fmtlib compilation fails (consteval) on clang main branch

[kamrann]

https://godbolt.org/z/bf5MeK3TW

It's not entirely clear since this issue does not show up if using fmtlib master branch, but only on the latest 11.0.2 release. However, since 11.0.2 builds fine with MSVC, GCC and Clang 19, it suggests a probable regression.

[llvmbot]

@llvm/issue-subscribers-clang-frontend

Author: Cameron Angus (kamrann)

https://godbolt.org/z/bf5MeK3TW

It's not entirely clear since this issue does not show up if using fmtlib master branch, but only on the latest 11.0.2 release. However, since 11.0.2 builds fine with MSVC, GCC and Clang 19, it suggests a probable regression.

[tbaederr]

The error doesn't ring a bell here. Can you provide the preprocessed sources for that file?

The only thing that comes to mind is the string literal change, wasn't there a problem in fmtlib that got fixed in their master branch, @zygoloid?

[kamrann]

Can you provide the preprocessed sources for that file?

For fmt? I just added -E to the CE invocation and pasted the output back into the input. If you meant something else, let me know.

[zygoloid]

This was a bug in fmtlib that's fixed in their trunk, combined with all compilers previously being overly permissive in repeated constant evaluation of string literals.

[kamrann]

Understood, sorry for the false report then. I searched on fmtlib initially but missed that issue somehow.

[zygoloid]

No worries, thanks for reporting!