Rust is not required to use (or build) Mercurial, but using it

improves performance in some areas.

There are currently three independent rust projects:

- chg. An implementation of chg, in rust instead of C.

- hgcli. A experiment for starting hg in rust rather than in python,

  by linking with the python runtime. Probably meant to be replaced by

  PyOxidizer at some point.

- hg-core (and hg-cpython/hg-directffi): implementation of some

  functionality of mercurial in rust, e.g. ancestry computations in

  revision graphs or pull discovery. The top-level ``Cargo.toml`` file

  defines a workspace containing these crates.

Using hg-core

=============

Local use (you need to clean previous build artifacts if you have

built without rust previously)::

  $ HGWITHRUSTEXT=cpython make local # to use ./hg

  $ HGWITHRUSTEXT=cpython make tests # to run all tests

  $ (cd tests; HGWITHRUSTEXT=cpython ./run-tests.py) # only the .t

  $ ./hg debuginstall | grep rust # to validate rust is in use

  checking module policy (rust+c-allow)

Setting ``HGWITHRUSTEXT`` to other values like ``true`` is deprecated

and enables only a fraction of the rust code.

Developing hg-core

==================

Simply run::

It is possible to build without ``--release``, but it is not

recommended if performance is of any interest: there can be an order

of magnitude of degradation when removing ``--release``.

For faster builds, you may want to skip code generation::

  $ cargo check

You can run only the rust-specific tests (as opposed to tests of

mercurial as a whole) with::

  $ cargo test --all