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rust-2018: switch hg-core and hg-cpython to rust 2018 edition...
rust-2018: switch hg-core and hg-cpython to rust 2018 edition Many interesting changes have happened in Rust since the Oxidation Plan was introduced, like the 2018 edition and procedural macros: - Opting in to the 2018 edition is a clear benefit in terms of future proofing, new (nice to have) syntactical sugar notwithstanding. It also has a new non-lexical, non-AST based borrow checker that has fewer bugs(!) and allows us to write correct code that in some cases would have been rejected by the old one. - Procedural macros allow us to use the PyO3 crate which maintainers have expressed the clear goal of compiling on stable, which would help in code maintainability compared to rust-cpython. In this patch are the following changes: - Removing most `extern crate` uses - Updating `use` clauses (`crate` keyword, nested `use`) - Removing `mod.rs` in favor of an aptly named module file Like discussed in the mailing list ( https://www.mercurial-scm.org/pipermail/mercurial-devel/2019-July/132316.html ), until Rust integration in Mercurial is considered to be out of the experimental phase, the maximum version of Rust allowed is whatever the latest version Debian packages. Differential Revision: https://phab.mercurial-scm.org/D6597
Raphaël Gomès -
r42815:988cf984 default
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Mercurial Rust Code

This directory contains various Rust code for the Mercurial project.

The top-level Cargo.toml file defines a workspace containing all primary Mercurial crates.

Building

To build the Rust components:

$ cargo build

If you prefer a non-debug / release configuration:

$ cargo build --release

Features

The following Cargo features are available:

localdev (default)

Produce files that work with an in-source-tree build.

In this mode, the build finds and uses a python2.7 binary from PATH. The hg binary assumes it runs from rust/target/<target>hg and it finds Mercurial files at dirname($0)/../../../.

Build Mechanism

The produced hg binary is bound to a CPython installation. The binary links against and loads a CPython library that is discovered at build time (by a build.rs Cargo build script). The Python standard library defined by this CPython installation is also used.

Finding the appropriate CPython installation to use is done by the python27-sys crate's build.rs. Its search order is:

  1. PYTHON_SYS_EXECUTABLE environment variable.
  2. python executable on PATH
  3. python2 executable on PATH
  4. python2.7 executable on PATH

Additional verification of the found Python will be performed by our build.rs to ensure it meets Mercurial's requirements.

Details about the build-time configured Python are built into the produced hg binary. This means that a built hg binary is only suitable for a specific, well-defined role. These roles are controlled by Cargo features (see above).

Running

The hgcli crate produces an hg binary. You can run this binary via cargo run:

$ cargo run --manifest-path hgcli/Cargo.toml

Or directly:

$ target/debug/hg
$ target/release/hg

You can also run the test harness with this binary:

$ ./run-tests.py --with-hg ../rust/target/debug/hg

Note

Integration with the test harness is still preliminary. Remember to cargo build after changes because the test harness doesn't yet automatically build Rust code.