From 34ec63f1b5c2a4d39aa3b13ade96bcd44e294066 Mon Sep 17 00:00:00 2001
From: Jason Merrill <jason@redhat.com>
Date: Tue, 13 Apr 2021 14:49:29 -0400
Subject: [PATCH] c++: alias template equivalence and cv-quals [PR100032]
We also need to check that the cv-qualifiers are the same.
gcc/cp/ChangeLog:
PR c++/100032
* pt.c (get_underlying_template): Compare TYPE_QUALS.
gcc/testsuite/ChangeLog:
PR c++/100032
* g++.dg/cpp0x/alias-decl-equiv1.C: New test.
---
gcc/cp/pt.c | 4 ++++
gcc/testsuite/g++.dg/cpp0x/alias-decl-equiv1.C | 13 +++++++++++++
2 files changed, 17 insertions(+)
create mode 100644 gcc/testsuite/g++.dg/cpp0x/alias-decl-equiv1.C
diff --git a/gcc/cp/pt.c b/gcc/cp/pt.c
index 106dfe556f7f..59df79484bfd 100644
--- a/gcc/cp/pt.c
+++ b/gcc/cp/pt.c
@@ -6584,6 +6584,10 @@ get_underlying_template (tree tmpl)
!= num_innermost_template_parms (underlying)))
break;
+ /* Does the alias add cv-quals? */
+ if (TYPE_QUALS (TREE_TYPE (underlying)) != TYPE_QUALS (TREE_TYPE (tmpl)))
+ break;
+
tree alias_args = INNERMOST_TEMPLATE_ARGS (generic_targs_for (tmpl));
if (!comp_template_args (TI_ARGS (tinfo), alias_args))
break;
diff --git a/gcc/testsuite/g++.dg/cpp0x/alias-decl-equiv1.C b/gcc/testsuite/g++.dg/cpp0x/alias-decl-equiv1.C
new file mode 100644
index 000000000000..ae27c43bc0a0
--- /dev/null
+++ b/gcc/testsuite/g++.dg/cpp0x/alias-decl-equiv1.C
@@ -0,0 +1,13 @@
+// PR c++/100032
+// { dg-do compile { target c++11 } }
+
+template <template<class> class> struct X { };
+template <class> struct Y { };
+template <class T> using Z = const Y<T>;
+
+template <class T> using W = Z<T>;
+using U = X<Z>;
+using U = X<W>;
+
+using T = X<Y>;
+using T = X<Z>; // { dg-error "conflicting declaration" }
--
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