Re: [C++ Patch] PR 84644 ("internal compiler error: in warn_misplaced_attr_for_class_type, at cp/decl.c:4718")

[Jason Merrill <jason@redhat.com>]

On 12/14/18 4:33 PM, Paolo Carlini wrote:
> Hi,
> 
> On 14/12/18 21:19, Jason Merrill wrote:
>> On 12/14/18 1:44 PM, Paolo Carlini wrote:
>>> Hi,
>>>
>>> On 13/12/18 22:03, Jason Merrill wrote:
>>>> On 10/30/18 9:22 PM, Paolo Carlini wrote:
>>>>> Hi,
>>>>>
>>>>> On 30/10/18 21:37, Jason Merrill wrote:
>>>>>> On 10/26/18 2:02 PM, Paolo Carlini wrote:
>>>>>>> On 26/10/18 17:18, Jason Merrill wrote:
>>>>>>>> On Fri, Oct 26, 2018 at 4:52 AM Paolo Carlini 
>>>>>>>> <paolo.carlini@oracle.com> wrote:
>>>>>>>>> On 24/10/18 22:41, Jason Merrill wrote:
>>>>>>>>>> On 10/15/18 12:45 PM, Paolo Carlini wrote:
>>>>>>>>>>>          && ((TREE_CODE (declspecs->type) != TYPENAME_TYPE
>>>>>>>>>>> +       && TREE_CODE (declspecs->type) != DECLTYPE_TYPE
>>>>>>>>>>>           && MAYBE_CLASS_TYPE_P (declspecs->type))
>>>>>>>>>> I would think that the MAYBE_CLASS_TYPE_P here should be 
>>>>>>>>>> CLASS_TYPE_P,
>>>>>>>>>> and then we can remove the TYPENAME_TYPE check. Or do we want to
>>>>>>>>>> allow template type parameters for some reason?
>>>>>>>>> Indeed, it would be nice to just use OVERLOAD_TYPE_P. However 
>>>>>>>>> it seems
>>>>>>>>> we at least want to let through TEMPLATE_TYPE_PARMs 
>>>>>>>>> representing 'auto'
>>>>>>>>> - otherwise Dodji's check a few lines below which fixed c++/51473
>>>>>>>>> doesn't work anymore - and also BOUND_TEMPLATE_TEMPLATE_PARM, 
>>>>>>>>> otherwise
>>>>>>>>> we regress on template/spec32.C and template/ttp22.C because we 
>>>>>>>>> don't
>>>>>>>>> diagnose the shadowing anymore. Thus, I would say either we 
>>>>>>>>> keep on
>>>>>>>>> using MAYBE_CLASS_TYPE_P or we pick what we need, possibly we 
>>>>>>>>> add a comment?
>>>>>>>> Aha.  I guess the answer is not to restrict that test any more, but
>>>>>>>> instead to fix the code further down so it gives a proper 
>>>>>>>> diagnostic
>>>>>>>> rather than call warn_misplaced_attr_for_class_type.
>>>>>>>
>>>>>>> I see. Thus something like the below? It passes testing on 
>>>>>>> x86_64-linux.
>>>>>>
>>>>>>> +  if ((!declared_type || TREE_CODE (declared_type) == 
>>>>>>> DECLTYPE_TYPE)
>>>>>>> +      && ! saw_friend && !error_p)
>>>>>>>      permerror (input_location, "declaration does not declare 
>>>>>>> anything");
>>>>>>
>>>>>> I see no reason to make this specific to decltype.  Maybe move 
>>>>>> this diagnostic into the final 'else' block with the other 
>>>>>> declspec diagnostics and not look at declared_type at all?
>>>>>
>>>>> I'm not sure to fully understand: if we do that we still want to at 
>>>>> least minimally check that declared_type is null, like we already 
>>>>> do, and then we simply accept the new testcase. Is that Ok? 
>>>>> Because, as I probably mentioned at some point, all the other 
>>>>> compilers I have at hand issue a "does not declare anything" 
>>>>> diagnostic, and we likewise do that for the legacy __typeof. Not 
>>>>> looking into declared_type *at all* doesn't work with plain class 
>>>>> types and enums, of course. Or you meant something entirely 
>>>>> different??
>>>>>
>>>>>>> +  if (declspecs->attributes && warn_attributes && declared_type
>>>>>>> +      && TREE_CODE (declared_type) != DECLTYPE_TYPE)
>>>>>>
>>>>>> I think we do want to give a diagnostic about useless attributes, 
>>>>>> not skip it.
>>>>>
>>>>> Agreed. FWIW the attached tests fine.
>>>>
>>>> The problem here is that the code toward the bottom expects 
>>>> "declared_type" to be the tagged type declared by a declaration with 
>>>> no declarator, and in this testcase it's ending up as a DECLTYPE_TYPE.
>>>>
>>>> I think once we've checked for 'auto' we don't want declared_type to 
>>>> be anything that isn't OVERLOAD_TYPE_P.  We can arrange that either 
>>>> by checking for 'auto' first and then changing the code that sets 
>>>> declared_type to use OVERLOAD_TYPE_P, or by clearing declared_type 
>>>> after checking for 'auto' if it isn't OVERLOAD_TYPE_P.
>>>
>>> Thanks. I'm slowly catching up on this issue... Any suggestion about 
>>> BOUND_TEMPLATE_TEMPLATE_PARM? If we don't let through such tree nodes 
>>> - which are MAYBE_CLASS_TYPE_P and aren't OVERLOAD_TYPE_P - we 
>>> regress on template/spec32.C, we don't reject it anymore.
>> If we clear declared_type for a BOUND_TEMPLATE_TEMPLATE_PARM, we 
>> should get the "does not declare anything" error.
> 
> Ah, now I see, I didn't realize that we would also change the errors we 
> issue for those testcases. Thus the below is finishing testing, appears 
> to work fine.

OK.

Jason