[Bug libstdc++/121765] `std::formatter` specialization for user-defined type inheriting from `std::formatter<tuple-like>` fails concept `std::formattable` check unexpectedly

[tkaminsk at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=121765

Tomasz Kamiński <tkaminsk at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
         Resolution|---                         |FIXED
             Status|NEW                         |RESOLVED

--- Comment #6 from Tomasz Kamiński <tkaminsk at gcc dot gnu.org> ---
Fixed for v16.
We decided to continue to use a separate iterator for concept checks,
see attached patch.