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

src/Type/Php/ClosureBindDynamicReturnTypeExtension.php

@@ -7,8 +7,11 @@
 use PHPStan\Analyser\Scope;
 use PHPStan\DependencyInjection\AutowiredService;
 use PHPStan\Reflection\MethodReflection;
+use PHPStan\TrinaryLogic;
+use PHPStan\Type\BenevolentUnionType;
 use PHPStan\Type\ClosureType;
 use PHPStan\Type\DynamicStaticMethodReturnTypeExtension;
+use PHPStan\Type\NullType;
 use PHPStan\Type\Type;
 
 #[AutowiredService]
@@ -27,12 +30,29 @@ public function isStaticMethodSupported(MethodReflection $methodReflection): boo
 
 	public function getTypeFromStaticMethodCall(MethodReflection $methodReflection, StaticCall $methodCall, Scope $scope): ?Type
 	{
-		$closureType = $scope->getType($methodCall->getArgs()[0]->value);
+		$args = $methodCall->getArgs();
+		if (!isset($args[0])) {
+			return null;
+		}
+
+		$closureType = $scope->getType($args[0]->value);
 		if (!($closureType instanceof ClosureType)) {
 			return null;
 		}
 
-		return $closureType;
+		if ($closureType->isStaticClosure()->yes()) {
+			$newThisIsNull = isset($args[1]) ? $scope->getType($args[1]->value)->isNull() : TrinaryLogic::createYes();
+			if ($newThisIsNull->yes()) {
+				return $closureType;
+			}
+			if ($newThisIsNull->no()) {
+				return new NullType();
+			}
+
+			return new BenevolentUnionType([$closureType, new NullType()]);
+		}
+
+		return new BenevolentUnionType([$closureType, new NullType()]);
 	}
 
 }

src/Type/Php/ClosureBindToDynamicReturnTypeExtension.php

@@ -7,8 +7,11 @@
 use PHPStan\Analyser\Scope;
 use PHPStan\DependencyInjection\AutowiredService;
 use PHPStan\Reflection\MethodReflection;
+use PHPStan\TrinaryLogic;
+use PHPStan\Type\BenevolentUnionType;
 use PHPStan\Type\ClosureType;
 use PHPStan\Type\DynamicMethodReturnTypeExtension;
+use PHPStan\Type\NullType;
 use PHPStan\Type\Type;
 
 #[AutowiredService]
@@ -32,7 +35,20 @@ public function getTypeFromMethodCall(MethodReflection $methodReflection, Method
 			return null;
 		}
 
-		return $closureType;
+		if ($closureType->isStaticClosure()->yes()) {
+			$args = $methodCall->getArgs();
+			$newThisIsNull = isset($args[0]) ? $scope->getType($args[0]->value)->isNull() : TrinaryLogic::createYes();
+			if ($newThisIsNull->yes()) {
+				return $closureType;
+			}
+			if ($newThisIsNull->no()) {
+				return new NullType();
+			}
+
+			return new BenevolentUnionType([$closureType, new NullType()]);
+		}
+
+		return new BenevolentUnionType([$closureType, new NullType()]);
 	}
 
 }

tests/PHPStan/Analyser/AnalyserIntegrationTest.php

@@ -473,13 +473,14 @@ public function testBug4734(): void
 	{
 		// false positive
 		$errors = $this->runAnalyse(__DIR__ . '/data/bug-4734.php');
-		$this->assertCount(5, $errors); // could be 3
+		$this->assertCount(6, $errors); // could be 4
 
 		$this->assertSame('Static property Bug4734\Foo::$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 null but it\'s not a callable.', $errors[3]->getMessage()); // binding a static closure to an object returns null
+		$this->assertSame('Access to an undefined static property static(Bug4734\Foo)::$httpMethodParameterOverride3.', $errors[4]->getMessage());
+		$this->assertSame('Access to an undefined property Bug4734\Foo::$httpMethodParameterOverride4.', $errors[5]->getMessage());
 	}
 
 	#[RequiresPhp('>= 8.1.0')]

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

@@ -0,0 +1,46 @@
+<?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)', $bound2);
+
+$static = static function (): void {};
+$boundStatic = $static->bindTo($newThis);
+assertType('null', $boundStatic);
+
+$boundStaticNull = $static->bindTo(null);
+assertType('static-Closure(): void', $boundStaticNull);
+
+$staticBound2 = Closure::bind($static, $newThis);
+assertType('null', $staticBound2);
+
+$staticBoundNull = Closure::bind($static, null);
+assertType('static-Closure(): void', $staticBoundNull);
+
+/** @var \stdClass|null $maybeNull */
+$maybeNull = null;
+$boundMaybe = $foo->bindTo($maybeNull);
+assertType('((Closure(): void)|null)', $boundMaybe);
+
+$staticBoundMaybe = $static->bindTo($maybeNull);
+assertType('((static-Closure(): void)|null)', $staticBoundMaybe);

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);

tests/PHPStan/Analyser/nsrt/closure-static-type.php

@@ -26,37 +26,37 @@ public function doFoo(): void
 	public function doBindTo(): void
 	{
 		$static = static function (): void {};
-		assertType('static-Closure(): void', $static->bindTo($this));
+		assertType('null', $static->bindTo($this));
 
 		$nonStatic = function (): void {};
-		assertType('Closure(): void', $nonStatic->bindTo($this));
+		assertType('((Closure(): void)|null)', $nonStatic->bindTo($this));
 	}
 
 	public function doBind(): void
 	{
 		$static = static function (): void {};
-		assertType('static-Closure(): void', Closure::bind($static, $this));
+		assertType('null', Closure::bind($static, $this));
 
 		$nonStatic = function (): void {};
-		assertType('Closure(): void', Closure::bind($nonStatic, $this));
+		assertType('((Closure(): void)|null)', Closure::bind($nonStatic, $this));
 	}
 
 	/**
 	 * @param Closure(): void $unknownClosure
 	 */
 	public function doUnknown(Closure $unknownClosure): void
 	{
-		assertType('Closure(): void', $unknownClosure->bindTo($this));
-		assertType('Closure(): void', Closure::bind($unknownClosure, $this));
+		assertType('((Closure(): void)|null)', $unknownClosure->bindTo($this));
+		assertType('((Closure(): void)|null)', Closure::bind($unknownClosure, $this));
 	}
 
 	public function doFromCallable(): void
 	{
 		$fn = Closure::fromCallable(static function (): void {});
-		assertType('static-Closure(): void', $fn->bindTo($this));
+		assertType('null', $fn->bindTo($this));
 
 		$fn2 = Closure::fromCallable(function (): void {});
-		assertType('Closure(): void', $fn2->bindTo($this));
+		assertType('((Closure(): void)|null)', $fn2->bindTo($this));
 	}
 
 }

tests/PHPStan/Rules/Variables/NullCoalesceRuleTest.php

@@ -244,6 +244,11 @@ public function testNullCoalesceInGlobalScope(): void
 		]);
 	}
 
+	public function testBug5009(): void
+	{
+		$this->analyse([__DIR__ . '/data/bug-5009.php'], []);
+	}
+
 	public function testBug5933(): void
 	{
 		$this->analyse([__DIR__ . '/data/bug-5933.php'], []);

tests/PHPStan/Rules/Variables/data/bug-5009.php

@@ -0,0 +1,18 @@
+<?php declare(strict_types = 1);
+
+namespace Bug5009;
+
+use Closure;
+
+class Test
+{
+	protected Closure $callback;
+
+	/**
+	 * @param Closure(): void $callback
+	 */
+	public function __construct(Closure $callback)
+	{
+		$this->callback = $callback->bindTo($this, $this) ?? $callback;
+	}
+}