c++: diagnose auto in template arg

We were failing to diagnose this Concepts TS feature that didn't make it
into C++20 because the 'auto' was getting converted to a template parameter
before we checked for it.  So also check in cp_parser_simple_type_specifier.

The code in cp_parser_template_type_arg that I initially expected to
diagnose this seems unreachable because cp_parser_type_id_1 already checks
auto.

gcc/cp/ChangeLog:

	* parser.cc (cp_parser_simple_type_specifier): Check for auto
	in template argument.
	(cp_parser_template_type_arg): Remove auto checking.

gcc/testsuite/ChangeLog:

	* g++.dg/concepts/auto7.C: New test.
	* g++.dg/concepts/auto7a.C: New test.

diff --git a/gcc/cp/parser.cc b/gcc/cp/parser.cc
index d77fbd20e56e751ef9d829a4ba0699b69b2045b6..09cba71343741b1136fb2c7c9f4fca1657ed8113 100644 (file)
--- a/gcc/cp/parser.cc
+++ b/gcc/cp/parser.cc
@@ -19823,15 +19823,19 @@ cp_parser_simple_type_specifier (cp_parser* parser,
                         "only available with "
                         "%<-std=c++14%> or %<-std=gnu++14%>");
            }
+         else if (!flag_concepts_ts && parser->in_template_argument_list_p)
+           pedwarn (token->location, 0,
+                    "use of %<auto%> in template argument "
+                    "only available with %<-fconcepts-ts%>");
+         else if (!flag_concepts)
+           pedwarn (token->location, 0,
+                    "use of %<auto%> in parameter declaration "
+                    "only available with %<-std=c++20%> or %<-fconcepts%>");
          else if (cxx_dialect < cxx14)
            error_at (token->location,
                     "use of %<auto%> in parameter declaration "
                     "only available with "
                     "%<-std=c++14%> or %<-std=gnu++14%>");
-         else if (!flag_concepts)
-           pedwarn (token->location, 0,
-                    "use of %<auto%> in parameter declaration "
-                    "only available with %<-std=c++20%> or %<-fconcepts%>");
        }
       else
        type = make_auto ();
@@ -24522,11 +24526,6 @@ cp_parser_template_type_arg (cp_parser *parser)
     = G_("types may not be defined in template arguments");
   r = cp_parser_type_id_1 (parser, CP_PARSER_FLAGS_NONE, true, false, NULL);
   parser->type_definition_forbidden_message = saved_message;
-  if (cxx_dialect >= cxx14 && !flag_concepts && type_uses_auto (r))
-    {
-      error ("invalid use of %<auto%> in template argument");
-      r = error_mark_node;
-    }
   return r;
 }
 

diff --git a/gcc/testsuite/g++.dg/concepts/auto7.C b/gcc/testsuite/g++.dg/concepts/auto7.C
new file mode 100644 (file)
index 0000000..3cbf5dd
--- /dev/null
+++ b/gcc/testsuite/g++.dg/concepts/auto7.C
@@ -0,0 +1,9 @@
+// { dg-do compile { target c++14 } }
+// { dg-additional-options -fconcepts-ts }
+
+template <class T> struct A { };
+void f(A<auto> a) { }
+int main()
+{
+  f(A<int>());
+}

diff --git a/gcc/testsuite/g++.dg/concepts/auto7a.C b/gcc/testsuite/g++.dg/concepts/auto7a.C
new file mode 100644 (file)
index 0000000..88868f4
--- /dev/null
+++ b/gcc/testsuite/g++.dg/concepts/auto7a.C
@@ -0,0 +1,8 @@
+// { dg-do compile { target c++14 } }
+
+template <class T> struct A { };
+void f(A<auto> a) { }          // { dg-error "auto. in template argument" }
+int main()
+{
+  f(A<int>());
+}