Fix libfmt errors from not finding enum formatter

[mhx]

Recent versions of libfmt have become more strict and require enum types to be formattable:

static assertion failed due to requirement 'formattable': Cannot format an argument. To make type T formattable provide a formatter<T> specialization: https://fmt.dev/latest/api.html#udt

This is a quick fix to simply use the underlying type.

[mhx]

cc @ot as this was introduced in a42f818

[ot]

Thanks for the fix, I think that fmt::underlying would be a terser option, but it's not clear from the documentation whether it's available in fmt/core.h or we need fmt/format.h.

@vitaut Do you have recommendations?

[mhx]

Thanks for the fix, I think that fmt::underlying would be a terser option [...]

Agreed, I just wasn't sure if this is already in libfmt 8.x which folly currently lists in its build manifest. At least libfmt 10.x defines underlying in fmt/format.h.

[vitaut]

As documented, fmt::underlying is defined in fmt/format.h. You could also use std::to_underlying instead.

[mhx]

As documented, fmt::underlying is defined in fmt/format.h. You could also use std::to_underlying instead.

std::to_underlying is C++23, though, so I don't think this would make it into folly yet.

@ot, if fmt/format.h is too heavy, would you prefer to stick to static_cast for now?

[Orvid]

Folly has folly::to_underlying which does this without the need to worry about C++ language versions, or where fmt::underlying lives. I would recommend just using that.

[mhx]

Updated PR using folly::to_underlying.

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@ot has imported this pull request. If you are a Meta employee, you can view this diff on Phabricator.

[facebook-github-bot]

@ot merged this pull request in e74fe5c.