Support parent::class inside constexpr contexts

Author: nikic

Zend/tests/class_name_as_scalar_error_002.phpt

@@ -7,7 +7,11 @@ namespace Foo\Bar {
     class One {
         const Baz = parent::class;
     }
+    var_dump(One::Baz);
 }
 ?>
 --EXPECTF--
-Fatal error: parent::class cannot be used for compile-time class name resolution in %s on line %d
+Fatal error: Uncaught Error: Cannot use "parent" when current class scope has no parent in %s:%d
+Stack trace:
+#0 {main}
+  thrown in %s on line %d

Zend/tests/class_name_as_scalar_error_004.phpt

@@ -4,10 +4,14 @@ class name as scalar from ::class keyword error using parent in method signature
 <?php
 
 namespace Foo\Bar {
-    class One {
-        public function baz($x = parent::class) {}
+    class One {}
+    class Two extends One {
+        public function baz($x = parent::class) {
+            var_dump($x);
+        }
     }
+    (new Two)->baz();
 }
 ?>
---EXPECTF--
-Fatal error: parent::class cannot be used for compile-time class name resolution in %s on line %d
+--EXPECT--
+string(11) "Foo\Bar\One"

Zend/zend_ast.c

@@ -511,19 +511,28 @@ ZEND_API int ZEND_FASTCALL zend_ast_evaluate(zval *result, zend_ast *ast, zend_c
 			break;
 		}
 		case ZEND_AST_CONSTANT_CLASS:
-			if (scope && scope->name) {
+			if (scope) {
 				ZVAL_STR_COPY(result, scope->name);
 			} else {
 				ZVAL_EMPTY_STRING(result);
 			}
 			break;
 		case ZEND_AST_CLASS_NAME:
-			ZEND_ASSERT(ast->attr == ZEND_FETCH_CLASS_SELF);
-			if (scope && scope->name) {
+			if (!scope) {
+				zend_throw_error(NULL, "Cannot use \"self\" when no class scope is active");
+				return FAILURE;
+			}
+			if (ast->attr == ZEND_FETCH_CLASS_SELF) {
 				ZVAL_STR_COPY(result, scope->name);
+			} else if (ast->attr == ZEND_FETCH_CLASS_PARENT) {
+				if (!scope->parent) {
+					zend_throw_error(NULL,
+						"Cannot use \"parent\" when current class scope has no parent");
+					return FAILURE;
+				}
+				ZVAL_STR_COPY(result, scope->parent->name);
 			} else {
-				zend_throw_error(NULL, "Cannot use \"self\" when no class scope is active");
-				ret = FAILURE;
+				ZEND_ASSERT(0 && "Should have errored during compilation");
 			}
 			break;
 		case ZEND_AST_AND:

Zend/zend_compile.c

@@ -7958,18 +7958,20 @@ void zend_compile_const_expr_class_name(zend_ast **ast_ptr) /* {{{ */
 	zend_string *class_name = zend_ast_get_str(class_ast);
 	uint32_t fetch_type = zend_get_class_fetch_type(class_name);
 
-	/* For the const-eval representation store the fetch type instead of the name. */
-	if (fetch_type == ZEND_FETCH_CLASS_SELF) {
-		zend_string_release(class_name);
-		ast->child[0] = NULL;
-		ast->attr = fetch_type;
-		return;
+	switch (fetch_type) {
+		case ZEND_FETCH_CLASS_SELF:
+		case ZEND_FETCH_CLASS_PARENT:
+			/* For the const-eval representation store the fetch type instead of the name. */
+			zend_string_release(class_name);
+			ast->child[0] = NULL;
+			ast->attr = fetch_type;
+			return;
+		case ZEND_FETCH_CLASS_STATIC:
+			zend_error_noreturn(E_COMPILE_ERROR,
+				"static::class cannot be used for compile-time class name resolution");
+			return;
+		EMPTY_SWITCH_DEFAULT_CASE()
 	}
-
-	zend_error_noreturn(E_COMPILE_ERROR,
-		"%s::class cannot be used for compile-time class name resolution",
-		fetch_type == ZEND_FETCH_CLASS_STATIC ? "static" : "parent"
-	);
 }
 
 void zend_compile_const_expr_const(zend_ast **ast_ptr) /* {{{ */