[Bug libstdc++/113500] Using std::format with float or double based std::chrono::time_point causes error: no match for 'operator<<'

["Hirthammer@allterra-dno.de" <gcc-bugzilla@gcc.gnu.org>]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=113500

--- Comment #11 from Hirthammer@allterra-dno.de ---
(In reply to Jonathan Wakely from comment #7)
> (In reply to Jonathan Wakely from comment #6)
> > (In reply to Hirthammer from comment #5)
> > > This whole thing with std::format and std::chrono::time_point is currently a
> > > total minefield.
> > 
> > That seems like an exaggeration.
> > 
> > > In MSVC it is even more complicated and I already reported
> > > the bug in October 2023. See:
> > > 
> > > https://developercommunity.visualstudio.com/t/Using-std::format-with-
> > > unsigned-integer-/10501153
> > > 
> > > If you change the clock to utc_clock or gps_clock the code compiles with
> > > MSVC (but not with GCC) on Compiler Explorer.
> > 
> > It compiles fine with GCC for me.
> 
> Ah, maybe you mean your original example. The one at in the MSVC bug report
> compiles fine with GCC using utc_clock and gps_clock.
> 
> Your original example doesn't, because formatting a utc_time or gps_time is
> specified in terms of a sys_time, and that's how libstdc++ implements it. So
> if the utc_time or gps_time uses a float rep, we're back to square one.
> 
> I'll ask the committee to clarify that too.

Yes, I was referring to my original example because it helped me to understand
which combinations worked and which did not. 

I wrote a wrapper class around std::chrono::time_point, because I am dealing a
lot with different time formats. I am also doing multi-platform development,
and during the testing phase, it turned out that no compiler was able to
compile all templated test cases (Clang uses libstdc++ if you do not explicitly
tell it not to do, as you pointed out on the llvm bug report). Since the error
case parameter combinations differed from MSVC and GCC, I had to use many
different compiler-specific sections to get consistent and valid behavior in
the tests. That's why I called it a minefield. Maybe it was exaggerated ;).

Anyways, thank you a lot for your effort and clarifications and especially for
the fast fix.