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discovery: introduce a partialdiscovery object...
discovery: introduce a partialdiscovery object This object will ultimately gather the data about common, undecided and missing revs in a single place and deal with most graph related computations. The goal is both to clarify the algorithm and to help provides a simple and clear API that can be reimplemented in Rust. For now, we only moved the `common` set in the object. In this commit, some direct access to the "private" `disco._common` attribute persist. They have not been removed yet because we won't need to expose a full API identical to `incrementalmissingancestors` and it seems simpler to access the attribute directly until the replacement is in place.

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README.rst
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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.