Track static-ness of closures in ClosureType to exclude null from bindTo()/bind() return type

Add an optional `?TrinaryLogic $isStatic` parameter to ClosureType's
constructor to track whether a closure was declared with the `static`
keyword. ClosureTypeResolver now passes this from the AST node.

The bind extensions use this to exclude null from the return type when
the closure is known to be non-static (binding always succeeds for
non-static closures regardless of $newThis). For static or
possibly-static closures with non-null $newThis, the return type
remains BenevolentUnionType(Closure|null) since PHP returns null when
binding an object to a static closure.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

Author: 2 people

src/Type/ClosureType.php

@@ -493,6 +493,11 @@ public function isCommonCallable(): bool
 		return $this->isCommonCallable;
 	}
 
+	public function isStaticClosure(): TrinaryLogic
+	{
+		return $this->isStatic;
+	}
+
 	public function getCallableParametersAcceptors(ClassMemberAccessAnswerer $scope): array
 	{
 		return [$this];

src/Type/Php/ClosureBindDynamicReturnTypeExtension.php

@@ -35,6 +35,10 @@ public function getTypeFromStaticMethodCall(MethodReflection $methodReflection,
 			return null;
 		}
 
+		if ($closureType->isStaticClosure()->no()) {
+			return $closureType;
+		}
+
 		if (isset($args[1]) && $scope->getType($args[1]->value)->isNull()->yes()) {
 			return $closureType;
 		}

src/Type/Php/ClosureBindToDynamicReturnTypeExtension.php

@@ -34,6 +34,10 @@ public function getTypeFromMethodCall(MethodReflection $methodReflection, Method
 			return null;
 		}
 
+		if ($closureType->isStaticClosure()->no()) {
+			return $closureType;
+		}
+
 		$args = $methodCall->getArgs();
 		if (isset($args[0]) && $scope->getType($args[0]->value)->isNull()->yes()) {
 			return $closureType;

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

@@ -16,13 +16,13 @@
 
 $newThis = new \stdClass();
 $bound = $foo->bindTo($newThis);
-assertType('((Closure(): void)|null)', $bound);
+assertType('Closure(): void', $bound);
 
 $staticBound = Closure::bind($foo, $newThis);
-assertType('((Closure(): void)|null)', $staticBound);
+assertType('Closure(): void', $staticBound);
 
 $bound2 = $foo->bindTo($newThis, 'stdClass');
-assertType('((Closure(): void)|null)', $bound2);
+assertType('Closure(): void', $bound2);
 
 $static = static function (): void {};
 $boundStatic = $static->bindTo($newThis);
@@ -31,7 +31,16 @@
 $boundStaticNull = $static->bindTo(null);
 assertType('Closure(): void', $boundStaticNull);
 
+$staticBound2 = Closure::bind($static, $newThis);
+assertType('((Closure(): void)|null)', $staticBound2);
+
+$staticBoundNull = Closure::bind($static, null);
+assertType('Closure(): void', $staticBoundNull);
+
 /** @var \stdClass|null $maybeNull */
 $maybeNull = null;
 $boundMaybe = $foo->bindTo($maybeNull);
-assertType('((Closure(): void)|null)', $boundMaybe);
+assertType('Closure(): void', $boundMaybe);
+
+$staticBoundMaybe = $static->bindTo($maybeNull);
+assertType('((Closure(): void)|null)', $staticBoundMaybe);