[gcc r9-10162] c++: alias template equivalence and cv-quals [PR100032]

[Jason Merrill <jason@gcc.gnu.org>]

https://gcc.gnu.org/g:945c2afcb390dd040510ee7a2dc996ad204031c5

commit r9-10162-g945c2afcb390dd040510ee7a2dc996ad204031c5
Author: Jason Merrill <jason@redhat.com>
Date:   Tue Apr 13 14:49:29 2021 -0400

    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.

Diff:
---
 gcc/cp/pt.c                                    |  4 ++++
 gcc/testsuite/g++.dg/cpp0x/alias-decl-equiv1.C | 13 +++++++++++++
 2 files changed, 17 insertions(+)

diff --git a/gcc/cp/pt.c b/gcc/cp/pt.c
index 08909e2c863..568d5155ea3 100644
--- a/gcc/cp/pt.c
+++ b/gcc/cp/pt.c
@@ -6255,6 +6255,10 @@ 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
 	(template_parms_to_args (DECL_TEMPLATE_PARMS (tmpl)));
       if (!comp_template_args (TI_ARGS (tinfo), alias_args))
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 00000000000..ae27c43bc0a
--- /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" }