Address fmt::format_to memory_buffer deprecation

[ischoegl]

Changes proposed in this pull request

The deprecation is addressed by replacing

fmt::memory_buffer b;
format_to(b, "The answer is {}.", 42);

by

fmt::memory_buffer b;
format_to(std::back_inserter(b), "The answer is {}.", 42);

The fix uses std::back_inserter rather than fmt::appender as the latter is not available in older versions of libfmt. The current GH Actions Sundials runners already use libfmt v8.0.1 where the deprecation warnings show up.

Also reformatted affected lines to stay within the 88 character line limits.

If applicable, fill in the issue number this pull request is fixing

Closes #1098

If applicable, provide an example illustrating new features this pull request is introducing

Checklist

• The pull request includes a clear description of this code change
• Commit messages have short titles and reference relevant issues
• Build passes (scons build & scons test) and unit tests address code coverage
• Style & formatting of contributed code follows contributing guidelines
• The pull request is ready for review

[codecov]

Codecov Report

Merging #1122 (6798c57) into main (f46c3bb) will increase coverage by 0.00%.
The diff coverage is 67.14%.

❗ Current head 6798c57 differs from pull request most recent head cf97245. Consider uploading reports for the commit cf97245 to get more accurate results

@@           Coverage Diff           @@
##             main    #1122   +/-   ##
=======================================
  Coverage   73.45%   73.45%           
=======================================
  Files         364      365    +1     
  Lines       47884    47912   +28     
=======================================
+ Hits        35172    35194   +22     
- Misses      12712    12718    +6     

Impacted Files	Coverage Δ
src/thermo/PureFluidPhase.cpp	60.08% <0.00%> (-1.10%)	⬇️
src/transport/GasTransport.cpp	87.52% <0.00%> (ø)
src/thermo/RedlichKwongMFTP.cpp	84.91% <50.00%> (ø)
src/base/AnyMap.cpp	89.51% <76.92%> (-0.11%)	⬇️
src/thermo/MolalityVPSSTP.cpp	75.17% <78.94%> (-0.37%)	⬇️
src/thermo/ThermoPhase.cpp	77.85% <86.84%> (+0.20%)	⬆️
include/cantera/base/fmt.h	100.00% <100.00%> (ø)
src/kinetics/KineticsFactory.cpp	96.84% <100.00%> (ø)
src/kinetics/RxnRates.cpp	88.20% <100.00%> (+0.05%)	⬆️
src/numerics/CVodesIntegrator.cpp	73.27% <100.00%> (+0.10%)	⬆️
... and 4 more

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[bryanwweber]

as the latter is not available in older versions of libfmt

What's the oldest version that has fmt::appender? We could consider bumping the minimum version of libfmt.

[ischoegl]

What's the oldest version that has fmt::appender?

Hard to tell ... fmt::appender is implied to be preferable over std::back_inserter in fmtlib/fmt#2420, but it is also pointed out that it is undocumented (at least on their official documentation). It certainly isn't part of fmt v6.2.1 which is stock Ubuntu 18.04. There's also no information to be gleaned from the release notes.

[speth]

Writing format_to(std::back_inserter(b), ...) every time gets a little clunky. I wouldn't be opposed adding a simple utility function like

template <typename... Args>
void fmt_append(fmt::memory_buffer& b, Args... args) {
    format_to(std::.back_inserter(b), args...);
}

which probably belongs in include/cantera/base/fmt.h. If you look in that file, you may notice that this isn't the first time that the API for building up a formatted string this way has changed -- we have a workaround to implement format_to using the API that was used before version 5.0.

[ischoegl]

@speth ... thanks for the comment. There are pro's and con's to both options:

• pro of format_to(std::back_inserter(b), ...) is that it uses fmt directly / con is that it's clunky and doesn't allow fmt::appender
• pro of the template is that it's more flexible (we get to differentiate between fmt versions) / con is that it's no longer a standard fmt function.

I don't have a strong preference here.

[ischoegl]

OK. I added the template version in a separate commit (i.e. should be squashed), where I used fmt::appender (introduced in v8.0.0). Also fixed a minor compilation warning that I noticed.

PS: I noticed a couple of minor alignment glitches, which I'll fix when squashing.

[ischoegl]

@speth / @bryanwweber ... done.

[speth]

Thanks, @ischoegl! This looks good to me.