On Tue, Apr 10, 2018 at 9:50 AM, Jason Merrill <ja...@redhat.com> wrote:
> On Mon, Apr 9, 2018 at 6:55 PM, Paolo Carlini <paolo.carl...@oracle.com> 
> wrote:
>> On 09/04/2018 21:39, Jason Merrill wrote:
>>> cp_parser_check_template_parameters is supposed to catch when we have
>>> the wrong number of template parameter lists, but it wasn't diagnosing
>>> this case.  Fixed by checking whether the thing we're declaring used a
>>> template-id; the case of declaring a primary template, when we allow
>>> one more template parameter list, uses a plain identifier.
>> Nice, it looks like this also fixes the prehistoric c++/24314, which I still
>> had assigned.
> Great!
>> When I worked a bit on it, relatively recently, in 2012, I
>> failed to properly follow-up to your feedback on the mailing list, but I
>> don't think we really nailed the problem, did we?
>>     https://gcc.gnu.org/ml/gcc-patches/2012-09/msg00504.html
>> Or maybe we just tried to do too much, like doing away completely with
>> cp_parser_check_template_parameters in favor of a bit of additional checking
>> in maybe_process_partial_specialization.
> I'm sure late checking like we discussed there can also work, but this
> ended up being a simple way to make the current code work better...

But as discussed in that thread, we should still improve the comment:
commit 2072134d123d64535baac00ea4bb6ffbce045caf
Author: Jason Merrill <ja...@redhat.com>
Date:   Tue Apr 10 09:42:54 2018 -0400

            * parser.c (cp_parser_check_template_parameters): Improve comment.

diff --git a/gcc/cp/parser.c b/gcc/cp/parser.c
index d4b62c75c44..849a75a1a51 100644
--- a/gcc/cp/parser.c
+++ b/gcc/cp/parser.c
@@ -26452,8 +26452,8 @@ cp_parser_check_template_parameters (cp_parser* parser,
      lists, that's OK.  */
   if (parser->num_template_parameter_lists == num_templates)
     return true;
-  /* If there are more, but only one more, then we are referring to a
-     member template.  That's OK too.  */
+  /* If there are more, but only one more, and the name ends in an identifier,
+     then we are declaring a primary template.  That's OK too.  */
   if (!template_id_p
       && parser->num_template_parameter_lists == num_templates + 1)
     return true;

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