Address code review

Author: kocsismate

Zend/tests/type_declarations/mixed/syntax/mixed_parameter_sucess4.phpt

@@ -0,0 +1,11 @@
+--TEST--
+Test that the mixed parameter type can have any default value
+--FILE--
+<?php
+
+function foo(mixed $a = null, mixed $b = false, mixed $c = 1, mixed $d = 3.13, mixed $e = "", mixed $f = [])
+{
+}
+
+?>
+--EXPECT--

Zend/tests/type_declarations/mixed/syntax/nullable_mixed_parameter_error.phpt

@@ -9,4 +9,4 @@ function foo(?mixed $a)
 
 ?>
 --EXPECTF--
-Fatal error: Type mixed cannot be nullable in %s on line %d
+Fatal error: Type mixed cannot be marked as nullable since mixed already includes null in %s on line %d

Zend/tests/type_declarations/mixed/syntax/nullable_mixed_property_error.phpt

@@ -10,4 +10,4 @@ class Foo
 
 ?>
 --EXPECTF--
-Fatal error: Type mixed cannot be nullable in %s on line %d
+Fatal error: Type mixed cannot be marked as nullable since mixed already includes null in %s on line %d

Zend/tests/type_declarations/mixed/syntax/nullable_mixed_return_error.phpt

@@ -9,4 +9,4 @@ function foo(): ?mixed
 
 ?>
 --EXPECTF--
-Fatal error: Type mixed cannot be nullable in %s on line %d
+Fatal error: Type mixed cannot be marked as nullable since mixed already includes null in %s on line %d

Zend/zend_compile.c

@@ -5671,8 +5671,8 @@ static zend_type zend_compile_typename(
 			ZSTR_VAL(type_str));
 	}
 
-	if ((type_mask == MAY_BE_ANY) && allow_null) {
-		zend_error_noreturn(E_COMPILE_ERROR, "Type mixed cannot be nullable");
+	if (type_mask == MAY_BE_ANY && allow_null && !force_allow_null) {
+		zend_error_noreturn(E_COMPILE_ERROR, "Type mixed cannot be marked as nullable since mixed already includes null");
 	}
 
 	if ((type_mask & MAY_BE_OBJECT) && (ZEND_TYPE_HAS_CLASS(type) || (type_mask & MAY_BE_STATIC))) {

ext/reflection/tests/mixed_type.phpt

@@ -17,8 +17,17 @@ $method = new ReflectionMethod($a, "test");
 var_dump($object->getProperty("a")->getType()->getName());
 var_dump($method->getParameters()[0]->getType()->getName());
 var_dump($method->getReturnType()->getName());
+
+var_dump((string) $object->getProperty("a"));
+var_dump((string) $method->getParameters()[0]);
+var_dump((string) $method->getReturnType());
+
 ?>
 --EXPECT--
 string(5) "mixed"
 string(5) "mixed"
 string(5) "mixed"
+string(29) "Property [ public mixed $a ]
+"
+string(36) "Parameter #0 [ <required> mixed $a ]"
+string(5) "mixed"