[Bug c++/98768] Improve diagnostics for incorrect result type checking "-> Type" in concepts

[redi at gcc dot gnu.org via Gcc-bugs]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=98768

--- Comment #1 from Jonathan Wakely <redi at gcc dot gnu.org> ---
(In reply to Antony Polukhin from comment #0)
> For such cases a warning like "Unused `T` in concept definition. Did you
> mean `-> std::same_as<T>`"  would be really helpful.

That wouldn't fix it though, the correct form would be:

  { func() } -> T;