rust/hg-cpython/src/ancestors.rs

run-tests: stuff a `python3.exe` into the test bin directory on Windows

Windows doesn't have `python3.exe` as part of the python.org distribution, and
that broke every script with a shebang after c102b704edb5.  Windows itself
provides a `python3.exe` app execution alias[1], but it is some sort of reparse
point that MSYS is incapable of handling[2].  When run by MSYS, it simply prints

    $ python3 -V
     - Cannot open

That in turn caused every `hghave` check, and test that invokes shebang scripts
directly, to fail.  Rather than try to patch up every script call to be invoked
with `$PYTHON` (and regress when non Windows developers forget), copying the
executable into the test binary directory with the new name just works.  Since
this directory is prepended to the system PATH value, it also overrides the
broken execution alias.  (The `_tmpbindir` is used instead of `_bindir` because
the latter causes python3.exe to be copied into the repo next to hg.exe when
`test-run-tests.t` runs.  Something runs with this version of the executable and
subsequent runs of `run-tests.py` inside `test-run-tests.t` try to copy over it
while it is in use, and fail.  This avoids the failures and the clutter.)

I didn't conditionalize this on py3 because `python3.exe` needs to be present
(for the shebangs) even when running py2 tests.  It shouldn't matter to these
simple scripts, and I think the intention is to make the test runner use py3
always, even if testing a py2 build.  For now, still supporting py2 is helping
to clean up the mess that is py3 tests.

[1] https://stackoverflow.com/a/57168165
[2] https://stackoverflow.com/questions/59148628/solved-unable-to-run-python-3-7-on-windows-10-permission-denied#comment104524397_59148666

Differential Revision: https://phab.mercurial-scm.org/D9543

// 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::pyindex_to_graph;
use crate::{
    cindex::Index, conversion::rev_pyiter_collect, exceptions::GraphError,
};
use cpython::{
    ObjectProtocol, PyClone, PyDict, PyList, PyModule, PyObject, PyResult,
    Python, PythonObject, ToPyObject,
};
use hg::Revision;
use hg::{
    AncestorsIterator as CoreIterator, LazyAncestors as CoreLazy,
    MissingAncestors as CoreMissing,
};
use std::cell::RefCell;
use std::collections::HashSet;

py_class!(pub class AncestorsIterator |py| {
    data inner: RefCell<Box<CoreIterator<Index>>>;

    def __next__(&self) -> PyResult<Option<Revision>> {
        match self.inner(py).borrow_mut().next() {
            Some(Err(e)) => Err(GraphError::pynew(py, e)),
            None => Ok(None),
            Some(Ok(r)) => Ok(Some(r)),
        }
    }

    def __contains__(&self, rev: Revision) -> PyResult<bool> {
        self.inner(py).borrow_mut().contains(rev)
            .map_err(|e| GraphError::pynew(py, e))
    }

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

    def __new__(_cls, index: PyObject, initrevs: PyObject, stoprev: Revision,
                inclusive: bool) -> PyResult<AncestorsIterator> {
        let initvec: Vec<Revision> = rev_pyiter_collect(py, &initrevs)?;
        let ait = CoreIterator::new(
            pyindex_to_graph(py, index)?,
            initvec,
            stoprev,
            inclusive,
        )
        .map_err(|e| GraphError::pynew(py, e))?;
        AncestorsIterator::from_inner(py, ait)
    }

});

impl AncestorsIterator {
    pub fn from_inner(py: Python, ait: CoreIterator<Index>) -> PyResult<Self> {
        Self::create_instance(py, RefCell::new(Box::new(ait)))
    }
}

py_class!(pub class LazyAncestors |py| {
    data inner: RefCell<Box<CoreLazy<Index>>>;

    def __contains__(&self, rev: Revision) -> PyResult<bool> {
        self.inner(py)
            .borrow_mut()
            .contains(rev)
            .map_err(|e| GraphError::pynew(py, e))
    }

    def __iter__(&self) -> PyResult<AncestorsIterator> {
        AncestorsIterator::from_inner(py, self.inner(py).borrow().iter())
    }

    def __bool__(&self) -> PyResult<bool> {
        Ok(!self.inner(py).borrow().is_empty())
    }

    def __new__(_cls, index: PyObject, initrevs: PyObject, stoprev: Revision,
                inclusive: bool) -> PyResult<Self> {
        let initvec: Vec<Revision> = rev_pyiter_collect(py, &initrevs)?;

        let lazy =
            CoreLazy::new(pyindex_to_graph(py, index)?,
                          initvec, stoprev, inclusive)
                .map_err(|e| GraphError::pynew(py, e))?;

        Self::create_instance(py, RefCell::new(Box::new(lazy)))
        }

});

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

    def __new__(
        _cls,
        index: PyObject,
        bases: PyObject
    )
    -> PyResult<MissingAncestors> {
        let bases_vec: Vec<Revision> = rev_pyiter_collect(py, &bases)?;
        let inner = CoreMissing::new(pyindex_to_graph(py, index)?, bases_vec);
        MissingAncestors::create_instance(py, RefCell::new(Box::new(inner)))
    }

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

    def addbases(&self, bases: PyObject) -> PyResult<PyObject> {
        let mut inner = self.inner(py).borrow_mut();
        let bases_vec: Vec<Revision> = rev_pyiter_collect(py, &bases)?;
        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<Revision>> {
        Ok(self.inner(py).borrow().get_bases().clone())
    }

    def basesheads(&self) -> PyResult<HashSet<Revision>> {
        let inner = self.inner(py).borrow();
        inner.bases_heads().map_err(|e| GraphError::pynew(py, e))
    }

    def removeancestorsfrom(&self, revs: PyObject) -> PyResult<PyObject> {
        let mut inner = self.inner(py).borrow_mut();
        // 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)?;
        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(rev.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 mut inner = self.inner(py).borrow_mut();
        let revs_vec: Vec<Revision> = rev_pyiter_collect(py, &revs)?;
        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(rev.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)
}