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

gcc/cp/ChangeLog

@@ -1,3 +1,10 @@
+2017-01-09  Jason Merrill  <jason@redhat.com>
+
+	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.
+
 2017-01-09  Jakub Jelinek  <jakub@redhat.com>
 
 	PR translation/79019

gcc/cp/cp-tree.def

@@ -199,7 +199,8 @@ DEFTREECODE (BOUND_TEMPLATE_TEMPLATE_PARM, "bound_template_template_parm",
 DEFTREECODE (UNBOUND_CLASS_TEMPLATE, "unbound_class_template", tcc_type, 0)
 
 /* A using declaration.  USING_DECL_SCOPE contains the specified
-   scope.  In a member using decl, unless DECL_DEPENDENT_P is true,
+   scope.  In a variadic using-declaration, this is a TYPE_PACK_EXPANSION.
+   In a member using decl, unless DECL_DEPENDENT_P is true,
    USING_DECL_DECLS contains the _DECL or OVERLOAD so named.  This is
    not an alias, but is later expanded into multiple aliases.  */
 DEFTREECODE (USING_DECL, "using_decl", tcc_declaration, 0)

gcc/cp/error.c

@@ -1268,10 +1268,21 @@ dump_decl (cxx_pretty_printer *pp, tree t, int flags)
       break;
 
     case USING_DECL:
-      pp_cxx_ws_string (pp, "using");
-      dump_type (pp, USING_DECL_SCOPE (t), flags);
-      pp_cxx_colon_colon (pp);
-      dump_decl (pp, DECL_NAME (t), flags);
+      {
+	pp_cxx_ws_string (pp, "using");
+	tree scope = USING_DECL_SCOPE (t);
+	bool variadic = false;
+	if (PACK_EXPANSION_P (scope))
+	  {
+	    scope = PACK_EXPANSION_PATTERN (scope);
+	    variadic = true;
+	  }
+	dump_type (pp, scope, flags);
+	pp_cxx_colon_colon (pp);
+	dump_decl (pp, DECL_NAME (t), flags);
+	if (variadic)
+	  pp_cxx_ws_string (pp, "...");
+      }
       break;
 
     case STATIC_ASSERT:

gcc/cp/parser.c

       /* Look for the `using' keyword.  */
       cp_parser_require_keyword (parser, RID_USING, RT_USING);
 
+ again:
       /* Peek at the next token.  */
       token = cp_lexer_peek_token (parser->lexer);
       /* See if it's `typename'.  */
       if (!cp_parser_parse_definitely (parser))
 	return false;
     }
+  else if (cp_lexer_next_token_is (parser->lexer, CPP_ELLIPSIS))
+    {
+      cp_token *ell = cp_lexer_consume_token (parser->lexer);
+      if (cxx_dialect < cxx1z
+	  && !in_system_header_at (ell->location))
+	pedwarn (ell->location, 0,
+		 "pack expansion in using-declaration only available "
+		 "with -std=c++1z or -std=gnu++1z");
+      qscope = make_pack_expansion (qscope);
+    }
 
   /* The function we call to handle a using-declaration is different
      depending on what scope we are in.  */
       if (at_class_scope_p ())
 	{
 	  /* Create the USING_DECL.  */
-	  decl = do_class_using_decl (parser->scope, identifier);
+	  decl = do_class_using_decl (qscope, identifier);
 
 	  if (decl && typename_p)
 	    USING_DECL_TYPENAME_P (decl) = 1;
 	}
     }
 
+  if (!access_declaration_p
+      && cp_lexer_next_token_is (parser->lexer, CPP_COMMA))
+    {
+      cp_token *comma = cp_lexer_consume_token (parser->lexer);
+      if (cxx_dialect < cxx1z)
+	pedwarn (comma->location, 0,
+		 "comma-separated list in using-declaration only available "
+		 "with -std=c++1z or -std=gnu++1z");
+      goto again;
+    }
+
   /* Look for the final `;'.  */
   cp_parser_require (parser, CPP_SEMICOLON, RT_SEMICOLON);
 

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

gcc/testsuite/g++.dg/cpp1z/using2.C

@@ -0,0 +1,19 @@
+// Test for P0195R2 variadic using.
+// { dg-do compile { target c++11 } }
+// { dg-options "" }
+
+struct A { void f(); };
+struct B { void f(int); };
+
+template <class... Bases> struct C: Bases...
+{
+  using Bases::f...; // { dg-warning "pack expansion" "" { target c++14_down } }
+};
+
+int main()
+{
+  C<A,B> c;
+  c.f();
+  c.f(42);
+}
+

gcc/testsuite/g++.dg/cpp1z/using3.C

@@ -0,0 +1,20 @@
+// Test for P0195R2 multiple using.
+// { dg-options "" }
+
+namespace A {
+  int i;
+}
+
+namespace A1 {
+  using A::i, A::i;	 // OK: double declaration
+  // { dg-warning "comma" "" { target c++14_down } .-1 }
+}
+
+struct B {
+  int i;
+};
+
+struct X : B {
+  using B::i, B::i; // { dg-error "redeclaration" }
+  // { dg-warning "comma" "" { target c++14_down } .-1 }
+};