Implement P0195R2, C++17 variadic using.

	* parser.c (cp_parser_using_declaration): Handle ellipsis and comma.
	* pt.c (tsubst_decl): Handle pack expansion in USING_DECL_SCOPE.
	* error.c (dump_decl): Likewise.

git-svn-id: svn+ssh://gcc.gnu.org/svn/gcc/trunk@244246 138bc75d-0d04-0410-961f-82ee72b054a4

1 files changed, 33 insertions, 7 deletions

diff --git a/gcc/cp/pt.c b/gcc/cp/pt.c
index 366c59a2486..dec7d39f0d0 100644
--- a/gcc/cp/pt.c
+++ b/gcc/cp/pt.c
@@ -12591,16 +12591,42 @@ tsubst_decl (tree t, tree args, tsubst_flags_t complain)
       if (DECL_DEPENDENT_P (t)
 	  || uses_template_parms (USING_DECL_SCOPE (t)))
 	{
-	  tree inst_scope = tsubst_copy (USING_DECL_SCOPE (t), args,
-					 complain, in_decl);
+	  tree scope = USING_DECL_SCOPE (t);
 	  tree name = tsubst_copy (DECL_NAME (t), args, complain, in_decl);
-	  r = do_class_using_decl (inst_scope, name);
-	  if (!r)
-	    r = error_mark_node;
+	  if (PACK_EXPANSION_P (scope))
+	    {
+	      tree vec = tsubst_pack_expansion (scope, args, complain, in_decl);
+	      int len = TREE_VEC_LENGTH (vec);
+	      r = make_tree_vec (len);
+	      for (int i = 0; i < len; ++i)
+		{
+		  tree escope = TREE_VEC_ELT (vec, i);
+		  tree elt = do_class_using_decl (escope, name);
+		  if (!elt)
+		    {
+		      r = error_mark_node;
+		      break;
+		    }
+		  else
+		    {
+		      TREE_PROTECTED (elt) = TREE_PROTECTED (t);
+		      TREE_PRIVATE (elt) = TREE_PRIVATE (t);
+		    }
+		  TREE_VEC_ELT (r, i) = elt;
+		}
+	    }
 	  else
 	    {
-	      TREE_PROTECTED (r) = TREE_PROTECTED (t);
-	      TREE_PRIVATE (r) = TREE_PRIVATE (t);
+	      tree inst_scope = tsubst_copy (USING_DECL_SCOPE (t), args,
+					     complain, in_decl);
+	      r = do_class_using_decl (inst_scope, name);
+	      if (!r)
+		r = error_mark_node;
+	      else
+		{
+		  TREE_PROTECTED (r) = TREE_PROTECTED (t);
+		  TREE_PRIVATE (r) = TREE_PRIVATE (t);
+		}
 	    }
 	}
       else