view rust/hg-cpython/src/dagops.rs @ 50979:4c5f6e95df84

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

// dagops.rs
//
// Copyright 2019 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.

//! Bindings for the `hg::dagops` module provided by the
//! `hg-core` package.
//!
//! From Python, this will be seen as `mercurial.rustext.dagop`
use crate::PyRevision;
use crate::{conversion::rev_pyiter_collect, exceptions::GraphError};
use cpython::{PyDict, PyModule, PyObject, PyResult, Python};
use hg::dagops;
use hg::Revision;
use std::collections::HashSet;
use vcsgraph::ancestors::node_rank;
use vcsgraph::graph::{Parents, Rank};

use crate::revlog::pyindex_to_graph;

/// Using the the `index`, return heads out of any Python iterable of Revisions
///
/// This is the Rust counterpart for `mercurial.dagop.headrevs`
pub fn headrevs(
    py: Python,
    index: PyObject,
    revs: PyObject,
) -> PyResult<HashSet<PyRevision>> {
    let index = pyindex_to_graph(py, index)?;
    let mut as_set: HashSet<Revision> = rev_pyiter_collect(py, &revs, &index)?;
    dagops::retain_heads(&index, &mut as_set)
        .map_err(|e| GraphError::pynew(py, e))?;
    Ok(as_set.into_iter().map(Into::into).collect())
}

/// Computes the rank, i.e. the number of ancestors including itself,
/// of a node represented by its parents.
pub fn rank(
    py: Python,
    index: PyObject,
    p1r: PyRevision,
    p2r: PyRevision,
) -> PyResult<Rank> {
    node_rank(&pyindex_to_graph(py, index)?, &Parents([p1r.0, p2r.0]))
        .map_err(|e| GraphError::pynew_from_vcsgraph(py, e))
}

/// Create the module, with `__package__` given from parent
pub fn init_module(py: Python, package: &str) -> PyResult<PyModule> {
    let dotted_name = &format!("{}.dagop", package);
    let m = PyModule::new(py, dotted_name)?;
    m.add(py, "__package__", package)?;
    m.add(py, "__doc__", "DAG operations - Rust implementation")?;
    m.add(
        py,
        "headrevs",
        py_fn!(py, headrevs(index: PyObject, revs: PyObject)),
    )?;
    m.add(
        py,
        "rank",
        py_fn!(py, rank(index: PyObject, p1r: PyRevision, p2r: PyRevision)),
    )?;

    let sys = PyModule::import(py, "sys")?;
    let sys_modules: PyDict = sys.get(py, "modules")?.extract(py)?;
    sys_modules.set_item(py, dotted_name, &m)?;
    // Example C code (see pyexpat.c and import.c) will "give away the
    // reference", but we won't because it will be consumed once the
    // Rust PyObject is dropped.
    Ok(m)
}