Change away from pytoml for pip's TOML needs

[pradyunsg]

https://pypi.org/project/tomlkit/ is a style-preserving TOML parser, which makes it a much better fit for pip's needs and can be a better UX when we (I hope) adopt TOML as a new, preferred, configuration format.

[uranusjr]

Pipenv also plans to switch to TOMLkit, but IIRC it has some issues on Python 2. Nothing serious (related to a couple of backport dependencies), but some work is required.

[pradyunsg]

Thanks for the info @uranusjr! :)

[auvipy]

Should I start work on this?

[pradyunsg]

Sure!

[auvipy]

thank you!! feel free to assign me on the issue. I am going to add a draft pr soon!

[auvipy]

A PR work in progress #6460 will be back to it tomorrow.

[pradyunsg]

One of our vendored dependencies -- pep517 has switched to using toml (not pytoml or tomlkit). We might want to consider switching to that.

[uranusjr]

toml is a good choice IMO for its minimal feature surface. tomlkit is nice but adds unnecessary bloat for features pip is unlikely to need in the foreseeable future.

[pfmoore]

+1 for toml. The main advantage of tomlkit is that it preserves formatting, which isn't something we need right now. Let's wait until we need that feature before picking the bigger library.