annotate rust/hg-cpython/src/ancestors.rs @ 51260:7eea2e4109ae

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.

// ancestors.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.

//! Bindings for the `hg::ancestors` module provided by the
//! `hg-core` crate. From Python, this will be seen as `rustext.ancestor`
//! and can be used as replacement for the the pure `ancestor` Python module.
//!
//! # Classes visible from Python:
//! - [`LazyAncestors`] is the Rust implementation of
//!   `mercurial.ancestor.lazyancestors`. The only difference is that it is
//!   instantiated with a C `parsers.index` instance instead of a parents
//!   function.
//!
//! - [`MissingAncestors`] is the Rust implementation of
//!   `mercurial.ancestor.incrementalmissingancestors`.
//!
//!   API differences:
//!    + it is instantiated with a C `parsers.index`
//!      instance instead of a parents function.
//!    + `MissingAncestors.bases` is a method returning a tuple instead of
//!      a set-valued attribute. We could return a Python set easily if our
//!      [PySet PR](https://github.com/dgrunwald/rust-cpython/pull/165)
//!      is accepted.
//!
//! - [`AncestorsIterator`] is the Rust counterpart of the
//!   `ancestor._lazyancestorsiter` Python generator. From Python, instances of
//!   this should be mainly obtained by calling `iter()` on a [`LazyAncestors`]
//!   instance.
//!
//! [`LazyAncestors`]: struct.LazyAncestors.html
//! [`MissingAncestors`]: struct.MissingAncestors.html
//! [`AncestorsIterator`]: struct.AncestorsIterator.html
use crate::revlog::{py_rust_index_to_graph, pyindex_to_graph};
use crate::PyRevision;
use crate::{
    cindex::Index, conversion::rev_pyiter_collect, exceptions::GraphError,
    revlog::PySharedIndex,
};
use cpython::{
    ObjectProtocol, PyClone, PyDict, PyErr, PyList, PyModule, PyObject,
    PyResult, Python, PythonObject, ToPyObject, UnsafePyLeaked,
};

use hg::MissingAncestors as CoreMissing;
use hg::Revision;
use std::cell::RefCell;
use std::collections::HashSet;
use vcsgraph::lazy_ancestors::{
    AncestorsIterator as VCGAncestorsIterator,
    LazyAncestors as VCGLazyAncestors,
};

// Error propagation for an [`UnsafePyLeaked`] wrapping a [`Result`]
//
// It would be nice for UnsharedPyLeaked to provide this directly as a variant
// of the `map` method with a signature such as:
//
// ```
//   unafe fn map_or_err(py: Python,
//                       f: impl FnOnce(T) -> Result(U, E),
//                       convert_err: impl FnOnce(Python, E) -> PyErr)
// ```
//
// This would spare users of the `cpython` crate the additional `unsafe` deref
// to inspect the error and return it outside `UnsafePyLeaked`, and the
// subsequent unwrapping that this function performs.
fn pyleaked_or_map_err<T, E: std::fmt::Debug + Copy>(
    py: Python,
    leaked: UnsafePyLeaked<Result<T, E>>,
    convert_err: impl FnOnce(Python, E) -> PyErr,
) -> PyResult<UnsafePyLeaked<T>> {
    // Result.inspect_err is unstable in Rust 1.61
    if let Err(e) = *unsafe { leaked.try_borrow(py)? } {
        return Err(convert_err(py, e));
    }
    Ok(unsafe {
        leaked.map(py, |res| {
            res.expect("Error case should have already be treated")
        })
    })
}

py_class!(pub class AncestorsIterator |py| {
    data inner: RefCell<UnsafePyLeaked<VCGAncestorsIterator<PySharedIndex>>>;

    def __next__(&self) -> PyResult<Option<PyRevision>> {
        let mut leaked = self.inner(py).borrow_mut();
        let mut inner = unsafe { leaked.try_borrow_mut(py)? };
        match inner.next() {
            Some(Err(e)) => Err(GraphError::pynew_from_vcsgraph(py, e)),
            None => Ok(None),
            Some(Ok(r)) => Ok(Some(PyRevision(r))),
        }
    }

    def __contains__(&self, rev: PyRevision) -> PyResult<bool> {
        let mut leaked = self.inner(py).borrow_mut();
        let mut inner = unsafe { leaked.try_borrow_mut(py)? };
        inner.contains(rev.0)
            .map_err(|e| GraphError::pynew_from_vcsgraph(py, e))
    }

    def __iter__(&self) -> PyResult<Self> {
        Ok(self.clone_ref(py))
    }

    def __new__(
        _cls,
        index: PyObject,
        initrevs: PyObject,
        stoprev: PyRevision,
        inclusive: bool
    ) -> PyResult<AncestorsIterator> {
        Self::inner_new(py, index, initrevs, stoprev, inclusive)
    }

});

impl AncestorsIterator {
    pub fn from_inner(
        py: Python,
        ait: UnsafePyLeaked<VCGAncestorsIterator<PySharedIndex>>,
    ) -> PyResult<Self> {
        Self::create_instance(py, RefCell::new(ait))
    }

    pub fn inner_new(
        py: Python,
        index: PyObject,
        initrevs: PyObject,
        stoprev: PyRevision,
        inclusive: bool,
    ) -> PyResult<AncestorsIterator> {
        let index = py_rust_index_to_graph(py, index)?;
        let initvec: Vec<_> = {
            let borrowed_idx = unsafe { index.try_borrow(py)? };
            rev_pyiter_collect(py, &initrevs, &*borrowed_idx)?
        };
        let res_ait = unsafe {
            index.map(py, |idx| {
                VCGAncestorsIterator::new(
                    idx,
                    initvec.into_iter().map(|r| r.0),
                    stoprev.0,
                    inclusive,
                )
            })
        };
        let ait =
            pyleaked_or_map_err(py, res_ait, GraphError::pynew_from_vcsgraph)?;
        AncestorsIterator::from_inner(py, ait)
    }
}

py_class!(pub class LazyAncestors |py| {
    data inner: RefCell<UnsafePyLeaked<
        RefCell<VCGLazyAncestors<PySharedIndex>>
        >>;
    data index: PyObject;
    data initrevs: PyObject;
    data stoprev: PyRevision;
    data inclusive: bool;

    def __contains__(&self, rev: PyRevision) -> PyResult<bool> {
        let leaked = self.inner(py).borrow();
        let inner: &RefCell<VCGLazyAncestors<PySharedIndex>> =
            &*unsafe { leaked.try_borrow(py)? };
        let inner_mut: &mut VCGLazyAncestors<PySharedIndex> =
            &mut *inner.borrow_mut();
        inner_mut.contains(rev.0)
            .map_err(|e| GraphError::pynew_from_vcsgraph(py, e))
    }

    def __iter__(&self) -> PyResult<AncestorsIterator> {
        let index = self.index(py).clone_ref(py);
        let initrevs = self.initrevs(py).clone_ref(py);
        AncestorsIterator::inner_new(py, index, initrevs,
                                     *self.stoprev(py),
                                     *self.inclusive(py))
    }

    def __bool__(&self) -> PyResult<bool> {
        let leaked = self.inner(py).borrow();
        let inner = unsafe { leaked.try_borrow(py)? };
        let empty = inner.borrow().is_empty();
        Ok(!empty)
    }

    def __new__(
        _cls,
        index: PyObject,
        initrevs: PyObject,
        stoprev: PyRevision,
        inclusive: bool
    ) -> PyResult<Self> {
        let cloned_index = index.clone_ref(py);
        let index = py_rust_index_to_graph(py, index)?;
        let initvec: Vec<_> = {
            let borrowed_idx =  unsafe {index.try_borrow(py)?};
            rev_pyiter_collect(py, &initrevs, &*borrowed_idx)?
        };

        let res_lazy =
            unsafe { index.map(py, |idx| VCGLazyAncestors::new(
                idx,
                initvec.into_iter().map(|r| r.0),
                stoprev.0,
                inclusive
            ))};
        let lazy = pyleaked_or_map_err(py, res_lazy,
                                       GraphError::pynew_from_vcsgraph)?;
        let lazy_cell = unsafe { lazy.map(py, RefCell::new)};
        let res = Self::create_instance(
            py, RefCell::new(lazy_cell),
            cloned_index, initrevs, stoprev, inclusive)?;
        Ok(res)
        }

});

py_class!(pub class MissingAncestors |py| {
    data inner: RefCell<Box<CoreMissing<Index>>>;
    data index: RefCell<Index>;

    def __new__(
        _cls,
        index: PyObject,
        bases: PyObject
    )
    -> PyResult<MissingAncestors> {
        let index = pyindex_to_graph(py, index)?;
        let bases_vec: Vec<_> = rev_pyiter_collect(py, &bases, &index)?;

        let inner = CoreMissing::new(index.clone_ref(py), bases_vec);
        MissingAncestors::create_instance(
            py,
            RefCell::new(Box::new(inner)),
            RefCell::new(index)
        )
    }

    def hasbases(&self) -> PyResult<bool> {
        Ok(self.inner(py).borrow().has_bases())
    }

    def addbases(&self, bases: PyObject) -> PyResult<PyObject> {
        let index = self.index(py).borrow();
        let bases_vec: Vec<_> = rev_pyiter_collect(py, &bases, &*index)?;
        let mut inner = self.inner(py).borrow_mut();
        inner.add_bases(bases_vec);
        // cpython doc has examples with PyResult<()> but this gives me
        //   the trait `cpython::ToPyObject` is not implemented for `()`
        // so let's return an explicit None
        Ok(py.None())
    }

    def bases(&self) -> PyResult<HashSet<PyRevision>> {
        Ok(
            self.inner(py)
                .borrow()
                .get_bases()
                .iter()
                .map(|r| PyRevision(r.0))
                .collect()
        )
    }

    def basesheads(&self) -> PyResult<HashSet<PyRevision>> {
        let inner = self.inner(py).borrow();
        Ok(
            inner
                .bases_heads()
                .map_err(|e| GraphError::pynew(py, e))?
                .into_iter()
                .map(|r| PyRevision(r.0))
                .collect()
        )
    }

    def removeancestorsfrom(&self, revs: PyObject) -> PyResult<PyObject> {
        let index = self.index(py).borrow();
        // this is very lame: we convert to a Rust set, update it in place
        // and then convert back to Python, only to have Python remove the
        // excess (thankfully, Python is happy with a list or even an iterator)
        // Leads to improve this:
        //  - have the CoreMissing instead do something emit revisions to
        //    discard
        //  - define a trait for sets of revisions in the core and implement
        //    it for a Python set rewrapped with the GIL marker
        let mut revs_pyset: HashSet<Revision> = rev_pyiter_collect(
            py, &revs, &*index
        )?;
        let mut inner = self.inner(py).borrow_mut();
        inner.remove_ancestors_from(&mut revs_pyset)
            .map_err(|e| GraphError::pynew(py, e))?;

        // convert as Python list
        let mut remaining_pyint_vec: Vec<PyObject> = Vec::with_capacity(
            revs_pyset.len());
        for rev in revs_pyset {
            remaining_pyint_vec.push(
                PyRevision(rev.0).to_py_object(py).into_object()
            );
        }
        let remaining_pylist = PyList::new(py, remaining_pyint_vec.as_slice());
        revs.call_method(py, "intersection_update", (remaining_pylist, ), None)
    }

    def missingancestors(&self, revs: PyObject) -> PyResult<PyList> {
        let index = self.index(py).borrow();
        let revs_vec: Vec<Revision> = rev_pyiter_collect(py, &revs, &*index)?;

        let mut inner = self.inner(py).borrow_mut();
        let missing_vec = match inner.missing_ancestors(revs_vec) {
            Ok(missing) => missing,
            Err(e) => {
                return Err(GraphError::pynew(py, e));
            }
        };
        // convert as Python list
        let mut missing_pyint_vec: Vec<PyObject> = Vec::with_capacity(
            missing_vec.len());
        for rev in missing_vec {
            missing_pyint_vec.push(
                PyRevision(rev.0).to_py_object(py).into_object()
            );
        }
        Ok(PyList::new(py, missing_pyint_vec.as_slice()))
    }
});

/// Create the module, with __package__ given from parent
pub fn init_module(py: Python, package: &str) -> PyResult<PyModule> {
    let dotted_name = &format!("{}.ancestor", package);
    let m = PyModule::new(py, dotted_name)?;
    m.add(py, "__package__", package)?;
    m.add(
        py,
        "__doc__",
        "Generic DAG ancestor algorithms - Rust implementation",
    )?;
    m.add_class::<AncestorsIterator>(py)?;
    m.add_class::<LazyAncestors>(py)?;
    m.add_class::<MissingAncestors>(py)?;

    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)
}