Include null in return type of Closure::bindTo() and Closure::bind() dynamic return type extensions

src/Type/Php/ClosureBindDynamicReturnTypeExtension.php

@@ -9,7 +9,9 @@
 use PHPStan\Reflection\MethodReflection;
 use PHPStan\Type\ClosureType;
 use PHPStan\Type\DynamicStaticMethodReturnTypeExtension;
+use PHPStan\Type\NullType;
 use PHPStan\Type\Type;
+use PHPStan\Type\TypeCombinator;
 
 #[AutowiredService]
 final class ClosureBindDynamicReturnTypeExtension implements DynamicStaticMethodReturnTypeExtension
@@ -32,7 +34,7 @@ public function getTypeFromStaticMethodCall(MethodReflection $methodReflection,
 			return null;
 		}
 
-		return $closureType;
+		return TypeCombinator::union($closureType, new NullType());
 	}
 
 }

src/Type/Php/ClosureBindToDynamicReturnTypeExtension.php

@@ -9,7 +9,9 @@
 use PHPStan\Reflection\MethodReflection;
 use PHPStan\Type\ClosureType;
 use PHPStan\Type\DynamicMethodReturnTypeExtension;
+use PHPStan\Type\NullType;
 use PHPStan\Type\Type;
+use PHPStan\Type\TypeCombinator;
 
 #[AutowiredService]
 final class ClosureBindToDynamicReturnTypeExtension implements DynamicMethodReturnTypeExtension
@@ -32,7 +34,7 @@ public function getTypeFromMethodCall(MethodReflection $methodReflection, Method
 			return null;
 		}
 
-		return $closureType;
+		return TypeCombinator::union($closureType, new NullType());
 	}
 
 }

tests/PHPStan/Analyser/AnalyserIntegrationTest.php

@@ -473,13 +473,17 @@ public function testBug4734(): void
 	{
 		// false positive
 		$errors = $this->runAnalyse(__DIR__ . '/data/bug-4734.php');
-		$this->assertCount(5, $errors); // could be 3
+		$this->assertCount(9, $errors); // could be 3
 
 		$this->assertSame('Static property Bug4734\Foo::$httpMethodParameterOverride (bool) is never assigned false so the property type can be changed to true.', $errors[0]->getMessage()); // should not error
 		$this->assertSame('Property Bug4734\Foo::$httpMethodParameterOverride2 (bool) is never assigned false so the property type can be changed to true.', $errors[1]->getMessage()); // should not error
 		$this->assertSame('Unsafe access to private property Bug4734\Foo::$httpMethodParameterOverride through static::.', $errors[2]->getMessage());
-		$this->assertSame('Access to an undefined static property static(Bug4734\Foo)::$httpMethodParameterOverride3.', $errors[3]->getMessage());
-		$this->assertSame('Access to an undefined property Bug4734\Foo::$httpMethodParameterOverride4.', $errors[4]->getMessage());
+		$this->assertSame('Trying to invoke (Closure(): void)|null but it might not be a callable.', $errors[3]->getMessage());
+		$this->assertSame('Trying to invoke (Closure(): void)|null but it might not be a callable.', $errors[4]->getMessage());
+		$this->assertSame('Access to an undefined static property static(Bug4734\Foo)::$httpMethodParameterOverride3.', $errors[5]->getMessage());
+		$this->assertSame('Trying to invoke (Closure(): void)|null but it might not be a callable.', $errors[6]->getMessage());
+		$this->assertSame('Access to an undefined property Bug4734\Foo::$httpMethodParameterOverride4.', $errors[7]->getMessage());
+		$this->assertSame('Trying to invoke (Closure(): void)|null but it might not be a callable.', $errors[8]->getMessage());
 	}
 
 	#[RequiresPhp('>= 8.1.0')]

tests/PHPStan/Analyser/nsrt/bug-5009.php

@@ -0,0 +1,25 @@
+<?php
+
+declare(strict_types = 1);
+
+namespace Bug5009;
+
+use Closure;
+use function PHPStan\Testing\assertType;
+
+$foo = function (): void {};
+$bar = $foo->bindTo(null);
+assertType('(Closure(): void)|null', $bar);
+
+$baz = Closure::bind($foo, null);
+assertType('(Closure(): void)|null', $baz);
+
+$newThis = new \stdClass();
+$bound = $foo->bindTo($newThis);
+assertType('(Closure(): void)|null', $bound);
+
+$staticBound = Closure::bind($foo, $newThis);
+assertType('(Closure(): void)|null', $staticBound);
+
+$bound2 = $foo->bindTo($newThis, 'stdClass');
+assertType('(Closure(): void)|null', $bound2);

tests/PHPStan/Analyser/nsrt/closure-return-type-extensions.php

@@ -11,13 +11,13 @@
 
 $newThis = new class {};
 $boundClosure = $closure->bindTo($newThis);
-assertType('Closure(object): true', $boundClosure);
+assertType('(Closure(object): true)|null', $boundClosure);
 
 $staticallyBoundClosure = \Closure::bind($closure, $newThis);
-assertType('Closure(object): true', $staticallyBoundClosure);
+assertType('(Closure(object): true)|null', $staticallyBoundClosure);
 
 $returnType = $closure->call($newThis, new class {});
 assertType('true', $returnType);
 
 $staticallyBoundClosureCaseInsensitive = \closure::bind($closure, $newThis);
-assertType('Closure(object): true', $staticallyBoundClosureCaseInsensitive);
+assertType('(Closure(object): true)|null', $staticallyBoundClosureCaseInsensitive);