Fix phpstan/phpstan#9844: Static method call on class-string returns mixed instead of ErrorType

- When calling a static method on a non-generic class-string variable, return mixed instead of ErrorType
- The fix only applies to class-string types, not to named class or typed object expressions
- New regression test in tests/PHPStan/Analyser/nsrt/bug-9844.php
- Root cause: class-string converts to ObjectWithoutClassType which has hasMethod() = MAYBE, causing filterTypeWithMethod to bail out and fall back to ErrorType

Author: VincentLanglet

src/Analyser/ExprHandler/StaticCallHandler.php

@@ -291,20 +291,28 @@ public function resolveType(MutatingScope $scope, Expr $expr): Type
 				return $callType;
 			}
 
+			$calledOnClassString = false;
 			if ($expr->class instanceof Name) {
 				$staticMethodCalledOnType = $this->resolveTypeByNameWithLateStaticBinding($scope, $expr->class, $expr->name);
 			} else {
-				$staticMethodCalledOnType = TypeCombinator::removeNull($scope->getType($expr->class))->getObjectTypeOrClassStringObjectType();
+				$classType = TypeCombinator::removeNull($scope->getType($expr->class));
+				$calledOnClassString = $classType->isClassString()->yes();
+				$staticMethodCalledOnType = $classType->getObjectTypeOrClassStringObjectType();
 			}
 
+			$methodName = $expr->name->toString();
 			$callType = $this->methodCallReturnTypeHelper->methodCallReturnType(
 				$scope,
 				$staticMethodCalledOnType,
-				$expr->name->toString(),
+				$methodName,
 				$expr,
 			);
 			if ($callType === null) {
-				$callType = new ErrorType();
+				if ($calledOnClassString && $staticMethodCalledOnType->hasMethod($methodName)->maybe()) {
+					$callType = new MixedType();
+				} else {
+					$callType = new ErrorType();
+				}
 			}
 
 			if ($expr->class instanceof Expr) {

tests/PHPStan/Analyser/nsrt/bug-9844.php

@@ -0,0 +1,17 @@
+<?php declare(strict_types = 1);
+
+namespace Bug9844;
+
+use function PHPStan\Testing\assertType;
+
+class HelloWorld
+{
+
+	/**
+	 * @param class-string $class
+	 */
+	public function sayHello(string $class): void
+	{
+		assertType('mixed', $class::foo());
+	}
+}