[gcc r15-9231] c++: maybe_dependent_member_ref and typenames [PR118626]

[Patrick Palka via Gcc-cvs]

https://gcc.gnu.org/g:7a91400c142899ea0aeb8b62577496cf24c68156

commit r15-9231-g7a91400c142899ea0aeb8b62577496cf24c68156
Author: Patrick Palka <ppa...@redhat.com>
Date:   Sat Apr 5 22:39:15 2025 -0400

    c++: maybe_dependent_member_ref and typenames [PR118626]
    
    Here during maybe_dependent_member_ref for accepted_type<_Up>, we
    correctly don't strip the typedef because it's a complex one (its
    defaulted template parameter isn't used in its definition) and so
    we recurse to consider its corresponding TYPE_DECL.
    
    We then incorrectly decide to not rewrite this use because of the
    TYPENAME_TYPE shortcut.  But I don't think this shortcut should apply to
    a typedef TYPE_DECL.
    
            PR c++/118626
    
    gcc/cp/ChangeLog:
    
            * pt.cc (maybe_dependent_member_ref): Restrict TYPENAME_TYPE
            shortcut to non-typedef TYPE_DECL.
    
    gcc/testsuite/ChangeLog:
    
            * g++.dg/cpp2a/class-deduction-alias25a.C: New test.
    
    Reviewed-by: Jason Merrill <ja...@redhat.com>

Diff:
---
 gcc/cp/pt.cc                                          |  3 ++-
 gcc/testsuite/g++.dg/cpp2a/class-deduction-alias25a.C | 19 +++++++++++++++++++
 2 files changed, 21 insertions(+), 1 deletion(-)

diff --git a/gcc/cp/pt.cc b/gcc/cp/pt.cc
index 23e41a0fdcb1..95b89f1281ba 100644
--- a/gcc/cp/pt.cc
+++ b/gcc/cp/pt.cc
@@ -17789,7 +17789,8 @@ maybe_dependent_member_ref (tree t, tree args, 
tsubst_flags_t complain,
 
   if (TREE_CODE (t) == TYPE_DECL)
     {
-      if (TREE_CODE (TREE_TYPE (t)) == TYPENAME_TYPE
+      if (!is_typedef_decl (t)
+         && TREE_CODE (TREE_TYPE (t)) == TYPENAME_TYPE
          && TYPE_NAME (TREE_TYPE (t)) == t)
        /* The TYPE_DECL for a typename has DECL_CONTEXT of the typename
           scope, but it doesn't need to be rewritten again.  */
diff --git a/gcc/testsuite/g++.dg/cpp2a/class-deduction-alias25a.C 
b/gcc/testsuite/g++.dg/cpp2a/class-deduction-alias25a.C
new file mode 100644
index 000000000000..74ef1e4d890b
--- /dev/null
+++ b/gcc/testsuite/g++.dg/cpp2a/class-deduction-alias25a.C
@@ -0,0 +1,19 @@
+// PR c++/118626
+// { dg-do compile { target c++20 } }
+
+template<long> struct _Nth_type { using type = _Nth_type; };
+
+template<class _Up>
+struct variant {
+  template<class _Tp> static constexpr long __accepted_index = 0;
+  template<long _Np> using __to_type = typename _Nth_type<_Np>::type;
+  template<class _Tp, int = sizeof(_Tp)> using __accepted_type = 
__to_type<__accepted_index<_Tp>>;
+  template<class = __accepted_type<_Up>> variant(_Up);
+};
+
+template<class _Tp>
+struct Node { Node(_Tp); };
+
+template<class R> using Tree = variant<Node<R>>;
+using type = decltype(Tree{Node{42}});
+using type = Tree<int>;