libc++ formatter concept depends on itself

[kelbon]

It is fixable with returning -> decltype(ctx.out()), but something went wrong, other libraries and compilers do not produce such errors.

https://godbolt.org/z/v1b13Mhb3

Localy (msvc library, clang17) error is worse (there are no consteval functions)

error localy

In file included from E:/dev/projects/BC/src/sema.cpp:8: In file included from E:/dev/projects/BC/include\utility/print.h:3: C:\Program Files\Microsoft Visual Studio\2022\Community\VC\Tools\MSVC\14.36.32532\include\format:649:42: error: call to immediate function 'std::formatter::format>, char>>' is not a constant expression 649 | _Format_ctx.advance_to(_Formatter.format(

[mordante]

Thanks for the report, I just created a fix.

[frederick-vs-ja]

FYI, LWG4061 makes the example code ill-formed - auto& ctx should be written instead.