rust: new rust options in setup.py The --rust global option turns on usage (and by default compilation) of the rust-cpython based mercurial.rustext. Similarly to what's previously done for zstd, there is a --no-rust option for the build_ext subcommand in order not to build mercurial.rustext, allowing for an OS distribution to prebuild it. The HGWITHRUSTEXT environment variable is still honored, and has the same effect as before, but now it works mostly by making the --rust global option defaulting to True, with some special cases for the direct-ffi case (see more about that below) Coincidentally, the --rust flag can also be passed from the make commands, like actually all global options, in the PURE variable make local PURE=--rust This feels inappropriate, though, and we should follow up with a proper make variable for that case. Although the direct-ffi bindings aren't directly useful any more, we keep them at this stage because - they provide a short prototyping path for experiments in which a C extension module has to call into a Rust extension. The proper way of doing that would be to use capsules, and it's best to wait for our pull request onto rust-cpython for that: https://github.com/dgrunwald/rust-cpython/pull/169 - Build support for capsules defined in Rust will probably need to reuse some of what's currently in use for direct-ffi.

rust: using policy.importrust from Python callers This commit converts all current Python callers of mercurial.rustext to the new policy.importrust system. After this point, going through policy.importrust or policy.importmod (in some more distant future) is mandatory for callers of Rust code outside of Python tests. We felt it to be appropriate to keep Rust-specific tests run inconditionally if the Rust extensions are present.

rust: module policy with importrust We introduce two rust+c module policies and a new `policy.importrust()` that makes use of them. This simple approach provides runtime switching of implementations, which is crucial for the performance measurements such as those Octobus does with ASV. It can also be useful for bug analysis. It also has the advantage of making conditionals in Rust callers more uniform, in particular abstracting over specifics like `demandimport` At this point, the build stays unchanged, with the rust-cpython based `rustext` module being built if HGWITHRUSTEXT=cpython. More transparency for the callers, i.e., just using `policy.importmod` would be a much longer term and riskier effort for the following reasons: 1. It would require to define common module boundaries for the three or four cases (pure, c, rust+ext, cffi) and that is premature with the Rust extension currently under heavy development in areas that are outside the scope of the C extensions. 2. It would imply internal API changes that are not currently wished, as the case of ancestors demonstrates. 3. The lack of data or property-like attributes (tp_member and tp_getset) in current `rust-cpython` makes it impossible to achieve direct transparent replacement of pure Python classes by Rust extension code, meaning that the caller sometimes has to be able to make adjustments or provide additional wrapping.

help: add help entry for internals.mergestate This patch adds an entry for `internals.mergestate` as suggested by @marmoute. Most of the help text is taken from `merge.mergestate`. Differential Revision: https://phab.mercurial-scm.org/D6448 Differential Revision: https://phab.mercurial-scm.org/D6528

phabricator: use parents.set to always set dependencies Now that Mercurial's Phabricator instance has been updated to a version that supports the parents.set transaction on revision.edit we can use that to set dependency relationships in patch stacks instead of abusing the summary. This has the advantage that we can use it on every `phabsend` so commit reordering is picked up without spamming changes like abusing the summary would, and using parents.set will clear previous parents unlike parents.add. Differential Revision: https://phab.mercurial-scm.org/D6514

help: remove repeated word in 'hg help rebase' Specifically, the second 'with' in 'with which to merge with'. Differential Revision: https://phab.mercurial-scm.org/D6483

rebase: tweak description of inmemory working even w/ dirty working dir One of our users was confused because they read this, and then attempted to run `hg rebase` with a dirty working directory, and it still complained. The reason was that they were attempting to rebase the commit they currently had checked out, which (at least with evolve workflows enabled) involves updating the working directory to be based on the newly rebased commit. Differential Revision: https://phab.mercurial-scm.org/D6507

revlog: speed up isancestor Currently, it is implemented on top of commonancestorsheads. Implement it on top of reachableroots instead, as reachableroots could stop walking the graph much sooner than commonancestorsheads. Measuring repo.changelog.isancestorrev on two revisions in a private repository: before: ! wall 0.005175 comb 0.010000 user 0.010000 sys 0.000000 (best of 550) after : ! wall 0.000072 comb 0.000000 user 0.000000 sys 0.000000 (best of 36199) When hg does this kind of operations 1500 times in pull -> bookmarks.comparebookmarks -> bookmarks.validdest, that's 11s that drop from the --profile output. Differential Revision: https://phab.mercurial-scm.org/D6506

dagop: fix documentation of reachableroots The previous revset couldn't be correct as it is symmetric in <roots> and <heads>, but reachableroots has no such symmetry. It makes a difference with for instance reachableroots(2, 3) where 2 and 3 are both children of 1. Differential Revision: https://phab.mercurial-scm.org/D6505

phabricator: add --blocker argument to phabsend to specify blocking reviewers The way to signal to Conduit that a reviewer is considered blocking is just to wrap their PHID in "blocking()" when including it in the list of PHIDs passed to `reviewers.add`. arc doesn't have a --blocker, instead one is supposed to append a '!' to the end of reviewer names (I think reviewers are usually added in an editor rather than the command line, where '!'s can be more hazardous). moz-phab (Mozilla's arcanist wrapper) does have a --blocker argument, and being explicit like this is also more discoverable. Even `arc diff`'s help doesn't seem to mention the reviewer! syntax. Differential Revision: https://phab.mercurial-scm.org/D6512