Closures are impure by default

Author: ondrejmirtes

src/PhpDoc/TypeNodeResolver.php

@@ -36,6 +36,7 @@
 use PHPStan\PhpDocParser\Ast\Type\ThisTypeNode;
 use PHPStan\PhpDocParser\Ast\Type\TypeNode;
 use PHPStan\PhpDocParser\Ast\Type\UnionTypeNode;
+use PHPStan\Reflection\Callables\SimpleImpurePoint;
 use PHPStan\Reflection\InitializerExprContext;
 use PHPStan\Reflection\InitializerExprTypeResolver;
 use PHPStan\Reflection\Native\NativeParameterReflection;
@@ -933,7 +934,13 @@ function (CallableTypeParameterNode $parameterNode) use ($nameScope, &$isVariadi
 			$mainType instanceof ObjectType
 			&& $mainType->getClassName() === Closure::class
 		) {
-			return new ClosureType($parameters, $returnType, $isVariadic, $templateTypeMap, null, null, $templateTags, [], []);
+			return new ClosureType($parameters, $returnType, $isVariadic, $templateTypeMap, null, null, $templateTags, [], [
+				new SimpleImpurePoint(
+					'functionCall',
+					'call to a Closure',
+					false,
+				),
+			]);
 		}
 
 		return new ErrorType();

src/Reflection/TrivialParametersAcceptor.php

@@ -8,13 +8,14 @@
 use PHPStan\Type\Generic\TemplateTypeVarianceMap;
 use PHPStan\Type\MixedType;
 use PHPStan\Type\Type;
+use function sprintf;
 
 /** @api */
 class TrivialParametersAcceptor implements ParametersAcceptorWithPhpDocs, CallableParametersAcceptor
 {
 
 	/** @api */
-	public function __construct()
+	public function __construct(private string $callableName = 'callable')
 	{
 	}
 
@@ -68,7 +69,7 @@ public function getImpurePoints(): array
 		return [
 			new SimpleImpurePoint(
 				'functionCall',
-				'call to a callable',
+				sprintf('call to a %s', $this->callableName),
 				false,
 			),
 		];

src/Type/ObjectType.php

@@ -1249,7 +1249,7 @@ public function isCallable(): TrinaryLogic
 	public function getCallableParametersAcceptors(ClassMemberAccessAnswerer $scope): array
 	{
 		if ($this->className === Closure::class) {
-			return [new TrivialParametersAcceptor()];
+			return [new TrivialParametersAcceptor('Closure')];
 		}
 		$parametersAcceptors = $this->findCallableParametersAcceptors();
 		if ($parametersAcceptors === null) {

tests/PHPStan/Rules/Pure/PureFunctionRuleTest.php

@@ -92,6 +92,14 @@ public function testRule(): void
 				'Impure static variable in pure function PureFunction\functionWithStaticVariable().',
 				128,
 			],
+			[
+				'Possibly impure call to a Closure in pure function PureFunction\callsClosures().',
+				139,
+			],
+			[
+				'Possibly impure call to a Closure in pure function PureFunction\callsClosures().',
+				140,
+			],
 		]);
 	}
 

tests/PHPStan/Rules/Pure/data/pure-function.php

@@ -129,3 +129,13 @@ function functionWithStaticVariable(): int
 
 	return $v;
 }
+
+/**
+ * @phpstan-pure
+ * @param \Closure(): int $closure2
+ */
+function callsClosures(\Closure $closure1, \Closure $closure2): int
+{
+	$closure1();
+	return $closure2();
+}