Re: [histogram][type_traits] strange compile error in boost.histogram for gcc-7.1+ with -std=c++17; possible bug in gcc?

From: John Maddock (jz.maddock_at_[hidden])
Date: 2020-10-30 18:17:56

On 30/10/2020 15:39, Thomas Ferrand via Boost wrote:
> Le 30/10/2020 à 15:16, Hans Dembinski via Boost a écrit :
>>> On 30. Oct 2020, at 14:52, Hans Dembinski <hans.dembinski_at_[hidden]> 
>>> wrote:
>>>
>>> Dear John and the other gurus,
>>>
>>> a strange bug was reported for Boost.Histogram. It is a difficult 
>>> one for which I would like to ask for help. To me it looks like a 
>>> bug in gcc.
>>>
>>> Here is the issue:
>>> https://github.com/boostorg/histogram/issues/290
>> Here is an absolute minimal example which does not include boost at all.
>>
>> https://godbolt.org/z/hrcYao
>>
>> clang is ok, msvc is ok, gcc fails.

A bit of messing about shows that:

* Returning T is OK.

* Returning std::size_t is OK

* Returning "unsigned int" is OK

* Returning "signed int" is OK

But:

* Returning "unsigned" fails.

* Returning "signed" fails.

So is changing the return type to "unsigned int" a viable option?

Weird, and does look like a bug.

HTH, John.

>>
>>
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>
> Not, an expert but I would say it looks like a gcc bug.
>
> As a workaround the function in the nested namespace can be declared 
> with a trailing return type, this doesn't seem to trigger the bug: 
> https://godbolt.org/z/fY979r
>
> Thomas
>
>
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