[Clang] Implement P2841R7 Concept and variable-template template-parameters

[cor3ntin]

https://isocpp.org/files/papers/P2841R7.pdf

I have an implementation that I plan to upstream over the next few months

[llvmbot]

@llvm/issue-subscribers-clang-frontend

Author: cor3ntin (cor3ntin)

https://isocpp.org/files/papers/P2841R7.pdf

I have an implementation that I plan to upstream over the next few months

[philnik777]

@cor3ntin Is there any update on this? I'd really like to play with this a bit.

[cor3ntin]

We are sort of stuck on #141776, unfortunately. And we should try to finish that first - although it's not needed for variable template parameters at all, so I guess I could do that in parallel