Allow field definitions to be defined as any iterable, not just array

CHANGELOG.md

@@ -33,6 +33,7 @@ You can find and compare releases at the [GitHub release page](https://github.co
 - Expose structured enumeration of directive locations
 - Add `AST::concatAST()` utility
 - Allow lazy input object fields
+- Allow field definitions to be defined as any `iterable`, not just `array`
 
 ### Optimized
 

src/Type/Definition/FieldDefinition.php

@@ -11,6 +11,7 @@
 
 use function is_array;
 use function is_callable;
+use function is_iterable;
 use function is_string;
 use function sprintf;
 
@@ -86,9 +87,9 @@ public static function defineFieldMap(Type $type, $fields): array
             $fields = $fields();
         }
 
-        if (! is_array($fields)) {
+        if (! is_iterable($fields)) {
             throw new InvariantViolation(
-                "{$type->name} fields must be an array or a callable which returns such an array."
+                "{$type->name} fields must be an iterable or a callable which returns such an iterable."
             );
         }
 

src/Type/Definition/InputObjectType.php

@@ -13,6 +13,7 @@
 use function count;
 use function is_array;
 use function is_callable;
+use function is_iterable;
 use function is_string;
 use function sprintf;
 
@@ -96,9 +97,9 @@ protected function initializeFields(): void
             $fields = $fields();
         }
 
-        if (! is_array($fields)) {
+        if (! is_iterable($fields)) {
             throw new InvariantViolation(
-                sprintf('%s fields must be an array or a callable which returns such an array.', $this->name)
+                sprintf('%s fields must be an iterable or a callable which returns such an iterable.', $this->name)
             );
         }
 

tests/Type/DefinitionTest.php

@@ -5,6 +5,7 @@
 namespace GraphQL\Tests\Type;
 
 use DMS\PHPUnitExtensions\ArraySubset\ArraySubsetAsserts;
+use Generator;
 use GraphQL\Error\InvariantViolation;
 use GraphQL\Tests\Type\TestClasses\MyCustomType;
 use GraphQL\Tests\Type\TestClasses\OtherCustom;
@@ -14,9 +15,11 @@
 use GraphQL\Type\Definition\InputObjectField;
 use GraphQL\Type\Definition\InputObjectType;
 use GraphQL\Type\Definition\InterfaceType;
+use GraphQL\Type\Definition\IntType;
 use GraphQL\Type\Definition\ListOfType;
 use GraphQL\Type\Definition\NonNull;
 use GraphQL\Type\Definition\ObjectType;
+use GraphQL\Type\Definition\StringType;
 use GraphQL\Type\Definition\Type;
 use GraphQL\Type\Definition\UnionType;
 use GraphQL\Type\Schema;
@@ -2040,4 +2043,27 @@ public function testThrowsWhenLazyLoadedFieldHasInvalidArgs(): void
 
         $objType->assertValid();
     }
+
+    public function testReturningFieldsUsingYield()
+    {
+        $type = new ObjectType([
+            'name'   => 'Query',
+            'fields' => static function (): Generator {
+                yield 'url'    => ['type' => Type::string()];
+                yield 'width'  => ['type' => Type::int()];
+            },
+        ]);
+
+        $blogSchema = new Schema(['query' => $type]);
+
+        self::assertSame($blogSchema->getQueryType(), $type);
+
+        $field = $type->getField('url');
+        self::assertSame($field->name, 'url');
+        self::assertInstanceOf(StringType::class, $field->getType());
+
+        $field = $type->getField('width');
+        self::assertSame($field->name, 'width');
+        self::assertInstanceOf(IntType::class, $field->getType());
+    }
 }