format_as fails when called with certain std::views

[fennewald]

Reproduction

Godbolt link

Summary

A format_as definition that returns a std::views::filter_view, like so:

auto format_as(CodecMask m) {
    return CodecMask::k_codecs | std::views::filter([&](auto c) { return m.has(c); });
}

does not compile:

CodecMask m;
m.add(Codec::H264);

fmt::println("{}", format_as(m)); // valid
fmt::pritnln("{}", m); // invalid

Stack Overflow

I posted this to stack overflow originally, expecting some mistake of my own. People there suggested that this may be a bug with fmt itself, hence this issue. The explanation given there may prove to be of value.

Notes

I expected the most recent commit (274ba26) may have helped, as it appears to be related to this type of issue. It is worth noting the error message changes when tested against 10.1.1 and trunk in godbolt, but both still do fail.

[vitaut]

There is a simpler repro for the set_debug_format error in #3763 (comment).

[fennewald]

Understood, closing as duplicated!

[vitaut]

Let's keep this one open for tracking the issue.

[vitaut]

The set_debug_format issue is fixed in 3eb3aef but looks like there is another problem.

[Arghnews]

@vitaut This issue should be fixed by #3955

[vitaut]

The original repro compiles now: https://godbolt.org/z/ahh86ME13. Thanks @Arghnews for the fix!