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rust-matchers: improve `Matcher` trait ergonomics

Authored by Alphare on Nov 29 2019, 12:56 PM.



VisitChildrenSet has no need to own the set, this will save allocations.

The file_set return type change is motivated by both ergonomics and... being
able to compile code.
The AlwaysMatcher does not store a file_set, which requires it to return an
owned HashSet, which in turn would change our return type to Cow<&HgPath>
(lifetimes omitted). This is both un-ergonomic and troublesome for more
complex lifetime issues (especially with the upcoming FileMatcher in the
following patch).

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Event Timeline

Alphare created this revision.Nov 29 2019, 12:56 PM
kevincox accepted this revision.Dec 2 2019, 8:09 AM
kevincox added inline comments.

Another option here would just to have a global empty hash set.

Alphare added inline comments.Dec 2 2019, 9:20 AM

I feel like an Option is more explicit and less contrived, but yes.

pulkit accepted this revision.Dec 10 2019, 10:13 AM
This revision is now accepted and ready to land.Dec 10 2019, 10:13 AM
This revision was automatically updated to reflect the committed changes.