yq: use tomllib if available

[intelfx]

I'm not sure if tomlkit gives any sort of extended representation that is specially handled for the TOML->TOML roundtrip case, so this tries to be smart and only uses tomllib if it is available AND output format is not TOML.

(One dirty commit for now, I'll make separate commits if the entire thing makes sense.)

Fixes #184.

[kislyuk]

This looks good, thanks. Can you transition out of draft and make any other changes you planned? It would be great to add a test that asserts on the new error messages too.

[intelfx]

This looks good, thanks. Can you transition out of draft and make any other changes you planned? It would be great to add a test that asserts on the new error messages too.

Okay, I'll do it when I get around to this again.

One question, is there actually any sort of special style-preserving handling for TOML->TOML roundtrip (like there is for YAML with yq -Y), or should I not try to be smart and just use tomllib when it's available and only fall back to tomlkit if running on <3.11? I didn't find any but I wasn't looking very hard.

[kislyuk]

Thanks for asking. Part of the reason I went with tomlkit is that it preserves style information - but I never got around to plumbing the comments and whitespace using __yq metadata keys through the JSON representation, as we do with yq -Y.

Given the fact that I don't intend to actively invest in further TOML support, I think it's time to switch things up:

• When installing on Python 3.8-3.10, depend on tomli and tomli-w
• When installing on Python 3.11+, depend on tomli-w
• Lazily Import tomllib or tomli, conditionally on sys.python_version, in decode_toml()
• Lazily import tomli-w in encode_toml()

[kislyuk]

Thanks for your input here. I went ahead and implemented the changes you suggested, only when using Python 3.11+ and not round-tripping (i.e. when using tomlq without the -t option). I realized I needed to stay with tomlkit when using the -t option due to a variety of usability issues with other options, and I will not be introducing any new dependencies (i.e. tomli) to the package, so this change will remain exclusive to Python 3.11+.

I released the changes in yq-3.3.0. In my testing, this yields a roughly 2x speedup when using tomlq to parse many small TOML files in a loop.

I'm going to close this PR now - let me know if there's anything I missed.