revert: extract origvfs logic in a sub-function The subrepo's "revert" logic could benefit from it.

vfs: treat 'undo.' file the same as 'journal.' file They are the same kind of file, they are protected by the store lock, but directly lives inside the '.hg' directory. No warnings were ever raised about them because `vfs.rename` is not audited. Something we are trying to change.

perf: add a perfignore command The command is meant to benchmark operations related to hgignore. Right now the command is benchmarking the loading time of the hgignore rules.

py3: use pycompat.xrange instead of xrange xrange does not exists on Python 3. Differential Revision: https://phab.mercurial-scm.org/D5302

store: write fncache only once if there are both adds and removes Differential Revision: https://phab.mercurial-scm.org/D5307

perf: disable revlogs clearing in `perftags` by default This aligns things with what `perfbookmarks` does. I decided to disable the revlogs clearing by default to focus on the core logic by default, ignoring side effects. If we prefer to emphasize the side effect, we can instead keep this on in `perftags` and enable it by default in `perfbookmarks`.

perf: add a `clear-revlogs` flag to `perfbookmarks` This flag (off by default) makes it possible to enable the refresh of the changelog and revlog. This is useful to check for costly side effects of bookmark loading. Usually, these side effects are shared with other logics (eg: tags). example output in my mercurial repo (with 1 bookmark, so not a great example): $ hg perfbookmarks ! wall 0.000044 $ hg perfbookmarks --clear-revlogs ! wall 0.001380

tags: cache `repo.changelog` access when checking tags nodes The tags reading process checks if the nodes referenced in tags exist. Caching the access to `repo.changelog` provides a large speedup for repositories with many tags. running `hg perftags` in a large private repository before: ! wall 0.393464 comb 0.390000 user 0.330000 sys 0.060000 (median of 25) after: ! wall 0.267711 comb 0.270000 user 0.210000 sys 0.060000 (median of 38)

perf: add a `clear-revlogs` flag to `perftags` This flag (on by default) makes it possible to disable the refresh of the changelog and revlog. This is useful to check for the time spent in the core tags logic without the associated side effects. Usually, these side effects are shared with other logics (eg: bookmarks). Example output in my Mercurial repository $ hg perftags ! wall 0.017919 comb 0.020000 user 0.020000 sys 0.000000 (best of 141) $ hg perftags --no-clear-revlogs ! wall 0.012982 comb 0.010000 user 0.010000 sys 0.000000 (best of 207)

perf: stop creating new revlog by hand in perftags It's better to let the repository logic create its own object. We now just clear the cache. New object will be automatically created from there.

revlog: update the documentation for `trim_endidx` The function role drifted since the function was commented.

revlog: properly detect corrupted revlog in `index_get_length` Pointed out by Yuya Nishihara.

perf: rename `perfhelper-tracecopies` to `perfhelper-pathcopies` The command it supports is called `perfpathcopies`. It seems better to align the names.

perf: add a docstring to `perfpathcopies` This will help people to find this command.