D7525: rust-matchers: improve `Matcher` trait ergonomics

[Alphare (Raphaël Gomès)]

Alphare added inline comments.

INLINE COMMENTS

> kevincox wrote in matchers.rs:87
> Another option here would just to have a global empty hash set.

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

REPOSITORY
  rHG Mercurial

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  https://phab.mercurial-scm.org/D7525/new/

REVISION DETAIL
  https://phab.mercurial-scm.org/D7525

To: Alphare, #hg-reviewers, kevincox
Cc: durin42, kevincox, mercurial-devel