annotate rust/hg-cpython/src/revlog.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.

// revlog.rs
//
// Copyright 2019-2020 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.

use crate::{
    cindex,
    conversion::{rev_pyiter_collect, rev_pyiter_collect_or_else},
    utils::{node_from_py_bytes, node_from_py_object},
    PyRevision,
};
use cpython::{
    buffer::{Element, PyBuffer},
    exc::{IndexError, ValueError},
    ObjectProtocol, PyBool, PyBytes, PyClone, PyDict, PyErr, PyInt, PyList,
    PyModule, PyObject, PyResult, PySet, PyString, PyTuple, Python,
    PythonObject, ToPyObject, UnsafePyLeaked,
};
use hg::{
    errors::HgError,
    index::{
        IndexHeader, Phase, RevisionDataParams, SnapshotsCache,
        INDEX_ENTRY_SIZE,
    },
    nodemap::{Block, NodeMapError, NodeTree},
    revlog::{nodemap::NodeMap, Graph, NodePrefix, RevlogError, RevlogIndex},
    BaseRevision, Node, Revision, UncheckedRevision, NULL_REVISION,
};
use std::{cell::RefCell, collections::HashMap};
use vcsgraph::graph::Graph as VCSGraph;

/// Return a Struct implementing the Graph trait
pub(crate) fn pyindex_to_graph(
    py: Python,
    index: PyObject,
) -> PyResult<cindex::Index> {
    match index.extract::<MixedIndex>(py) {
        Ok(midx) => Ok(midx.clone_cindex(py)),
        Err(_) => cindex::Index::new(py, index),
    }
}

pub struct PySharedIndex {
    /// The underlying hg-core index
    pub(crate) inner: &'static hg::index::Index,
}

/// Return a Struct implementing the Graph trait
pub(crate) fn py_rust_index_to_graph(
    py: Python,
    index: PyObject,
) -> PyResult<UnsafePyLeaked<PySharedIndex>> {
    let midx = index.extract::<MixedIndex>(py)?;
    let leaked = midx.index(py).leak_immutable();
    Ok(unsafe { leaked.map(py, |idx| PySharedIndex { inner: idx }) })
}

impl Clone for PySharedIndex {
    fn clone(&self) -> Self {
        Self { inner: self.inner }
    }
}

impl Graph for PySharedIndex {
    fn parents(&self, rev: Revision) -> Result<[Revision; 2], hg::GraphError> {
        self.inner.parents(rev)
    }
}

impl VCSGraph for PySharedIndex {
    fn parents(
        &self,
        rev: BaseRevision,
    ) -> Result<vcsgraph::graph::Parents, vcsgraph::graph::GraphReadError>
    {
        // FIXME This trait should be reworked to decide between Revision
        // and UncheckedRevision, get better errors names, etc.
        match Graph::parents(self, Revision(rev)) {
            Ok(parents) => {
                Ok(vcsgraph::graph::Parents([parents[0].0, parents[1].0]))
            }
            Err(hg::GraphError::ParentOutOfRange(rev)) => {
                Err(vcsgraph::graph::GraphReadError::KeyedInvalidKey(rev.0))
            }
        }
    }
}

impl RevlogIndex for PySharedIndex {
    fn len(&self) -> usize {
        self.inner.len()
    }
    fn node(&self, rev: Revision) -> Option<&Node> {
        self.inner.node(rev)
    }
}

py_class!(pub class MixedIndex |py| {
    data cindex: RefCell<cindex::Index>;
    @shared data index: hg::index::Index;
    data nt: RefCell<Option<NodeTree>>;
    data docket: RefCell<Option<PyObject>>;
    // Holds a reference to the mmap'ed persistent nodemap data
    data nodemap_mmap: RefCell<Option<PyBuffer>>;
    // Holds a reference to the mmap'ed persistent index data
    data index_mmap: RefCell<Option<PyBuffer>>;

    def __new__(
        _cls,
        cindex: PyObject,
        data: PyObject,
        default_header: u32,
    ) -> PyResult<MixedIndex> {
        Self::new(py, cindex, data, default_header)
    }

    /// Compatibility layer used for Python consumers needing access to the C index
    ///
    /// Only use case so far is `scmutil.shortesthexnodeidprefix`,
    /// that may need to build a custom `nodetree`, based on a specified revset.
    /// With a Rust implementation of the nodemap, we will be able to get rid of
    /// this, by exposing our own standalone nodemap class,
    /// ready to accept `MixedIndex`.
    def get_cindex(&self) -> PyResult<PyObject> {
        Ok(self.cindex(py).borrow().inner().clone_ref(py))
    }

    // Index API involving nodemap, as defined in mercurial/pure/parsers.py

    /// Return Revision if found, raises a bare `error.RevlogError`
    /// in case of ambiguity, same as C version does
    def get_rev(&self, node: PyBytes) -> PyResult<Option<PyRevision>> {
        let opt = self.get_nodetree(py)?.borrow();
        let nt = opt.as_ref().unwrap();
        let idx = &*self.cindex(py).borrow();
        let ridx = &*self.index(py).borrow();
        let node = node_from_py_bytes(py, &node)?;
        let rust_rev =
            nt.find_bin(ridx, node.into()).map_err(|e| nodemap_error(py, e))?;
        let c_rev =
            nt.find_bin(idx, node.into()).map_err(|e| nodemap_error(py, e))?;
        assert_eq!(rust_rev, c_rev);
        Ok(rust_rev.map(Into::into))

    }

    /// same as `get_rev()` but raises a bare `error.RevlogError` if node
    /// is not found.
    ///
    /// No need to repeat `node` in the exception, `mercurial/revlog.py`
    /// will catch and rewrap with it
    def rev(&self, node: PyBytes) -> PyResult<PyRevision> {
        self.get_rev(py, node)?.ok_or_else(|| revlog_error(py))
    }

    /// return True if the node exist in the index
    def has_node(&self, node: PyBytes) -> PyResult<bool> {
        // TODO OPTIM we could avoid a needless conversion here,
        // to do when scaffolding for pure Rust switch is removed,
        // as `get_rev()` currently does the necessary assertions
        self.get_rev(py, node).map(|opt| opt.is_some())
    }

    /// find length of shortest hex nodeid of a binary ID
    def shortest(&self, node: PyBytes) -> PyResult<usize> {
        let opt = self.get_nodetree(py)?.borrow();
        let nt = opt.as_ref().unwrap();
        let idx = &*self.index(py).borrow();
        match nt.unique_prefix_len_node(idx, &node_from_py_bytes(py, &node)?)
        {
            Ok(Some(l)) => Ok(l),
            Ok(None) => Err(revlog_error(py)),
            Err(e) => Err(nodemap_error(py, e)),
        }
    }

    def partialmatch(&self, node: PyObject) -> PyResult<Option<PyBytes>> {
        let opt = self.get_nodetree(py)?.borrow();
        let nt = opt.as_ref().unwrap();
        let idx = &*self.index(py).borrow();

        let node_as_string = if cfg!(feature = "python3-sys") {
            node.cast_as::<PyString>(py)?.to_string(py)?.to_string()
        }
        else {
            let node = node.extract::<PyBytes>(py)?;
            String::from_utf8_lossy(node.data(py)).to_string()
        };

        let prefix = NodePrefix::from_hex(&node_as_string)
            .map_err(|_| PyErr::new::<ValueError, _>(
                py, format!("Invalid node or prefix '{}'", node_as_string))
            )?;

        nt.find_bin(idx, prefix)
            // TODO make an inner API returning the node directly
            .map(|opt| opt.map(
                |rev| PyBytes::new(py, idx.node(rev).unwrap().as_bytes())))
            .map_err(|e| nodemap_error(py, e))

    }

    /// append an index entry
    def append(&self, tup: PyTuple) -> PyResult<PyObject> {
        if tup.len(py) < 8 {
            // this is better than the panic promised by tup.get_item()
            return Err(
                PyErr::new::<IndexError, _>(py, "tuple index out of range"))
        }
        let node_bytes = tup.get_item(py, 7).extract(py)?;
        let node = node_from_py_object(py, &node_bytes)?;

        let rev = self.len(py)? as BaseRevision;
        let mut idx = self.cindex(py).borrow_mut();

        // This is ok since we will just add the revision to the index
        let rev = Revision(rev);
        idx.append(py, tup.clone_ref(py))?;
        self.index(py)
            .borrow_mut()
            .append(py_tuple_to_revision_data_params(py, tup)?)
            .unwrap();
        self.get_nodetree(py)?.borrow_mut().as_mut().unwrap()
            .insert(&*idx, &node, rev)
            .map_err(|e| nodemap_error(py, e))?;
        Ok(py.None())
    }

    def __delitem__(&self, key: PyObject) -> PyResult<()> {
        // __delitem__ is both for `del idx[r]` and `del idx[r1:r2]`
        self.cindex(py).borrow().inner().del_item(py, &key)?;
        let start = key.getattr(py, "start")?;
        let start = UncheckedRevision(start.extract(py)?);
        let start = self.index(py)
            .borrow()
            .check_revision(start)
            .ok_or_else(|| {
                nodemap_error(py, NodeMapError::RevisionNotInIndex(start))
            })?;
        self.index(py).borrow_mut().remove(start).unwrap();
        let mut opt = self.get_nodetree(py)?.borrow_mut();
        let nt = opt.as_mut().unwrap();
        nt.invalidate_all();
        self.fill_nodemap(py, nt)?;
        Ok(())
    }

    //
    // Reforwarded C index API
    //

    // index_methods (tp_methods). Same ordering as in revlog.c

    /// return the gca set of the given revs
    def ancestors(&self, *args, **kw) -> PyResult<PyObject> {
        let rust_res = self.inner_ancestors(py, args)?;

        let c_res = self.call_cindex(py, "ancestors", args, kw)?;
        // the algorithm should always provide the results in reverse ordering
        assert_py_eq(py, "ancestors", &rust_res, &c_res)?;

        Ok(rust_res)
    }

    /// return the heads of the common ancestors of the given revs
    def commonancestorsheads(&self, *args, **kw) -> PyResult<PyObject> {
        let rust_res = self.inner_commonancestorsheads(py, args)?;

        let c_res = self.call_cindex(py, "commonancestorsheads", args, kw)?;
        // the algorithm should always provide the results in reverse ordering
        assert_py_eq(py, "commonancestorsheads", &rust_res, &c_res)?;

        Ok(rust_res)
    }

    /// Clear the index caches and inner py_class data.
    /// It is Python's responsibility to call `update_nodemap_data` again.
    def clearcaches(&self, *args, **kw) -> PyResult<PyObject> {
        self.nt(py).borrow_mut().take();
        self.docket(py).borrow_mut().take();
        self.nodemap_mmap(py).borrow_mut().take();
        self.index(py).borrow().clear_caches();
        self.call_cindex(py, "clearcaches", args, kw)
    }

    /// return the raw binary string representing a revision
    def entry_binary(&self, *args, **kw) -> PyResult<PyObject> {
        let rindex = self.index(py).borrow();
        let rev = UncheckedRevision(args.get_item(py, 0).extract(py)?);
        let rust_bytes = rindex.check_revision(rev).and_then(
            |r| rindex.entry_binary(r))
            .ok_or_else(|| rev_not_in_index(py, rev))?;
        let rust_res = PyBytes::new(py, rust_bytes).into_object();

        let c_res = self.call_cindex(py, "entry_binary", args, kw)?;
        assert_py_eq(py, "entry_binary", &rust_res, &c_res)?;
        Ok(rust_res)
    }

    /// return a binary packed version of the header
    def pack_header(&self, *args, **kw) -> PyResult<PyObject> {
        let rindex = self.index(py).borrow();
        let packed = rindex.pack_header(args.get_item(py, 0).extract(py)?);
        let rust_res = PyBytes::new(py, &packed).into_object();

        let c_res = self.call_cindex(py, "pack_header", args, kw)?;
        assert_py_eq(py, "pack_header", &rust_res, &c_res)?;
        Ok(rust_res)
    }

    /// compute phases
    def computephasesmapsets(&self, *args, **kw) -> PyResult<PyObject> {
        let py_roots = args.get_item(py, 0).extract::<PyDict>(py)?;
        let rust_res = self.inner_computephasesmapsets(py, py_roots)?;

        let c_res = self.call_cindex(py, "computephasesmapsets", args, kw)?;
        assert_py_eq(py, "computephasesmapsets", &rust_res, &c_res)?;
        Ok(rust_res)
    }

    /// reachableroots
    def reachableroots2(&self, *args, **kw) -> PyResult<PyObject> {
        let rust_res = self.inner_reachableroots2(
            py,
            UncheckedRevision(args.get_item(py, 0).extract(py)?),
            args.get_item(py, 1),
            args.get_item(py, 2),
            args.get_item(py, 3).extract(py)?,
        )?;

        let c_res = self.call_cindex(py, "reachableroots2", args, kw)?;
        // ordering of C result depends on how the computation went, and
        // Rust result ordering is arbitrary. Hence we compare after
        // sorting the results (in Python to avoid reconverting everything
        // back to Rust structs).
        assert_py_eq_normalized(py, "reachableroots2", &rust_res, &c_res,
                                |v| format!("sorted({})", v))?;

        Ok(rust_res)
    }

    /// get head revisions
    def headrevs(&self, *args, **kw) -> PyResult<PyObject> {
        let rust_res = self.inner_headrevs(py)?;

        let c_res = self.call_cindex(py, "headrevs", args, kw)?;
        assert_py_eq(py, "headrevs", &rust_res, &c_res)?;
        Ok(rust_res)
    }

    /// get filtered head revisions
    def headrevsfiltered(&self, *args, **kw) -> PyResult<PyObject> {
        let rust_res = self.inner_headrevsfiltered(py, &args.get_item(py, 0))?;
        let c_res = self.call_cindex(py, "headrevsfiltered", args, kw)?;

        assert_py_eq(py, "headrevsfiltered", &rust_res, &c_res)?;
        Ok(rust_res)
    }

    /// True if the object is a snapshot
    def issnapshot(&self, *args, **kw) -> PyResult<bool> {
        let index = self.index(py).borrow();
        let result = index
            .is_snapshot(UncheckedRevision(args.get_item(py, 0).extract(py)?))
            .map_err(|e| {
                PyErr::new::<cpython::exc::ValueError, _>(py, e.to_string())
            })?;
        let cresult = self.call_cindex(py, "issnapshot", args, kw)?;
        assert_eq!(result, cresult.extract(py)?);
        Ok(result)
    }

    /// Gather snapshot data in a cache dict
    def findsnapshots(&self, *args, **kw) -> PyResult<PyObject> {
        let index = self.index(py).borrow();
        let cache: PyDict = args.get_item(py, 0).extract(py)?;
        // this methods operates by setting new values in the cache,
        // hence we will compare results by letting the C implementation
        // operate over a deepcopy of the cache, and finally compare both
        // caches.
        let c_cache = PyDict::new(py);
        for (k, v) in cache.items(py) {
            c_cache.set_item(py, k, PySet::new(py, v)?)?;
        }

        let start_rev = UncheckedRevision(args.get_item(py, 1).extract(py)?);
        let end_rev = UncheckedRevision(args.get_item(py, 2).extract(py)?);
        let mut cache_wrapper = PySnapshotsCache{ py, dict: cache };
        index.find_snapshots(
            start_rev,
            end_rev,
            &mut cache_wrapper,
        ).map_err(|_| revlog_error(py))?;

        let c_args = PyTuple::new(
            py,
            &[
                c_cache.clone_ref(py).into_object(),
                args.get_item(py, 1),
                args.get_item(py, 2)
            ]
        );
        self.call_cindex(py, "findsnapshots", &c_args, kw)?;
        assert_py_eq(py, "findsnapshots cache",
                     &cache_wrapper.into_object(),
                     &c_cache.into_object())?;
        Ok(py.None())
    }

    /// determine revisions with deltas to reconstruct fulltext
    def deltachain(&self, *args, **kw) -> PyResult<PyObject> {
        let index = self.index(py).borrow();
        let rev = args.get_item(py, 0).extract::<BaseRevision>(py)?.into();
        let stop_rev =
            args.get_item(py, 1).extract::<Option<BaseRevision>>(py)?;
        let rev = index.check_revision(rev).ok_or_else(|| {
            nodemap_error(py, NodeMapError::RevisionNotInIndex(rev))
        })?;
        let stop_rev = if let Some(stop_rev) = stop_rev {
            let stop_rev = UncheckedRevision(stop_rev);
            Some(index.check_revision(stop_rev).ok_or_else(|| {
                nodemap_error(py, NodeMapError::RevisionNotInIndex(stop_rev))
            })?)
        } else {None};
        let using_general_delta = args.get_item(py, 2)
            .extract::<Option<u32>>(py)?
            .map(|i| i != 0);
        let (chain, stopped) = index.delta_chain(
            rev, stop_rev, using_general_delta
        ).map_err(|e| {
            PyErr::new::<cpython::exc::ValueError, _>(py, e.to_string())
        })?;

        let cresult = self.call_cindex(py, "deltachain", args, kw)?;
        let cchain: Vec<BaseRevision> =
            cresult.get_item(py, 0)?.extract::<Vec<BaseRevision>>(py)?;
        let chain: Vec<_> = chain.into_iter().map(|r| r.0).collect();
        assert_eq!(chain, cchain);
        assert_eq!(stopped, cresult.get_item(py, 1)?.extract(py)?);

        Ok(
            PyTuple::new(
                py,
                &[
                    chain.into_py_object(py).into_object(),
                    stopped.into_py_object(py).into_object()
                ]
            ).into_object()
        )

    }

    /// slice planned chunk read to reach a density threshold
    def slicechunktodensity(&self, *args, **kw) -> PyResult<PyObject> {
        let rust_res = self.inner_slicechunktodensity(
            py,
            args.get_item(py, 0),
            args.get_item(py, 1).extract(py)?,
            args.get_item(py, 2).extract(py)?
        )?;

        let c_res = self.call_cindex(py, "slicechunktodensity", args, kw)?;
        assert_py_eq(py, "slicechunktodensity", &rust_res, &c_res)?;
        Ok(rust_res)
    }

    // index_sequence_methods and index_mapping_methods.
    //
    // Since we call back through the high level Python API,
    // there's no point making a distinction between index_get
    // and index_getitem.
    // gracinet 2023: this above is no longer true for the pure Rust impl

    def __len__(&self) -> PyResult<usize> {
        self.len(py)
    }

    def __getitem__(&self, key: PyObject) -> PyResult<PyObject> {
        let rust_res = self.inner_getitem(py, key.clone_ref(py))?;

        // this conversion seems needless, but that's actually because
        // `index_getitem` does not handle conversion from PyLong,
        // which expressions such as [e for e in index] internally use.
        // Note that we don't seem to have a direct way to call
        // PySequence_GetItem (does the job), which would possibly be better
        // for performance
        // gracinet 2023: the above comment can be removed when we use
        // the pure Rust impl only. Note also that `key` can be a binary
        // node id.
        let c_key = match key.extract::<BaseRevision>(py) {
            Ok(rev) => rev.to_py_object(py).into_object(),
            Err(_) => key,
        };
        let c_res = self.cindex(py).borrow().inner().get_item(py, c_key)?;

        assert_py_eq(py, "__getitem__", &rust_res, &c_res)?;
        Ok(rust_res)
    }

    def __contains__(&self, item: PyObject) -> PyResult<bool> {
        // ObjectProtocol does not seem to provide contains(), so
        // this is an equivalent implementation of the index_contains()
        // defined in revlog.c
        let cindex = self.cindex(py).borrow();
        match item.extract::<i32>(py) {
            Ok(rev) => {
                Ok(rev >= -1 && rev < self.len(py)? as BaseRevision)
            }
            Err(_) => {
                let item_bytes: PyBytes = item.extract(py)?;
                let rust_res = self.has_node(py, item_bytes)?;

                let c_res = cindex.inner().call_method(
                    py,
                    "has_node",
                    PyTuple::new(py, &[item.clone_ref(py)]),
                    None)?
                .extract(py)?;

                assert_eq!(rust_res, c_res);
                Ok(rust_res)
            }
        }
    }

    def nodemap_data_all(&self) -> PyResult<PyBytes> {
        self.inner_nodemap_data_all(py)
    }

    def nodemap_data_incremental(&self) -> PyResult<PyObject> {
        self.inner_nodemap_data_incremental(py)
    }
    def update_nodemap_data(
        &self,
        docket: PyObject,
        nm_data: PyObject
    ) -> PyResult<PyObject> {
        self.inner_update_nodemap_data(py, docket, nm_data)
    }

    @property
    def entry_size(&self) -> PyResult<PyInt> {
        let rust_res: PyInt = INDEX_ENTRY_SIZE.to_py_object(py);

        let c_res = self.cindex(py).borrow().inner()
            .getattr(py, "entry_size")?;
        assert_py_eq(py, "entry_size", rust_res.as_object(), &c_res)?;

        Ok(rust_res)
    }

    @property
    def rust_ext_compat(&self) -> PyResult<PyInt> {
        // will be entirely removed when the Rust index yet useful to
        // implement in Rust to detangle things when removing `self.cindex`
        let rust_res: PyInt = 1.to_py_object(py);

        let c_res = self.cindex(py).borrow().inner()
            .getattr(py, "rust_ext_compat")?;
        assert_py_eq(py, "rust_ext_compat", rust_res.as_object(), &c_res)?;

        Ok(rust_res)
    }

});

/// Take a (potentially) mmap'ed buffer, and return the underlying Python
/// buffer along with the Rust slice into said buffer. We need to keep the
/// Python buffer around, otherwise we'd get a dangling pointer once the buffer
/// is freed from Python's side.
///
/// # Safety
///
/// The caller must make sure that the buffer is kept around for at least as
/// long as the slice.
#[deny(unsafe_op_in_unsafe_fn)]
unsafe fn mmap_keeparound(
    py: Python,
    data: PyObject,
) -> PyResult<(
    PyBuffer,
    Box<dyn std::ops::Deref<Target = [u8]> + Send + Sync + 'static>,
)> {
    let buf = PyBuffer::get(py, &data)?;
    let len = buf.item_count();

    // Build a slice from the mmap'ed buffer data
    let cbuf = buf.buf_ptr();
    let bytes = if std::mem::size_of::<u8>() == buf.item_size()
        && buf.is_c_contiguous()
        && u8::is_compatible_format(buf.format())
    {
        unsafe { std::slice::from_raw_parts(cbuf as *const u8, len) }
    } else {
        return Err(PyErr::new::<ValueError, _>(
            py,
            "Nodemap data buffer has an invalid memory representation"
                .to_string(),
        ));
    };

    Ok((buf, Box::new(bytes)))
}

fn py_tuple_to_revision_data_params(
    py: Python,
    tuple: PyTuple,
) -> PyResult<RevisionDataParams> {
    if tuple.len(py) < 8 {
        // this is better than the panic promised by tup.get_item()
        return Err(PyErr::new::<IndexError, _>(
            py,
            "tuple index out of range",
        ));
    }
    let offset_or_flags: u64 = tuple.get_item(py, 0).extract(py)?;
    let node_id = tuple
        .get_item(py, 7)
        .extract::<PyBytes>(py)?
        .data(py)
        .try_into()
        .unwrap();
    let flags = (offset_or_flags & 0xFFFF) as u16;
    let data_offset = offset_or_flags >> 16;
    Ok(RevisionDataParams {
        flags,
        data_offset,
        data_compressed_length: tuple.get_item(py, 1).extract(py)?,
        data_uncompressed_length: tuple.get_item(py, 2).extract(py)?,
        data_delta_base: tuple.get_item(py, 3).extract(py)?,
        link_rev: tuple.get_item(py, 4).extract(py)?,
        parent_rev_1: tuple.get_item(py, 5).extract(py)?,
        parent_rev_2: tuple.get_item(py, 6).extract(py)?,
        node_id,
        ..Default::default()
    })
}
fn revision_data_params_to_py_tuple(
    py: Python,
    params: RevisionDataParams,
) -> PyTuple {
    PyTuple::new(
        py,
        &[
            params.data_offset.into_py_object(py).into_object(),
            params
                .data_compressed_length
                .into_py_object(py)
                .into_object(),
            params
                .data_uncompressed_length
                .into_py_object(py)
                .into_object(),
            params.data_delta_base.into_py_object(py).into_object(),
            params.link_rev.into_py_object(py).into_object(),
            params.parent_rev_1.into_py_object(py).into_object(),
            params.parent_rev_2.into_py_object(py).into_object(),
            PyBytes::new(py, &params.node_id)
                .into_py_object(py)
                .into_object(),
            params._sidedata_offset.into_py_object(py).into_object(),
            params
                ._sidedata_compressed_length
                .into_py_object(py)
                .into_object(),
            params
                .data_compression_mode
                .into_py_object(py)
                .into_object(),
            params
                ._sidedata_compression_mode
                .into_py_object(py)
                .into_object(),
            params._rank.into_py_object(py).into_object(),
        ],
    )
}

struct PySnapshotsCache<'p> {
    py: Python<'p>,
    dict: PyDict,
}

impl<'p> PySnapshotsCache<'p> {
    fn into_object(self) -> PyObject {
        self.dict.into_object()
    }
}

impl<'p> SnapshotsCache for PySnapshotsCache<'p> {
    fn insert_for(
        &mut self,
        rev: BaseRevision,
        value: BaseRevision,
    ) -> Result<(), RevlogError> {
        let pyvalue = value.into_py_object(self.py).into_object();
        match self.dict.get_item(self.py, rev) {
            Some(obj) => obj
                .extract::<PySet>(self.py)
                .and_then(|set| set.add(self.py, pyvalue)),
            None => PySet::new(self.py, vec![pyvalue])
                .and_then(|set| self.dict.set_item(self.py, rev, set)),
        }
        .map_err(|_| {
            RevlogError::Other(HgError::unsupported(
                "Error in Python caches handling",
            ))
        })
    }
}

impl MixedIndex {
    fn new(
        py: Python,
        cindex: PyObject,
        data: PyObject,
        header: u32,
    ) -> PyResult<MixedIndex> {
        // Safety: we keep the buffer around inside the class as `index_mmap`
        let (buf, bytes) = unsafe { mmap_keeparound(py, data)? };

        Self::create_instance(
            py,
            RefCell::new(cindex::Index::new(py, cindex)?),
            hg::index::Index::new(
                bytes,
                IndexHeader::parse(&header.to_be_bytes())
                    .expect("default header is broken")
                    .unwrap(),
            )
            .map_err(|e| {
                revlog_error_with_msg(py, e.to_string().as_bytes())
            })?,
            RefCell::new(None),
            RefCell::new(None),
            RefCell::new(None),
            RefCell::new(Some(buf)),
        )
    }

    fn len(&self, py: Python) -> PyResult<usize> {
        let rust_index_len = self.index(py).borrow().len();
        let cindex_len = self.cindex(py).borrow().inner().len(py)?;
        assert_eq!(rust_index_len, cindex_len);
        Ok(rust_index_len)
    }

    /// This is scaffolding at this point, but it could also become
    /// a way to start a persistent nodemap or perform a
    /// vacuum / repack operation
    fn fill_nodemap(
        &self,
        py: Python,
        nt: &mut NodeTree,
    ) -> PyResult<PyObject> {
        let index = self.index(py).borrow();
        for r in 0..self.len(py)? {
            let rev = Revision(r as BaseRevision);
            // in this case node() won't ever return None
            nt.insert(&*index, index.node(rev).unwrap(), rev)
                .map_err(|e| nodemap_error(py, e))?
        }
        Ok(py.None())
    }

    fn get_nodetree<'a>(
        &'a self,
        py: Python<'a>,
    ) -> PyResult<&'a RefCell<Option<NodeTree>>> {
        if self.nt(py).borrow().is_none() {
            let readonly = Box::<Vec<_>>::default();
            let mut nt = NodeTree::load_bytes(readonly, 0);
            self.fill_nodemap(py, &mut nt)?;
            self.nt(py).borrow_mut().replace(nt);
        }
        Ok(self.nt(py))
    }

    /// forward a method call to the underlying C index
    fn call_cindex(
        &self,
        py: Python,
        name: &str,
        args: &PyTuple,
        kwargs: Option<&PyDict>,
    ) -> PyResult<PyObject> {
        self.cindex(py)
            .borrow()
            .inner()
            .call_method(py, name, args, kwargs)
    }

    pub fn clone_cindex(&self, py: Python) -> cindex::Index {
        self.cindex(py).borrow().clone_ref(py)
    }

    /// Returns the full nodemap bytes to be written as-is to disk
    fn inner_nodemap_data_all(&self, py: Python) -> PyResult<PyBytes> {
        let nodemap = self.get_nodetree(py)?.borrow_mut().take().unwrap();
        let (readonly, bytes) = nodemap.into_readonly_and_added_bytes();

        // If there's anything readonly, we need to build the data again from
        // scratch
        let bytes = if readonly.len() > 0 {
            let mut nt = NodeTree::load_bytes(Box::<Vec<_>>::default(), 0);
            self.fill_nodemap(py, &mut nt)?;

            let (readonly, bytes) = nt.into_readonly_and_added_bytes();
            assert_eq!(readonly.len(), 0);

            bytes
        } else {
            bytes
        };

        let bytes = PyBytes::new(py, &bytes);
        Ok(bytes)
    }

    /// Returns the last saved docket along with the size of any changed data
    /// (in number of blocks), and said data as bytes.
    fn inner_nodemap_data_incremental(
        &self,
        py: Python,
    ) -> PyResult<PyObject> {
        let docket = self.docket(py).borrow();
        let docket = match docket.as_ref() {
            Some(d) => d,
            None => return Ok(py.None()),
        };

        let node_tree = self.get_nodetree(py)?.borrow_mut().take().unwrap();
        let masked_blocks = node_tree.masked_readonly_blocks();
        let (_, data) = node_tree.into_readonly_and_added_bytes();
        let changed = masked_blocks * std::mem::size_of::<Block>();

        Ok((docket, changed, PyBytes::new(py, &data))
            .to_py_object(py)
            .into_object())
    }

    /// Update the nodemap from the new (mmaped) data.
    /// The docket is kept as a reference for later incremental calls.
    fn inner_update_nodemap_data(
        &self,
        py: Python,
        docket: PyObject,
        nm_data: PyObject,
    ) -> PyResult<PyObject> {
        // Safety: we keep the buffer around inside the class as `nodemap_mmap`
        let (buf, bytes) = unsafe { mmap_keeparound(py, nm_data)? };
        let len = buf.item_count();
        self.nodemap_mmap(py).borrow_mut().replace(buf);

        let mut nt = NodeTree::load_bytes(bytes, len);

        let data_tip = docket
            .getattr(py, "tip_rev")?
            .extract::<BaseRevision>(py)?
            .into();
        self.docket(py).borrow_mut().replace(docket.clone_ref(py));
        let idx = self.index(py).borrow();
        let data_tip = idx.check_revision(data_tip).ok_or_else(|| {
            nodemap_error(py, NodeMapError::RevisionNotInIndex(data_tip))
        })?;
        let current_tip = idx.len();

        for r in (data_tip.0 + 1)..current_tip as BaseRevision {
            let rev = Revision(r);
            // in this case node() won't ever return None
            nt.insert(&*idx, idx.node(rev).unwrap(), rev)
                .map_err(|e| nodemap_error(py, e))?
        }

        *self.nt(py).borrow_mut() = Some(nt);

        Ok(py.None())
    }

    fn inner_getitem(&self, py: Python, key: PyObject) -> PyResult<PyObject> {
        let idx = self.index(py).borrow();
        Ok(match key.extract::<BaseRevision>(py) {
            Ok(key_as_int) => {
                let entry_params = if key_as_int == NULL_REVISION.0 {
                    RevisionDataParams::default()
                } else {
                    let rev = UncheckedRevision(key_as_int);
                    match idx.entry_as_params(rev) {
                        Some(e) => e,
                        None => {
                            return Err(PyErr::new::<IndexError, _>(
                                py,
                                "revlog index out of range",
                            ));
                        }
                    }
                };
                revision_data_params_to_py_tuple(py, entry_params)
                    .into_object()
            }
            _ => self.get_rev(py, key.extract::<PyBytes>(py)?)?.map_or_else(
                || py.None(),
                |py_rev| py_rev.into_py_object(py).into_object(),
            ),
        })
    }

    fn inner_headrevs(&self, py: Python) -> PyResult<PyObject> {
        let index = &*self.index(py).borrow();
        let as_vec: Vec<PyObject> = index
            .head_revs()
            .map_err(|e| graph_error(py, e))?
            .iter()
            .map(|r| PyRevision::from(*r).into_py_object(py).into_object())
            .collect();
        Ok(PyList::new(py, &as_vec).into_object())
    }

    fn inner_headrevsfiltered(
        &self,
        py: Python,
        filtered_revs: &PyObject,
    ) -> PyResult<PyObject> {
        let index = &mut *self.index(py).borrow_mut();
        let filtered_revs = rev_pyiter_collect(py, filtered_revs, index)?;

        let as_vec: Vec<PyObject> = index
            .head_revs_filtered(&filtered_revs)
            .map_err(|e| graph_error(py, e))?
            .iter()
            .map(|r| PyRevision::from(*r).into_py_object(py).into_object())
            .collect();
        Ok(PyList::new(py, &as_vec).into_object())
    }

    fn inner_ancestors(
        &self,
        py: Python,
        py_revs: &PyTuple,
    ) -> PyResult<PyObject> {
        let index = &*self.index(py).borrow();
        let revs: Vec<_> = rev_pyiter_collect(py, py_revs.as_object(), index)?;
        let as_vec: Vec<_> = index
            .ancestors(&revs)
            .map_err(|e| graph_error(py, e))?
            .iter()
            .map(|r| PyRevision::from(*r).into_py_object(py).into_object())
            .collect();
        Ok(PyList::new(py, &as_vec).into_object())
    }

    fn inner_commonancestorsheads(
        &self,
        py: Python,
        py_revs: &PyTuple,
    ) -> PyResult<PyObject> {
        let index = &*self.index(py).borrow();
        let revs: Vec<_> = rev_pyiter_collect(py, py_revs.as_object(), index)?;
        let as_vec: Vec<_> = index
            .common_ancestor_heads(&revs)
            .map_err(|e| graph_error(py, e))?
            .iter()
            .map(|r| PyRevision::from(*r).into_py_object(py).into_object())
            .collect();
        Ok(PyList::new(py, &as_vec).into_object())
    }

    fn inner_computephasesmapsets(
        &self,
        py: Python,
        py_roots: PyDict,
    ) -> PyResult<PyObject> {
        let index = &*self.index(py).borrow();
        let opt = self.get_nodetree(py)?.borrow();
        let nt = opt.as_ref().unwrap();
        let roots: Result<HashMap<Phase, Vec<Revision>>, PyErr> = py_roots
            .items_list(py)
            .iter(py)
            .map(|r| {
                let phase = r.get_item(py, 0)?;
                let nodes = r.get_item(py, 1)?;
                // Transform the nodes from Python to revs here since we
                // have access to the nodemap
                let revs: Result<_, _> = nodes
                    .iter(py)?
                    .map(|node| match node?.extract::<PyBytes>(py) {
                        Ok(py_bytes) => {
                            let node = node_from_py_bytes(py, &py_bytes)?;
                            nt.find_bin(index, node.into())
                                .map_err(|e| nodemap_error(py, e))?
                                .ok_or_else(|| revlog_error(py))
                        }
                        Err(e) => Err(e),
                    })
                    .collect();
                let phase = Phase::try_from(phase.extract::<usize>(py)?)
                    .map_err(|_| revlog_error(py));
                Ok((phase?, revs?))
            })
            .collect();
        let (len, phase_maps) = index
            .compute_phases_map_sets(roots?)
            .map_err(|e| graph_error(py, e))?;

        // Ugly hack, but temporary
        const IDX_TO_PHASE_NUM: [usize; 4] = [1, 2, 32, 96];
        let py_phase_maps = PyDict::new(py);
        for (idx, roots) in phase_maps.iter().enumerate() {
            let phase_num = IDX_TO_PHASE_NUM[idx].into_py_object(py);
            // OPTIM too bad we have to collect here. At least, we could
            // reuse the same Vec and allocate it with capacity at
            // max(len(phase_maps)
            let roots_vec: Vec<PyInt> = roots
                .iter()
                .map(|r| PyRevision::from(*r).into_py_object(py))
                .collect();
            py_phase_maps.set_item(
                py,
                phase_num,
                PySet::new(py, roots_vec)?,
            )?;
        }
        Ok(PyTuple::new(
            py,
            &[
                len.into_py_object(py).into_object(),
                py_phase_maps.into_object(),
            ],
        )
        .into_object())
    }

    fn inner_slicechunktodensity(
        &self,
        py: Python,
        revs: PyObject,
        target_density: f64,
        min_gap_size: usize,
    ) -> PyResult<PyObject> {
        let index = &*self.index(py).borrow();
        let revs: Vec<_> = rev_pyiter_collect(py, &revs, index)?;
        let as_nested_vec =
            index.slice_chunk_to_density(&revs, target_density, min_gap_size);
        let mut res = Vec::with_capacity(as_nested_vec.len());
        let mut py_chunk = Vec::new();
        for chunk in as_nested_vec {
            py_chunk.clear();
            py_chunk.reserve_exact(chunk.len());
            for rev in chunk {
                py_chunk.push(
                    PyRevision::from(rev).into_py_object(py).into_object(),
                );
            }
            res.push(PyList::new(py, &py_chunk).into_object());
        }
        // This is just to do the same as C, not sure why it does this
        if res.len() == 1 {
            Ok(PyTuple::new(py, &res).into_object())
        } else {
            Ok(PyList::new(py, &res).into_object())
        }
    }

    fn inner_reachableroots2(
        &self,
        py: Python,
        min_root: UncheckedRevision,
        heads: PyObject,
        roots: PyObject,
        include_path: bool,
    ) -> PyResult<PyObject> {
        let index = &*self.index(py).borrow();
        let heads = rev_pyiter_collect_or_else(py, &heads, index, |_rev| {
            PyErr::new::<IndexError, _>(py, "head out of range")
        })?;
        let roots: Result<_, _> = roots
            .iter(py)?
            .map(|r| {
                r.and_then(|o| match o.extract::<PyRevision>(py) {
                    Ok(r) => Ok(UncheckedRevision(r.0)),
                    Err(e) => Err(e),
                })
            })
            .collect();
        let as_set = index
            .reachable_roots(min_root, heads, roots?, include_path)
            .map_err(|e| graph_error(py, e))?;
        let as_vec: Vec<PyObject> = as_set
            .iter()
            .map(|r| PyRevision::from(*r).into_py_object(py).into_object())
            .collect();
        Ok(PyList::new(py, &as_vec).into_object())
    }
}

fn revlog_error(py: Python) -> PyErr {
    match py
        .import("mercurial.error")
        .and_then(|m| m.get(py, "RevlogError"))
    {
        Err(e) => e,
        Ok(cls) => PyErr::from_instance(
            py,
            cls.call(py, (py.None(),), None).ok().into_py_object(py),
        ),
    }
}

fn revlog_error_with_msg(py: Python, msg: &[u8]) -> PyErr {
    match py
        .import("mercurial.error")
        .and_then(|m| m.get(py, "RevlogError"))
    {
        Err(e) => e,
        Ok(cls) => PyErr::from_instance(
            py,
            cls.call(py, (PyBytes::new(py, msg),), None)
                .ok()
                .into_py_object(py),
        ),
    }
}

fn graph_error(py: Python, _err: hg::GraphError) -> PyErr {
    // ParentOutOfRange is currently the only alternative
    // in `hg::GraphError`. The C index always raises this simple ValueError.
    PyErr::new::<ValueError, _>(py, "parent out of range")
}

fn nodemap_rev_not_in_index(py: Python, rev: UncheckedRevision) -> PyErr {
    PyErr::new::<ValueError, _>(
        py,
        format!(
            "Inconsistency: Revision {} found in nodemap \
             is not in revlog index",
            rev
        ),
    )
}

fn rev_not_in_index(py: Python, rev: UncheckedRevision) -> PyErr {
    PyErr::new::<ValueError, _>(
        py,
        format!("revlog index out of range: {}", rev),
    )
}

/// Standard treatment of NodeMapError
fn nodemap_error(py: Python, err: NodeMapError) -> PyErr {
    match err {
        NodeMapError::MultipleResults => revlog_error(py),
        NodeMapError::RevisionNotInIndex(r) => nodemap_rev_not_in_index(py, r),
    }
}

/// assert two Python objects to be equal from a Python point of view
///
/// `method` is a label for the assertion error message, intended to be the
/// name of the caller.
/// `normalizer` is a function that takes a Python variable name and returns
/// an expression that the conparison will actually use.
/// Foe example: `|v| format!("sorted({})", v)`
fn assert_py_eq_normalized(
    py: Python,
    method: &str,
    rust: &PyObject,
    c: &PyObject,
    normalizer: impl FnOnce(&str) -> String + Copy,
) -> PyResult<()> {
    let locals = PyDict::new(py);
    locals.set_item(py, "rust".into_py_object(py).into_object(), rust)?;
    locals.set_item(py, "c".into_py_object(py).into_object(), c)?;
    //    let lhs = format!(normalizer_fmt, "rust");
    //    let rhs = format!(normalizer_fmt, "c");
    let is_eq: PyBool = py
        .eval(
            &format!("{} == {}", &normalizer("rust"), &normalizer("c")),
            None,
            Some(&locals),
        )?
        .extract(py)?;
    assert!(
        is_eq.is_true(),
        "{} results differ. Rust: {:?} C: {:?} (before any normalization)",
        method,
        rust,
        c
    );
    Ok(())
}

fn assert_py_eq(
    py: Python,
    method: &str,
    rust: &PyObject,
    c: &PyObject,
) -> PyResult<()> {
    assert_py_eq_normalized(py, method, rust, c, |v| v.to_owned())
}

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

    m.add_class::<MixedIndex>(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)
}