[libcxx-commits] [libcxx] [libc++][format] Handle range-underlying-spec (PR #81914)

[Po-yao Chang via libcxx-commits]

poyaoc97 wrote:

Because the tuple formatter like the range formatter prohibits ':' as a `fill` (__use_range_fill_ = true) but it doesn't have an underlying format-spec. So `{::<}` for tuples is a no-go but OK (align left, no fill for the underlying formatter) for ranges (`__has_range_underlying_spec_ = true` for this case).

https://github.com/llvm/llvm-project/pull/81914