rust-matchers: add doctests for `AlwaysMatcher` Differential Revision: https://phab.mercurial-scm.org/D7527

rust-hg-path: add method to get part of a path relative to a prefix This will be used in the next patch in this series. Differential Revision: https://phab.mercurial-scm.org/D7526

rust-matchers: improve `Matcher` trait ergonomics `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). Differential Revision: https://phab.mercurial-scm.org/D7525

rust-dirs-multiset: use `AsRef` instead of concrete types when possible I also renamed `vec` to `dirstate`, because it was not a great name. Differential Revision: https://phab.mercurial-scm.org/D7524

logcmdutil: call _exthook() in changesettemplater Class changesetprinter has an _exthook() method that is called in _show() before the patch is displayed. Call the method as well in changesettemplater._show(). Differential Revision: https://phab.mercurial-scm.org/D7505

phabricator: fix processing of tags/desc in getoldnodedrevmap() It seems that the previous logic was wrong (it essentially comes from changeset 3ab0d5767b54 where the result got accumulated instead of early returned). First of all, the "continue" in first "if m:" is useless because we're at the end of the loop. Then, the algorithm seems weird because we will process all predecessors of a node and possibly override `toconfirm[node]` for each of these having a tag (maybe this doesn't happen, but still). Finally, we would also override `toconfirm[node]` when the "Differential Revision: " is found in changeset description. Maybe this is not a big deal when there is no mix of local tag and changeset description update? The logic is changed so that the loop on predecessors stops upon first match of a tag and so that the changeset description is only checked if no tag was found. Therefore, `toconfirm[node]` is only set once. Differential Revision: https://phab.mercurial-scm.org/D7513