view rust/hg-cpython/src/cindex.rs @ 46563:c19c662097e1

copies: detect case when a merge decision overwrite previous data

We now detect and record when a merge case required special logic (eg: thing
that append during the merge, ambiguity leading to picking p1 data, etc) and we
explicitly mark the result as superseding the previous data.

This fixes the family of test we previously added.

Differential Revision: https://phab.mercurial-scm.org/D9613

// cindex.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 to use the Index defined by the parsers C extension
//!
//! Ideally, we should use an Index entirely implemented in Rust,
//! but this will take some time to get there.

use cpython::{
    exc::ImportError, ObjectProtocol, PyClone, PyErr, PyObject, PyResult,
    PyTuple, Python, PythonObject,
};
use hg::revlog::{Node, RevlogIndex};
use hg::{Graph, GraphError, Revision, WORKING_DIRECTORY_REVISION};
use libc::{c_int, ssize_t};

const REVLOG_CABI_VERSION: c_int = 2;

#[repr(C)]
pub struct Revlog_CAPI {
    abi_version: c_int,
    index_length:
        unsafe extern "C" fn(index: *mut revlog_capi::RawPyObject) -> ssize_t,
    index_node: unsafe extern "C" fn(
        index: *mut revlog_capi::RawPyObject,
        rev: ssize_t,
    ) -> *const Node,
    index_parents: unsafe extern "C" fn(
        index: *mut revlog_capi::RawPyObject,
        rev: c_int,
        ps: *mut [c_int; 2],
    ) -> c_int,
}

py_capsule!(
    from mercurial.cext.parsers import revlog_CAPI
        as revlog_capi for Revlog_CAPI);

/// A `Graph` backed up by objects and functions from revlog.c
///
/// This implementation of the `Graph` trait, relies on (pointers to)
/// - the C index object (`index` member)
/// - the `index_get_parents()` function (`parents` member)
///
/// # Safety
///
/// The C index itself is mutable, and this Rust exposition is **not
/// protected by the GIL**, meaning that this construct isn't safe with respect
/// to Python threads.
///
/// All callers of this `Index` must acquire the GIL and must not release it
/// while working.
///
/// # TODO find a solution to make it GIL safe again.
///
/// This is non trivial, and can wait until we have a clearer picture with
/// more Rust Mercurial constructs.
///
/// One possibility would be to a `GILProtectedIndex` wrapper enclosing
/// a `Python<'p>` marker and have it be the one implementing the
/// `Graph` trait, but this would mean the `Graph` implementor would become
/// likely to change between subsequent method invocations of the `hg-core`
/// objects (a serious change of the `hg-core` API):
/// either exposing ways to mutate the `Graph`, or making it a non persistent
/// parameter in the relevant methods that need one.
///
/// Another possibility would be to introduce an abstract lock handle into
/// the core API, that would be tied to `GILGuard` / `Python<'p>`
/// in the case of the `cpython` crate bindings yet could leave room for other
/// mechanisms in other contexts.
pub struct Index {
    index: PyObject,
    capi: &'static Revlog_CAPI,
}

impl Index {
    pub fn new(py: Python, index: PyObject) -> PyResult<Self> {
        let capi = unsafe { revlog_capi::retrieve(py)? };
        if capi.abi_version != REVLOG_CABI_VERSION {
            return Err(PyErr::new::<ImportError, _>(
                py,
                format!(
                    "ABI version mismatch: the C ABI revlog version {} \
                     does not match the {} expected by Rust hg-cpython",
                    capi.abi_version, REVLOG_CABI_VERSION
                ),
            ));
        }
        Ok(Index { index, capi })
    }

    /// return a reference to the CPython Index object in this Struct
    pub fn inner(&self) -> &PyObject {
        &self.index
    }

    pub fn append(&mut self, py: Python, tup: PyTuple) -> PyResult<PyObject> {
        self.index.call_method(
            py,
            "append",
            PyTuple::new(py, &[tup.into_object()]),
            None,
        )
    }
}

impl Clone for Index {
    fn clone(&self) -> Self {
        let guard = Python::acquire_gil();
        Index {
            index: self.index.clone_ref(guard.python()),
            capi: self.capi,
        }
    }
}

impl PyClone for Index {
    fn clone_ref(&self, py: Python) -> Self {
        Index {
            index: self.index.clone_ref(py),
            capi: self.capi,
        }
    }
}

impl Graph for Index {
    /// wrap a call to the C extern parents function
    fn parents(&self, rev: Revision) -> Result<[Revision; 2], GraphError> {
        if rev == WORKING_DIRECTORY_REVISION {
            return Err(GraphError::WorkingDirectoryUnsupported);
        }
        let mut res: [c_int; 2] = [0; 2];
        let code = unsafe {
            (self.capi.index_parents)(
                self.index.as_ptr(),
                rev as c_int,
                &mut res as *mut [c_int; 2],
            )
        };
        match code {
            0 => Ok(res),
            _ => Err(GraphError::ParentOutOfRange(rev)),
        }
    }
}

impl RevlogIndex for Index {
    /// Note C return type is Py_ssize_t (hence signed), but we shall
    /// force it to unsigned, because it's a length
    fn len(&self) -> usize {
        unsafe { (self.capi.index_length)(self.index.as_ptr()) as usize }
    }

    fn node(&self, rev: Revision) -> Option<&Node> {
        let raw = unsafe {
            (self.capi.index_node)(self.index.as_ptr(), rev as ssize_t)
        };
        if raw.is_null() {
            None
        } else {
            // TODO it would be much better for the C layer to give us
            // a length, since the hash length will change in the near
            // future, but that's probably out of scope for the nodemap
            // patch series.
            //
            // The root of that unsafety relies in the signature of
            // `capi.index_node()` itself: returning a `Node` pointer
            // whereas it's a `char *` in the C counterpart.
            Some(unsafe { &*raw })
        }
    }
}