {
-        return "Field \"{$fieldName}\" is not defined by type {$typeName}"
-            . (
-                null !== $message && '' !== $message
-                ? "; {$message}"
-                : '.'
-            );
-    }
-
-    protected static function getBadValueMessage(
-        string $typeName,
-        string $valueName,
-        ?string $message = null,
-        ?ValidationContext $context = null,
-        ?string $fieldName = null
-    ): string {
-        if (null !== $context) {
-            $arg = $context->getArgument();
-            if (null !== $arg) {
-                return static::badArgumentValueMessage($typeName, $valueName, $fieldName, $arg->name, $message);
+            if ($error instanceof Error) {
+                $context->reportError($error);
+            } else {
+                $typeStr = Utils::printSafe($type);
+                $nodeStr = Printer::doPrint($node);
+                $context->reportError(
+                    new Error(
+                        "Expected value of type \"{$typeStr}\", found {$nodeStr}; " . $error->getMessage(),
+                        $node,
+                        null,
+                        [],
+                        null,
+                        $error // Ensure a reference to the original error is maintained.
+                    )
+                );
             }
         }
-
-        return static::badValueMessage($typeName, $valueName, $message);
     }
 }
diff --git a/src/Validator/ValidationContext.php b/src/Validator/ValidationContext.php
index b2f838a6f..3691dc339 100644
--- a/src/Validator/ValidationContext.php
+++ b/src/Validator/ValidationContext.php
@@ -36,7 +36,6 @@
  * allowing access to commonly useful contextual information from within a
  * validation rule.
  *
- * @phpstan-import-type InputTypeAlias from InputType
  * @phpstan-type VariableUsage array{node: VariableNode, type: (Type&InputType)|null, defaultValue: mixed}
  */
 class ValidationContext extends ASTValidationContext
@@ -92,7 +91,7 @@ public function getRecursiveVariableUsages(OperationDefinitionNode $operation):
     }
 
     /**
-     * @param HasSelectionSet &Node $node
+     * @param HasSelectionSet&Node $node
      *
      * @phpstan-return array<int, VariableUsage>
      */
@@ -228,7 +227,7 @@ public function getType(): ?OutputType
     }
 
     /**
-     * @return (CompositeType & Type) | null
+     * @return (CompositeType&Type)|null
      */
     public function getParentType(): ?CompositeType
     {
@@ -236,8 +235,7 @@ public function getParentType(): ?CompositeType
     }
 
     /**
-     * @return (Type & InputType) | null
-     * @phpstan-return InputTypeAlias
+     * @return (Type&InputType)|null
      */
     public function getInputType(): ?InputType
     {
diff --git a/tests/Error/ErrorTest.php b/tests/Error/ErrorTest.php
index 40774c85d..c53b2dfc8 100644
--- a/tests/Error/ErrorTest.php
+++ b/tests/Error/ErrorTest.php
@@ -4,7 +4,6 @@
 
 namespace GraphQL\Tests\Error;
 
-use function array_merge;
 use Exception;
 use GraphQL\Error\Error;
 use GraphQL\Error\FormattedError;
@@ -42,7 +41,7 @@ public function testConvertsNodesToPositionsAndLocations(): void
         $fieldNode = $operationDefinition->selectionSet->selections[0];
         $e = new Error('msg', [$fieldNode]);
 
-        self::assertEquals([$fieldNode], $e->nodes);
+        self::assertEquals([$fieldNode], $e->getNodes());
         self::assertEquals($source, $e->getSource());
         self::assertEquals([8], $e->getPositions());
         self::assertEquals([new SourceLocation(2, 7)], $e->getLocations());
@@ -62,7 +61,7 @@ public function testConvertSingleNodeToPositionsAndLocations(): void
         $fieldNode = $operationDefinition->selectionSet->selections[0];
         $e = new Error('msg', $fieldNode); // Non-array value.
 
-        self::assertEquals([$fieldNode], $e->nodes);
+        self::assertEquals([$fieldNode], $e->getNodes());
         self::assertEquals($source, $e->getSource());
         self::assertEquals([8], $e->getPositions());
         self::assertEquals([new SourceLocation(2, 7)], $e->getLocations());
@@ -80,7 +79,7 @@ public function testConvertsNodeWithStart0ToPositionsAndLocations(): void
         $operationNode = $ast->definitions[0];
         $e = new Error('msg', [$operationNode]);
 
-        self::assertEquals([$operationNode], $e->nodes);
+        self::assertEquals([$operationNode], $e->getNodes());
         self::assertEquals($source, $e->getSource());
         self::assertEquals([0], $e->getPositions());
         self::assertEquals([new SourceLocation(1, 1)], $e->getLocations());
@@ -96,7 +95,7 @@ public function testConvertsSourceAndPositionsToLocations(): void
     }');
         $e = new Error('msg', null, $source, [10]);
 
-        self::assertEquals(null, $e->nodes);
+        self::assertEquals(null, $e->getNodes());
         self::assertEquals($source, $e->getSource());
         self::assertEquals([10], $e->getPositions());
         self::assertEquals([new SourceLocation(2, 9)], $e->getLocations());
@@ -175,7 +174,10 @@ public function testErrorReadsOverridenMethods(): void
         $error = new class('msg', null, null, [], null, null, ['foo' => 'bar']) extends Error {
             public function getExtensions(): ?array
             {
-                return array_merge(parent::getExtensions(), ['subfoo' => 'subbar']);
+                $extensions = parent::getExtensions();
+                $extensions['subfoo'] = 'subbar';
+
+                return $extensions;
             }
 
             public function getPositions(): array
diff --git a/tests/Executor/DeferredFieldsTest.php b/tests/Executor/DeferredFieldsTest.php
index c933a37a3..c7d014c8e 100644
--- a/tests/Executor/DeferredFieldsTest.php
+++ b/tests/Executor/DeferredFieldsTest.php
@@ -14,8 +14,8 @@
 use GraphQL\Type\Definition\Type;
 use GraphQL\Type\Schema;
 use function in_array;
-use function json_encode;
 use PHPUnit\Framework\TestCase;
+use function Safe\json_encode;
 
 class DeferredFieldsTest extends TestCase
 {
diff --git a/tests/Executor/ExecutorLazySchemaTest.php b/tests/Executor/ExecutorLazySchemaTest.php
index 0f91d0d04..8e9903c71 100644
--- a/tests/Executor/ExecutorLazySchemaTest.php
+++ b/tests/Executor/ExecutorLazySchemaTest.php
@@ -277,8 +277,11 @@ public function loadType(string $name, bool $isExecutorCall = false): ?Type
                     'interfaces' => function (): array {
                         $this->calls[] = 'SomeObject.interfaces';
 
+                        /** @var InterfaceType $someInterface */
+                        $someInterface = $this->loadType('SomeInterface');
+
                         return [
-                            $this->loadType('SomeInterface'),
+                            $someInterface,
                         ];
                     },
                 ]);
@@ -289,9 +292,14 @@ public function loadType(string $name, bool $isExecutorCall = false): ?Type
                     'fields' => function (): array {
                         $this->calls[] = 'OtherObject.fields';
 
+                        /** @var UnionType $someUnion */
+                        $someUnion = $this->loadType('SomeUnion');
+                        /** @var InterfaceType $someInterface */
+                        $someInterface = $this->loadType('SomeInterface');
+
                         return [
-                            'union' => ['type' => $this->loadType('SomeUnion')],
-                            'iface' => ['type' => Type::nonNull($this->loadType('SomeInterface'))],
+                            'union' => ['type' => $someUnion],
+                            'iface' => ['type' => Type::nonNull($someInterface)],
                         ];
                     },
                 ]);
@@ -318,12 +326,18 @@ public function loadType(string $name, bool $isExecutorCall = false): ?Type
                     'resolveType' => function () {
                         $this->calls[] = 'SomeUnion.resolveType';
 
-                        return $this->loadType('DeeperObject');
+                        /** @var ObjectType $deeperObject */
+                        $deeperObject = $this->loadType('DeeperObject');
+
+                        return $deeperObject;
                     },
                     'types' => function (): array {
                         $this->calls[] = 'SomeUnion.types';
 
-                        return [$this->loadType('DeeperObject')];
+                        /** @var ObjectType $deeperObject */
+                        $deeperObject = $this->loadType('DeeperObject');
+
+                        return [$deeperObject];
                     },
                 ]);
 
@@ -333,7 +347,10 @@ public function loadType(string $name, bool $isExecutorCall = false): ?Type
                     'resolveType' => function () {
                         $this->calls[] = 'SomeInterface.resolveType';
 
-                        return $this->loadType('SomeObject');
+                        /** @var ObjectType $someObject */
+                        $someObject = $this->loadType('SomeObject');
+
+                        return $someObject;
                     },
                     'fields' => function (): array {
                         $this->calls[] = 'SomeInterface.fields';
diff --git a/tests/Executor/ExecutorTest.php b/tests/Executor/ExecutorTest.php
index da508c2be..4441e76b3 100644
--- a/tests/Executor/ExecutorTest.php
+++ b/tests/Executor/ExecutorTest.php
@@ -25,9 +25,9 @@
 use GraphQL\Type\Definition\ResolveInfo;
 use GraphQL\Type\Definition\Type;
 use GraphQL\Type\Schema;
-use function json_encode;
 use PHPUnit\Framework\TestCase;
 use ReturnTypeWillChange;
+use function Safe\json_encode;
 use stdClass;
 
 class ExecutorTest extends TestCase
diff --git a/tests/Executor/ListsTest.php b/tests/Executor/ListsTest.php
index 5346769e1..3751c6024 100644
--- a/tests/Executor/ListsTest.php
+++ b/tests/Executor/ListsTest.php
@@ -60,8 +60,8 @@ private function checkHandlesNullableLists($testData, array $expected): void
     }
 
     /**
-     * @param Type                 &OutputType $testType
-     * @param mixed                $testData
+     * @param Type&OutputType $testType
+     * @param mixed $testData
      * @param array<string, mixed> $expected
      */
     private function check(Type $testType, $testData, array $expected, int $debug = DebugFlag::NONE): void
diff --git a/tests/Executor/NonNullTest.php b/tests/Executor/NonNullTest.php
index 35563ccdf..2e4d563ae 100644
--- a/tests/Executor/NonNullTest.php
+++ b/tests/Executor/NonNullTest.php
@@ -18,37 +18,31 @@
 use GraphQL\Type\Definition\Type;
 use GraphQL\Type\Schema;
 use function is_string;
-use function json_encode;
 use PHPUnit\Framework\ExpectationFailedException;
 use PHPUnit\Framework\TestCase;
+use function Safe\json_encode;
 
 class NonNullTest extends TestCase
 {
     use ArraySubsetAsserts;
 
-    /** @var Exception */
-    public $syncError;
+    public Exception $syncError;
 
-    /** @var Exception */
-    public $syncNonNullError;
+    public Exception $syncNonNullError;
 
-    /** @var Exception */
-    public $promiseError;
+    public Exception $promiseError;
 
-    /** @var Exception */
-    public $promiseNonNullError;
+    public Exception $promiseNonNullError;
 
-    /** @var callable[] */
-    public $throwingData;
+    /** @var array<string, callable(): mixed> */
+    public array $throwingData;
 
-    /** @var callable[] */
-    public $nullingData;
+    /** @var array<string, callable(): mixed> */
+    public array $nullingData;
 
-    /** @var Schema */
-    public $schema;
+    public Schema $schema;
 
-    /** @var Schema */
-    public $schemaWithNonNullArg;
+    public Schema $schemaWithNonNullArg;
 
     public function setUp(): void
     {
@@ -361,55 +355,55 @@ public function testNullsAComplexTreeOfNullableFieldsThatThrow(): void
 
         $ast = Parser::parse($doc);
 
-        $expected = [
-            'data' => [
+        $expectedData = [
+            'syncNest' => [
+                'sync' => null,
+                'promise' => null,
                 'syncNest' => [
                     'sync' => null,
                     'promise' => null,
-                    'syncNest' => [
-                        'sync' => null,
-                        'promise' => null,
-                    ],
-                    'promiseNest' => [
-                        'sync' => null,
-                        'promise' => null,
-                    ],
                 ],
                 'promiseNest' => [
                     'sync' => null,
                     'promise' => null,
-                    'syncNest' => [
-                        'sync' => null,
-                        'promise' => null,
-                    ],
-                    'promiseNest' => [
-                        'sync' => null,
-                        'promise' => null,
-                    ],
                 ],
             ],
-            'errors' => [
-                ErrorHelper::create($this->syncError->getMessage(), [new SourceLocation(4, 11)]),
-                ErrorHelper::create($this->syncError->getMessage(), [new SourceLocation(7, 13)]),
-                ErrorHelper::create($this->syncError->getMessage(), [new SourceLocation(11, 13)]),
-                ErrorHelper::create($this->syncError->getMessage(), [new SourceLocation(16, 11)]),
-                ErrorHelper::create($this->syncError->getMessage(), [new SourceLocation(19, 13)]),
-                ErrorHelper::create($this->promiseError->getMessage(), [new SourceLocation(5, 11)]),
-                ErrorHelper::create($this->promiseError->getMessage(), [new SourceLocation(8, 13)]),
-                ErrorHelper::create($this->syncError->getMessage(), [new SourceLocation(23, 13)]),
-                ErrorHelper::create($this->promiseError->getMessage(), [new SourceLocation(12, 13)]),
-                ErrorHelper::create($this->promiseError->getMessage(), [new SourceLocation(17, 11)]),
-                ErrorHelper::create($this->promiseError->getMessage(), [new SourceLocation(20, 13)]),
-                ErrorHelper::create($this->promiseError->getMessage(), [new SourceLocation(24, 13)]),
+            'promiseNest' => [
+                'sync' => null,
+                'promise' => null,
+                'syncNest' => [
+                    'sync' => null,
+                    'promise' => null,
+                ],
+                'promiseNest' => [
+                    'sync' => null,
+                    'promise' => null,
+                ],
             ],
         ];
+        $expectedErrors = [
+            ErrorHelper::create($this->syncError->getMessage(), [new SourceLocation(4, 11)]),
+            ErrorHelper::create($this->syncError->getMessage(), [new SourceLocation(7, 13)]),
+            ErrorHelper::create($this->syncError->getMessage(), [new SourceLocation(11, 13)]),
+            ErrorHelper::create($this->syncError->getMessage(), [new SourceLocation(16, 11)]),
+            ErrorHelper::create($this->syncError->getMessage(), [new SourceLocation(19, 13)]),
+            ErrorHelper::create($this->promiseError->getMessage(), [new SourceLocation(5, 11)]),
+            ErrorHelper::create($this->promiseError->getMessage(), [new SourceLocation(8, 13)]),
+            ErrorHelper::create($this->syncError->getMessage(), [new SourceLocation(23, 13)]),
+            ErrorHelper::create($this->promiseError->getMessage(), [new SourceLocation(12, 13)]),
+            ErrorHelper::create($this->promiseError->getMessage(), [new SourceLocation(17, 11)]),
+            ErrorHelper::create($this->promiseError->getMessage(), [new SourceLocation(20, 13)]),
+            ErrorHelper::create($this->promiseError->getMessage(), [new SourceLocation(24, 13)]),
+        ];
 
         $result = Executor::execute($this->schema, $ast, $this->throwingData, null, [], 'Q')->toArray();
 
-        self::assertEquals($expected['data'], $result['data']);
+        self::assertArrayHasKey('data', $result);
+        self::assertEquals($expectedData, $result['data']);
 
-        self::assertCount(count($expected['errors']), $result['errors']);
-        foreach ($expected['errors'] as $expectedError) {
+        self::assertArrayHasKey('errors', $result);
+        self::assertCount(count($expectedErrors), $result['errors']);
+        foreach ($expectedErrors as $expectedError) {
             $found = false;
             foreach ($result['errors'] as $error) {
                 try {
diff --git a/tests/Executor/Promise/SyncPromiseAdapterTest.php b/tests/Executor/Promise/SyncPromiseAdapterTest.php
index 8c6bc22e3..bc324e652 100644
--- a/tests/Executor/Promise/SyncPromiseAdapterTest.php
+++ b/tests/Executor/Promise/SyncPromiseAdapterTest.php
@@ -50,7 +50,6 @@ public function testConvert(): void
 
         $this->expectException(InvariantViolation::class);
         $this->expectExceptionMessage('Expected instance of GraphQL\Deferred, got (empty string)');
-        // @phpstan-ignore-next-line purposefully wrong
         $this->promises->convertThenable('');
     }
 
@@ -216,8 +215,15 @@ public function testWait(): void
         // Having single promise queue means that we won't stop in wait
         // until all pending promises are resolved
         self::assertEquals(2, $result);
-        self::assertEquals(SyncPromise::FULFILLED, $p3->adoptedPromise->state);
-        self::assertEquals(SyncPromise::FULFILLED, $all->adoptedPromise->state);
+
+        $p3AdoptedPromise = $p3->adoptedPromise;
+        self::assertInstanceOf(SyncPromise::class, $p3AdoptedPromise);
+        self::assertEquals(SyncPromise::FULFILLED, $p3AdoptedPromise->state);
+
+        $allAdoptedPromise = $all->adoptedPromise;
+        self::assertInstanceOf(SyncPromise::class, $allAdoptedPromise);
+        self::assertEquals(SyncPromise::FULFILLED, $allAdoptedPromise->state);
+
         self::assertEquals([1, 2, 3, 4], $called);
 
         $expectedResult = [0, 1, 2, 3, 4];
diff --git a/tests/Executor/ResolveTest.php b/tests/Executor/ResolveTest.php
index 97f80a952..2d54ec7f6 100644
--- a/tests/Executor/ResolveTest.php
+++ b/tests/Executor/ResolveTest.php
@@ -10,8 +10,8 @@
 use GraphQL\Type\Definition\ObjectType;
 use GraphQL\Type\Definition\Type;
 use GraphQL\Type\Schema;
-use function json_encode;
 use PHPUnit\Framework\TestCase;
+use function Safe\json_encode;
 use function uniqid;
 
 /**
diff --git a/tests/Executor/TestClasses/ComplexScalar.php b/tests/Executor/TestClasses/ComplexScalar.php
index d6d6b5750..d7cb462fb 100644
--- a/tests/Executor/TestClasses/ComplexScalar.php
+++ b/tests/Executor/TestClasses/ComplexScalar.php
@@ -39,10 +39,14 @@ public function parseValue($value): string
 
     public function parseLiteral(Node $valueNode, ?array $variables = null): string
     {
-        if ('SerializedValue' === $valueNode->value) {
+        $value = property_exists($valueNode, 'value')
+            ? $valueNode->value
+            : null;
+
+        if ('SerializedValue' === $value) {
             return 'DeserializedValue';
         }
 
-        throw new Error('Cannot represent literal as ComplexScalar: ' . Utils::printSafe($valueNode->value));
+        throw new Error('Cannot represent literal as ComplexScalar: ' . Utils::printSafe($value));
     }
 }
diff --git a/tests/Executor/UnionInterfaceTest.php b/tests/Executor/UnionInterfaceTest.php
index e11ea5c4e..7025160bd 100644
--- a/tests/Executor/UnionInterfaceTest.php
+++ b/tests/Executor/UnionInterfaceTest.php
@@ -4,8 +4,8 @@
 
 namespace GraphQL\Tests\Executor;
 
-use GraphQL\Error\DebugFlag;
 use GraphQL\Error\InvariantViolation;
+use GraphQL\Executor\ExecutionResult;
 use GraphQL\Executor\Executor;
 use GraphQL\GraphQL;
 use GraphQL\Language\Parser;
@@ -147,6 +147,16 @@ public function setUp(): void
         $this->john = new Person('John', [$this->garfield, $this->odie], [$this->liz, $this->odie]);
     }
 
+    /**
+     * @param array<string, mixed> $expected
+     * @param mixed $result
+     */
+    protected static function assertExecutionResultEquals(array $expected, $result): void
+    {
+        self::assertInstanceOf(ExecutionResult::class, $result);
+        self::assertEquals($expected, $result->toArray());
+    }
+
     // Execute: Union and intersection types
 
     /**
@@ -236,7 +246,7 @@ enumValues { name }
                 ],
             ],
         ];
-        self::assertEquals($expected, Executor::execute($this->schema, $ast)->toArray());
+        self::assertExecutionResultEquals($expected, Executor::execute($this->schema, $ast));
     }
 
     /**
@@ -276,7 +286,7 @@ public function testExecutesUsingUnionTypes(): void
             ],
         ];
 
-        self::assertEquals($expected, Executor::execute($this->schema, $ast, $this->john)->toArray());
+        self::assertExecutionResultEquals($expected, Executor::execute($this->schema, $ast, $this->john));
     }
 
     /**
@@ -320,7 +330,7 @@ public function testExecutesUnionTypesWithInlineFragments(): void
                 ],
             ],
         ];
-        self::assertEquals($expected, Executor::execute($this->schema, $ast, $this->john)->toArray());
+        self::assertExecutionResultEquals($expected, Executor::execute($this->schema, $ast, $this->john));
     }
 
     /**
@@ -352,7 +362,7 @@ public function testExecutesUsingInterfaceTypes(): void
             ],
         ];
 
-        self::assertEquals($expected, Executor::execute($this->schema, $ast, $this->john)->toArray());
+        self::assertExecutionResultEquals($expected, Executor::execute($this->schema, $ast, $this->john));
     }
 
     /**
@@ -415,7 +425,7 @@ public function testExecutesInterfaceTypesWithInlineFragments(): void
             ],
         ];
 
-        self::assertEquals($expected, Executor::execute($this->schema, $ast, $this->john)->toArray(DebugFlag::INCLUDE_DEBUG_MESSAGE));
+        self::assertExecutionResultEquals($expected, Executor::execute($this->schema, $ast, $this->john));
     }
 
     /**
@@ -507,8 +517,7 @@ public function testAllowsFragmentConditionsToBeAbstractTypes(): void
                 ],
             ],
         ];
-
-        self::assertEquals($expected, Executor::execute($this->schema, $ast, $this->john)->toArray(DebugFlag::RETHROW_INTERNAL_EXCEPTIONS));
+        self::assertExecutionResultEquals($expected, Executor::execute($this->schema, $ast, $this->john));
     }
 
     /**
diff --git a/tests/Language/AST/NodeTest.php b/tests/Language/AST/NodeTest.php
index 23d99a069..6206744b7 100644
--- a/tests/Language/AST/NodeTest.php
+++ b/tests/Language/AST/NodeTest.php
@@ -10,8 +10,8 @@
 use GraphQL\Language\Parser;
 use GraphQL\Utils\AST;
 use function json_decode;
-use function json_encode;
 use PHPUnit\Framework\TestCase;
+use function Safe\json_encode;
 
 class NodeTest extends TestCase
 {
diff --git a/tests/Language/NodeListTest.php b/tests/Language/NodeListTest.php
index b30f5ec7a..d6a4fa075 100644
--- a/tests/Language/NodeListTest.php
+++ b/tests/Language/NodeListTest.php
@@ -21,6 +21,27 @@ public function testConvertArrayToASTNode(): void
         self::assertEquals($nameNode, $nodeList[$key]);
     }
 
+    public function testCloneDeep(): void
+    {
+        $nameNode = new NameNode(['value' => 'bar']);
+
+        $nodeList = new NodeList([
+            'array' => $nameNode->toArray(),
+            'instance' => $nameNode,
+        ]);
+
+        $cloned = $nodeList->cloneDeep();
+
+        self::assertNotSameButEquals($nodeList['array'], $cloned['array']);
+        self::assertNotSameButEquals($nodeList['instance'], $cloned['instance']);
+    }
+
+    private static function assertNotSameButEquals(object $node, object $clone): void
+    {
+        self::assertNotSame($node, $clone);
+        self::assertEquals($node, $clone);
+    }
+
     public function testThrowsOnInvalidArrays(): void
     {
         $nodeList = new NodeList([]);
diff --git a/tests/Language/ParserTest.php b/tests/Language/ParserTest.php
index 89492c3e4..e67647e7c 100644
--- a/tests/Language/ParserTest.php
+++ b/tests/Language/ParserTest.php
@@ -4,7 +4,6 @@
 
 namespace GraphQL\Tests\Language;
 
-use function file_get_contents;
 use GraphQL\Error\SyntaxError;
 use GraphQL\Language\AST\ArgumentNode;
 use GraphQL\Language\AST\FieldNode;
@@ -21,7 +20,7 @@
 use GraphQL\Tests\TestCaseBase;
 use GraphQL\Utils\Utils;
 use function is_array;
-use function sprintf;
+use function Safe\file_get_contents;
 
 class ParserTest extends TestCaseBase
 {
@@ -210,9 +209,9 @@ public function testParsesMultiByteCharacters(): void
                     'arguments' => new NodeList([
                         new ArgumentNode([
                             'name' => new NameNode(['value' => 'arg']),
-                            'value' => new StringValueNode(
-                                ['value' => sprintf('Has a %s multi-byte character.', $char)]
-                            ),
+                            'value' => new StringValueNode([
+                                'value' => "Has a {$char} multi-byte character.",
+                            ]),
                         ]),
                     ]),
                     'directives' => new NodeList([]),
diff --git a/tests/Language/PrinterTest.php b/tests/Language/PrinterTest.php
index e465e3e2f..833b39e13 100644
--- a/tests/Language/PrinterTest.php
+++ b/tests/Language/PrinterTest.php
@@ -4,7 +4,6 @@
 
 namespace GraphQL\Tests\Language;
 
-use function file_get_contents;
 use GraphQL\Language\AST\FieldNode;
 use GraphQL\Language\AST\NameNode;
 use GraphQL\Language\AST\NodeList;
@@ -13,6 +12,7 @@
 use GraphQL\Type\Definition\Type;
 use GraphQL\Utils\AST;
 use PHPUnit\Framework\TestCase;
+use function Safe\file_get_contents;
 
 class PrinterTest extends TestCase
 {
diff --git a/tests/Language/SchemaPrinterTest.php b/tests/Language/SchemaPrinterTest.php
index 8d3f76b8f..98d4f6a32 100644
--- a/tests/Language/SchemaPrinterTest.php
+++ b/tests/Language/SchemaPrinterTest.php
@@ -4,14 +4,14 @@
 
 namespace GraphQL\Tests\Language;
 
-use function file_get_contents;
 use GraphQL\Language\AST\NameNode;
 use GraphQL\Language\AST\NodeList;
 use GraphQL\Language\AST\ScalarTypeDefinitionNode;
 use GraphQL\Language\Parser;
 use GraphQL\Language\Printer;
-use function json_encode;
 use PHPUnit\Framework\TestCase;
+use function Safe\file_get_contents;
+use function Safe\json_encode;
 
 /**
  * @see describe('Printer: SDL document')
diff --git a/tests/Language/SerializationTest.php b/tests/Language/SerializationTest.php
index aa444e418..aa4cf25f5 100644
--- a/tests/Language/SerializationTest.php
+++ b/tests/Language/SerializationTest.php
@@ -6,7 +6,6 @@
 
 use function array_keys;
 use function count;
-use function file_get_contents;
 use function get_class;
 use function get_object_vars;
 use GraphQL\Language\AST\Location;
@@ -17,6 +16,7 @@
 use function implode;
 use function json_decode;
 use PHPUnit\Framework\TestCase;
+use function Safe\file_get_contents;
 
 class SerializationTest extends TestCase
 {
@@ -40,7 +40,7 @@ public function testUnserializesAst(): void
     /**
      * Compares two nodes by actually iterating over all NodeLists, properly comparing locations (ignoring tokens), etc.
      *
-     * @param string[] $path
+     * @param array<string> $path
      */
     private static function assertNodesAreEqual(Node $expected, Node $actual, array $path = []): void
     {
@@ -50,7 +50,6 @@ private static function assertNodesAreEqual(Node $expected, Node $actual, array
 
         $expectedVars = get_object_vars($expected);
         $actualVars = get_object_vars($actual);
-        self::assertCount(count($expectedVars), $actualVars, $err);
         self::assertEquals(array_keys($expectedVars), array_keys($actualVars), $err);
 
         foreach ($expectedVars as $name => $expectedValue) {
diff --git a/tests/Language/VisitorTest.php b/tests/Language/VisitorTest.php
index 1b3f2094a..b046ba059 100644
--- a/tests/Language/VisitorTest.php
+++ b/tests/Language/VisitorTest.php
@@ -8,10 +8,7 @@
 use function array_pop;
 use function array_slice;
 use function count;
-use function file_get_contents;
 use function func_get_args;
-use function gettype;
-use GraphQL\Language\AST\DefinitionNode;
 use GraphQL\Language\AST\DocumentNode;
 use GraphQL\Language\AST\FieldNode;
 use GraphQL\Language\AST\NameNode;
@@ -29,6 +26,7 @@
 use GraphQL\Type\Definition\Type;
 use GraphQL\Utils\TypeInfo;
 use function is_numeric;
+use function Safe\file_get_contents;
 
 class VisitorTest extends ValidatorTestCase
 {
@@ -129,11 +127,11 @@ private function checkVisitorFnArgs(DocumentNode $ast, array $args, bool $isEdit
             return;
         }
 
-        self::assertContains(gettype($key), ['integer', 'string']);
-        /** @var int|string $key */
         if ($parent instanceof NodeList) {
-            self::assertArrayHasKey($key, $parent);
+            self::assertIsInt($key);
+            self::assertTrue(isset($parent[$key]));
         } else {
+            self::assertIsString($key);
             self::assertObjectHasAttribute($key, $parent);
         }
 
@@ -233,10 +231,9 @@ public function testAllowsEditingRootNodeOnEnterAndLeave(): void
                 NodeKind::DOCUMENT => [
                     'enter' => function (DocumentNode $node) use ($ast): DocumentNode {
                         $this->checkVisitorFnArgs($ast, func_get_args());
-                        /** @var NodeList<DefinitionNode&Node> $definitionNodeList */
-                        $definitionNodeList = new NodeList([]);
                         $tmp = clone $node;
-                        $tmp->definitions = $definitionNodeList;
+                        // @phpstan-ignore-next-line generic type of empty NodeList is not initialized
+                        $tmp->definitions = new NodeList([]);
                         $tmp->didEnter = true;
 
                         return $tmp;
diff --git a/tests/PhpStan/Type/Definition/Type/IsAbstractTypeStaticMethodTypeSpecifyingExtension.php b/tests/PhpStan/Type/Definition/Type/IsAbstractTypeStaticMethodTypeSpecifyingExtension.php
new file mode 100644
index 000000000..f623f56f9
--- /dev/null
+++ b/tests/PhpStan/Type/Definition/Type/IsAbstractTypeStaticMethodTypeSpecifyingExtension.php
@@ -0,0 +1,44 @@
+<?php
+
+declare(strict_types=1);
+
+namespace GraphQL\Tests\PhpStan\Type\Definition\Type;
+
+use GraphQL\Type\Definition\AbstractType;
+use GraphQL\Type\Definition\Type;
+use PhpParser\Node\Expr\StaticCall;
+use PHPStan\Analyser\Scope;
+use PHPStan\Analyser\SpecifiedTypes;
+use PHPStan\Analyser\TypeSpecifier;
+use PHPStan\Analyser\TypeSpecifierAwareExtension;
+use PHPStan\Analyser\TypeSpecifierContext;
+use PHPStan\Reflection\MethodReflection;
+use PHPStan\Type\ObjectType;
+use PHPStan\Type\StaticMethodTypeSpecifyingExtension;
+
+final class IsAbstractTypeStaticMethodTypeSpecifyingExtension implements StaticMethodTypeSpecifyingExtension, TypeSpecifierAwareExtension
+{
+    /** @var TypeSpecifier */
+    private $typeSpecifier;
+
+    public function getClass(): string
+    {
+        return Type::class;
+    }
+
+    public function setTypeSpecifier(TypeSpecifier $typeSpecifier): void
+    {
+        $this->typeSpecifier = $typeSpecifier;
+    }
+
+    public function isStaticMethodSupported(MethodReflection $staticMethodReflection, StaticCall $node, TypeSpecifierContext $context): bool
+    {
+        // The $context argument tells us if we're in an if condition or not (as in this case).
+        return 'isAbstractType' === $staticMethodReflection->getName() && ! $context->null();
+    }
+
+    public function specifyTypes(MethodReflection $staticMethodReflection, StaticCall $node, Scope $scope, TypeSpecifierContext $context): SpecifiedTypes
+    {
+        return $this->typeSpecifier->create($node->getArgs()[0]->value, new ObjectType(AbstractType::class), $context);
+    }
+}
diff --git a/tests/PhpStan/Type/Definition/Type/IsCompositeTypeStaticMethodTypeSpecifyingExtension.php b/tests/PhpStan/Type/Definition/Type/IsCompositeTypeStaticMethodTypeSpecifyingExtension.php
index bdad1f404..71e33cd8c 100644
--- a/tests/PhpStan/Type/Definition/Type/IsCompositeTypeStaticMethodTypeSpecifyingExtension.php
+++ b/tests/PhpStan/Type/Definition/Type/IsCompositeTypeStaticMethodTypeSpecifyingExtension.php
@@ -39,6 +39,6 @@ public function isStaticMethodSupported(MethodReflection $staticMethodReflection
 
     public function specifyTypes(MethodReflection $staticMethodReflection, StaticCall $node, Scope $scope, TypeSpecifierContext $context): SpecifiedTypes
     {
-        return $this->typeSpecifier->create($node->args[0]->value, new ObjectType(CompositeType::class), $context);
+        return $this->typeSpecifier->create($node->getArgs()[0]->value, new ObjectType(CompositeType::class), $context);
     }
 }
diff --git a/tests/PhpStan/Type/Definition/Type/IsInputTypeStaticMethodTypeSpecifyingExtension.php b/tests/PhpStan/Type/Definition/Type/IsInputTypeStaticMethodTypeSpecifyingExtension.php
index c8a1eb6f9..4668bfe7d 100644
--- a/tests/PhpStan/Type/Definition/Type/IsInputTypeStaticMethodTypeSpecifyingExtension.php
+++ b/tests/PhpStan/Type/Definition/Type/IsInputTypeStaticMethodTypeSpecifyingExtension.php
@@ -39,6 +39,6 @@ public function isStaticMethodSupported(MethodReflection $staticMethodReflection
 
     public function specifyTypes(MethodReflection $staticMethodReflection, StaticCall $node, Scope $scope, TypeSpecifierContext $context): SpecifiedTypes
     {
-        return $this->typeSpecifier->create($node->args[0]->value, new ObjectType(InputType::class), $context);
+        return $this->typeSpecifier->create($node->getArgs()[0]->value, new ObjectType(InputType::class), $context);
     }
 }
diff --git a/tests/PhpStan/Type/Definition/Type/IsOutputTypeStaticMethodTypeSpecifyingExtension.php b/tests/PhpStan/Type/Definition/Type/IsOutputTypeStaticMethodTypeSpecifyingExtension.php
index afc8b0e35..b7283c9a9 100644
--- a/tests/PhpStan/Type/Definition/Type/IsOutputTypeStaticMethodTypeSpecifyingExtension.php
+++ b/tests/PhpStan/Type/Definition/Type/IsOutputTypeStaticMethodTypeSpecifyingExtension.php
@@ -39,6 +39,6 @@ public function isStaticMethodSupported(MethodReflection $staticMethodReflection
 
     public function specifyTypes(MethodReflection $staticMethodReflection, StaticCall $node, Scope $scope, TypeSpecifierContext $context): SpecifiedTypes
     {
-        return $this->typeSpecifier->create($node->args[0]->value, new ObjectType(OutputType::class), $context);
+        return $this->typeSpecifier->create($node->getArgs()[0]->value, new ObjectType(OutputType::class), $context);
     }
 }
diff --git a/tests/Regression/Issue396Test.php b/tests/Regression/Issue396Test.php
index 94a6d9518..98ee80e1b 100644
--- a/tests/Regression/Issue396Test.php
+++ b/tests/Regression/Issue396Test.php
@@ -32,15 +32,15 @@ public function testUnionResolveType(): void
             'types' => [$a, $b, $c],
             'resolveType' => static function ($result, $value, ResolveInfo $info) use ($a, $b, $c, &$log): ?Type {
                 $log[] = [$result, $info->path];
-                if (stristr($result['name'], 'A')) {
+                if (false !== stristr($result['name'], 'A')) {
                     return $a;
                 }
 
-                if (stristr($result['name'], 'B')) {
+                if (false !== stristr($result['name'], 'B')) {
                     return $b;
                 }
 
-                if (stristr($result['name'], 'C')) {
+                if (false !== stristr($result['name'], 'C')) {
                     return $c;
                 }
 
@@ -103,15 +103,15 @@ public function testInterfaceResolveType(): void
             ],
             'resolveType' => static function ($result, $value, ResolveInfo $info) use (&$a, &$b, &$c, &$log): ?ObjectType {
                 $log[] = [$result, $info->path];
-                if (stristr($result['name'], 'A')) {
+                if (false !== stristr($result['name'], 'A')) {
                     return $a;
                 }
 
-                if (stristr($result['name'], 'B')) {
+                if (false !== stristr($result['name'], 'B')) {
                     return $b;
                 }
 
-                if (stristr($result['name'], 'C')) {
+                if (false !== stristr($result['name'], 'C')) {
                     return $c;
                 }
 
@@ -119,9 +119,24 @@ public function testInterfaceResolveType(): void
             },
         ]);
 
-        $a = new ObjectType(['name' => 'A', 'fields' => ['name' => Type::string()], 'interfaces' => [$interfaceResult]]);
-        $b = new ObjectType(['name' => 'B', 'fields' => ['name' => Type::string()], 'interfaces' => [$interfaceResult]]);
-        $c = new ObjectType(['name' => 'C', 'fields' => ['name' => Type::string()], 'interfaces' => [$interfaceResult]]);
+        $a = new ObjectType(
+            [
+                'name' => 'A',
+                'fields' => ['name' => Type::string()],
+                'interfaces' => [$interfaceResult], ]
+        );
+        $b = new ObjectType(
+            [
+                'name' => 'B',
+                'fields' => ['name' => Type::string()],
+                'interfaces' => [$interfaceResult], ]
+        );
+        $c = new ObjectType(
+            [
+                'name' => 'C',
+                'fields' => ['name' => Type::string()],
+                'interfaces' => [$interfaceResult], ]
+        );
 
         $exampleType = new ObjectType([
             'name' => 'Example',
@@ -154,11 +169,13 @@ public function testInterfaceResolveType(): void
 
         GraphQL::executeQuery($schema, $query);
 
-        $expected = [
-            [['name' => 'A 1'], ['field', 0]],
-            [['name' => 'B 2'], ['field', 1]],
-            [['name' => 'C 3'], ['field', 2]],
-        ];
-        self::assertEquals($expected, $log);
+        self::assertEquals(
+            [
+                [['name' => 'A 1'], ['field', 0]],
+                [['name' => 'B 2'], ['field', 1]],
+                [['name' => 'C 3'], ['field', 2]],
+            ],
+            $log
+        );
     }
 }
diff --git a/tests/Server/PsrResponseTest.php b/tests/Server/PsrResponseTest.php
index 88e285759..b108db455 100644
--- a/tests/Server/PsrResponseTest.php
+++ b/tests/Server/PsrResponseTest.php
@@ -6,10 +6,11 @@
 
 use GraphQL\Executor\ExecutionResult;
 use GraphQL\Server\Helper;
-use function json_encode;
 use Nyholm\Psr7\Response;
 use Nyholm\Psr7\Stream;
 use PHPUnit\Framework\TestCase;
+use Psr\Http\Message\ResponseInterface;
+use function Safe\json_encode;
 
 final class PsrResponseTest extends TestCase
 {
@@ -19,10 +20,10 @@ public function testConvertsResultToPsrResponse(): void
         $stream = Stream::create();
         $psrResponse = new Response();
 
-        $helper = new Helper();
+        $response = (new Helper())->toPsrResponse($result, $psrResponse, $stream);
 
-        $resp = $helper->toPsrResponse($result, $psrResponse, $stream);
-        self::assertSame(json_encode($result), (string) $resp->getBody());
-        self::assertSame(['Content-Type' => ['application/json']], $resp->getHeaders());
+        self::assertInstanceOf(ResponseInterface::class, $response);
+        self::assertSame(json_encode($result), (string) $response->getBody());
+        self::assertSame(['Content-Type' => ['application/json']], $response->getHeaders());
     }
 }
diff --git a/tests/Server/QueryExecutionTest.php b/tests/Server/QueryExecutionTest.php
index c20285245..16148a93e 100644
--- a/tests/Server/QueryExecutionTest.php
+++ b/tests/Server/QueryExecutionTest.php
@@ -73,7 +73,10 @@ private function executeQuery(string $query, ?array $variables = null, bool $rea
             $readonly
         );
 
-        return (new Helper())->executeOperation($this->config, $op);
+        $result = (new Helper())->executeOperation($this->config, $op);
+        self::assertInstanceOf(ExecutionResult::class, $result);
+
+        return $result;
     }
 
     public function testReturnsSyntaxErrors(): void
@@ -292,7 +295,10 @@ private function executePersistedQuery(string $queryId, ?array $variables = null
             'variables' => $variables,
         ]);
 
-        return (new Helper())->executeOperation($this->config, $op);
+        $result = (new Helper())->executeOperation($this->config, $op);
+        self::assertInstanceOf(ExecutionResult::class, $result);
+
+        return $result;
     }
 
     public function testBatchedQueriesAreDisabledByDefault(): void
@@ -638,11 +644,12 @@ public function testAppliesErrorFormatter(): void
     {
         $called = false;
         $error = null;
-        $this->config->setErrorFormatter(static function ($e) use (&$called, &$error): array {
+        $formattedError = ['message' => 'formatted'];
+        $this->config->setErrorFormatter(static function ($e) use (&$called, &$error, $formattedError): array {
             $called = true;
             $error = $e;
 
-            return ['test' => 'formatted'];
+            return $formattedError;
         });
 
         $result = $this->executeQuery('{fieldWithSafeException}');
@@ -650,7 +657,7 @@ public function testAppliesErrorFormatter(): void
         $formatted = $result->toArray();
         $expected = [
             'errors' => [
-                ['test' => 'formatted'],
+                $formattedError,
             ],
         ];
         self::assertTrue($called);
@@ -661,12 +668,14 @@ public function testAppliesErrorFormatter(): void
         $formatted = $result->toArray(DebugFlag::INCLUDE_TRACE);
         $expected = [
             'errors' => [
-                [
-                    'test' => 'formatted',
-                    'extensions' => [
-                        'trace' => [],
+                array_merge(
+                    $formattedError,
+                    [
+                        'extensions' => [
+                            'trace' => [],
+                        ],
                     ],
-                ],
+                ),
             ],
         ];
         self::assertArraySubset($expected, $formatted);
@@ -677,14 +686,15 @@ public function testAppliesErrorsHandler(): void
         $called = false;
         $errors = null;
         $formatter = null;
-        $this->config->setErrorsHandler(static function ($e, $f) use (&$called, &$errors, &$formatter): array {
+        $handledErrors = [
+            ['message' => 'handled'],
+        ];
+        $this->config->setErrorsHandler(static function ($e, $f) use (&$called, &$errors, &$formatter, $handledErrors): array {
             $called = true;
             $errors = $e;
             $formatter = $f;
 
-            return [
-                ['test' => 'handled'],
-            ];
+            return $handledErrors;
         });
 
         $result = $this->executeQuery('{fieldWithSafeException,test: fieldWithSafeException}');
@@ -692,9 +702,7 @@ public function testAppliesErrorsHandler(): void
         self::assertFalse($called);
         $formatted = $result->toArray();
         $expected = [
-            'errors' => [
-                ['test' => 'handled'],
-            ],
+            'errors' => $handledErrors,
         ];
         self::assertTrue($called);
         self::assertArraySubset($expected, $formatted);
diff --git a/tests/Server/RequestParsingTest.php b/tests/Server/RequestParsingTest.php
index ee05e62dd..88f21c0f4 100644
--- a/tests/Server/RequestParsingTest.php
+++ b/tests/Server/RequestParsingTest.php
@@ -10,12 +10,12 @@
 use GraphQL\Server\RequestError;
 use function http_build_query;
 use InvalidArgumentException;
-use function json_encode;
 use Nyholm\Psr7\Request;
 use Nyholm\Psr7\ServerRequest;
 use Nyholm\Psr7\Stream;
 use Nyholm\Psr7\Uri;
 use PHPUnit\Framework\TestCase;
+use function Safe\json_encode;
 
 class RequestParsingTest extends TestCase
 {
@@ -28,6 +28,7 @@ public function testParsesGraphqlRequest(): void
         ];
 
         foreach ($parsed as $source => $parsedBody) {
+            self::assertInstanceOf(OperationParams::class, $parsedBody);
             self::assertValidOperationParams($parsedBody, $query, null, null, null, null, $source);
             self::assertFalse($parsedBody->readOnly, $source);
         }
@@ -41,9 +42,7 @@ private function parseRawRequest(?string $contentType, string $content, string $
         $_SERVER['CONTENT_TYPE'] = $contentType;
         $_SERVER['REQUEST_METHOD'] = $method;
 
-        $helper = new Helper();
-
-        return $helper->parseHttpRequest(static fn (): string => $content);
+        return (new Helper())->parseHttpRequest(static fn (): string => $content);
     }
 
     /**
@@ -58,13 +57,11 @@ private function parsePsrRequest(?string $contentType, string $content, string $
             Stream::create($content)
         );
 
-        $helper = new Helper();
-
-        return $helper->parsePsrRequest($psrRequest);
+        return (new Helper())->parsePsrRequest($psrRequest);
     }
 
     /**
-     * @param mixed                $variables
+     * @param mixed $variables
      * @param array<string, mixed> $extensions
      */
     private static function assertValidOperationParams(
@@ -102,39 +99,36 @@ public function testParsesUrlencodedRequest(): void
         ];
 
         foreach ($parsed as $method => $parsedBody) {
+            self::assertInstanceOf(OperationParams::class, $parsedBody);
             self::assertValidOperationParams($parsedBody, $query, null, $variables, $operation, null, $method);
             self::assertFalse($parsedBody->readOnly, $method);
         }
     }
 
     /**
-     * @param mixed[] $postValue
+     * @param array<string, mixed> $postValue
      *
-     * @return OperationParams|OperationParams[]
+     * @return OperationParams|array<int, OperationParams>
      */
-    private function parseRawFormUrlencodedRequest($postValue)
+    private function parseRawFormUrlencodedRequest(array $postValue)
     {
         $_SERVER['CONTENT_TYPE'] = 'application/x-www-form-urlencoded';
         $_SERVER['REQUEST_METHOD'] = 'POST';
         $_POST = $postValue;
 
-        $helper = new Helper();
-
-        return $helper->parseHttpRequest(static function (): void {
+        return (new Helper())->parseHttpRequest(static function (): void {
             throw new InvariantViolation("Shouldn't read from php://input for urlencoded request");
         });
     }
 
     /**
-     * @param mixed[] $postValue
+     * @param array<string, mixed> $postValue
      *
-     * @return OperationParams[]|OperationParams
+     * @return OperationParams|array<int, OperationParams>
      */
-    private function parsePsrFormUrlEncodedRequest($postValue)
+    private function parsePsrFormUrlEncodedRequest(array $postValue)
     {
-        $helper = new Helper();
-
-        return $helper->parsePsrRequest(
+        return (new Helper())->parsePsrRequest(
             new Request(
                 'POST',
                 '',
@@ -146,11 +140,11 @@ private function parsePsrFormUrlEncodedRequest($postValue)
 
     /**
      * @param array<string, mixed> $postValue
+     *
+     * @return OperationParams|array<int, OperationParams>
      */
-    private function parsePsrFormUrlEncodedServerRequest(array $postValue, bool $parsed): OperationParams
+    private function parsePsrFormUrlEncodedServerRequest(array $postValue, bool $parsed)
     {
-        $helper = new Helper();
-
         $request = new ServerRequest(
             'POST',
             '',
@@ -162,7 +156,7 @@ private function parsePsrFormUrlEncodedServerRequest(array $postValue, bool $par
             $request = $request->withParsedBody($postValue);
         }
 
-        return $helper->parsePsrRequest($request);
+        return (new Helper())->parsePsrRequest($request);
     }
 
     public function testParsesGetRequest(): void
@@ -182,36 +176,35 @@ public function testParsesGetRequest(): void
         ];
 
         foreach ($parsed as $method => $parsedBody) {
+            self::assertInstanceOf(OperationParams::class, $parsedBody);
             self::assertValidOperationParams($parsedBody, $query, null, $variables, $operation, null, $method);
             self::assertTrue($parsedBody->readOnly, $method);
         }
     }
 
     /**
-     * @param mixed[] $getValue
+     * @param array<string, mixed> $getValue
+     *
+     * @return OperationParams|array<int, OperationParams>
      */
-    private function parseRawGetRequest($getValue): OperationParams
+    private function parseRawGetRequest(array $getValue)
     {
         $_SERVER['REQUEST_METHOD'] = 'GET';
         $_GET = $getValue;
 
-        $helper = new Helper();
-
-        return $helper->parseHttpRequest(static function (): void {
+        return (new Helper())->parseHttpRequest(static function (): void {
             throw new InvariantViolation("Shouldn't read from php://input for urlencoded request");
         });
     }
 
     /**
-     * @param mixed[] $getValue
+     * @param array<string, mixed> $getValue
      *
-     * @return OperationParams[]|OperationParams
+     * @return OperationParams|array<int, OperationParams>
      */
     private function parsePsrGetRequest(array $getValue)
     {
-        $helper = new Helper();
-
-        return $helper->parsePsrRequest(
+        return (new Helper())->parsePsrRequest(
             new Request('GET', (new Uri())->withQuery(http_build_query($getValue)))
         );
     }
@@ -233,39 +226,36 @@ public function testParsesMultipartFormdataRequest(): void
         ];
 
         foreach ($parsed as $method => $parsedBody) {
+            self::assertInstanceOf(OperationParams::class, $parsedBody);
             self::assertValidOperationParams($parsedBody, $query, null, $variables, $operation, null, $method);
             self::assertFalse($parsedBody->readOnly, $method);
         }
     }
 
     /**
-     * @param mixed[] $postValue
+     * @param array<string, mixed> $postValue
      *
-     * @return OperationParams|OperationParams[]
+     * @return OperationParams|array<int, OperationParams>
      */
-    private function parseRawMultipartFormDataRequest($postValue)
+    private function parseRawMultipartFormDataRequest(array $postValue)
     {
         $_SERVER['CONTENT_TYPE'] = 'multipart/form-data; boundary=----FormBoundary';
         $_SERVER['REQUEST_METHOD'] = 'POST';
         $_POST = $postValue;
 
-        $helper = new Helper();
-
-        return $helper->parseHttpRequest(static function (): void {
+        return (new Helper())->parseHttpRequest(static function (): void {
             throw new InvariantViolation("Shouldn't read from php://input for multipart/form-data request");
         });
     }
 
     /**
-     * @param mixed[] $postValue
+     * @param array<string, mixed> $postValue
      *
-     * @return OperationParams|OperationParams[]
+     * @return OperationParams|array<int, OperationParams>
      */
-    private function parsePsrMultipartFormDataRequest($postValue)
+    private function parsePsrMultipartFormDataRequest(array $postValue)
     {
-        $helper = new Helper();
-
-        return $helper->parsePsrRequest(
+        return (new Helper())->parsePsrRequest(
             new Request(
                 'POST',
                 '',
@@ -291,6 +281,7 @@ public function testParsesJSONRequest(): void
             'psr' => $this->parsePsrRequest('application/json', json_encode($body)),
         ];
         foreach ($parsed as $method => $parsedBody) {
+            self::assertInstanceOf(OperationParams::class, $parsedBody);
             self::assertValidOperationParams($parsedBody, $query, null, $variables, $operation, null, $method);
             self::assertFalse($parsedBody->readOnly, $method);
         }
@@ -314,6 +305,7 @@ public function testParsesParamsAsJSON(): void
             'psr' => $this->parsePsrRequest('application/json', json_encode($body)),
         ];
         foreach ($parsed as $method => $parsedBody) {
+            self::assertInstanceOf(OperationParams::class, $parsedBody);
             self::assertValidOperationParams($parsedBody, $query, null, $variables, $operation, $extensions, $method);
             self::assertFalse($parsedBody->readOnly, $method);
         }
@@ -335,6 +327,7 @@ public function testIgnoresInvalidVariablesJson(): void
             'psr' => $this->parsePsrRequest('application/json', json_encode($body)),
         ];
         foreach ($parsed as $method => $parsedBody) {
+            self::assertInstanceOf(OperationParams::class, $parsedBody);
             self::assertValidOperationParams($parsedBody, $query, null, $variables, $operation, null, $method);
             self::assertFalse($parsedBody->readOnly, $method);
         }
@@ -357,6 +350,7 @@ public function testParsesApolloPersistedQueryJSONRequest(): void
             'psr' => $this->parsePsrRequest('application/json', json_encode($body)),
         ];
         foreach ($parsed as $method => $parsedBody) {
+            self::assertInstanceOf(OperationParams::class, $parsedBody);
             self::assertValidOperationParams($parsedBody, null, $queryId, $variables, $operation, $extensions, $method);
             self::assertFalse($parsedBody->readOnly, $method);
         }
diff --git a/tests/Server/ServerConfigTest.php b/tests/Server/ServerConfigTest.php
index 4c35d5f10..66ccb4d99 100644
--- a/tests/Server/ServerConfigTest.php
+++ b/tests/Server/ServerConfigTest.php
@@ -7,6 +7,7 @@
 use Closure;
 use GraphQL\Error\DebugFlag;
 use GraphQL\Error\InvariantViolation;
+use GraphQL\Executor\ExecutionResult;
 use GraphQL\Executor\Promise\Adapter\SyncPromiseAdapter;
 use GraphQL\Server\ServerConfig;
 use GraphQL\Type\Definition\ObjectType;
@@ -16,6 +17,10 @@
 use PHPUnit\Framework\TestCase;
 use stdClass;
 
+/**
+ * @phpstan-import-type SerializableError from ExecutionResult
+ * @phpstan-import-type SerializableErrors from ExecutionResult
+ */
 class ServerConfigTest extends TestCase
 {
     public function testDefaults(): void
@@ -87,11 +92,11 @@ public function testAllowsSettingErrorFormatter(): void
     }
 
     /**
-     * @return array<string, mixed>
+     * @return SerializableError
      */
     public static function formatError(): array
     {
-        return [];
+        return ['message' => 'irrelevant'];
     }
 
     public function testAllowsSettingErrorsHandler(): void
@@ -108,7 +113,7 @@ public function testAllowsSettingErrorsHandler(): void
     }
 
     /**
-     * @return array<int, array<string, mixed>>
+     * @return SerializableErrors
      */
     public static function handleError(): array
     {
@@ -237,12 +242,14 @@ public function testThrowsOnInvalidArrayKey(): void
 
     public function testInvalidValidationRules(): void
     {
-        $rules = new stdClass();
         $config = ServerConfig::create();
+        $rules = new stdClass();
 
-        $this->expectException(InvariantViolation::class);
-        $this->expectExceptionMessage('Server config expects array of validation rules or callable returning such array, but got instance of stdClass');
+        $this->expectExceptionObject(new InvariantViolation(
+            'Server config expects array of validation rules or callable returning such array, but got instance of stdClass'
+        ));
 
+        // @phpstan-ignore-next-line intentionally wrong
         $config->setValidationRules($rules);
     }
 }
diff --git a/tests/Server/StandardServerTest.php b/tests/Server/StandardServerTest.php
index 9c6c1699b..be2934864 100644
--- a/tests/Server/StandardServerTest.php
+++ b/tests/Server/StandardServerTest.php
@@ -11,9 +11,9 @@
 use GraphQL\Server\OperationParams;
 use GraphQL\Server\ServerConfig;
 use GraphQL\Server\StandardServer;
-use function json_encode;
 use Nyholm\Psr7\Request;
 use Psr\Http\Message\RequestInterface;
+use function Safe\json_encode;
 
 class StandardServerTest extends ServerTestCase
 {
@@ -37,11 +37,14 @@ public function testSimpleRequestExecutionWithOutsideParsing(): void
         $server = new StandardServer($this->config);
 
         $result = $server->executeRequest($parsedBody);
-        $expected = [
-            'data' => ['f1' => 'f1'],
-        ];
 
-        self::assertEquals($expected, $result->toArray(DebugFlag::INCLUDE_DEBUG_MESSAGE));
+        self::assertInstanceOf(ExecutionResult::class, $result);
+        self::assertSame(
+            [
+                'data' => ['f1' => 'f1'],
+            ],
+            $result->toArray(DebugFlag::INCLUDE_DEBUG_MESSAGE)
+        );
     }
 
     private function parseRawRequest(string $contentType, string $content, string $method = 'POST'): OperationParams
@@ -51,7 +54,10 @@ private function parseRawRequest(string $contentType, string $content, string $m
 
         $helper = new Helper();
 
-        return $helper->parseHttpRequest(static fn () => $content);
+        $operationParams = $helper->parseHttpRequest(static fn () => $content);
+        self::assertInstanceOf(OperationParams::class, $operationParams);
+
+        return $operationParams;
     }
 
     public function testSimplePsrRequestExecution(): void
@@ -89,7 +95,10 @@ private function assertPsrRequestEquals(array $expected, RequestInterface $reque
 
     private function executePsrRequest(RequestInterface $psrRequest): ExecutionResult
     {
-        return (new StandardServer($this->config))->executePsrRequest($psrRequest);
+        $result = (new StandardServer($this->config))->executePsrRequest($psrRequest);
+        self::assertInstanceOf(ExecutionResult::class, $result);
+
+        return $result;
     }
 
     public function testMultipleOperationPsrRequestExecution(): void
diff --git a/tests/StarWarsSchema.php b/tests/StarWarsSchema.php
index 453332106..d3a1e5728 100644
--- a/tests/StarWarsSchema.php
+++ b/tests/StarWarsSchema.php
@@ -90,6 +90,7 @@ public static function build(): Schema
 
         /** @var ObjectType $humanType */
         $humanType = null;
+
         /** @var ObjectType $humanType */
         $droidType = null;
 
diff --git a/tests/Type/DefinitionTest.php b/tests/Type/DefinitionTest.php
index a69a5fb94..3cd49fdfa 100644
--- a/tests/Type/DefinitionTest.php
+++ b/tests/Type/DefinitionTest.php
@@ -27,8 +27,8 @@
 use GraphQL\Type\Definition\Type;
 use GraphQL\Type\Definition\UnionType;
 use GraphQL\Type\Schema;
-use function json_encode;
 use RuntimeException;
+use function Safe\json_encode;
 use function sprintf;
 use stdClass;
 
@@ -354,7 +354,6 @@ public function testAcceptsAWellDefinedEnumTypeWithInternalValueDefinition(): vo
      */
     public function testRejectsAnEnumTypeWithIncorrectlyTypedValues(): void
     {
-        // @phpstan-ignore-next-line intentionally wrong
         $enumType = new EnumType([
             'name' => 'SomeEnum',
             'values' => [['FOO' => 10]],
@@ -960,15 +959,16 @@ public function testAcceptsAnObjectTypeWithInterfacesAsAFunctionReturningAnArray
      */
     public function testRejectsAnObjectTypeWithIncorrectlyTypedInterfaces(): void
     {
+        // @phpstan-ignore-next-line intentionally wrong
         $objType = new ObjectType([
             'name' => 'SomeObject',
             'interfaces' => new stdClass(),
             'fields' => ['f' => ['type' => Type::string()]],
         ]);
-        $this->expectException(InvariantViolation::class);
-        $this->expectExceptionMessage(
+
+        $this->expectExceptionObject(new InvariantViolation(
             'SomeObject interfaces must be an iterable or a callable which returns an iterable.'
-        );
+        ));
         $objType->assertValid();
     }
 
@@ -1108,15 +1108,16 @@ public function testAcceptsAnInterfaceTypeWithInterfacesAsAFunctionReturningAnAr
      */
     public function testRejectsAnInterfaceTypeWithIncorrectlyTypedInterfaces(): void
     {
+        // @phpstan-ignore-next-line intentionally wrong
         $objType = new InterfaceType([
             'name' => 'AnotherInterface',
             'interfaces' => new stdClass(),
             'fields' => [],
         ]);
-        $this->expectException(InvariantViolation::class);
-        $this->expectExceptionMessage(
+
+        $this->expectExceptionObject(new InvariantViolation(
             'AnotherInterface interfaces must be an iterable or a callable which returns an iterable.'
-        );
+        ));
         $objType->assertValid();
     }
 
@@ -1201,16 +1202,17 @@ public function testAcceptsAnInterfaceTypeDefiningResolveTypeWithImplementingTyp
      */
     public function testRejectsAnInterfaceTypeWithAnIncorrectTypeForResolveType(): void
     {
-        // Slightly deviating from the reference implementation in order to be idiomatic for PHP
-        $this->expectExceptionObject(new InvariantViolation(
-            'AnotherInterface must provide "resolveType" as a callable, but got: instance of stdClass'
-        ));
-
+        // @phpstan-ignore-next-line intentionally wrong
         $type = new InterfaceType([
             'name' => 'AnotherInterface',
             'resolveType' => new stdClass(),
             'fields' => ['f' => ['type' => Type::string()]],
         ]);
+
+        // Slightly deviating from the reference implementation in order to be idiomatic for PHP
+        $this->expectExceptionObject(new InvariantViolation(
+            'AnotherInterface must provide "resolveType" as a callable, but got: instance of stdClass'
+        ));
         $type->assertValid();
     }
 
@@ -1267,7 +1269,9 @@ public function testRejectsAnUnionTypeWithAnIncorrectTypeForResolveType(): void
         $this->expectExceptionObject(new InvariantViolation(
             'SomeUnion must provide "resolveType" as a callable, but got: instance of stdClass'
         ));
+
         $this->schemaWithFieldType(
+            // @phpstan-ignore-next-line intentionally wrong
             new UnionType([
                 'name' => 'SomeUnion',
                 'resolveType' => new stdClass(),
@@ -1294,35 +1298,19 @@ public function testAcceptsAScalarTypeDefiningSerialize(): void
 
     // Type System: Scalar types must be serializable
 
-    /**
-     * @see it('rejects a Scalar type not defining serialize')
-     */
-    public function testRejectsAScalarTypeNotDefiningSerialize(): void
-    {
-        $this->expectException(InvariantViolation::class);
-        $this->expectExceptionMessage(
-            'SomeScalar must provide "serialize" function. If this custom Scalar '
-            . 'is also used as an input type, ensure "parseValue" and "parseLiteral" '
-            . 'functions are also provided.'
-        );
-        $this->schemaWithFieldType(
-            // @phpstan-ignore-next-line intentionally wrong
-            new CustomScalarType(['name' => 'SomeScalar'])
-        );
-    }
-
     /**
      * @see it('rejects a Scalar type defining serialize with an incorrect type')
      */
     public function testRejectsAScalarTypeDefiningSerializeWithAnIncorrectType(): void
     {
-        $this->expectException(InvariantViolation::class);
-        $this->expectExceptionMessage(
+        $this->expectExceptionObject(new InvariantViolation(
             'SomeScalar must provide "serialize" function. If this custom Scalar '
             . 'is also used as an input type, ensure "parseValue" and "parseLiteral" '
             . 'functions are also provided.'
-        );
+        ));
+
         $this->schemaWithFieldType(
+            // @phpstan-ignore-next-line intentionally wrong
             new CustomScalarType([
                 'name' => 'SomeScalar',
                 'serialize' => new stdClass(),
@@ -1354,10 +1342,10 @@ public function testAcceptsAScalarTypeDefiningParseValueAndParseLiteral(): void
      */
     public function testRejectsAScalarTypeDefiningParseValueButNotParseLiteral(): void
     {
-        $this->expectException(InvariantViolation::class);
-        $this->expectExceptionMessage(
+        $this->expectExceptionObject(new InvariantViolation(
             'SomeScalar must provide both "parseValue" and "parseLiteral" functions.'
-        );
+        ));
+
         $this->schemaWithFieldType(
             new CustomScalarType([
                 'name' => 'SomeScalar',
@@ -1374,10 +1362,10 @@ public function testRejectsAScalarTypeDefiningParseValueButNotParseLiteral(): vo
      */
     public function testRejectsAScalarTypeDefiningParseLiteralButNotParseValue(): void
     {
-        $this->expectException(InvariantViolation::class);
-        $this->expectExceptionMessage(
+        $this->expectExceptionObject(new InvariantViolation(
             'SomeScalar must provide both "parseValue" and "parseLiteral" functions.'
-        );
+        ));
+
         $this->schemaWithFieldType(
             new CustomScalarType([
                 'name' => 'SomeScalar',
@@ -1394,11 +1382,12 @@ public function testRejectsAScalarTypeDefiningParseLiteralButNotParseValue(): vo
      */
     public function testRejectsAScalarTypeDefiningParseValueAndParseLiteralWithAnIncorrectType(): void
     {
-        $this->expectException(InvariantViolation::class);
-        $this->expectExceptionMessage(
+        $this->expectExceptionObject(new InvariantViolation(
             'SomeScalar must provide both "parseValue" and "parseLiteral" functions.'
-        );
+        ));
+
         $this->schemaWithFieldType(
+            // @phpstan-ignore-next-line intentionally wrong
             new CustomScalarType([
                 'name' => 'SomeScalar',
                 'serialize' => static function (): void {
@@ -1434,7 +1423,9 @@ public function testRejectsAnObjectTypeWithAnIncorrectTypeForIsTypeOf(): void
         $this->expectExceptionObject(new InvariantViolation(
             'AnotherObject must provide "isTypeOf" as a callable, but got: instance of stdClass'
         ));
+
         $this->schemaWithFieldType(
+            // @phpstan-ignore-next-line intentionally wrong
             new ObjectType([
                 'name' => 'AnotherObject',
                 'isTypeOf' => new stdClass(),
@@ -1480,10 +1471,10 @@ public function testAcceptsAUnionTypeWithFunctionReturningAnArrayOfTypes(): void
      */
     public function testRejectsAUnionTypeWithoutTypes(): void
     {
-        $this->expectException(InvariantViolation::class);
-        $this->expectExceptionMessage(
+        $this->expectExceptionObject(new InvariantViolation(
             'Must provide iterable of types or a callable which returns such an iterable for Union SomeUnion'
-        );
+        ));
+
         $this->schemaWithFieldType(
             // @phpstan-ignore-next-line intentionally wrong
             new UnionType(['name' => 'SomeUnion'])
@@ -1495,11 +1486,12 @@ public function testRejectsAUnionTypeWithoutTypes(): void
      */
     public function testRejectsAUnionTypeWithIncorrectlyTypedTypes(): void
     {
-        $this->expectException(InvariantViolation::class);
-        $this->expectExceptionMessage(
+        $this->expectExceptionObject(new InvariantViolation(
             'Must provide iterable of types or a callable which returns such an iterable for Union SomeUnion'
-        );
+        ));
+
         $this->schemaWithFieldType(
+            // @phpstan-ignore-next-line intentionally wrong
             new UnionType([
                 'name' => 'SomeUnion',
                 'types' => (object) ['test' => $this->objectType],
@@ -1720,6 +1712,8 @@ public function testRejectsAnInputObjectTypeWithResolverConstant(): void
         $inputObjType->assertValid();
     }
 
+    // Type System: A Schema must contain uniquely named types
+
     /**
      * @see it('rejects a Schema which redefines a built-in type')
      */
@@ -1748,7 +1742,26 @@ public function testRejectsASchemaWhichRedefinesABuiltInType(): void
         $schema->assertValid();
     }
 
-    // Type System: A Schema must contain uniquely named types
+    /**
+     * @see it('rejects a Schema when a provided type has no name')
+     */
+    public function testRejectsASchemaWhenAProvidedTypeHasNoName(): void
+    {
+        self::markTestSkipped('Our types are more strict by default, given we use classes');
+
+        $QueryType = new ObjectType([
+            'name' => 'Query',
+            'fields' => [
+                'foo' => ['type' => Type::string()],
+            ],
+        ]);
+
+        new Schema(
+            [
+                'query' => $QueryType,
+                'types' => [new stdClass()], ]
+        );
+    }
 
     /**
      * @see it('rejects a Schema which defines an object type twice')
@@ -1772,18 +1785,46 @@ public function testRejectsASchemaWhichDefinesAnObjectTypeTwice(): void
                 'b' => ['type' => $B],
             ],
         ]);
-        $this->expectException(InvariantViolation::class);
-        $this->expectExceptionMessage(
+
+        $this->expectExceptionObject(new InvariantViolation(
             'Schema must contain unique named types but contains multiple types named "SameName" '
             . '(see https://webonyx.github.io/graphql-php/type-definitions/#type-registry).'
-        );
-        $schema = new Schema(['query' => $QueryType]);
-        $schema->assertValid();
+        ));
+        new Schema(['query' => $QueryType]);
     }
 
     /**
-     * @see it('rejects a Schema which have same named objects implementing an interface')
+     * @see it('rejects a Schema which defines fields with conflicting types'
      */
+    public function testRejectsASchemaWhichDefinesFieldsWithConflictingTypes(): void
+    {
+        $fields = ['f' => ['type' => Type::string()]];
+
+        $A = new ObjectType([
+            'name' => 'SameName',
+            'fields' => $fields,
+        ]);
+
+        $B = new ObjectType([
+            'name' => 'SameName',
+            'fields' => $fields,
+        ]);
+
+        $QueryType = new ObjectType([
+            'name' => 'Query',
+            'fields' => [
+                'a' => ['type' => $A],
+                'b' => ['type' => $B],
+            ],
+        ]);
+
+        $this->expectExceptionObject(new InvariantViolation(
+            'Schema must contain unique named types but contains multiple types named "SameName" '
+            . '(see https://webonyx.github.io/graphql-php/type-definitions/#type-registry).'
+        ));
+        new Schema(['query' => $QueryType]);
+    }
+
     public function testRejectsASchemaWhichHaveSameNamedObjectsImplementingAnInterface(): void
     {
         $AnotherInterface = new InterfaceType([
@@ -1822,11 +1863,6 @@ public function testRejectsASchemaWhichHaveSameNamedObjectsImplementingAnInterfa
         $schema->assertValid();
     }
 
-    // Lazy Fields
-
-    /**
-     * @see it('allows a type to define its fields as closure returning array field definition to be lazy loaded')
-     */
     public function testAllowsTypeWhichDefinesItFieldsAsClosureReturningFieldDefinitionAsArray(): void
     {
         $objType = new ObjectType([
@@ -1843,17 +1879,15 @@ public function testAllowsTypeWhichDefinesItFieldsAsClosureReturningFieldDefinit
         self::assertSame(Type::string(), $objType->getField('f')->getType());
     }
 
-    /**
-     * @see it('allows a type to define its fields as closure returning object field definition to be lazy loaded')
-     */
     public function testAllowsTypeWhichDefinesItFieldsAsClosureReturningFieldDefinitionAsObject(): void
     {
         $objType = new ObjectType([
             'name' => 'SomeObject',
             'fields' => [
-                'f' => static function (): FieldDefinition {
-                    return FieldDefinition::create(['name' => 'f', 'type' => Type::string()]);
-                },
+                'f' => static fn (): FieldDefinition => new FieldDefinition([
+                    'name' => 'f',
+                    'type' => Type::string(),
+                ]),
             ],
         ]);
 
@@ -1907,9 +1941,6 @@ public function testFieldClosureNotExecutedIfNotAccessed(): void
         self::assertSame(1, $resolvedCount);
     }
 
-    /**
-     * @see it('does resolve all field definitions when validating the type')
-     */
     public function testAllUnresolvedFieldsAreResolvedWhenValidatingType(): void
     {
         $resolvedCount = 0;
@@ -1932,88 +1963,17 @@ public function testAllUnresolvedFieldsAreResolvedWhenValidatingType(): void
         self::assertSame(2, $resolvedCount);
     }
 
-    /**
-     * @see it('does throw when lazy loaded array field definition changes its name')
-     */
-    public function testThrowsWhenLazyLoadedArrayFieldDefinitionChangesItsName(): void
-    {
-        $objType = new ObjectType([
-            'name' => 'SomeObject',
-            'fields' => [
-                'f' => static function (): array {
-                    return ['name' => 'foo', 'type' => Type::string()];
-                },
-            ],
-        ]);
-
-        $this->expectException(InvariantViolation::class);
-        $this->expectExceptionMessage(
-            'SomeObject.f should not dynamically change its name when resolved lazily.'
-        );
-
-        $objType->assertValid();
-    }
-
-    /**
-     * @see it('does throw when lazy loaded object field definition changes its name')
-     */
-    public function testThrowsWhenLazyLoadedObjectFieldDefinitionChangesItsName(): void
-    {
-        $objType = new ObjectType([
-            'name' => 'SomeObject',
-            'fields' => [
-                'f' => static function (): FieldDefinition {
-                    return FieldDefinition::create(['name' => 'foo', 'type' => Type::string()]);
-                },
-            ],
-        ]);
-
-        $this->expectException(InvariantViolation::class);
-        $this->expectExceptionMessage(
-            'SomeObject.f should not dynamically change its name when resolved lazily.'
-        );
-
-        $objType->assertValid();
-    }
-
-    /**
-     * @see it('does throw when lazy loaded field definition has no keys for field names')
-     */
     public function testThrowsWhenLazyLoadedFieldDefinitionHasNoKeysForFieldNames(): void
     {
         $objType = new ObjectType([
             'name' => 'SomeObject',
             'fields' => [
-                static function (): array {
-                    return ['type' => Type::string()];
-                },
-            ],
-        ]);
-
-        $this->expectException(InvariantViolation::class);
-        $this->expectExceptionMessage(
-            'SomeObject lazy fields must be an associative array with field names as keys.'
-        );
-
-        $objType->assertValid();
-    }
-
-    /**
-     * @see it('does throw when lazy loaded field definition has invalid args')
-     */
-    public function testThrowsWhenLazyLoadedFieldHasInvalidArgs(): void
-    {
-        $objType = new ObjectType([
-            'name' => 'SomeObject',
-            'fields' => [
-                'f' => static function (): array {
-                    return ['args' => 'invalid', 'type' => Type::string()];
-                },
+                static fn (): array => ['type' => Type::string()],
             ],
         ]);
 
         $this->expectExceptionObject(new InvariantViolation(
-            'SomeObject.f args must be an array.'
+            'SomeObject lazy fields must be an associative array with field names as keys.'
         ));
 
         $objType->assertValid();
diff --git a/tests/Type/EnumTypeTest.php b/tests/Type/EnumTypeTest.php
index 34a385997..d236b093d 100644
--- a/tests/Type/EnumTypeTest.php
+++ b/tests/Type/EnumTypeTest.php
@@ -28,7 +28,7 @@ class EnumTypeTest extends TestCase
     private EnumType $ComplexEnum;
 
     /** @var array{someRandomFunction: callable(): void} */
-    private $Complex1;
+    private array $Complex1;
 
     /** @var ArrayObject<string, int> */
     private ArrayObject $Complex2;
@@ -293,7 +293,7 @@ public function testDoesNotAcceptStringLiterals(): void
             '{ colorEnum(fromEnum: "GREEN") }',
             null,
             [
-                'message' => 'Field "colorEnum" argument "fromEnum" requires type Color, found "GREEN"; Did you mean the enum value GREEN?',
+                'message' => 'Enum "Color" cannot represent non-enum value: "GREEN". Did you mean the enum value "GREEN"?',
                 'locations' => [new SourceLocation(1, 23)],
             ]
         );
@@ -326,7 +326,7 @@ private function expectFailure(string $query, ?array $vars, $err): void
     }
 
     /**
-     * @see it('does not accept valuesNotInTheEnum')
+     * @see it('does not accept values not in the enum')
      */
     public function testDoesNotAcceptValuesNotInTheEnum(): void
     {
@@ -334,7 +334,7 @@ public function testDoesNotAcceptValuesNotInTheEnum(): void
             '{ colorEnum(fromEnum: GREENISH) }',
             null,
             [
-                'message' => 'Field "colorEnum" argument "fromEnum" requires type Color, found GREENISH; Did you mean the enum value GREEN?',
+                'message' => 'Value "GREENISH" does not exist in "Color" enum. Did you mean the enum value "GREEN"?',
                 'locations' => [new SourceLocation(1, 23)],
             ]
         );
@@ -349,7 +349,8 @@ public function testDoesNotAcceptValuesWithIncorrectCasing(): void
             '{ colorEnum(fromEnum: green) }',
             null,
             [
-                'message' => 'Field "colorEnum" argument "fromEnum" requires type Color, found green; Did you mean the enum value GREEN?',
+                // Improves upon the reference implementation
+                'message' => 'Value "green" does not exist in "Color" enum. Did you mean the enum value "GREEN"?',
                 'locations' => [new SourceLocation(1, 23)],
             ]
         );
@@ -379,7 +380,7 @@ public function testDoesNotAcceptInternalValueInPlaceOfEnumLiteral(): void
         $this->expectFailure(
             '{ colorEnum(fromEnum: 1) }',
             null,
-            'Field "colorEnum" argument "fromEnum" requires type Color, found 1.'
+            'Enum "Color" cannot represent non-enum value: 1.'
         );
     }
 
@@ -391,7 +392,7 @@ public function testDoesNotAcceptEnumLiteralInPlaceOfInt(): void
         $this->expectFailure(
             '{ colorEnum(fromInt: GREEN) }',
             null,
-            'Field "colorEnum" argument "fromInt" requires type Int, found GREEN.'
+            'Int cannot represent non-integer value: GREEN'
         );
     }
 
diff --git a/tests/Type/IntrospectionTest.php b/tests/Type/IntrospectionTest.php
index 5f483fdee..cd9f83368 100644
--- a/tests/Type/IntrospectionTest.php
+++ b/tests/Type/IntrospectionTest.php
@@ -15,8 +15,8 @@
 use GraphQL\Type\Introspection;
 use GraphQL\Type\Schema;
 use GraphQL\Validator\Rules\ProvidedRequiredArguments;
-use function json_encode;
 use PHPUnit\Framework\TestCase;
+use function Safe\json_encode;
 use function sprintf;
 
 class IntrospectionTest extends TestCase
@@ -1000,8 +1000,7 @@ public function testIntrospectsOnInputObject(): void
         ];
 
         $result = GraphQL::executeQuery($schema, $request)->toArray();
-        $result = $result['data']['__type'];
-        self::assertEquals($expectedFragment, $result);
+        self::assertEquals($expectedFragment, $result['data']['__type'] ?? null);
     }
 
     /**
diff --git a/tests/Type/LazyTypeLoaderTest.php b/tests/Type/LazyTypeLoaderTest.php
index e62b68b67..47d091730 100644
--- a/tests/Type/LazyTypeLoaderTest.php
+++ b/tests/Type/LazyTypeLoaderTest.php
@@ -19,7 +19,7 @@ final class LazyTypeLoaderTest extends TypeLoaderTest
     /** @var callable(): InterfaceType */
     private $node;
 
-    /** @var callable(): ObjectType */
+    /** @var callable(): InterfaceType */
     private $content;
 
     /** @var callable(): ObjectType */
diff --git a/tests/Type/QueryPlanTest.php b/tests/Type/QueryPlanTest.php
index 8baa92d70..53d160df4 100644
--- a/tests/Type/QueryPlanTest.php
+++ b/tests/Type/QueryPlanTest.php
@@ -950,9 +950,11 @@ public function testQueryPlanGroupingImplementorFieldsForAbstractTypes(): void
             'fields' => [
                 'item' => [
                     'type' => $item,
-                    'resolve' => static function ($value, $args, $context, ResolveInfo $info) use (&$hasCalled, &$queryPlan) {
+                    'resolve' => static function ($value, array $args, $context, ResolveInfo $info) use (&$hasCalled, &$queryPlan) {
                         $hasCalled = true;
-                        $queryPlan = $info->lookAhead(['group-implementor-fields']);
+                        $queryPlan = $info->lookAhead([
+                            'groupImplementorFields' => true,
+                        ]);
 
                         return null;
                     },
diff --git a/tests/Type/ScalarSerializationTest.php b/tests/Type/ScalarSerializationTest.php
index dd9d364ca..47973e389 100644
--- a/tests/Type/ScalarSerializationTest.php
+++ b/tests/Type/ScalarSerializationTest.php
@@ -204,11 +204,11 @@ public function testSerializesOutputAsID(): void
     public function badIDValues(): iterable
     {
         return [
-            [new stdClass(), 'ID cannot represent value: instance of stdClass'],
-            [true, 'ID cannot represent value: true'],
-            [false, 'ID cannot represent value: false'],
-            [-1.1, 'ID cannot represent value: -1.1'],
-            [['abc'], 'ID cannot represent value: ["abc"]'],
+            [new stdClass(), 'ID cannot represent a non-string and non-integer value: instance of stdClass'],
+            [true, 'ID cannot represent a non-string and non-integer value: true'],
+            [false, 'ID cannot represent a non-string and non-integer value: false'],
+            [-1.1, 'ID cannot represent a non-string and non-integer value: -1.1'],
+            [['abc'], 'ID cannot represent a non-string and non-integer value: ["abc"]'],
         ];
     }
 
@@ -221,8 +221,9 @@ public function testSerializesOutputAsIDError($value, string $expectedError): vo
     {
         $idType = Type::id();
 
-        $this->expectException(SerializationError::class);
-        $this->expectExceptionMessage($expectedError);
+        $this->expectExceptionObject(new SerializationError(
+            $expectedError
+        ));
         $idType->serialize($value);
     }
 }
diff --git a/tests/Type/SchemaTest.php b/tests/Type/SchemaTest.php
index 1e2bc9931..f87075324 100644
--- a/tests/Type/SchemaTest.php
+++ b/tests/Type/SchemaTest.php
@@ -4,16 +4,14 @@
 
 namespace GraphQL\Tests\Type;
 
+use GraphQL\Error\Error;
 use GraphQL\Error\InvariantViolation;
-use GraphQL\Type\Definition\AbstractType;
 use GraphQL\Type\Definition\Directive;
 use GraphQL\Type\Definition\InputObjectType;
 use GraphQL\Type\Definition\InterfaceType;
 use GraphQL\Type\Definition\ObjectType;
-use GraphQL\Type\Definition\ResolveInfo;
 use GraphQL\Type\Definition\Type;
 use GraphQL\Type\Schema;
-use InvalidArgumentException;
 use PHPUnit\Framework\TestCase;
 
 class SchemaTest extends TestCase
@@ -127,32 +125,4 @@ public function testIncludesInputTypesOnlyUsedInDirectives(): void
         self::assertArrayHasKey('DirInput', $typeMap);
         self::assertArrayHasKey('WrappedDirInput', $typeMap);
     }
-
-    // Sub Type
-
-    /**
-     * @see it('validates argument to isSubType to be of the correct type')
-     */
-    public function testThrowsInvalidArgumentExceptionWhenInvalidTypeIsPassedToIsSubType(): void
-    {
-        $this->expectException(InvalidArgumentException::class);
-
-        $anonymousAbstractType = new class() implements AbstractType {
-            public function resolveType($objectValue, $context, ResolveInfo $info)
-            {
-                return null;
-            }
-        };
-
-        $this->schema->isSubType(
-            // @phpstan-ignore-next-line purposefully wrong
-            $anonymousAbstractType,
-            new InterfaceType([
-                'name' => 'Interface',
-                'fields' => [
-                    'irrelevant' => Type::int(),
-                ],
-            ])
-        );
-    }
 }
diff --git a/tests/Type/ValidationTest.php b/tests/Type/ValidationTest.php
index b016a197b..3bcbcf3b4 100644
--- a/tests/Type/ValidationTest.php
+++ b/tests/Type/ValidationTest.php
@@ -21,6 +21,7 @@
 use GraphQL\Type\Definition\InterfaceType;
 use GraphQL\Type\Definition\ListOfType;
 use GraphQL\Type\Definition\NonNull;
+use GraphQL\Type\Definition\NullableType;
 use GraphQL\Type\Definition\ObjectType;
 use GraphQL\Type\Definition\ScalarType;
 use GraphQL\Type\Definition\Type;
@@ -153,7 +154,10 @@ private function withModifiers(array $types): array
                 $types
             ),
             array_map(
-                static fn (Type $type): NonNull => Type::nonNull($type),
+                static function (Type $type): NonNull {
+                    /** @var Type&NullableType $type */
+                    return Type::nonNull($type);
+                },
                 $types
             ),
             array_map(
@@ -183,7 +187,6 @@ public function testRejectsTypesWithoutNames(): void
                 static fn (): UnionType => new UnionType([]),
                 // @phpstan-ignore-next-line intentionally wrong
                 static fn (): InterfaceType => new InterfaceType([]),
-                // @phpstan-ignore-next-line intentionally wrong
                 static fn (): ScalarType => new CustomScalarType([]),
             ],
             'Must provide name.'
@@ -352,7 +355,7 @@ private function formatLocations(Error $error): array
     /**
      * @param array<Error> $errors
      *
-     * @return array<int, array{message: string, locations: array<int, array{line: int, column: int}>}>
+     * @return array<int, array{message: string, locations?: array<int, array{line: int, column: int}>}>
      */
     private function formatErrors(array $errors, bool $withLocation = true): array
     {
@@ -815,7 +818,11 @@ public function testRejectsAUnionTypeWithNonObjectMembersType(): void
 
         foreach ($badUnionMemberTypes as $memberType) {
             $badSchema = $this->schemaWithFieldType(
-                new UnionType(['name' => 'BadUnion', 'types' => [$memberType]])
+                // @phpstan-ignore-next-line intentionally wrong
+                new UnionType([
+                    'name' => 'BadUnion',
+                    'types' => [$memberType],
+                ])
             );
             $this->assertMatchesValidationMessage(
                 $badSchema->validate(),
@@ -1661,10 +1668,13 @@ public function testAcceptsAnInputTypeAsAnInputFieldType(): void
 
     private function schemaWithInputFieldOfType(Type $inputFieldType): Schema
     {
+        // @phpstan-ignore-next-line intentionally wrong
         $badInputObjectType = new InputObjectType([
             'name' => 'BadInputObject',
             'fields' => [
-                'badField' => ['type' => $inputFieldType],
+                'badField' => [
+                    'type' => $inputFieldType,
+                ],
             ],
         ]);
 
@@ -2958,6 +2968,7 @@ public function testRejectsASchemaWithDirectivesWithWrongArgs(): void
                 ],
             ],
         ]);
+        // @phpstan-ignore-next-line intentionally wrong
         $directive = new Directive([
             'name' => 'test',
             'args' => [
diff --git a/tests/UserArgsTest.php b/tests/UserArgsTest.php
index 4eab1d9cb..05dedc239 100644
--- a/tests/UserArgsTest.php
+++ b/tests/UserArgsTest.php
@@ -24,7 +24,7 @@ public function testErrorForNonExistentScalarInputField(): void
         }
         ';
         $result = GraphQL::executeQuery($this->schema(), $query)->toArray();
-        self::assertEquals('Field "scalar" is not defined by type InputType.', $result['errors'][0]['message']);
+        self::assertEquals('Field "scalar" is not defined by type "InputType".', $result['errors'][0]['message'] ?? null);
     }
 
     public function testErrorForNonExistentArrayInputField(): void
@@ -38,7 +38,7 @@ public function testErrorForNonExistentArrayInputField(): void
         }
         ';
         $result = GraphQL::executeQuery($this->schema(), $query)->toArray();
-        self::assertEquals('Field "array" is not defined by type InputType.', $result['errors'][0]['message']);
+        self::assertEquals('Field "array" is not defined by type "InputType".', $result['errors'][0]['message'] ?? null);
     }
 
     private function schema(): Schema
diff --git a/tests/Utils/BuildSchemaTest.php b/tests/Utils/BuildSchemaTest.php
index 6c76c029a..60b1e0c38 100644
--- a/tests/Utils/BuildSchemaTest.php
+++ b/tests/Utils/BuildSchemaTest.php
@@ -47,8 +47,14 @@ public function testUseBuiltSchemaForLimitedExecution(): void
             }
         '));
 
-        $result = GraphQL::executeQuery($schema, '{ str }', ['str' => 123]);
-        self::assertEquals(['str' => 123], $result->toArray(DebugFlag::INCLUDE_DEBUG_MESSAGE)['data']);
+        $data = ['str' => 123];
+
+        self::assertEquals(
+            [
+                'data' => $data,
+            ],
+            GraphQL::executeQuery($schema, '{ str }', $data)->toArray()
+        );
     }
 
     /**
diff --git a/tests/Utils/CoerceValueTest.php b/tests/Utils/CoerceValueTest.php
index 76ecf8b18..303b29d99 100644
--- a/tests/Utils/CoerceValueTest.php
+++ b/tests/Utils/CoerceValueTest.php
@@ -71,11 +71,11 @@ public function testCoercingAnArrayToGraphQLIDProducesAnError(): void
         $result = Value::coerceValue([1, 2, 3], Type::id());
         $this->expectGraphQLError(
             $result,
-            'Expected type ID; ID cannot represent value: [1,2,3]'
+            'Expected type ID; ID cannot represent a non-string and non-integer value: [1,2,3]'
         );
 
         self::assertEquals(
-            'ID cannot represent value: [1,2,3]',
+            'ID cannot represent a non-string and non-integer value: [1,2,3]',
             $result['errors'][0]->getPrevious()->getMessage()
         );
     }
diff --git a/tests/Utils/SchemaExtenderTest.php b/tests/Utils/SchemaExtenderTest.php
index af5fa01cf..056dfcf14 100644
--- a/tests/Utils/SchemaExtenderTest.php
+++ b/tests/Utils/SchemaExtenderTest.php
@@ -14,6 +14,7 @@
 use GraphQL\GraphQL;
 use GraphQL\Language\AST\DefinitionNode;
 use GraphQL\Language\AST\DocumentNode;
+use GraphQL\Language\AST\IntValueNode;
 use GraphQL\Language\AST\Node;
 use GraphQL\Language\AST\NodeList;
 use GraphQL\Language\DirectiveLocation;
@@ -588,15 +589,17 @@ enum EnumWithDeprecatedValue {
             }
         ');
 
-        /** @var ObjectType $typeWithDeprecatedField */
         $typeWithDeprecatedField = $extendedSchema->getType('TypeWithDeprecatedField');
+        self::assertInstanceOf(ObjectType::class, $typeWithDeprecatedField);
+
         $deprecatedFieldDef = $typeWithDeprecatedField->getField('newDeprecatedField');
 
         self::assertEquals(true, $deprecatedFieldDef->isDeprecated());
         self::assertEquals('not used anymore', $deprecatedFieldDef->deprecationReason);
 
-        /** @var EnumType $enumWithDeprecatedValue */
         $enumWithDeprecatedValue = $extendedSchema->getType('EnumWithDeprecatedValue');
+        self::assertInstanceOf(EnumType::class, $enumWithDeprecatedValue);
+
         $deprecatedEnumDef = $enumWithDeprecatedValue->getValue('DEPRECATED');
 
         self::assertEquals(true, $deprecatedEnumDef->isDeprecated());
@@ -613,8 +616,10 @@ public function testExtendsObjectsWithDeprecatedFields(): void
             deprecatedField: String @deprecated(reason: "not used anymore")
           }
         ');
-        /** @var ObjectType $fooType */
+
         $fooType = $extendedSchema->getType('Foo');
+        self::assertInstanceOf(ObjectType::class, $fooType);
+
         $deprecatedFieldDef = $fooType->getField('deprecatedField');
 
         self::assertTrue($deprecatedFieldDef->isDeprecated());
@@ -632,8 +637,9 @@ public function testExtendsEnumsWithDeprecatedValues(): void
           }
         ');
 
-        /** @var EnumType $someEnumType */
         $someEnumType = $extendedSchema->getType('SomeEnum');
+        self::assertInstanceOf(EnumType::class, $someEnumType);
+
         $deprecatedEnumDef = $someEnumType->getValue('DEPRECATED');
 
         self::assertTrue($deprecatedEnumDef->isDeprecated());
@@ -1685,7 +1691,7 @@ public function testPreservesScalarClassMethods(): void
         self::assertInstanceOf(CustomScalarType::class, $extendedScalar);
         self::assertSame(SomeScalarClassType::SERIALIZE_RETURN, $extendedScalar->serialize(null));
         self::assertSame(SomeScalarClassType::PARSE_VALUE_RETURN, $extendedScalar->parseValue(null));
-        self::assertSame(SomeScalarClassType::PARSE_LITERAL_RETURN, $extendedScalar->parseLiteral(Parser::valueLiteral('1')));
+        self::assertSame(SomeScalarClassType::PARSE_LITERAL_RETURN, $extendedScalar->parseLiteral(new IntValueNode(['value' => '1'])));
     }
 
     public function testPreservesResolveTypeMethod(): void
diff --git a/tests/Validator/ValidationTest.php b/tests/Validator/ValidationTest.php
index cb7fb3fc7..4a785372b 100644
--- a/tests/Validator/ValidationTest.php
+++ b/tests/Validator/ValidationTest.php
@@ -27,30 +27,6 @@ public function testValidatesQueries(): void
         ');
     }
 
-    /**
-     * @see it('detects bad scalar parse')
-     */
-    public function testDetectsBadScalarParse(): void
-    {
-        $doc = '
-      query {
-        invalidArg(arg: "bad value")
-      }
-        ';
-
-        $expectedError = [
-            'message' => 'Field "invalidArg" argument "arg" requires type Invalid, found "bad value"; Invalid scalar is always invalid: bad value',
-            'locations' => [['line' => 3, 'column' => 25]],
-        ];
-
-        $this->expectInvalid(
-            self::getTestSchema(),
-            null,
-            $doc,
-            [$expectedError]
-        );
-    }
-
     public function testPassesValidationWithEmptyRules(): void
     {
         $query = '{invalid}';
diff --git a/tests/Validator/ValidatorTestCase.php b/tests/Validator/ValidatorTestCase.php
index 6d14b5f0d..b550b6ff0 100644
--- a/tests/Validator/ValidatorTestCase.php
+++ b/tests/Validator/ValidatorTestCase.php
@@ -7,6 +7,8 @@
 use function array_map;
 use GraphQL\Error\Error;
 use GraphQL\Error\FormattedError;
+use GraphQL\Error\UserError;
+use GraphQL\Language\AST\Node;
 use GraphQL\Language\DirectiveLocation;
 use GraphQL\Language\Parser;
 use GraphQL\Type\Definition\CustomScalarType;
@@ -307,11 +309,11 @@ public static function getTestSchema(): Schema
             'serialize' => static function ($value) {
                 return $value;
             },
-            'parseLiteral' => static function ($node): void {
-                throw new Error('Invalid scalar is always invalid: ' . $node->value);
+            'parseLiteral' => static function (Node $node): void {
+                throw new UserError('Invalid scalar is always invalid: ' . $node->value);
             },
             'parseValue' => static function ($node): void {
-                throw new Error('Invalid scalar is always invalid: ' . $node);
+                throw new UserError('Invalid scalar is always invalid: ' . $node);
             },
         ]);
 
diff --git a/tests/Validator/ValuesOfCorrectTypeTest.php b/tests/Validator/ValuesOfCorrectTypeTest.php
index 57c4f19dd..69a36315a 100644
--- a/tests/Validator/ValuesOfCorrectTypeTest.php
+++ b/tests/Validator/ValuesOfCorrectTypeTest.php
@@ -6,6 +6,10 @@
 
 use GraphQL\Language\SourceLocation;
 use GraphQL\Tests\ErrorHelper;
+use GraphQL\Type\Definition\CustomScalarType;
+use GraphQL\Type\Definition\ObjectType;
+use GraphQL\Type\Definition\Type;
+use GraphQL\Type\Schema;
 use GraphQL\Validator\Rules\ValuesOfCorrectType;
 
 /**
@@ -243,30 +247,13 @@ public function testIntIntoString(): void
         }
         ',
             [
-                $this->badValueWithMessage('Field "stringArgField" argument "stringArg" requires type String, found 1.', 4, 39),
+                $this->badValueWithMessage('String cannot represent a non string value: 1', 4, 39),
             ]
         );
 
         self::assertTrue($errors[0]->isClientSafe());
     }
 
-    /**
-     * @param mixed $value anything
-     *
-     * @phpstan-return ErrorArray
-     */
-    private function badValue(string $typeName, $value, int $line, int $column, ?string $message = null): array
-    {
-        return ErrorHelper::create(
-            ValuesOfCorrectType::badValueMessage(
-                $typeName,
-                $value,
-                $message
-            ),
-            [new SourceLocation($line, $column)]
-        );
-    }
-
     /**
      * @phpstan-return ErrorArray
      */
@@ -290,7 +277,7 @@ public function testFloatIntoString(): void
         }
         ',
             [
-                $this->badValueWithMessage('Field "stringArgField" argument "stringArg" requires type String, found 1.0.', 4, 39),
+                $this->badValueWithMessage('String cannot represent a non string value: 1.0', 4, 39),
             ]
         );
 
@@ -314,7 +301,7 @@ public function testBooleanIntoString(): void
         }
         ',
             [
-                $this->badValueWithMessage('Field "stringArgField" argument "stringArg" requires type String, found true.', 4, 39),
+                $this->badValueWithMessage('String cannot represent a non string value: true', 4, 39),
             ]
         );
 
@@ -336,7 +323,7 @@ public function testUnquotedStringIntoString(): void
         }
         ',
             [
-                $this->badValueWithMessage('Field "stringArgField" argument "stringArg" requires type String, found BAR.', 4, 39),
+                $this->badValueWithMessage('String cannot represent a non string value: BAR', 4, 39),
             ]
         );
 
@@ -358,7 +345,7 @@ public function testStringIntoInt(): void
         }
         ',
             [
-                $this->badValueWithMessage('Field "intArgField" argument "intArg" requires type Int, found "3".', 4, 33),
+                $this->badValueWithMessage('Int cannot represent non-integer value: "3"', 4, 33),
             ]
         );
 
@@ -380,7 +367,7 @@ public function testBigIntIntoInt(): void
         }
         ',
             [
-                $this->badValueWithMessage('Field "intArgField" argument "intArg" requires type Int, found 829384293849283498239482938.', 4, 33),
+                $this->badValueWithMessage('Int cannot represent non-integer value: 829384293849283498239482938', 4, 33),
             ]
         );
 
@@ -404,7 +391,7 @@ public function testUnquotedStringIntoInt(): void
         }
         ',
             [
-                $this->badValueWithMessage('Field "intArgField" argument "intArg" requires type Int, found FOO.', 4, 33),
+                $this->badValueWithMessage('Int cannot represent non-integer value: FOO', 4, 33),
             ]
         );
 
@@ -426,7 +413,7 @@ public function testSimpleFloatIntoInt(): void
         }
         ',
             [
-                $this->badValueWithMessage('Field "intArgField" argument "intArg" requires type Int, found 3.0.', 4, 33),
+                $this->badValueWithMessage('Int cannot represent non-integer value: 3.0', 4, 33),
             ]
         );
 
@@ -448,7 +435,7 @@ public function testFloatIntoInt(): void
         }
         ',
             [
-                $this->badValueWithMessage('Field "intArgField" argument "intArg" requires type Int, found 3.333.', 4, 33),
+                $this->badValueWithMessage('Int cannot represent non-integer value: 3.333', 4, 33),
             ]
         );
 
@@ -470,7 +457,7 @@ public function testStringIntoFloat(): void
         }
         ',
             [
-                $this->badValueWithMessage('Field "floatArgField" argument "floatArg" requires type Float, found "3.333".', 4, 37),
+                $this->badValueWithMessage('Float cannot represent non numeric value: "3.333"', 4, 37),
             ]
         );
 
@@ -492,7 +479,7 @@ public function testBooleanIntoFloat(): void
         }
         ',
             [
-                $this->badValueWithMessage('Field "floatArgField" argument "floatArg" requires type Float, found true.', 4, 37),
+                $this->badValueWithMessage('Float cannot represent non numeric value: true', 4, 37),
             ]
         );
 
@@ -516,7 +503,7 @@ public function testUnquotedIntoFloat(): void
         }
         ',
             [
-                $this->badValueWithMessage('Field "floatArgField" argument "floatArg" requires type Float, found FOO.', 4, 37),
+                $this->badValueWithMessage('Float cannot represent non numeric value: FOO', 4, 37),
             ]
         );
 
@@ -538,7 +525,7 @@ public function testIntIntoBoolean(): void
         }
         ',
             [
-                $this->badValueWithMessage('Field "booleanArgField" argument "booleanArg" requires type Boolean, found 2.', 4, 41),
+                $this->badValueWithMessage('Boolean cannot represent a non boolean value: 2', 4, 41),
             ]
         );
 
@@ -560,7 +547,7 @@ public function testFloatIntoBoolean(): void
         }
         ',
             [
-                $this->badValueWithMessage('Field "booleanArgField" argument "booleanArg" requires type Boolean, found 1.0.', 4, 41),
+                $this->badValueWithMessage('Boolean cannot represent a non boolean value: 1.0', 4, 41),
             ]
         );
 
@@ -584,7 +571,7 @@ public function testStringIntoBoolean(): void
         }
         ',
             [
-                $this->badValueWithMessage('Field "booleanArgField" argument "booleanArg" requires type Boolean, found "true".', 4, 41),
+                $this->badValueWithMessage('Boolean cannot represent a non boolean value: "true"', 4, 41),
             ]
         );
 
@@ -606,7 +593,7 @@ public function testUnquotedIntoBoolean(): void
         }
         ',
             [
-                $this->badValueWithMessage('Field "booleanArgField" argument "booleanArg" requires type Boolean, found TRUE.', 4, 41),
+                $this->badValueWithMessage('Boolean cannot represent a non boolean value: TRUE', 4, 41),
             ]
         );
 
@@ -628,7 +615,7 @@ public function testFloatIntoID(): void
         }
         ',
             [
-                $this->badValueWithMessage('Field "idArgField" argument "idArg" requires type ID, found 1.0.', 4, 31),
+                $this->badValueWithMessage('ID cannot represent a non-string and non-integer value: 1.0', 4, 31),
             ]
         );
 
@@ -650,7 +637,7 @@ public function testBooleanIntoID(): void
         }
         ',
             [
-                $this->badValueWithMessage('Field "idArgField" argument "idArg" requires type ID, found true.', 4, 31),
+                $this->badValueWithMessage('ID cannot represent a non-string and non-integer value: true', 4, 31),
             ]
         );
 
@@ -674,7 +661,7 @@ public function testUnquotedIntoID(): void
         }
         ',
             [
-                $this->badValueWithMessage('Field "idArgField" argument "idArg" requires type ID, found SOMETHING.', 4, 31),
+                $this->badValueWithMessage('ID cannot represent a non-string and non-integer value: SOMETHING', 4, 31),
             ]
         );
 
@@ -696,7 +683,7 @@ public function testIntIntoEnum(): void
         }
         ',
             [
-                $this->badValueWithMessage('Field "doesKnowCommand" argument "dogCommand" requires type DogCommand, found 2.', 4, 41),
+                $this->badValueWithMessage('Enum "DogCommand" cannot represent non-enum value: 2.', 4, 41),
             ]
         );
 
@@ -718,7 +705,7 @@ public function testFloatIntoEnum(): void
         }
         ',
             [
-                $this->badValueWithMessage('Field "doesKnowCommand" argument "dogCommand" requires type DogCommand, found 1.0.', 4, 41),
+                $this->badValueWithMessage('Enum "DogCommand" cannot represent non-enum value: 1.0.', 4, 41),
             ]
         );
 
@@ -742,7 +729,7 @@ public function testStringIntoEnum(): void
         }
         ',
             [
-                $this->badValueWithMessage('Field "doesKnowCommand" argument "dogCommand" requires type DogCommand, found "SIT"; Did you mean the enum value SIT?', 4, 41),
+                $this->badValueWithMessage('Enum "DogCommand" cannot represent non-enum value: "SIT". Did you mean the enum value "SIT"?', 4, 41),
             ]
         );
 
@@ -764,7 +751,7 @@ public function testBooleanIntoEnum(): void
         }
         ',
             [
-                $this->badValueWithMessage('Field "doesKnowCommand" argument "dogCommand" requires type DogCommand, found true.', 4, 41),
+                $this->badValueWithMessage('Enum "DogCommand" cannot represent non-enum value: true.', 4, 41),
             ]
         );
 
@@ -786,7 +773,7 @@ public function testUnknownEnumValueIntoEnum(): void
         }
         ',
             [
-                $this->badValueWithMessage('Field "doesKnowCommand" argument "dogCommand" requires type DogCommand, found JUGGLE.', 4, 41),
+                $this->badValueWithMessage('Value "JUGGLE" does not exist in "DogCommand" enum.', 4, 41),
             ]
         );
 
@@ -808,7 +795,7 @@ public function testDifferentCaseEnumValueIntoEnum(): void
         }
         ',
             [
-                $this->badValueWithMessage('Field "doesKnowCommand" argument "dogCommand" requires type DogCommand, found sit; Did you mean the enum value SIT?', 4, 41),
+                $this->badValueWithMessage('Value "sit" does not exist in "DogCommand" enum. Did you mean the enum value "SIT"?', 4, 41),
             ]
         );
 
@@ -900,7 +887,7 @@ public function testIncorrectItemtype(): void
         }
         ',
             [
-                $this->badValueWithMessage('Field "stringListArgField" argument "stringListArg" requires type String, found 2.', 4, 55),
+                $this->badValueWithMessage('String cannot represent a non string value: 2', 4, 55),
             ]
         );
 
@@ -922,7 +909,7 @@ public function testSingleValueOfIncorrectType(): void
         }
         ',
             [
-                $this->badValueWithMessage('Field "stringListArgField" argument "stringListArg" requires type [String], found 1.', 4, 47),
+                $this->badValueWithMessage('String cannot represent a non string value: 1', 4, 47),
             ]
         );
 
@@ -1118,8 +1105,8 @@ public function testIncorrectValueType(): void
         }
         ',
             [
-                $this->badValueWithMessage('Field "multipleReqs" argument "req2" requires type Int!, found "two".', 4, 32),
-                $this->badValueWithMessage('Field "multipleReqs" argument "req1" requires type Int!, found "one".', 4, 45),
+                $this->badValueWithMessage('Int cannot represent non-integer value: "two"', 4, 32),
+                $this->badValueWithMessage('Int cannot represent non-integer value: "one"', 4, 45),
             ]
         );
 
@@ -1128,9 +1115,9 @@ public function testIncorrectValueType(): void
     }
 
     /**
-     * @see it('Incorrect value and missing argument (ProvidedRequiredArguments)')
+     * @see it('Incorrect value and missing argument (ProvidedRequiredArgumentsRule)')
      */
-    public function testIncorrectValueAndMissingArgumentProvidedRequiredArguments(): void
+    public function testIncorrectValueAndMissingArgumentProvidedRequiredArgumentsRule(): void
     {
         $errors = $this->expectFailsRule(
             new ValuesOfCorrectType(),
@@ -1142,7 +1129,7 @@ public function testIncorrectValueAndMissingArgumentProvidedRequiredArguments():
         }
         ',
             [
-                $this->badValueWithMessage('Field "multipleReqs" argument "req1" requires type Int!, found "one".', 4, 32),
+                $this->badValueWithMessage('Int cannot represent non-integer value: "one"', 4, 32),
             ]
         );
 
@@ -1166,7 +1153,7 @@ public function testNullValue2(): void
         }
         ',
             [
-                $this->badValueWithMessage('Field "multipleReqs" argument "req1" requires type Int!, found null.', 4, 32),
+                $this->badValueWithMessage('Expected value of type "Int!", found null.', 4, 32),
             ]
         );
 
@@ -1304,28 +1291,16 @@ public function testPartialObjectMissingRequired(): void
         }
         ',
             [
-                $this->requiredField('ComplexInput', 'requiredField', 'Boolean!', 4, 41),
+                [
+                    'message' => 'Field ComplexInput.requiredField of required type Boolean! was not provided.',
+                    'locations' => [['line' => 4, 'column' => 41]],
+                ],
             ]
         );
 
         self::assertTrue($errors[0]->isClientSafe());
     }
 
-    /**
-     * @phpstan-return ErrorArray
-     */
-    private function requiredField(string $typeName, string $fieldName, string $fieldTypeName, int $line, int $column): array
-    {
-        return ErrorHelper::create(
-            ValuesOfCorrectType::requiredFieldMessage(
-                $typeName,
-                $fieldName,
-                $fieldTypeName
-            ),
-            [new SourceLocation($line, $column)]
-        );
-    }
-
     // DESCRIBE: Invalid input object value
 
     /**
@@ -1346,7 +1321,7 @@ public function testPartialObjectInvalidFieldType(): void
         }
         ',
             [
-                $this->badValueWithMessage('Field "complexArgField" argument "complexArg" requires type String, found 2.', 5, 40),
+                $this->badValueWithMessage('String cannot represent a non string value: 2', 5, 40),
             ]
         );
 
@@ -1370,7 +1345,7 @@ public function testPartialObjectNullToNonNullField(): void
           }
         }
       ',
-            [$this->badValueWithMessage('Field "complexArgField" argument "complexArg" requires type Boolean!, found null.', 6, 29)]
+            [$this->badValueWithMessage('Expected value of type "Boolean!", found null.', 6, 29)]
         );
 
         self::assertTrue($errors[0]->isClientSafe());
@@ -1378,10 +1353,6 @@ public function testPartialObjectNullToNonNullField(): void
 
     /**
      * @see it('Partial object, unknown field arg')
-     *
-     * The sorting of equal elements has changed so that the test fails on php < 7
-     *
-     * @requires PHP 7.0
      */
     public function testPartialObjectUnknownFieldArg(): void
     {
@@ -1392,45 +1363,28 @@ public function testPartialObjectUnknownFieldArg(): void
           complicatedArgs {
             complexArgField(complexArg: {
               requiredField: true,
-              unknownField: "value"
+              invalidField: "value"
             })
           }
         }
         ',
             [
-                $this->unknownField(
-                    'ComplexInput',
-                    'unknownField',
-                    6,
-                    15
-                ),
+                [
+                    'message' => 'Field "invalidField" is not defined by type "ComplexInput". Did you mean "intField"?',
+                    'locations' => [['line' => 6, 'column' => 15]],
+                ],
             ]
         );
 
         self::assertTrue($errors[0]->isClientSafe());
     }
 
-    /**
-     * @phpstan-return ErrorArray
-     */
-    private function unknownField(string $typeName, string $fieldName, int $line, int $column, ?string $message = null): array
-    {
-        return ErrorHelper::create(
-            ValuesOfCorrectType::unknownFieldMessage(
-                $typeName,
-                $fieldName,
-                $message
-            ),
-            [new SourceLocation($line, $column)]
-        );
-    }
-
     /**
      * @see it('reports original error for custom scalar which throws')
      */
     public function testReportsOriginalErrorForCustomScalarWhichThrows(): void
     {
-        $errors = $this->expectFailsRule(
+        $this->expectFailsRule(
             new ValuesOfCorrectType(),
             '
         {
@@ -1438,7 +1392,7 @@ public function testReportsOriginalErrorForCustomScalarWhichThrows(): void
         }
         ',
             [
-                $this->badValueWithMessage('Field "invalidArg" argument "arg" requires type Invalid, found 123; Invalid scalar is always invalid: 123', 3, 27),
+                $this->badValueWithMessage('Expected value of type "Invalid", found 123; Invalid scalar is always invalid: 123', 3, 27),
             ]
         );
     }
@@ -1448,7 +1402,23 @@ public function testReportsOriginalErrorForCustomScalarWhichThrows(): void
      */
     public function testAllowsCustomScalarToAcceptComplexLiterals(): void
     {
-        $this->expectPassesRule(
+        $customScalar = new CustomScalarType(['name' => 'Any']);
+        $schema = new Schema([
+            'query' => new ObjectType([
+                'name' => 'Query',
+                'fields' => [
+                    'anyArg' => [
+                        'type' => Type::string(),
+                        'args' => [
+                            'arg' => $customScalar,
+                        ],
+                    ],
+                ],
+            ]),
+        ]);
+
+        $this->expectPassesRuleWithSchema(
+            $schema,
             new ValuesOfCorrectType(),
             '
         {
@@ -1498,8 +1468,8 @@ public function testWithDirectiveWithIncorrectTypes(): void
         }
         ',
             [
-                $this->badValueWithMessage('Field "dog" argument "if" requires type Boolean!, found "yes".', 3, 28),
-                $this->badValueWithMessage('Field "name" argument "if" requires type Boolean!, found ENUM.', 4, 28),
+                $this->badValueWithMessage('Boolean cannot represent a non boolean value: "yes"', 3, 28),
+                $this->badValueWithMessage('Boolean cannot represent a non boolean value: ENUM', 4, 28),
             ]
         );
 
@@ -1565,9 +1535,18 @@ public function testVariablesWithInvalidDefaultNullValues(): void
         }
         ',
             [
-                $this->badValue('Int!', 'null', 3, 22),
-                $this->badValue('String!', 'null', 4, 25),
-                $this->badValue('Boolean!', 'null', 5, 47),
+                [
+                    'message' => 'Expected value of type "Int!", found null.',
+                    'locations' => [['line' => 3, 'column' => 22]],
+                ],
+                [
+                    'message' => 'Expected value of type "String!", found null.',
+                    'locations' => [['line' => 4, 'column' => 25]],
+                ],
+                [
+                    'message' => 'Expected value of type "Boolean!", found null.',
+                    'locations' => [['line' => 5, 'column' => 47]],
+                ],
             ]
         );
 
@@ -1593,9 +1572,18 @@ public function testVariablesWithInvalidDefaultValues(): void
         }
         ',
             [
-                $this->badValue('Int', '"one"', 3, 21),
-                $this->badValue('String', '4', 4, 24),
-                $this->badValue('ComplexInput', '"notverycomplex"', 5, 30),
+                [
+                    'message' => 'Int cannot represent non-integer value: "one"',
+                    'locations' => [['line' => 3, 'column' => 21]],
+                ],
+                [
+                    'message' => 'String cannot represent a non string value: 4',
+                    'locations' => [['line' => 4, 'column' => 24]],
+                ],
+                [
+                    'message' => 'Expected value of type "ComplexInput", found "notverycomplex".',
+                    'locations' => [['line' => 5, 'column' => 30]],
+                ],
             ]
         );
 
@@ -1617,8 +1605,14 @@ public function testVariablesWithComplexInvalidDefaultValues(): void
         }
         ',
             [
-                $this->badValue('Boolean!', '123', 3, 47),
-                $this->badValue('Int', '"abc"', 3, 62),
+                [
+                    'message' => 'Boolean cannot represent a non boolean value: 123',
+                    'locations' => [['line' => 3, 'column' => 47]],
+                ],
+                [
+                    'message' => 'Int cannot represent non-integer value: "abc"',
+                    'locations' => [['line' => 3, 'column' => 62]],
+                ],
             ]
         );
 
@@ -1638,7 +1632,10 @@ public function testComplexVariablesMissingRequiredField(): void
         }
         ',
             [
-                $this->requiredField('ComplexInput', 'requiredField', 'Boolean!', 2, 55),
+                ErrorHelper::create(
+                    'Field ComplexInput.requiredField of required type Boolean! was not provided.',
+                    [new SourceLocation(2, 55)]
+                ),
             ]
         );
 
@@ -1658,7 +1655,10 @@ public function testListVariablesWithInvalidItem(): void
         }
         ',
             [
-                $this->badValue('String', '2', 2, 50),
+                [
+                    'message' => 'String cannot represent a non string value: 2',
+                    'locations' => [['line' => 2, 'column' => 50]],
+                ],
             ]
         );