rust/hg-cpython/src/lib.rs

rust: make `Revision` a newtype

This change is the one we've been building towards during this series.
The aim is to make `Revision` mean more than a simple integer, holding
the information that it is valid for a given revlog index.
While this still allows for programmer error, since creating a revision
directly and querying a different index with a "checked" revision are
still possible, the friction created by the newtype will hopefully make
us think twice about which type to use.

Enough of the Rust ecosystem relies on the newtype pattern to be
efficiently optimized away (even compiler in codegen tests¹), so I'm not
worried about this being a fundamental problem.

[1] https://github.com/rust-lang/rust/blob/7a70647f195f6b0a0f1ebd72b1542ba91a32f43a/tests/codegen/vec-in-place.rs#L47

// lib.rs
//
// Copyright 2018 Georges Racinet <[e-mail]>
//
// This software may be used and distributed according to the terms of the
// GNU General Public License version 2 or any later version.

//! Python bindings of `hg-core` objects using the `cpython` crate.
//! Once compiled, the resulting single shared library object can be placed in
//! the `mercurial` package directly as `rustext.so` or `rustext.dll`.
//! It holds several modules, so that from the point of view of Python,
//! it behaves as the `cext` package.
//!
//! Example:
//!
//! ```text
//! >>> from mercurial.rustext import ancestor
//! >>> ancestor.__doc__
//! 'Generic DAG ancestor algorithms - Rust implementation'
//! ```
#![allow(clippy::too_many_arguments)] // rust-cpython macros
#![allow(clippy::zero_ptr)] // rust-cpython macros
#![allow(clippy::needless_update)] // rust-cpython macros
#![allow(clippy::manual_strip)] // rust-cpython macros
#![allow(clippy::type_complexity)] // rust-cpython macros

use cpython::{FromPyObject, PyInt, Python, ToPyObject};
use hg::{BaseRevision, Revision};

/// This crate uses nested private macros, `extern crate` is still needed in
/// 2018 edition.
#[macro_use]
extern crate cpython;

pub mod ancestors;
mod cindex;
mod conversion;
#[macro_use]
pub mod ref_sharing;
pub mod copy_tracing;
pub mod dagops;
pub mod debug;
pub mod dirstate;
pub mod discovery;
pub mod exceptions;
mod pybytes_deref;
pub mod revlog;
pub mod utils;

/// Revision as exposed to/from the Python layer.
///
/// We need this indirection because of the orphan rule, meaning we can't
/// implement a foreign trait (like [`cpython::ToPyObject`])
/// for a foreign type (like [`hg::UncheckedRevision`]).
///
/// This also acts as a deterrent against blindly trusting Python to send
/// us valid revision numbers.
#[derive(Debug, Copy, Clone, PartialEq, Eq, PartialOrd, Ord, Hash)]
pub struct PyRevision(BaseRevision);

impl From<Revision> for PyRevision {
    fn from(r: Revision) -> Self {
        PyRevision(r.0)
    }
}

impl<'s> FromPyObject<'s> for PyRevision {
    fn extract(
        py: Python,
        obj: &'s cpython::PyObject,
    ) -> cpython::PyResult<Self> {
        Ok(Self(obj.extract::<BaseRevision>(py)?))
    }
}

impl ToPyObject for PyRevision {
    type ObjectType = PyInt;

    fn to_py_object(&self, py: Python) -> Self::ObjectType {
        self.0.to_py_object(py)
    }
}

py_module_initializer!(rustext, initrustext, PyInit_rustext, |py, m| {
    m.add(
        py,
        "__doc__",
        "Mercurial core concepts - Rust implementation",
    )?;

    let dotted_name: String = m.get(py, "__name__")?.extract(py)?;
    m.add(py, "ancestor", ancestors::init_module(py, &dotted_name)?)?;
    m.add(py, "dagop", dagops::init_module(py, &dotted_name)?)?;
    m.add(py, "debug", debug::init_module(py, &dotted_name)?)?;
    m.add(
        py,
        "copy_tracing",
        copy_tracing::init_module(py, &dotted_name)?,
    )?;
    m.add(py, "discovery", discovery::init_module(py, &dotted_name)?)?;
    m.add(py, "dirstate", dirstate::init_module(py, &dotted_name)?)?;
    m.add(py, "revlog", revlog::init_module(py, &dotted_name)?)?;
    m.add(py, "GraphError", py.get_type::<exceptions::GraphError>())?;
    Ok(())
});

#[cfg(not(feature = "python3-bin"))]
#[test]
#[ignore]
fn libpython_must_be_linked_to_run_tests() {
    // stub function to tell that some tests wouldn't run
}