Re: Possible bug in gcc-10.2 with non-type template parameter

[Edward Diener <eldlistmailingz@tropicsoft.com>]

On 1/6/2021 3:51 PM, Stefan Ring via Gcc-help wrote:
> On Mon, Jan 4, 2021 at 9:49 PM Edward Diener
> <eldlistmailingz@tropicsoft.com> wrote:
>>
>> The code, called test_predicate.cpp, simplified from a much more
>> elaborate implementation:
>>
>> template < typename T, T *d > class atmp { atmp() {} };
>>
>> template < typename T > struct ast
>> {
>> static T avar;
>> static atmp<T,&avar> acst;
>> };
>>
>> template < typename T > T ast<T>::avar;
>> template < typename T > atmp<T,&ast<T>::avar> ast<T>::acst;
>>
>> int main()
>> {
>> return 0;
>> }
>>
>> The command line compile flags for gcc-10.2:
>>
>> -fvisibility-inlines-hidden -Wno-unused-local-typedefs
>> -ftrack-macro-expansion=0 -Wno-unused-variable
>> -D_GLIBCXX_USE_CXX11_ABI=1 -Wa,-mbig-obj -m64 -mthreads -O0 -fno-inline
>> -Wall -g -fvisibility=hidden -std=c++11 -c
>>
>> The result:
>>
>> test_predicate.cpp:10:47: error: conflicting declaration 'atmp<T, (&
>> ast<T>::avar)> ast<T>::acst'
>> 10 | template < typename T > atmp<T,&ast<T>::avar> ast<T>::acst;
>> | ^~~~~~
>> test_predicate.cpp:6:26: note: previous declaration as 'atmp<T, (&
>> ast<T>::avar)> ast<T>::acst'
>> 6 | static atmp<T,&avar> acst;
>> | ^~~~
>>
>> The same source compiled with clang-11.0 and VC++14.2 succeeds with no
>> error.
>>
>> Is this s bug in gcc ? If so, is there a known workaround ?
>
> Hmm, I'm not a language lawyer, and the error message does not seem to
> make sense, but what happens when you remove the offending line in
> your real program?

A workaround which works with gcc-10.2 as pointed out to me is:

static atmp<T,&ast<T>::avar> acst;

instead of:

static atmp<T,&avar> acst;

However the workaround should not be needed and indeed is not needed by 
clang or VC++. I have reported this bug to gcc at 
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=98523.