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rust-index: using the `hg::index::Index` in ancestors iterator and lazy set...
rust-index: using the `hg::index::Index` in ancestors iterator and lazy set Since there is no Rust implementation for REVLOGV2/CHANGELOGv2, we declare them to be incompatible with Rust, hence indexes in these formats will use the implementations from Python `mercurial.ancestor`. If this is an unacceptable performance hit for current users of these formats, we can later on add Rust implementations based on the C index for them or implement these formats for the Rust indexes. Among the challenges that we had to meet, we wanted to avoid taking the GIL each time the inner (vcsgraph) iterator has to call the parents function. This would probably still be acceptable in terms of performance with `AncestorsIterator`, but not with `LazyAncestors` nor for the upcoming change in `MissingAncestors`. Hence we enclose the reference to the index in a `PySharedRef`, leading to more rigourous checking of mutations, which does pass now that there no logically immutable methods of `hg::index::Index` that take a mutable reference as input.
Georges Racinet -
r52132:7eea2e41 default
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rhg

The rhg executable implements a subset of the functionnality of hg
using only Rust, to avoid the startup cost of a Python interpreter.
This subset is initially small but grows over time as rhg is improved.
When fallback to the Python implementation is configured (see below),
rhg aims to be a drop-in replacement for hg that should behave the same,
except that some commands run faster.

Building

To compile rhg, either run cargo build --release from this rust/rhg/
directory, or run make build-rhg from the repository root.
The executable can then be found at rust/target/release/rhg.

Mercurial configuration

rhg reads Mercurial configuration from the usual sources:
the user’s ~/.hgrc, a repository’s .hg/hgrc, command line --config, etc.
It has some specific configuration in the [rhg] section.

See hg help config.rhg for details.

Installation and configuration example

For example, to install rhg as hg for the current user with fallback to
the system-wide install of Mercurial, and allow it to run even though the
rebase and absorb extensions are enabled, on a Unix-like platform:

  • Build rhg (see above)
  • Make sure the ~/.local/bin exists and is in $PATH
  • From the repository root, make a symbolic link with
    ln -s rust/target/release/rhg ~/.local/bin/hg
  • Configure ~/.hgrc with:
[rhg]
on-unsupported = fallback
fallback-executable = /usr/bin/hg
allowed-extensions = rebase, absorb

  • Check that the output of running
    hg notarealsubcommand
    starts with hg: unknown command, which indicates fallback.

  • Check that the output of running
    hg notarealsubcommand --config rhg.on-unsupported=abort
    starts with unsupported feature:.