FR: Allow exclusions in sparse checkouts

[kamalmarhubi]

I'd like to be able to specify a few prefixes to exclude from my working copy.

Currently jj sparse set only allows positive patterns. To get what I want, I have to

• jj sparse set --clear
• jj sparse set --add everything except the patterns I want to exclude
• continually repeat that previous step as new paths are introduced

It would be a lot more convenient to just be able to do something like jj sparse set --remove someprefix, or add some negated prefixes via jj sparse set --edit and have it work.

[kamalmarhubi]

(Assuming we only care to allow prefix exclusions, and not arbitrary globs for an initial pass.)

Forgetting the interface aspects for now, it seems to me that something like is roughly the right path:

• add a negated_prefixes to SparsePatterns
• update TreeState::sparse_matcher to return an IntersectionMatcher(PrefixMathcher(prefixes), DifferenceMatcher(EverythingMatcher, PrefixMatcher(negated_prefixes)))

(Possibly adding a NegatedMatcher instead of using DifferenceMatcher in that way.)

[martinvonz]

Yes, something like that sounds good.

• update TreeState::sparse_matcher to return an IntersectionMatcher(PrefixMathcher(prefixes), DifferenceMatcher(EverythingMatcher, PrefixMatcher(negated_prefixes)))

Is that the same as DifferenceMatcher(PrefixMatcher(prefixes), PrefixMatcher(negated_prefixes))?

[kamalmarhubi]

Is that the same as DifferenceMatcher(PrefixMatcher(prefixes), PrefixMatcher(negated_prefixes))?

yes, yes it is 🙈

[torquestomp]

I'm going to attempt to tackle this issue and issue #2288 simultaneously with a redesign of SparsePatterns from &[RepoPathBuf] into a structured format. I'll propose a design first