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  1. Oct 01, 2020
    • Martin von Zweigbergk's avatar
      rust: move rustfmt.toml to repo root so it can be used by `hg fix` · 426294d06ddc
      Martin von Zweigbergk authored
      `hg fix` runs the formatters from the repo root so it doesn't pick up
      the `rustfmt.toml` configs we had in each the `hg-core`, `hg-cpython`,
      and `rhg` packages, which resulted in warnings about `async fn` not
      existing in Rust 2015. This patch moves the `rustfmt.toml` file to the
      root so `hg fix` will use it.
      
      By putting the `rustfmt.toml` file in a higher-level directory, it
      also applies to the `chg` and `hgcli` packages. That makes
      `test-check-rust-format.t` fail, so this patch also applies the new
      formatting rules to those packages.
      
      Differential Revision: https://phab.mercurial-scm.org/D9142
      426294d06ddc
  2. Apr 16, 2020
  3. Apr 01, 2020
    • Gregory Szorc's avatar
      hgcli: add stub PyOxidizer project · af739894a4c1
      Gregory Szorc authored
      Using commit c772a1379c3026314eda1c8ea244b86c0658951d of
      PyOxidizer, I ran `pyoxidizer init-rust-project hgcli` to
      create a stub Rust project. The only modifications I made from
      what that command produced are:
      
      * Update location of pyembed crate to PyOxidizer's Git repository.
      * Removed some trailing whitespace from pyoxidizer.bzl
      * Added auto-generated Cargo.lock file
      
      Subsequent commits will modify the stub project to Mercurial's
      needs.
      
      Differential Revision: https://phab.mercurial-scm.org/D8350
      af739894a4c1
  4. Dec 07, 2019
  5. Jan 11, 2018
  6. Jan 10, 2018
    • Gregory Szorc's avatar
      rust: implementation of `hg` · 964212780daf
      Gregory Szorc authored
      This commit provides a mostly-working implementation of the
      `hg` script in Rust along with scaffolding to support Rust in
      the repository.
      
      If you are familiar with Rust, the contents of the added rust/
      directory should be pretty straightforward. We create an "hgcli"
      package that implements a binary application to run Mercurial.
      The output of this package is an "hg" binary.
      
      Our Rust `hg` (henceforth "rhg") essentially is a port of the existing
      `hg` Python script. The main difference is the creation of the embedded
      CPython interpreter is handled by the binary itself instead of relying
      on the shebang. In that sense, rhg is more similar to the "exe wrapper"
      we currently use on Windows. However, unlike the exe wrapper, rhg does
      not call the `hg` Python script. Instead, it uses the CPython APIs to
      import mercurial modules and call appropriate functions. The amount of
      code here is surprisingly small.
      
      It is my intent to replace the existing C-based exe wrapper with rhg.
      Preferably in the next Mercurial release. This should be achievable -
      at least for some Mercurial distributions. The future/timeline for
      rhg on other platforms is less clear. We already ship a hg.exe on
      Windows. So if we get the quirks with Rust worked out, shipping a
      Rust-based hg.exe should hopefully not be too contentious.
      
      Now onto the implementation.
      
      We're using python27-sys and the cpython crates for talking to the
      CPython API. We currently don't use too much functionality of the
      cpython crate and could have probably cut it out. However, it does
      provide a reasonable abstraction over unsafe {} CPython function
      calls. While we still have our fair share of those, at least we're
      not dealing with too much refcounting, error checking, etc. So I
      think the use of the cpython crate is justified. Plus, there is
      not-yet-implemented functionality that could benefit from cpython. I
      see our use of this crate only increasing.
      
      The cpython and python27-sys crates are not without their issues.
      The cpython crate didn't seem to account for the embedding use case
      in its design. Instead, it seems to assume that you are building
      a Python extension. It is making some questionable decisions around
      certain CPython APIs. For example, it insists that
      PyEval_ThreadsInitialized() is called and that the Python code
      likely isn't the main thread in the underlying application. It
      is also missing some functionality that is important for embedded
      use cases (such as exporting the path to the Python interpreter
      from its build script). After spending several hours trying to
      wrangle python27-sys and cpython, I gave up and forked the project
      on GitHub. Our Cargo.toml tracks this fork. I'm optimistic that
      the upstream project will accept our contributions and we can
      eventually unfork.
      
      There is a non-trivial amount of code in our custom Cargo build
      script. Our build.rs (which is called as part of building the hgcli
      crate):
      
      * Validates that the Python interpreter that was detected by the
        python27-sys crate provides a shared library (we only support
        shared library linking at this time - although this restriction
        could be loosened).
      * Validates that the Python is built with UCS-4 support. This ensures
        maximum Unicode compatibility.
      * Exports variables to the crate build allowing the built crate to e.g.
        find the path to the Python interpreter.
      
      The produced rhg should be considered alpha quality. There are several
      known deficiencies. Many of these are documented with inline TODOs.
      
      Probably the biggest limitation of rhg is that it assumes it is
      running from the ./rust/target/<target> directory of a source
      distribution. So, rhg is currently not very practical for real-world
      use. But, if you can `cargo build` it, running the binary *should*
      yield a working Mercurial CLI.
      
      In order to support using rhg with the test harness, we needed to hack
      up run-tests.py so the path to Mercurial's Python files is set properly.
      The change is extremely hacky and is only intended to be a stop-gap
      until the test harness gains first-class support for installing rhg.
      This will likely occur after we support running rhg outside the
      source directory.
      
      Despite its officially alpha quality, rhg copes extremely well with
      the test harness (at least on Linux). Using
      `run-tests.py --with-hg ../rust/target/debug/hg`, I only encounter
      the following failures:
      
      * test-run-tests.t -- Warnings emitted about using an unexpected
        Mercurial library. This is due to the hacky nature of setting the
        Python directory when run-tests.py detected rhg.
      * test-devel-warnings.t -- Expected stack trace missing frame for `hg`
        (This is expected since we no longer have an `hg` script!)
      * test-convert.t -- Test running `$PYTHON "$BINDIR"/hg`, which obviously
        assumes `hg` is a Python script.
      * test-merge-tools.t -- Same assumption about `hg` being executable with
        Python.
      * test-http-bad-server.t -- Seeing exit code 255 instead of 1 around
        line 358.
      * test-blackbox.t -- Exit code 255 instead of 1.
      * test-basic.t -- Exit code 255 instead of 1.
      
      It certainly looks like we have a bug around exit code handling. I
      don't think it is severe enough to hold up review and landing of this
      initial implementation. Perfect is the enemy of good.
      
      Differential Revision: https://phab.mercurial-scm.org/D1581
      964212780daf
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