From: Patrick Palka <ppalka@redhat.com>
Date: Mon, 15 Dec 2025 20:03:43 +0000 (-0500)
Subject: c++: avoid in-place modification of TYPENAME_TYPE
X-Git-Url: http://git.ipfire.org/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=880492a8cb10d046b0162c31c9567c1e72d1be8f;p=thirdparty%2Fgcc.git

c++: avoid in-place modification of TYPENAME_TYPE

Since we have a TYPENAME_TYPE cache, through which equivalent
TYPENAME_TYPEs are reused, in-place modification of a TYPENAME_TYPE is
generally unsafe.  This is a latent issue noticed when attempting a
different approach to fix PR122752.

gcc/cp/ChangeLog:

	* parser.cc (cp_parser_template_id): Rebuild instead of modifying
	a TYPENAME_TYPE corresponding to a dependently-scoped template.

Reviewed-by: Jason Merrill <jason@redhat.com>
---

diff --git a/gcc/cp/parser.cc b/gcc/cp/parser.cc
index 17199e013ba..394725fde39 100644
--- a/gcc/cp/parser.cc
+++ b/gcc/cp/parser.cc
@@ -20426,10 +20426,15 @@ cp_parser_template_id (cp_parser *parser,
 	   && TREE_CODE (TREE_TYPE (templ)) == TYPENAME_TYPE)
     {
       /* Some type template in dependent scope.  */
-      tree &name = TYPENAME_TYPE_FULLNAME (TREE_TYPE (templ));
-      name = build_min_nt_loc (combined_loc,
-			       TEMPLATE_ID_EXPR,
-			       name, arguments);
+      tree fullname = TYPENAME_TYPE_FULLNAME (TREE_TYPE (templ));
+      fullname = build_min_nt_loc (combined_loc,
+				   TEMPLATE_ID_EXPR,
+				   fullname, arguments);
+      TREE_TYPE (templ)
+	= build_typename_type (TYPE_CONTEXT (TREE_TYPE (templ)),
+			       TYPE_NAME (TREE_TYPE (templ)),
+			       fullname,
+			       get_typename_tag (TREE_TYPE (templ)));
       template_id = templ;
     }
   else