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

[Paolo Carlini]

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:
>>>>>>>> Â Â Â Â Â Â Â Â  && ((TREE_CODE (declspecs->type) != TYPENAME_TYPE
>>>>>>>> +Â Â Â Â Â Â  && TREE_CODE (declspecs->type) != DECLTYPE_TYPE
>>>>>>>> Â Â Â Â Â Â Â Â Â  && 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.
>>>
>>>> +Â  if ((!declared_type || TREE_CODE (declared_type) == DECLTYPE_TYPE)
>>>> +Â Â Â Â Â  && ! saw_friend && !error_p)
>>>> Â Â Â Â  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??
>>
>>>> +Â  if (declspecs->attributes && warn_attributes && declared_type
>>>> +Â Â Â Â Â  && 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.,

Paolo.