rust: hooking into Python code
We introduce a new class called 'rustlazyancestors'
in the ancestors module, which is used only if
parsers.rustlazyancestors does exist.
The implementation of __contains__ stays unchanged,
but is now backed by the Rust iterator. It would
probably be a good candidate for further development,
though, as it is mostly looping, and duplicates the
'seen' set.
The Rust code could be further optimized, however it already
gives rise to performance improvements:
median timing from hg perfancestors:
- on pypy:
before: 0.077566s
after: 0.016676s -79%
- on mozilla central:
before: 0.190037s
after: 0.082225s -58%
- on a private repository (about one million revisions):
before: 0.567085s
after: 0.108816s -80%
- on another private repository (about 400 000 revisions):
before: 1.440918s
after: 0.290116s -80%
median timing for hg perfbranchmap base
- on pypy:
before: 1.383413s
after: 0.507993s -63%
- on mozilla central:
before: 2.821940s
after: 1.258902s -55%
- on a private repository (about one million revisions):
before: 77.065076s
after: 16.158475s -80%
- on another private repository (about 401 000 revisions):
before: 7.835503s
after: 3.545331s -54%
===================
Mercurial Rust Code
===================
This directory contains various Rust code for the Mercurial project.
The top-level ``Cargo.toml`` file defines a workspace containing
all primary Mercurial crates.
Building
========
To build the Rust components::
$ cargo build
If you prefer a non-debug / release configuration::
$ cargo build --release
Features
--------
The following Cargo features are available:
localdev (default)
Produce files that work with an in-source-tree build.
In this mode, the build finds and uses a ``python2.7`` binary from
``PATH``. The ``hg`` binary assumes it runs from ``rust/target/<target>hg``
and it finds Mercurial files at ``dirname($0)/../../../``.
Build Mechanism
---------------
The produced ``hg`` binary is *bound* to a CPython installation. The
binary links against and loads a CPython library that is discovered
at build time (by a ``build.rs`` Cargo build script). The Python
standard library defined by this CPython installation is also used.
Finding the appropriate CPython installation to use is done by
the ``python27-sys`` crate's ``build.rs``. Its search order is::
1. ``PYTHON_SYS_EXECUTABLE`` environment variable.
2. ``python`` executable on ``PATH``
3. ``python2`` executable on ``PATH``
4. ``python2.7`` executable on ``PATH``
Additional verification of the found Python will be performed by our
``build.rs`` to ensure it meets Mercurial's requirements.
Details about the build-time configured Python are built into the
produced ``hg`` binary. This means that a built ``hg`` binary is only
suitable for a specific, well-defined role. These roles are controlled
by Cargo features (see above).
Running
=======
The ``hgcli`` crate produces an ``hg`` binary. You can run this binary
via ``cargo run``::
$ cargo run --manifest-path hgcli/Cargo.toml
Or directly::
$ target/debug/hg
$ target/release/hg
You can also run the test harness with this binary::
$ ./run-tests.py --with-hg ../rust/target/debug/hg
.. note::
Integration with the test harness is still preliminary. Remember to
``cargo build`` after changes because the test harness doesn't yet
automatically build Rust code.