Extract IssetHelper from MutatingScope

conf/config.neon

@@ -566,6 +566,11 @@ services:
 			ignoreErrors: %ignoreErrors%
 			reportUnmatchedIgnoredErrors: %reportUnmatchedIgnoredErrors%
 
+	-
+		class: PHPStan\Analyser\IssetHelper
+		arguments:
+			treatPhpDocTypesAsCertain: %treatPhpDocTypesAsCertain%
+
 	-
 		class: PHPStan\Analyser\LazyScopeFactory
 		arguments:

src/Analyser/DirectScopeFactory.php

@@ -40,6 +40,7 @@ public function __construct(
 		private bool $explicitMixedInUnknownGenericNew,
 		private bool $explicitMixedForGlobalVariables,
 		private ConstantResolver $constantResolver,
+		private IssetHelper $issetHelper,
 	)
 	{
 	}
@@ -91,6 +92,7 @@ public function create(
 			$this->parser,
 			$this->nodeScopeResolver,
 			$this->constantResolver,
+			$this->issetHelper,
 			$context,
 			$this->phpVersion,
 			$declareStrictTypes,

src/Analyser/IssetHelper.php

@@ -0,0 +1,192 @@
+<?php declare(strict_types = 1);
+
+namespace PHPStan\Analyser;
+
+use PhpParser\Node\Expr;
+use PHPStan\Rules\Properties\PropertyReflectionFinder;
+use PHPStan\Type\MixedType;
+use PHPStan\Type\Type;
+use function is_string;
+
+class IssetHelper
+{
+
+	public function __construct(
+		private readonly PropertyReflectionFinder $propertyReflectionFinder,
+		private readonly bool $treatPhpDocTypesAsCertain,
+	)
+	{
+	}
+
+	/**
+	 * @param callable(Type): ?bool $typeCallback
+	 */
+	public function isset(Expr $expr, Scope $scope, callable $typeCallback, ?bool $result = null): ?bool
+	{
+		// mirrored in PHPStan\Rules\IssetCheck
+		if ($expr instanceof Expr\Variable && is_string($expr->name)) {
+			$hasVariable = $scope->hasVariableType($expr->name);
+			if ($hasVariable->maybe()) {
+				return null;
+			}
+
+			if ($result === null) {
+				if ($hasVariable->yes()) {
+					if ($expr->name === '_SESSION') {
+						return null;
+					}
+
+					return $typeCallback($scope->getVariableType($expr->name));
+				}
+
+				return false;
+			}
+
+			return $result;
+		} elseif ($expr instanceof Expr\ArrayDimFetch && $expr->dim !== null) {
+			$type = $this->treatPhpDocTypesAsCertain
+				? $scope->getType($expr->var)
+				: $scope->getNativeType($expr->var);
+			$dimType = $this->treatPhpDocTypesAsCertain
+				? $scope->getType($expr->dim)
+				: $scope->getNativeType($expr->dim);
+			$hasOffsetValue = $type->hasOffsetValueType($dimType);
+			if (!$type->isOffsetAccessible()->yes()) {
+				return $result ?? $this->issetCheckUndefined($expr->var, $scope);
+			}
+
+			if ($hasOffsetValue->no()) {
+				if ($result !== null) {
+					return $result;
+				}
+
+				return false;
+			}
+
+			if ($hasOffsetValue->maybe()) {
+				return null;
+			}
+
+			// If offset is cannot be null, store this error message and see if one of the earlier offsets is.
+			// E.g. $array['a']['b']['c'] ?? null; is a valid coalesce if a OR b or C might be null.
+			if ($hasOffsetValue->yes()) {
+				if ($result !== null) {
+					return $result;
+				}
+
+				$result = $typeCallback($type->getOffsetValueType($dimType));
+
+				if ($result !== null) {
+					return $this->isset($expr->var, $scope, $typeCallback, $result);
+				}
+			}
+
+			// Has offset, it is nullable
+			return null;
+
+		} elseif ($expr instanceof Expr\PropertyFetch || $expr instanceof Expr\StaticPropertyFetch) {
+
+			$propertyReflection = $this->propertyReflectionFinder->findPropertyReflectionFromNode($expr, $scope);
+
+			if ($propertyReflection === null) {
+				if ($expr instanceof Expr\PropertyFetch) {
+					return $this->issetCheckUndefined($expr->var, $scope);
+				}
+
+				if ($expr->class instanceof Expr) {
+					return $this->issetCheckUndefined($expr->class, $scope);
+				}
+
+				return null;
+			}
+
+			if (!$propertyReflection->isNative()) {
+				if ($expr instanceof Expr\PropertyFetch) {
+					return $this->issetCheckUndefined($expr->var, $scope);
+				}
+
+				if ($expr->class instanceof Expr) {
+					return $this->issetCheckUndefined($expr->class, $scope);
+				}
+
+				return null;
+			}
+
+			$nativeType = $propertyReflection->getNativeType();
+			if (!$nativeType instanceof MixedType) {
+				if (!$scope->isSpecified($expr)) {
+					if ($expr instanceof Expr\PropertyFetch) {
+						return $this->issetCheckUndefined($expr->var, $scope);
+					}
+
+					if ($expr->class instanceof Expr) {
+						return $this->issetCheckUndefined($expr->class, $scope);
+					}
+
+					return null;
+				}
+			}
+
+			if ($result !== null) {
+				return $result;
+			}
+
+			$result = $typeCallback($propertyReflection->getWritableType());
+			if ($result !== null) {
+				if ($expr instanceof Expr\PropertyFetch) {
+					return $this->isset($expr->var, $scope, $typeCallback, $result);
+				}
+
+				if ($expr->class instanceof Expr) {
+					return $this->isset($expr->class, $scope, $typeCallback, $result);
+				}
+			}
+
+			return $result;
+		}
+
+		if ($result !== null) {
+			return $result;
+		}
+
+		return $typeCallback($scope->getType($expr));
+	}
+
+	private function issetCheckUndefined(Expr $expr, Scope $scope): ?bool
+	{
+		if ($expr instanceof Expr\Variable && is_string($expr->name)) {
+			$hasVariable = $scope->hasVariableType($expr->name);
+			if (!$hasVariable->no()) {
+				return null;
+			}
+
+			return false;
+		}
+
+		if ($expr instanceof Expr\ArrayDimFetch && $expr->dim !== null) {
+			$type = $scope->getType($expr->var);
+			$dimType = $scope->getType($expr->dim);
+			$hasOffsetValue = $type->hasOffsetValueType($dimType);
+			if (!$type->isOffsetAccessible()->yes()) {
+				return $this->issetCheckUndefined($expr->var, $scope);
+			}
+
+			if (!$hasOffsetValue->no()) {
+				return $this->issetCheckUndefined($expr->var, $scope);
+			}
+
+			return false;
+		}
+
+		if ($expr instanceof Expr\PropertyFetch) {
+			return $this->issetCheckUndefined($expr->var, $scope);
+		}
+
+		if ($expr instanceof Expr\StaticPropertyFetch && $expr->class instanceof Expr) {
+			return $this->issetCheckUndefined($expr->class, $scope);
+		}
+
+		return null;
+	}
+
+}

src/Analyser/LazyScopeFactory.php

@@ -85,6 +85,7 @@ public function create(
 			$this->container->getService('currentPhpVersionSimpleParser'),
 			$this->container->getByType(NodeScopeResolver::class),
 			$this->container->getByType(ConstantResolver::class),
+			$this->container->getByType(IssetHelper::class),
 			$context,
 			$this->container->getByType(PhpVersion::class),
 			$declareStrictTypes,