From: Patrick Palka <ppalka@redhat.com>
Date: Sun, 6 Apr 2025 02:39:15 +0000 (-0400)
Subject: c++: maybe_dependent_member_ref and typenames [PR118626]
X-Git-Tag: basepoints/gcc-16~322
X-Git-Url: http://git.ipfire.org/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=7a91400c142899ea0aeb8b62577496cf24c68156;p=thirdparty%2Fgcc.git

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 <jason@redhat.com>
---

diff --git a/gcc/cp/pt.cc b/gcc/cp/pt.cc
index 23e41a0fdcb..95b89f1281b 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 00000000000..74ef1e4d890
--- /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>;