discovery: move common heads computation inside partialdiscovery object This remove one of the private attribute access. In additions, head tracking and computation is a typical operation we can speed up using Rust.

discovery: introduce a partialdiscovery object This object will ultimately gather the data about common, undecided and missing revs in a single place and deal with most graph related computations. The goal is both to clarify the algorithm and to help provides a simple and clear API that can be reimplemented in Rust. For now, we only moved the `common` set in the object. In this commit, some direct access to the "private" `disco._common` attribute persist. They have not been removed yet because we won't need to expose a full API identical to `incrementalmissingancestors` and it seems simpler to access the attribute directly until the replacement is in place.

discovery: move handling of sampling special case inside sampling function The handling of cases where the number of revisions to sample is smaller than the sample size can be moved with the sample function themselves. This simplifies main logic, preparing a coming refactoring.

discovery: minor fix to some conditionals Since `size` is the upper limit of the sample, we should include it in the check. Otherwize the `more` variable will be zero and the sampling will be useless

delta: reuse _findsnapshot call from previous stage Two different stage of the sparse-revlog logic needs the _findsnapshot data. To avoid recomputing it twice, make it possible to reuse the first computation in the second step. example affected manifest write before: 0.067141s after: 0.064252s (-5%) (total gain since start of series: 95%)

delta: have a native implementation of _findsnapshot The function might traverse a lot of revision, a native implementation get significantly faster. example affected manifest write before: 0.114989 after: 0.067141 (-42%)

transaction: do not overwrite atomic-temp files on error Even though the original files can be restored from the backup, it should be better to not write back a temporary file if we know it can be corrupted.

help: fix typo

rust: use 'impl Trait' in method argument of AncestorsIterator I just didn't know it's stabilized. Let's switch to new convenient syntax. Differential Revision: https://phab.mercurial-scm.org/D5451

rust: use .rev() for reverse range Differential Revision: https://phab.mercurial-scm.org/D5450

histedit: add warning message on editing tagged commits (issue4017) Differential Revision: https://phab.mercurial-scm.org/D5489

strip: extract bookmark movement into a separate function We will need it for the soft-strip case.

strip: compute bookmark target only if we have bookmark to move This is a small change that seems to make sense.

strip: extract code to create strip backup We will reuse this for soft stripping.

strip: clarify comment around bundle create We may create two bundles, one for the changeset actually stripped, and one for the changeset affected by the strip we want to keep. (Changesets with a higher rev number than the striped ones). For soft stripping, we still need to the first one (used for "restoring" the changesets), but not the second one. We start with clarifying which bits of the code is used for what.

strip: move attributes shortcut assigned earlier This series will add support for "soft" stripping using the archived phase in addition to the usual heavy weight revlog stripping. First, we need to refactor the strip function to extract logic common to the "soft-strip" case. We are about to extract bits of the strip function into separate functions. Those blocks of code contain variables for frequently accessed attributes. We move those variables outside of the soon to be moved blocks.

log: fix line wrap on diffstat with -G/--graph (issue5800) Differential Revision: https://phab.mercurial-scm.org/D5485

registrar: minor cleanup to the merge function Pointed out by Yuya.

vfs: raise NotImplementedError in abstractvfs._auditvfs This make sure that auditing is implemented.

vfs: handle _auditpath in proxyvfs Just forward the call to the underlying vfs.

vfs: fix proxyvfs inheritance The proxyvfs class is designed to overwrite some of the vfs logic. Yet, it did not use normal class inheritance. This is becoming an issue as `abstractvfs` method could take precedence over their `proxyvfs` version. We fix the inheritance chain to be as expected.

vfs: also audit rename Renaming through the vfs is not used in many places, and none of them seems to be a security risk. However, it is still worthwhile to run the auditing on rename file to perform developer-warning level checks.

vfs: add a `_auditpath` to abstract vfs We are about to make `rename` audit path. Since rename lives in the `abstractvfs` layer, we need it to be aware of auditing to some extent. The default implementation is no-op because multiple existing vfs are not using auditing at all right now (eg: fncachevfs).

vfs: makes all audited path relative Only auditing relative path helps the vfs warning logic.

debugupgraderepo: add a --no-backup mode The process has been around for a while and is pretty safe now. Having an automated way to clean up the old data is useful when running many different conversion to compare delta algorithm.

upgrade: add '-' in optimization name The older name `redeltaall` was hard to type and read. The newer form should be more user-friendly. We keep backward compatibility with the old form (at least for a while). Having to use different form depending on the version is very impractical and error prone.

revlog: add test case for _findsnapshots Testing the method directly is more robust.

revlog: use the native implementation of issnapshot In some sparserevlog case where a lot of the history has to be searched for a snapshot, the cost of issnashot cost becomes significant. The computation done by the method is fairly low level, a native implementation provide a very significant speedup. example affected manifest write before: 0.490375s after: 0.114989s (-76%)

revlog: add a native implementation of issnapshot This will be used in the next changesets

revlog: more efficient implementation for issnapshot We avoid multiple method calls and tuple creation, this provides a significant speedup in some case: example affected manifest write before: 0.815520s after: 0.487767s (-40%)