Related to #6045. `P1222R4_flat_set` is missing test coverage for CTAD. (Again, we have decent libcxx coverage, so I'm not too worried, but it would be good to exercise CTAD in `tests/std`.)
Related to #6045.
P1222R4_flat_setis missing test coverage for CTAD.(Again, we have decent libcxx coverage, so I'm not too worried, but it would be good to exercise CTAD in
tests/std.)