view rust/README.rst @ 44426:66a05dbb8b4c

phabricator: don't infer the old `fctx` in `notutf8()`

This is used along with `fctx.isbinary()` to gate `addoldbinary()`, so it seems
like a good idea to provide the caller similar control over the current and
parent filecontext.  Unlike `addoldbinary()`, it doesn't need both previous and
current contexts at the same time, so make the caller responsible for testing
both cases, as appropriate.  I haven't worked out all of the problems around
marking files as binary for move/remove/copy, but this will definitely help with
`--no-stack` too.

It also turns out to have been doing too much- in the remove case, it tested not
just the removed file in the parent context (which is what gets passed in that
case), but also in the parent of the parent context (which should be
irrelevant).  The previous code also required the `fctx.parents()` check to work
in the add (but without rename) case.  Now the add and remove cases test only
what they need to.  But now that it is written this way, the fact that only the
current `fctx` is checked to be binary in the case of modification or being
renamed seems wrong.

Differential Revision: https://phab.mercurial-scm.org/D8220

===================
Mercurial Rust Code
===================

This directory contains various Rust code for the Mercurial project.
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::

   $ cargo build --release

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