[gcc r16-5937] c++: is_late_template_attribute and tsubst_attribute fixes

[Jakub Jelinek]

https://gcc.gnu.org/g:3b7e865779d03b4d29375a3c28dfaa2172eced4a

commit r16-5937-g3b7e865779d03b4d29375a3c28dfaa2172eced4a
Author: Jakub Jelinek <jakub@redhat.com>
Date:   Sat Dec 6 11:07:18 2025 +0100

    c++: is_late_template_attribute and tsubst_attribute fixes
    
    This has been discussed in the 1/9 Reflection thread, but doesn't depend on
    reglection in any way.
    cp_parser_std_attribute calls lookup_attribute_spec as:
        const attribute_spec *as
          = lookup_attribute_spec (TREE_PURPOSE (attribute));
    so with TREE_LIST where TREE_VALUE is attribute name and TREE_PURPOSE
    attribute ns.  Similarly c_parser_std_attribute.  And for
    attribute_takes_identifier_p those do:
        else if (attr_ns == gnu_identifier
                 && attribute_takes_identifier_p (attr_id))
    and
            bool takes_identifier
              = (ns != NULL_TREE
                 && strcmp (IDENTIFIER_POINTER (ns), "gnu") == 0
                 && attribute_takes_identifier_p (name));
    when handling std attributes (for GNU attributes they just call those
    with the IDENTIFIER_NODE name.
    is_late_template_attribute and tsubst_attribute pass to these functions
    just get_attribute_name though, so handle attributes in all namespaces
    as GNU attributes only, which means that lookup_attribute_spec can
    return NULL or find a different attribute if it is not from gnu:: or
    say standard attribute mapped to gnu::, or attribute_takes_identifier_p
    can return true even for attributes for which it shouldn't.
    
    I thought about changing attribute_takes_identifier_p to take optionally
    TREE_LIST, but that would mean handling it in the target hooks too and
    they only care about GNU attributes right now, so given the above
    parser.cc/c-parser.cc snippets, the following patch just follow
    what they do.
    
    2025-12-06  Jakub Jelinek  <jakub@redhat.com>
    
            * decl2.cc (is_late_template_attribute): Call lookup_attribute_spec
            on TREE_PURPOSE (attr) rather than name.  Only call
            attribute_takes_identifier_p if get_attribute_namespace (attr) is
            gnu_identifier.
            * pt.cc (tsubst_attribute): Only call attribute_takes_identifier_p
            if get_attribute_namespace (t) is gnu_identifier.

Diff:
---
 gcc/cp/decl2.cc | 7 +++++--
 gcc/cp/pt.cc    | 3 ++-
 2 files changed, 7 insertions(+), 3 deletions(-)

diff --git a/gcc/cp/decl2.cc b/gcc/cp/decl2.cc
index 9e135af41b34..8ec9740c8a9e 100644
--- a/gcc/cp/decl2.cc
+++ b/gcc/cp/decl2.cc
@@ -1468,7 +1468,8 @@ is_late_template_attribute (tree attr, tree decl)
 {
   tree name = get_attribute_name (attr);
   tree args = TREE_VALUE (attr);
-  const struct attribute_spec *spec = lookup_attribute_spec (name);
+  const struct attribute_spec *spec
+    = lookup_attribute_spec (TREE_PURPOSE (attr));
   tree arg;
 
   if (!spec)
@@ -1512,7 +1513,9 @@ is_late_template_attribute (tree attr, tree decl)
 	 second and following arguments.  Attributes like mode, format,
 	 cleanup and several target specific attributes aren't late
 	 just because they have an IDENTIFIER_NODE as first argument.  */
-      if (arg == args && attribute_takes_identifier_p (name)
+      if (arg == args
+	  && get_attribute_namespace (attr) == gnu_identifier
+	  && attribute_takes_identifier_p (name)
 	  && identifier_p (t))
 	continue;
 
diff --git a/gcc/cp/pt.cc b/gcc/cp/pt.cc
index 7a019d33bda1..8498730b6e43 100644
--- a/gcc/cp/pt.cc
+++ b/gcc/cp/pt.cc
@@ -12386,7 +12386,8 @@ tsubst_attribute (tree t, tree *decl_p, tree args,
      pass it through tsubst.  Attributes like mode, format,
      cleanup and several target specific attributes expect it
      unmodified.  */
-  else if (attribute_takes_identifier_p (get_attribute_name (t)))
+  else if (get_attribute_namespace (t) == gnu_identifier
+	   && attribute_takes_identifier_p (get_attribute_name (t)))
     {
       tree chain
 	= tsubst_expr (TREE_CHAIN (val), args, complain, in_decl);