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

Jason Merrill jason@redhat.com
Fri Dec 14 20:19:00 GMT 2018

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.


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