Rely on gitignore to exclude listed files in ghcide (#4665)

[blackheaven]

This aimes to fix #4665.

Note that I directly calling git, as th gitignore format is non-trivial.

I can roll a partial parsing implementation if requested.

[blackheaven]

I don't think the CI failure is related to my PR.

[sgillespie]

I don't think the CI failure is related to my PR.

Looks like a flaky thing, it fixed itself

[blackheaven]

Thanks, let's try again

[fendor]

Small comments, otherwise LGTM!

Unfortunately, there are not automated tests for this cli mode, we'd need to add some, but that's some fair amount of work...

[fendor]

Couple of issues when trying this patch on the HLS codebase, but otherwise I like the direction!

[blackheaven]

I won't lie, I have no clue about the broken pipe on windows error is related to my change.

[fendor]

@blackheaven it is not caused by you. As already said, iirc there is not a single test case for the code path you are changing, so you can safely ignore any CI failures except pre-commit and -Werror :D

[blackheaven]

Thanks a lot

[fendor]

Question, what should happen if a user explicitly asks for a file to load, but the file is .gitignored?

Should we perhaps still load it? I feel like, that might be more natural behaviour, but I am admittedly not sure.
If we do want to ignore ignored files, then I would still suggest that we should warn the user in this case, that we ingored a file they requested.