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

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

Using Rust code

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

  $ make PURE=--rust local # to use ./hg

  $ ./tests/run-tests.py --rust # to run all tests

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

  checking Rust extensions (installed)

  checking "re2" regexp engine Rust bindings (installed)

If the environment variable ``HGWITHRUSTEXT=cpython`` is set, the Rust

extension will be used by default unless ``--no-rust``.

One day we may use this environment variable to switch to new experimental

binding crates like a hypothetical ``HGWITHRUSTEXT=hpy``.

Using the full ``hg status`` extension

--------------------------------------

The code for ``hg status`` needs to conform to ``.hgignore`` rules, which are

all translated into regex. For compatibility and ease of development reasons

the Re2 regex engine is in use until we figure out if the ``regex`` crate has

similar enough behavior. This implies that you need to install ``Re2``

following Google's guidelines: https://github.com/google/re2/wiki/Install

Then, use ``HG_RUST_FEATURES=with-re2`` when building ``hg`` to use the full

status code.

Developing Rust

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

The current version of Rust in use is ``1.34.2``, because it's what Debian

stable has. You can use ``rustup override set 1.34.2`` at the root of the repo

to make it easier on you.

Go to the ``hg-cpython`` folder::

  $ cd rust/hg-cpython

Or, only the ``hg-core`` folder. Be careful not to break compatibility::

  $ cd rust/hg-core

For even faster typing::

  $ cargo c

Formatting the code

-------------------

We use ``rustfmt`` to keep the code formatted at all times. For now, we are

using the nightly version because it has been stable enough and provides

comment folding.

To format the entire Rust workspace::

  $ cargo +nightly fmt

This requires you to have the nightly toolchain installed.

Additional features

-------------------

As mentioned in the section about ``hg status``, code paths using ``re2`` are

opt-in.

For example::

  $ cargo check --features with-re2