view rust/hgcli/README.md @ 50423:b88e9c707c95

rust: configure MSRV in Clippy

This setting makes Clippy never apply lints that are meant for
later versions. In case the target precise toolchain is the one
running, it does not make a difference, but this gives us a
machine-parseable specification that is pretty standard.

The README and `hg help rust` are updated to state that `clippy.toml`
is the single source of truth about that, also lifting a minor ambiguity:
it is fine if the MSRV is lagging behind the version in Debian testing.

# Oxidized Mercurial

This project provides a Rust implementation of the Mercurial (`hg`)
version control tool.

Under the hood, the project uses
[PyOxidizer](https://github.com/indygreg/PyOxidizer) to embed a Python
interpreter in a binary built with Rust. At run-time, the Rust `fn main()`
is called and Rust code handles initial process startup. An in-process
Python interpreter is started (if needed) to provide additional
functionality.

# Building

First, acquire and build a copy of PyOxidizer; you probably want to do this in
some directory outside of your clone of Mercurial:

    $ git clone https://github.com/indygreg/PyOxidizer.git
    $ cd PyOxidizer
    $ cargo build --release

Then build this Rust project using the built `pyoxidizer` executable:

    $ /path/to/pyoxidizer/target/release/pyoxidizer build --release

If all goes according to plan, there should be an assembled application
under `build/<arch>/release/app/` with an `hg` executable:

    $ build/x86_64-unknown-linux-gnu/release/app/hg version
    Mercurial Distributed SCM (version 5.3.1+433-f99cd77d53dc+20200331)
    (see https://mercurial-scm.org for more information)

    Copyright (C) 2005-2020 Olivia Mackall and others
    This is free software; see the source for copying conditions. There is NO
    warranty; not even for MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.

# Running Tests

To run tests with a built `hg` executable, you can use the `--with-hg`
argument to `run-tests.py`. But there's a wrinkle: many tests run custom
Python scripts that need to `import` modules provided by Mercurial. Since
these modules are embedded in the produced `hg` executable, a regular
Python interpreter can't access them! To work around this, set `PYTHONPATH`
to the Mercurial source directory. e.g.:

    $ cd /path/to/hg/src/tests
    $ PYTHONPATH=`pwd`/.. python3.9 run-tests.py \
        --with-hg `pwd`/../rust/hgcli/build/x86_64-unknown-linux-gnu/release/app/hg