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revlog-native: introduced ABI version in capsule...
revlog-native: introduced ABI version in capsule Concerns that an inconsistency could arise between the actual contents of the capsule in revlog.c and the Rust consumer have been raised after the switch to the array of data and function pointers in f384d68d8ea8. It has been suggested that the `version` from parsers.c could be use for this. In this change, we introduce instead a separate ABI version number, which should have the following advantages: - no need to change the consuming Rust code for changes that have nothing to do with the contents of the capsule - the version number in parsers.c is not explicitely flagged as ABI. It's not obvious to me whether an ABI change that would be invisible to Python would warrant an increment The drawback is that developers now have to consider two version numbers. We expect the added cost of the check to be negligible because it occurs at instantiation of `CIndex` only, which in turn is tied to instantiation of Python objects such as `LazyAncestors` and `MixedIndex`. Frequent calls to `Cindex::new` should also probably hit the CPU branch predictor. Differential Revision: https://phab.mercurial-scm.org/D7856
Georges Racinet -
r44523:f5d2720f 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.