rust/hg-cpython/src/dirstate.rs

rust: switch hg-core and hg-cpython to rust 2018 edition

Many interesting changes have happened in Rust since the Oxidation Plan was
introduced, like the 2018 edition and procedural macros:

    - Opting in to the 2018 edition is a clear benefit in terms of future
      proofing, new (nice to have) syntactical sugar notwithstanding. It
      also has a new non-lexical, non-AST based borrow checker that has
      fewer bugs(!) and allows us to write correct code that in some cases
      would have been rejected by the old one.
    - Procedural macros allow us to use the PyO3 crate which maintainers have
      expressed the clear goal of compiling on stable, which would help in
      code maintainability compared to rust-cpython.

In this patch are the following changes:
    - Removing most `extern crate` uses
    - Updating `use` clauses (`crate` keyword, nested `use`)
    - Removing `mod.rs` in favor of an aptly named module file

Like discussed in the mailing list (
https://www.mercurial-scm.org/pipermail/mercurial-devel/2019-July/132316.html
), until Rust integration in Mercurial is considered to be out of the
experimental phase, the maximum version of Rust allowed is whatever the latest
version Debian packages.

Differential Revision: https://phab.mercurial-scm.org/D6597

// dirstate.rs
//
// Copyright 2019 Raphaël Gomès <[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::dirstate` module provided by the
//! `hg-core` package.
//!
//! From Python, this will be seen as `mercurial.rustext.dirstate`

use cpython::{
    exc, ObjectProtocol, PyBytes, PyDict, PyErr, PyInt, PyModule, PyObject,
    PyResult, PySequence, PyTuple, Python, PythonObject, ToPyObject,
};
use hg::{
    pack_dirstate, parse_dirstate, CopyVecEntry, DirsIterable, DirsMultiset,
    DirstateEntry, DirstateMapError, DirstatePackError, DirstateParents,
    DirstateParseError, DirstateVec,
};
use libc::{c_char, c_int};
#[cfg(feature = "python27")]
use python27_sys::PyCapsule_Import;
#[cfg(feature = "python3")]
use python3_sys::PyCapsule_Import;
use std::cell::RefCell;
use std::collections::HashMap;
use std::ffi::CStr;
use std::mem::transmute;

/// C code uses a custom `dirstate_tuple` type, checks in multiple instances
/// for this type, and raises a Python `Exception` if the check does not pass.
/// Because this type differs only in name from the regular Python tuple, it
/// would be a good idea in the near future to remove it entirely to allow
/// for a pure Python tuple of the same effective structure to be used,
/// rendering this type and the capsule below useless.
type MakeDirstateTupleFn = extern "C" fn(
    state: c_char,
    mode: c_int,
    size: c_int,
    mtime: c_int,
) -> PyObject;

/// This is largely a copy/paste from cindex.rs, pending the merge of a
/// `py_capsule_fn!` macro in the rust-cpython project:
/// https://github.com/dgrunwald/rust-cpython/pull/169
fn decapsule_make_dirstate_tuple(py: Python) -> PyResult<MakeDirstateTupleFn> {
    unsafe {
        let caps_name = CStr::from_bytes_with_nul_unchecked(
            b"mercurial.cext.parsers.make_dirstate_tuple_CAPI\0",
        );
        let from_caps = PyCapsule_Import(caps_name.as_ptr(), 0);
        if from_caps.is_null() {
            return Err(PyErr::fetch(py));
        }
        Ok(transmute(from_caps))
    }
}

fn parse_dirstate_wrapper(
    py: Python,
    dmap: PyDict,
    copymap: PyDict,
    st: PyBytes,
) -> PyResult<PyTuple> {
    match parse_dirstate(st.data(py)) {
        Ok((parents, dirstate_vec, copies)) => {
            for (filename, entry) in dirstate_vec {
                dmap.set_item(
                    py,
                    PyBytes::new(py, &filename[..]),
                    decapsule_make_dirstate_tuple(py)?(
                        entry.state as c_char,
                        entry.mode,
                        entry.size,
                        entry.mtime,
                    ),
                )?;
            }
            for CopyVecEntry { path, copy_path } in copies {
                copymap.set_item(
                    py,
                    PyBytes::new(py, path),
                    PyBytes::new(py, copy_path),
                )?;
            }
            Ok((PyBytes::new(py, parents.p1), PyBytes::new(py, parents.p2))
                .to_py_object(py))
        }
        Err(e) => Err(PyErr::new::<exc::ValueError, _>(
            py,
            match e {
                DirstateParseError::TooLittleData => {
                    "too little data for parents".to_string()
                }
                DirstateParseError::Overflow => {
                    "overflow in dirstate".to_string()
                }
                DirstateParseError::CorruptedEntry(e) => e,
            },
        )),
    }
}

fn extract_dirstate_vec(
    py: Python,
    dmap: &PyDict,
) -> Result<DirstateVec, PyErr> {
    dmap.items(py)
        .iter()
        .map(|(filename, stats)| {
            let stats = stats.extract::<PySequence>(py)?;
            let state = stats.get_item(py, 0)?.extract::<PyBytes>(py)?;
            let state = state.data(py)[0] as i8;
            let mode = stats.get_item(py, 1)?.extract(py)?;
            let size = stats.get_item(py, 2)?.extract(py)?;
            let mtime = stats.get_item(py, 3)?.extract(py)?;
            let filename = filename.extract::<PyBytes>(py)?;
            let filename = filename.data(py);
            Ok((
                filename.to_owned(),
                DirstateEntry {
                    state,
                    mode,
                    size,
                    mtime,
                },
            ))
        })
        .collect()
}

fn pack_dirstate_wrapper(
    py: Python,
    dmap: PyDict,
    copymap: PyDict,
    pl: PyTuple,
    now: PyInt,
) -> PyResult<PyBytes> {
    let p1 = pl.get_item(py, 0).extract::<PyBytes>(py)?;
    let p1: &[u8] = p1.data(py);
    let p2 = pl.get_item(py, 1).extract::<PyBytes>(py)?;
    let p2: &[u8] = p2.data(py);

    let dirstate_vec = extract_dirstate_vec(py, &dmap)?;

    let copies: Result<HashMap<Vec<u8>, Vec<u8>>, PyErr> = copymap
        .items(py)
        .iter()
        .map(|(key, value)| {
            Ok((
                key.extract::<PyBytes>(py)?.data(py).to_owned(),
                value.extract::<PyBytes>(py)?.data(py).to_owned(),
            ))
        })
        .collect();

    match pack_dirstate(
        &dirstate_vec,
        &copies?,
        DirstateParents { p1, p2 },
        now.as_object().extract::<i32>(py)?,
    ) {
        Ok((packed, new_dirstate_vec)) => {
            for (
                filename,
                DirstateEntry {
                    state,
                    mode,
                    size,
                    mtime,
                },
            ) in new_dirstate_vec
            {
                dmap.set_item(
                    py,
                    PyBytes::new(py, &filename[..]),
                    decapsule_make_dirstate_tuple(py)?(
                        state as c_char,
                        mode,
                        size,
                        mtime,
                    ),
                )?;
            }
            Ok(PyBytes::new(py, &packed))
        }
        Err(error) => Err(PyErr::new::<exc::ValueError, _>(
            py,
            match error {
                DirstatePackError::CorruptedParent => {
                    "expected a 20-byte hash".to_string()
                }
                DirstatePackError::CorruptedEntry(e) => e,
                DirstatePackError::BadSize(expected, actual) => {
                    format!("bad dirstate size: {} != {}", actual, expected)
                }
            },
        )),
    }
}

py_class!(pub class Dirs |py| {
    data dirs_map: RefCell<DirsMultiset>;

    // `map` is either a `dict` or a flat iterator (usually a `set`, sometimes
    // a `list`)
    def __new__(
        _cls,
        map: PyObject,
        skip: Option<PyObject> = None
    ) -> PyResult<Self> {
        let mut skip_state: Option<i8> = None;
        if let Some(skip) = skip {
            skip_state = Some(skip.extract::<PyBytes>(py)?.data(py)[0] as i8);
        }
        let dirs_map;

        if let Ok(map) = map.cast_as::<PyDict>(py) {
            let dirstate_vec = extract_dirstate_vec(py, &map)?;
            dirs_map = DirsMultiset::new(
                DirsIterable::Dirstate(dirstate_vec),
                skip_state,
            )
        } else {
            let map: Result<Vec<Vec<u8>>, PyErr> = map
                .iter(py)?
                .map(|o| Ok(o?.extract::<PyBytes>(py)?.data(py).to_owned()))
                .collect();
            dirs_map = DirsMultiset::new(
                DirsIterable::Manifest(map?),
                skip_state,
            )
        }

        Self::create_instance(py, RefCell::new(dirs_map))
    }

    def addpath(&self, path: PyObject) -> PyResult<PyObject> {
        self.dirs_map(py).borrow_mut().add_path(
            path.extract::<PyBytes>(py)?.data(py),
        );
        Ok(py.None())
    }

    def delpath(&self, path: PyObject) -> PyResult<PyObject> {
        self.dirs_map(py).borrow_mut().delete_path(
            path.extract::<PyBytes>(py)?.data(py),
        )
            .and(Ok(py.None()))
            .or_else(|e| {
                match e {
                    DirstateMapError::PathNotFound(_p) => {
                        Err(PyErr::new::<exc::ValueError, _>(
                            py,
                            "expected a value, found none".to_string(),
                        ))
                    }
                    DirstateMapError::EmptyPath => {
                        Ok(py.None())
                    }
                }
            })
    }

    // This is really inefficient on top of being ugly, but it's an easy way
    // of having it work to continue working on the rest of the module
    // hopefully bypassing Python entirely pretty soon.
    def __iter__(&self) -> PyResult<PyObject> {
        let dict = PyDict::new(py);

        for (key, value) in self.dirs_map(py).borrow().iter() {
            dict.set_item(
                py,
                PyBytes::new(py, &key[..]),
                value.to_py_object(py),
            )?;
        }

        let locals = PyDict::new(py);
        locals.set_item(py, "obj", dict)?;

        py.eval("iter(obj)", None, Some(&locals))
    }

    def __contains__(&self, item: PyObject) -> PyResult<bool> {
        Ok(self
            .dirs_map(py)
            .borrow()
            .contains_key(item.extract::<PyBytes>(py)?.data(py).as_ref()))
    }
});

/// Create the module, with `__package__` given from parent
pub fn init_module(py: Python, package: &str) -> PyResult<PyModule> {
    let dotted_name = &format!("{}.dirstate", package);
    let m = PyModule::new(py, dotted_name)?;

    m.add(py, "__package__", package)?;
    m.add(py, "__doc__", "Dirstate - Rust implementation")?;
    m.add(
        py,
        "parse_dirstate",
        py_fn!(
            py,
            parse_dirstate_wrapper(dmap: PyDict, copymap: PyDict, st: PyBytes)
        ),
    )?;
    m.add(
        py,
        "pack_dirstate",
        py_fn!(
            py,
            pack_dirstate_wrapper(
                dmap: PyDict,
                copymap: PyDict,
                pl: PyTuple,
                now: PyInt
            )
        ),
    )?;

    m.add_class::<Dirs>(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)?;

    Ok(m)
}