GeezerVison

Assuming the tests are going to pass (last famous words), this is ready to review.
So far I have tested it only on my linux machine, if anybody has access to windows and macos it would be nice to do a "visual check" that things are going as intended.
This is how it looks like on my machine:

Compared to the initial version, I'm now using _colorize.get_theme() to get the colors.
I'm not 100% sure about _colorize.FancyCompleter though: for other use cases using a dataclass seems a good idea because the set of keys is known in advance, but here you potentially have an open ended set of types (ideally, users should be able to add their own types to the config).
So maybe we could turn the dataclass into a plain dict? This would also solve the ugly workaround to allow coloring method-wrapper here:
https://github.com/antocuni/cpython/blob/13a269807d24c4df0ec7bdca7b04369171c0db16/Lib/_pyrepl/fancycompleter.py#L153-L160

/cc @ambv as I think he's the one responsible for themes.

Also, I'm getting a warning from the doc builder but I'm not sure how to fix:

Warning: py:mod reference target not found: _pyrepl.fancycompleter [ref.mod]
/home/runner/work/cpython/cpython/Doc/using/cmdline.rst:1288: WARNING: py:mod reference target not found: _pyrepl.fancycompleter [ref.mod]

_pyrepl.fancycompleter is a module, do I need to add it somewhere else?

_pyrepl.fancycompleter is a module, do I need to add it somewhere else?

Yes, but it is not documented. You can add an exclamation mark at the start to remove the link.

So far I have tested it only on my linux machine, if anybody has access to windows and macos it would be nice to do a "visual check" that things are going as intended.

I tested it on Windows 10 using the Windows Terminal app.
This is using Powershell with Campbell theme:

Thanks for the great work on this, @antocuni . I rebased the branch and added a handful of follow-up fixes around the fancycompleter integration, including some edge cases and extra regression coverage.

This is in good shape now, and I’m planning to land it soon so it makes the next release.

I think this has some issues...: