zend_ast: Mark zend_ast_list_add() as ZEND_ATTRIBUTE_NODISCARD

This actually caught a bug in the implementation of attributes on regular
constants: A list of 4 constants with an attribute did not correctly result in
an error, since the reallocated list wasn't stored anywhere.

Author: TimWolla

Zend/tests/attributes/constants/multiple_constants_error.phpt

@@ -5,7 +5,9 @@ Error trying to add attributes to multiple constants at once
 
 #[\Foo]
 const First = 1,
-    Second = 2;
+    Second = 2,
+    Third = 3,
+    Fourth = 4;
 
 ?>
 --EXPECTF--

Zend/zend_ast.c

@@ -498,7 +498,7 @@ static inline bool is_power_of_two(uint32_t n) {
 	return ((n != 0) && (n == (n & (~n + 1))));
 }
 
-ZEND_API zend_ast * ZEND_FASTCALL zend_ast_list_add(zend_ast *ast, zend_ast *op) {
+ZEND_ATTRIBUTE_NODISCARD ZEND_API zend_ast * ZEND_FASTCALL zend_ast_list_add(zend_ast *ast, zend_ast *op) {
 	zend_ast_list *list = zend_ast_get_list(ast);
 	if (list->children >= 4 && is_power_of_two(list->children)) {
 			list = zend_ast_realloc(list,
@@ -2956,7 +2956,7 @@ zend_ast * ZEND_FASTCALL zend_ast_with_attributes(zend_ast *ast, zend_ast *attr)
 		/* Since constants are already stored in a list, just add the attributes
 		 * to that list instead of storing them elsewhere;
 		 * zend_compile_const_decl() checks the kind of the list elements. */
-		zend_ast_list_add(ast, attr);
+		ast = zend_ast_list_add(ast, attr);
 		break;
 	EMPTY_SWITCH_DEFAULT_CASE()
 	}

Zend/zend_ast.h

@@ -320,7 +320,7 @@ ZEND_API zend_ast *zend_ast_create_ex(zend_ast_kind kind, zend_ast_attr attr, ..
 ZEND_API zend_ast *zend_ast_create_list(uint32_t init_children, zend_ast_kind kind, ...);
 #endif
 
-ZEND_API zend_ast * ZEND_FASTCALL zend_ast_list_add(zend_ast *list, zend_ast *op);
+ZEND_ATTRIBUTE_NODISCARD ZEND_API zend_ast * ZEND_FASTCALL zend_ast_list_add(zend_ast *list, zend_ast *op);
 
 ZEND_API zend_ast *zend_ast_create_decl(
 	zend_ast_kind kind, uint32_t flags, uint32_t start_lineno, zend_string *doc_comment,

Zend/zend_compile.c

@@ -4391,7 +4391,7 @@ static void zend_compile_assert(znode *result, zend_ast_list *args, zend_string
 					ZSTR_INIT_LITERAL("description", 0));
 				arg = zend_ast_create(ZEND_AST_NAMED_ARG, name, arg);
 			}
-			zend_ast_list_add((zend_ast *) args, arg);
+			args = (zend_ast_list *)zend_ast_list_add((zend_ast *) args, arg);
 		}
 
 		zend_compile_call_common(result, (zend_ast*)args, fbc, lineno);