view rust/hg-cpython/src/dagops.rs @ 51239:7eea2e4109ae

rust-index: using the `hg::index::Index` in ancestors iterator and lazy set

Since there is no Rust implementation for REVLOGV2/CHANGELOGv2, we declare
them to be incompatible with Rust, hence indexes in these formats will use
the implementations from Python `mercurial.ancestor`. If this is an unacceptable
performance hit for current users of these formats, we can later on add Rust
implementations based on the C index for them or implement these formats for
the Rust indexes.

Among the challenges that we had to meet, we wanted to avoid taking the GIL each
time the inner (vcsgraph) iterator has to call the parents function. This would probably
still be acceptable in terms of performance with `AncestorsIterator`, but not with
`LazyAncestors` nor for the upcoming change in `MissingAncestors`.

Hence we enclose the reference to the index in a `PySharedRef`, leading to more
rigourous checking of mutations, which does pass now that there no logically immutable
methods of `hg::index::Index` that take a mutable reference as input.

// 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)
}