Implement GH-9826: Make class_alias() work with internal classes

We can't increase the refcount of internal classes during request time.
We fix this issue by not increasing refcount for internal classes upon
creating an alias and taking this into account during the destruction.

Author: nielsdos

UPGRADING

@@ -57,6 +57,7 @@ PHP 8.3 UPGRADE NOTES
     "full" => bool
     "buffer_size" => int
     See GH-9336
+  . class_alias() now supports creating an alias of an internal class.
 
 - MBString:
   . mb_strtolower, mb_strtotitle, and mb_convert_case implement conditional

UPGRADING.INTERNALS

@@ -30,6 +30,10 @@ PHP 8.3 INTERNALS UPGRADE NOTES
   for C99 features have been removed and therefore macro definitions
   from php_config.h have disappeared.  Do not use those feature
   macros.
+* Internal class aliases created during request time can now exist in
+  the class table. zend_register_class_alias_ex() will not increase
+  the refcount of such cases and the cleanup function takes this into
+  account.
 
 ========================
 2. Build system changes

Zend/tests/class_alias_006.phpt

@@ -3,12 +3,11 @@ Testing creation of alias to an internal class
 --FILE--
 <?php
 
-try {
-    class_alias('stdclass', 'foo');
-} catch (ValueError $exception) {
-    echo $exception->getMessage() . "\n";
-}
+class_alias('stdclass', 'foo');
+$foo = new foo();
+var_dump($foo);
 
 ?>
 --EXPECT--
-class_alias(): Argument #1 ($class) must be a user-defined class name, internal class name given
+object(stdClass)#1 (0) {
+}

Zend/zend_API.c

@@ -3296,7 +3296,11 @@ ZEND_API zend_result zend_register_class_alias_ex(const char *name, size_t name_
 	ret = zend_hash_add(CG(class_table), lcname, &zv);
 	zend_string_release_ex(lcname, 0);
 	if (ret) {
-		if (!(ce->ce_flags & ZEND_ACC_IMMUTABLE)) {
+		/* We cannot increase the refcount of an internal class during request time.
+		 * Only persistent internal classes, or user classes can increase the refcount.
+		 * We will make sure to check for the non-persistent internal class case in destroy_zend_class().
+		 */
+		if (ce->type != ZEND_INTERNAL_CLASS && !(ce->ce_flags & ZEND_ACC_IMMUTABLE)) {
 			ce->refcount++;
 		}
 		// avoid notifying at MINIT time

Zend/zend_builtin_functions.c

@@ -1074,16 +1074,11 @@ ZEND_FUNCTION(class_alias)
 	ce = zend_lookup_class_ex(class_name, NULL, !autoload ? ZEND_FETCH_CLASS_NO_AUTOLOAD : 0);
 
 	if (ce) {
-		if (ce->type == ZEND_USER_CLASS) {
-			if (zend_register_class_alias_ex(ZSTR_VAL(alias_name), ZSTR_LEN(alias_name), ce, 0) == SUCCESS) {
-				RETURN_TRUE;
-			} else {
-				zend_error(E_WARNING, "Cannot declare %s %s, because the name is already in use", zend_get_object_type(ce), ZSTR_VAL(alias_name));
-				RETURN_FALSE;
-			}
+		if (zend_register_class_alias_ex(ZSTR_VAL(alias_name), ZSTR_LEN(alias_name), ce, false) == SUCCESS) {
+			RETURN_TRUE;
 		} else {
-			zend_argument_value_error(1, "must be a user-defined class name, internal class name given");
-			RETURN_THROWS();
+			zend_error(E_WARNING, "Cannot declare %s %s, because the name is already in use", zend_get_object_type(ce), ZSTR_VAL(alias_name));
+			RETURN_FALSE;
 		}
 	} else {
 		zend_error(E_WARNING, "Class \"%s\" not found", ZSTR_VAL(class_name));

Zend/zend_opcode.c

@@ -301,6 +301,12 @@ ZEND_API void destroy_zend_class(zval *zv)
 		return;
 	}
 
+	/* As we could not increase the refcount of an internal class during request time,
+	 * we have to check for this case here. */
+	if (UNEXPECTED(ce->type == ZEND_INTERNAL_CLASS && Z_TYPE_INFO_P(zv) == IS_ALIAS_PTR)) {
+		return;
+	}
+
 	if (ce->ce_flags & ZEND_ACC_FILE_CACHED) {
 		zend_class_constant *c;
 		zval *p, *end;
@@ -323,6 +329,8 @@ ZEND_API void destroy_zend_class(zval *zv)
 		return;
 	}
 
+	ZEND_ASSERT(ce->refcount > 0);
+
 	if (--ce->refcount > 0) {
 		return;
 	}