[concepts] explicit specialization 'template<>' syntax permitted when declaring a terse function template

[zygoloid]

Bugzilla Link	50950
Version	unspecified
OS	All
CC	@zygoloid

Extended Description

Clang incorrectly permits this syntax:

template<typename T> concept X = true;     
template<> void f(X auto x);

... treating the second line as the declaration of a function template. But 'template<>' always means an explicit specialization is being declared. We should diagnose the 'template<>' in this case and suggest that it be removed.

[llvmbot]

@llvm/issue-subscribers-clang-frontend

Author: None (ec04fc15-fa35-46f2-80e1-5d271f2ef708)

| | | | --- | --- | | Bugzilla Link | [50950](https://llvm.org/bz50950) | | Version | unspecified | | OS | All | | CC | @zygoloid |

Extended Description

Clang incorrectly permits this syntax:

template<typename T> concept X = true;     
template<> void f(X auto x);

... treating the second line as the declaration of a function template. But 'template<>' always means an explicit specialization is being declared. We should diagnose the 'template<>' in this case and suggest that it be removed.