Fix static method call on non-generic class-string returning ErrorType

- When calling a static method on a non-generic class-string (e.g. $class::foo()
  where $class is class-string), the result was ErrorType instead of MixedType
- Root cause: class-string converts to ObjectWithoutClassType via
  getObjectTypeOrClassStringObjectType(), which returns maybe for hasMethod(),
  causing filterTypeWithMethod() to reject it and methodCallReturnType() to
  return null, falling back to ErrorType
- Fix checks if the static call is on an expression (not a class name), the
  resolved type has no known class names, and hasMethod is not definitively no,
  returning MixedType in that case
- New regression test in tests/PHPStan/Analyser/nsrt/bug-9844.php

Closes phpstan/phpstan#9844

Author: phpstan-bot

src/Analyser/MutatingScope.php

@@ -6390,7 +6390,15 @@ private function getStaticCallType(Expr\StaticCall $node): ?Type
 				$node,
 			);
 			if ($callType === null) {
-				$callType = new ErrorType();
+				if (
+					!$node->class instanceof Name
+					&& count($staticMethodCalledOnType->getObjectClassNames()) === 0
+					&& !$staticMethodCalledOnType->hasMethod($node->name->toString())->no()
+				) {
+					$callType = new MixedType();
+				} else {
+					$callType = new ErrorType();
+				}
 			}
 
 			if ($node->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());
+	}
+}