Returning object from new $class is too aggressive for minor version, let's return mixed~string for now

Author: ondrejmirtes

src/Analyser/MutatingScope.php

@@ -4641,7 +4641,7 @@ private function getTypeToInstantiateForNew(Type $type): Type
 			foreach ($type->getTypes() as $innerType) {
 				$decidedType = $decideType($innerType);
 				if ($decidedType === null) {
-					return new ObjectWithoutClassType();
+					return new MixedType(false, new StringType());
 				}
 
 				$types[] = $decidedType;
@@ -4652,7 +4652,7 @@ private function getTypeToInstantiateForNew(Type $type): Type
 
 		$decidedType = $decideType($type);
 		if ($decidedType === null) {
-			return new ObjectWithoutClassType();
+			return new MixedType(false, new StringType());
 		}
 
 		return $decidedType;

tests/PHPStan/Analyser/NodeScopeResolverTest.php

@@ -1712,7 +1712,7 @@ public function dataDeductedTypes(): array
 				'$loremObjectLiteral',
 			],
 			[
-				'object',
+				'mixed~string',
 				'$mixedObjectLiteral',
 			],
 			[

tests/PHPStan/Analyser/data/bug-4579.php

@@ -6,6 +6,7 @@
 
 function (string $class): void {
 	$foo = new $class();
+	assertType('mixed~string', $foo);
 	if (method_exists($foo, 'doFoo')) {
 		assertType('object&hasMethod(doFoo)', $foo);
 	}

tests/PHPStan/Analyser/data/generic-class-string.php

@@ -15,7 +15,7 @@ public static function f(): int {
  * @param mixed $a
  */
 function testMixed($a) {
-	assertType('object', new $a());
+	assertType('mixed~string', new $a());
 
 	if (is_subclass_of($a, 'DateTimeInterface')) {
 		assertType('class-string<DateTimeInterface>|DateTimeInterface', $a);
@@ -36,7 +36,7 @@ function testMixed($a) {
  * @param object $a
  */
 function testObject($a) {
-	assertType('object', new $a());
+	assertType('mixed~string', new $a());
 
 	if (is_subclass_of($a, 'DateTimeInterface')) {
 		assertType('DateTimeInterface', $a);
@@ -47,7 +47,7 @@ function testObject($a) {
  * @param string $a
  */
 function testString($a) {
-	assertType('object', new $a());
+	assertType('mixed~string', new $a());
 
 	if (is_subclass_of($a, 'DateTimeInterface')) {
 		assertType('class-string<DateTimeInterface>', $a);
@@ -63,7 +63,7 @@ function testString($a) {
  * @param string|object $a
  */
 function testStringObject($a) {
-	assertType('object', new $a());
+	assertType('mixed~string', new $a());
 
 	if (is_subclass_of($a, 'DateTimeInterface')) {
 		assertType('class-string<DateTimeInterface>|DateTimeInterface', $a);
@@ -92,7 +92,7 @@ function testClassExists(string $str)
 	assertType('string', $str);
 	if (class_exists($str)) {
 		assertType('class-string', $str);
-		assertType('object', new $str());
+		assertType('mixed~string', new $str());
 	}
 
 	$existentClass = \stdClass::class;