annotate rust/hg-core/src/dirstate_tree/dirstate_map.rs @ 49000:dd6b67d5c256 stable

rust: fix unsound `OwningDirstateMap`

As per the previous patch, `OwningDirstateMap` is unsound. Self-referential
structs are difficult to implement correctly in Rust since the compiler is
free to move structs around as much as it wants to. They are also very rarely
needed in practice, so the state-of-the-art on how they should be done within
the Rust rules is still a bit new.

The crate `ouroboros` is an attempt at providing a safe way (in the Rust sense)
of declaring self-referential structs. It is getting a lot attention and was
improved very quickly when soundness issues were found in the past: rather than
relying on our own (limited) review circle, we might as well use the de-facto
common crate to fix this problem. This will give us a much better chance of
finding issues should any new ones be discovered as well as the benefit of
fewer `unsafe` APIs of our own.

I was starting to think about how I would present a safe API to the old struct
but soon realized that the callback-based approach was already done in
`ouroboros`, along with a lot more care towards refusing incorrect structs.

In short: we don't return a mutable reference to the `DirstateMap` anymore, we
expect users of its API to pass a `FnOnce` that takes the map as an argument.
This allows our `OwningDirstateMap` to control the input and output lifetimes
of the code that modifies it to prevent such issues.

Changing to `ouroboros` meant changing every API with it, but it is relatively
low churn in the end. It correctly identified the example buggy modification of
`copy_map_insert` outlined in the previous patch as violating the borrow rules.

Differential Revision: https://phab.mercurial-scm.org/D12429

use bytes_cast::BytesCast;
use micro_timer::timed;
use std::borrow::Cow;
use std::path::PathBuf;

use super::on_disk;
use super::on_disk::DirstateV2ParseError;
use super::owning::OwningDirstateMap;
use super::path_with_basename::WithBasename;
use crate::dirstate::parsers::pack_entry;
use crate::dirstate::parsers::packed_entry_size;
use crate::dirstate::parsers::parse_dirstate_entries;
use crate::dirstate::CopyMapIter;
use crate::dirstate::StateMapIter;
use crate::dirstate::TruncatedTimestamp;
use crate::dirstate::SIZE_FROM_OTHER_PARENT;
use crate::dirstate::SIZE_NON_NORMAL;
use crate::matchers::Matcher;
use crate::utils::hg_path::{HgPath, HgPathBuf};
use crate::DirstateEntry;
use crate::DirstateError;
use crate::DirstateParents;
use crate::DirstateStatus;
use crate::EntryState;
use crate::FastHashMap;
use crate::PatternFileWarning;
use crate::StatusError;
use crate::StatusOptions;

/// Append to an existing data file if the amount of unreachable data (not used
/// anymore) is less than this fraction of the total amount of existing data.
const ACCEPTABLE_UNREACHABLE_BYTES_RATIO: f32 = 0.5;

pub struct DirstateMap<'on_disk> {
    /// Contents of the `.hg/dirstate` file
    pub(super) on_disk: &'on_disk [u8],

    pub(super) root: ChildNodes<'on_disk>,

    /// Number of nodes anywhere in the tree that have `.entry.is_some()`.
    pub(super) nodes_with_entry_count: u32,

    /// Number of nodes anywhere in the tree that have
    /// `.copy_source.is_some()`.
    pub(super) nodes_with_copy_source_count: u32,

    /// See on_disk::Header
    pub(super) ignore_patterns_hash: on_disk::IgnorePatternsHash,

    /// How many bytes of `on_disk` are not used anymore
    pub(super) unreachable_bytes: u32,
}

/// Using a plain `HgPathBuf` of the full path from the repository root as a
/// map key would also work: all paths in a given map have the same parent
/// path, so comparing full paths gives the same result as comparing base
/// names. However `HashMap` would waste time always re-hashing the same
/// string prefix.
pub(super) type NodeKey<'on_disk> = WithBasename<Cow<'on_disk, HgPath>>;

/// Similar to `&'tree Cow<'on_disk, HgPath>`, but can also be returned
/// for on-disk nodes that don’t actually have a `Cow` to borrow.
pub(super) enum BorrowedPath<'tree, 'on_disk> {
    InMemory(&'tree HgPathBuf),
    OnDisk(&'on_disk HgPath),
}

pub(super) enum ChildNodes<'on_disk> {
    InMemory(FastHashMap<NodeKey<'on_disk>, Node<'on_disk>>),
    OnDisk(&'on_disk [on_disk::Node]),
}

pub(super) enum ChildNodesRef<'tree, 'on_disk> {
    InMemory(&'tree FastHashMap<NodeKey<'on_disk>, Node<'on_disk>>),
    OnDisk(&'on_disk [on_disk::Node]),
}

pub(super) enum NodeRef<'tree, 'on_disk> {
    InMemory(&'tree NodeKey<'on_disk>, &'tree Node<'on_disk>),
    OnDisk(&'on_disk on_disk::Node),
}

impl<'tree, 'on_disk> BorrowedPath<'tree, 'on_disk> {
    pub fn detach_from_tree(&self) -> Cow<'on_disk, HgPath> {
        match *self {
            BorrowedPath::InMemory(in_memory) => Cow::Owned(in_memory.clone()),
            BorrowedPath::OnDisk(on_disk) => Cow::Borrowed(on_disk),
        }
    }
}

impl<'tree, 'on_disk> std::ops::Deref for BorrowedPath<'tree, 'on_disk> {
    type Target = HgPath;

    fn deref(&self) -> &HgPath {
        match *self {
            BorrowedPath::InMemory(in_memory) => in_memory,
            BorrowedPath::OnDisk(on_disk) => on_disk,
        }
    }
}

impl Default for ChildNodes<'_> {
    fn default() -> Self {
        ChildNodes::InMemory(Default::default())
    }
}

impl<'on_disk> ChildNodes<'on_disk> {
    pub(super) fn as_ref<'tree>(
        &'tree self,
    ) -> ChildNodesRef<'tree, 'on_disk> {
        match self {
            ChildNodes::InMemory(nodes) => ChildNodesRef::InMemory(nodes),
            ChildNodes::OnDisk(nodes) => ChildNodesRef::OnDisk(nodes),
        }
    }

    pub(super) fn is_empty(&self) -> bool {
        match self {
            ChildNodes::InMemory(nodes) => nodes.is_empty(),
            ChildNodes::OnDisk(nodes) => nodes.is_empty(),
        }
    }

    fn make_mut(
        &mut self,
        on_disk: &'on_disk [u8],
        unreachable_bytes: &mut u32,
    ) -> Result<
        &mut FastHashMap<NodeKey<'on_disk>, Node<'on_disk>>,
        DirstateV2ParseError,
    > {
        match self {
            ChildNodes::InMemory(nodes) => Ok(nodes),
            ChildNodes::OnDisk(nodes) => {
                *unreachable_bytes +=
                    std::mem::size_of_val::<[on_disk::Node]>(nodes) as u32;
                let nodes = nodes
                    .iter()
                    .map(|node| {
                        Ok((
                            node.path(on_disk)?,
                            node.to_in_memory_node(on_disk)?,
                        ))
                    })
                    .collect::<Result<_, _>>()?;
                *self = ChildNodes::InMemory(nodes);
                match self {
                    ChildNodes::InMemory(nodes) => Ok(nodes),
                    ChildNodes::OnDisk(_) => unreachable!(),
                }
            }
        }
    }
}

impl<'tree, 'on_disk> ChildNodesRef<'tree, 'on_disk> {
    pub(super) fn get(
        &self,
        base_name: &HgPath,
        on_disk: &'on_disk [u8],
    ) -> Result<Option<NodeRef<'tree, 'on_disk>>, DirstateV2ParseError> {
        match self {
            ChildNodesRef::InMemory(nodes) => Ok(nodes
                .get_key_value(base_name)
                .map(|(k, v)| NodeRef::InMemory(k, v))),
            ChildNodesRef::OnDisk(nodes) => {
                let mut parse_result = Ok(());
                let search_result = nodes.binary_search_by(|node| {
                    match node.base_name(on_disk) {
                        Ok(node_base_name) => node_base_name.cmp(base_name),
                        Err(e) => {
                            parse_result = Err(e);
                            // Dummy comparison result, `search_result` won’t
                            // be used since `parse_result` is an error
                            std::cmp::Ordering::Equal
                        }
                    }
                });
                parse_result.map(|()| {
                    search_result.ok().map(|i| NodeRef::OnDisk(&nodes[i]))
                })
            }
        }
    }

    /// Iterate in undefined order
    pub(super) fn iter(
        &self,
    ) -> impl Iterator<Item = NodeRef<'tree, 'on_disk>> {
        match self {
            ChildNodesRef::InMemory(nodes) => itertools::Either::Left(
                nodes.iter().map(|(k, v)| NodeRef::InMemory(k, v)),
            ),
            ChildNodesRef::OnDisk(nodes) => {
                itertools::Either::Right(nodes.iter().map(NodeRef::OnDisk))
            }
        }
    }

    /// Iterate in parallel in undefined order
    pub(super) fn par_iter(
        &self,
    ) -> impl rayon::iter::ParallelIterator<Item = NodeRef<'tree, 'on_disk>>
    {
        use rayon::prelude::*;
        match self {
            ChildNodesRef::InMemory(nodes) => rayon::iter::Either::Left(
                nodes.par_iter().map(|(k, v)| NodeRef::InMemory(k, v)),
            ),
            ChildNodesRef::OnDisk(nodes) => rayon::iter::Either::Right(
                nodes.par_iter().map(NodeRef::OnDisk),
            ),
        }
    }

    pub(super) fn sorted(&self) -> Vec<NodeRef<'tree, 'on_disk>> {
        match self {
            ChildNodesRef::InMemory(nodes) => {
                let mut vec: Vec<_> = nodes
                    .iter()
                    .map(|(k, v)| NodeRef::InMemory(k, v))
                    .collect();
                fn sort_key<'a>(node: &'a NodeRef) -> &'a HgPath {
                    match node {
                        NodeRef::InMemory(path, _node) => path.base_name(),
                        NodeRef::OnDisk(_) => unreachable!(),
                    }
                }
                // `sort_unstable_by_key` doesn’t allow keys borrowing from the
                // value: https://github.com/rust-lang/rust/issues/34162
                vec.sort_unstable_by(|a, b| sort_key(a).cmp(sort_key(b)));
                vec
            }
            ChildNodesRef::OnDisk(nodes) => {
                // Nodes on disk are already sorted
                nodes.iter().map(NodeRef::OnDisk).collect()
            }
        }
    }
}

impl<'tree, 'on_disk> NodeRef<'tree, 'on_disk> {
    pub(super) fn full_path(
        &self,
        on_disk: &'on_disk [u8],
    ) -> Result<&'tree HgPath, DirstateV2ParseError> {
        match self {
            NodeRef::InMemory(path, _node) => Ok(path.full_path()),
            NodeRef::OnDisk(node) => node.full_path(on_disk),
        }
    }

    /// Returns a `BorrowedPath`, which can be turned into a `Cow<'on_disk,
    /// HgPath>` detached from `'tree`
    pub(super) fn full_path_borrowed(
        &self,
        on_disk: &'on_disk [u8],
    ) -> Result<BorrowedPath<'tree, 'on_disk>, DirstateV2ParseError> {
        match self {
            NodeRef::InMemory(path, _node) => match path.full_path() {
                Cow::Borrowed(on_disk) => Ok(BorrowedPath::OnDisk(on_disk)),
                Cow::Owned(in_memory) => Ok(BorrowedPath::InMemory(in_memory)),
            },
            NodeRef::OnDisk(node) => {
                Ok(BorrowedPath::OnDisk(node.full_path(on_disk)?))
            }
        }
    }

    pub(super) fn base_name(
        &self,
        on_disk: &'on_disk [u8],
    ) -> Result<&'tree HgPath, DirstateV2ParseError> {
        match self {
            NodeRef::InMemory(path, _node) => Ok(path.base_name()),
            NodeRef::OnDisk(node) => node.base_name(on_disk),
        }
    }

    pub(super) fn children(
        &self,
        on_disk: &'on_disk [u8],
    ) -> Result<ChildNodesRef<'tree, 'on_disk>, DirstateV2ParseError> {
        match self {
            NodeRef::InMemory(_path, node) => Ok(node.children.as_ref()),
            NodeRef::OnDisk(node) => {
                Ok(ChildNodesRef::OnDisk(node.children(on_disk)?))
            }
        }
    }

    pub(super) fn has_copy_source(&self) -> bool {
        match self {
            NodeRef::InMemory(_path, node) => node.copy_source.is_some(),
            NodeRef::OnDisk(node) => node.has_copy_source(),
        }
    }

    pub(super) fn copy_source(
        &self,
        on_disk: &'on_disk [u8],
    ) -> Result<Option<&'tree HgPath>, DirstateV2ParseError> {
        match self {
            NodeRef::InMemory(_path, node) => {
                Ok(node.copy_source.as_ref().map(|s| &**s))
            }
            NodeRef::OnDisk(node) => node.copy_source(on_disk),
        }
    }
    /// Returns a `BorrowedPath`, which can be turned into a `Cow<'on_disk,
    /// HgPath>` detached from `'tree`
    pub(super) fn copy_source_borrowed(
        &self,
        on_disk: &'on_disk [u8],
    ) -> Result<Option<BorrowedPath<'tree, 'on_disk>>, DirstateV2ParseError>
    {
        Ok(match self {
            NodeRef::InMemory(_path, node) => {
                node.copy_source.as_ref().map(|source| match source {
                    Cow::Borrowed(on_disk) => BorrowedPath::OnDisk(on_disk),
                    Cow::Owned(in_memory) => BorrowedPath::InMemory(in_memory),
                })
            }
            NodeRef::OnDisk(node) => node
                .copy_source(on_disk)?
                .map(|source| BorrowedPath::OnDisk(source)),
        })
    }

    pub(super) fn entry(
        &self,
    ) -> Result<Option<DirstateEntry>, DirstateV2ParseError> {
        match self {
            NodeRef::InMemory(_path, node) => {
                Ok(node.data.as_entry().copied())
            }
            NodeRef::OnDisk(node) => node.entry(),
        }
    }

    pub(super) fn state(
        &self,
    ) -> Result<Option<EntryState>, DirstateV2ParseError> {
        Ok(self.entry()?.map(|e| e.state()))
    }

    pub(super) fn cached_directory_mtime(
        &self,
    ) -> Result<Option<TruncatedTimestamp>, DirstateV2ParseError> {
        match self {
            NodeRef::InMemory(_path, node) => Ok(match node.data {
                NodeData::CachedDirectory { mtime } => Some(mtime),
                _ => None,
            }),
            NodeRef::OnDisk(node) => node.cached_directory_mtime(),
        }
    }

    pub(super) fn descendants_with_entry_count(&self) -> u32 {
        match self {
            NodeRef::InMemory(_path, node) => {
                node.descendants_with_entry_count
            }
            NodeRef::OnDisk(node) => node.descendants_with_entry_count.get(),
        }
    }

    pub(super) fn tracked_descendants_count(&self) -> u32 {
        match self {
            NodeRef::InMemory(_path, node) => node.tracked_descendants_count,
            NodeRef::OnDisk(node) => node.tracked_descendants_count.get(),
        }
    }
}

/// Represents a file or a directory
#[derive(Default)]
pub(super) struct Node<'on_disk> {
    pub(super) data: NodeData,

    pub(super) copy_source: Option<Cow<'on_disk, HgPath>>,

    pub(super) children: ChildNodes<'on_disk>,

    /// How many (non-inclusive) descendants of this node have an entry.
    pub(super) descendants_with_entry_count: u32,

    /// How many (non-inclusive) descendants of this node have an entry whose
    /// state is "tracked".
    pub(super) tracked_descendants_count: u32,
}

pub(super) enum NodeData {
    Entry(DirstateEntry),
    CachedDirectory { mtime: TruncatedTimestamp },
    None,
}

impl Default for NodeData {
    fn default() -> Self {
        NodeData::None
    }
}

impl NodeData {
    fn has_entry(&self) -> bool {
        match self {
            NodeData::Entry(_) => true,
            _ => false,
        }
    }

    fn as_entry(&self) -> Option<&DirstateEntry> {
        match self {
            NodeData::Entry(entry) => Some(entry),
            _ => None,
        }
    }
}

impl<'on_disk> DirstateMap<'on_disk> {
    pub(super) fn empty(on_disk: &'on_disk [u8]) -> Self {
        Self {
            on_disk,
            root: ChildNodes::default(),
            nodes_with_entry_count: 0,
            nodes_with_copy_source_count: 0,
            ignore_patterns_hash: [0; on_disk::IGNORE_PATTERNS_HASH_LEN],
            unreachable_bytes: 0,
        }
    }

    #[timed]
    pub fn new_v2(
        on_disk: &'on_disk [u8],
        data_size: usize,
        metadata: &[u8],
    ) -> Result<Self, DirstateError> {
        if let Some(data) = on_disk.get(..data_size) {
            Ok(on_disk::read(data, metadata)?)
        } else {
            Err(DirstateV2ParseError.into())
        }
    }

    #[timed]
    pub fn new_v1(
        on_disk: &'on_disk [u8],
    ) -> Result<(Self, Option<DirstateParents>), DirstateError> {
        let mut map = Self::empty(on_disk);
        if map.on_disk.is_empty() {
            return Ok((map, None));
        }

        let parents = parse_dirstate_entries(
            map.on_disk,
            |path, entry, copy_source| {
                let tracked = entry.state().is_tracked();
                let node = Self::get_or_insert_node(
                    map.on_disk,
                    &mut map.unreachable_bytes,
                    &mut map.root,
                    path,
                    WithBasename::to_cow_borrowed,
                    |ancestor| {
                        if tracked {
                            ancestor.tracked_descendants_count += 1
                        }
                        ancestor.descendants_with_entry_count += 1
                    },
                )?;
                assert!(
                    !node.data.has_entry(),
                    "duplicate dirstate entry in read"
                );
                assert!(
                    node.copy_source.is_none(),
                    "duplicate dirstate entry in read"
                );
                node.data = NodeData::Entry(*entry);
                node.copy_source = copy_source.map(Cow::Borrowed);
                map.nodes_with_entry_count += 1;
                if copy_source.is_some() {
                    map.nodes_with_copy_source_count += 1
                }
                Ok(())
            },
        )?;
        let parents = Some(parents.clone());

        Ok((map, parents))
    }

    /// Assuming dirstate-v2 format, returns whether the next write should
    /// append to the existing data file that contains `self.on_disk` (true),
    /// or create a new data file from scratch (false).
    pub(super) fn write_should_append(&self) -> bool {
        let ratio = self.unreachable_bytes as f32 / self.on_disk.len() as f32;
        ratio < ACCEPTABLE_UNREACHABLE_BYTES_RATIO
    }

    fn get_node<'tree>(
        &'tree self,
        path: &HgPath,
    ) -> Result<Option<NodeRef<'tree, 'on_disk>>, DirstateV2ParseError> {
        let mut children = self.root.as_ref();
        let mut components = path.components();
        let mut component =
            components.next().expect("expected at least one components");
        loop {
            if let Some(child) = children.get(component, self.on_disk)? {
                if let Some(next_component) = components.next() {
                    component = next_component;
                    children = child.children(self.on_disk)?;
                } else {
                    return Ok(Some(child));
                }
            } else {
                return Ok(None);
            }
        }
    }

    /// Returns a mutable reference to the node at `path` if it exists
    ///
    /// This takes `root` instead of `&mut self` so that callers can mutate
    /// other fields while the returned borrow is still valid
    fn get_node_mut<'tree>(
        on_disk: &'on_disk [u8],
        unreachable_bytes: &mut u32,
        root: &'tree mut ChildNodes<'on_disk>,
        path: &HgPath,
    ) -> Result<Option<&'tree mut Node<'on_disk>>, DirstateV2ParseError> {
        let mut children = root;
        let mut components = path.components();
        let mut component =
            components.next().expect("expected at least one components");
        loop {
            if let Some(child) = children
                .make_mut(on_disk, unreachable_bytes)?
                .get_mut(component)
            {
                if let Some(next_component) = components.next() {
                    component = next_component;
                    children = &mut child.children;
                } else {
                    return Ok(Some(child));
                }
            } else {
                return Ok(None);
            }
        }
    }

    pub(super) fn get_or_insert<'tree, 'path>(
        &'tree mut self,
        path: &HgPath,
    ) -> Result<&'tree mut Node<'on_disk>, DirstateV2ParseError> {
        Self::get_or_insert_node(
            self.on_disk,
            &mut self.unreachable_bytes,
            &mut self.root,
            path,
            WithBasename::to_cow_owned,
            |_| {},
        )
    }

    fn get_or_insert_node<'tree, 'path>(
        on_disk: &'on_disk [u8],
        unreachable_bytes: &mut u32,
        root: &'tree mut ChildNodes<'on_disk>,
        path: &'path HgPath,
        to_cow: impl Fn(
            WithBasename<&'path HgPath>,
        ) -> WithBasename<Cow<'on_disk, HgPath>>,
        mut each_ancestor: impl FnMut(&mut Node),
    ) -> Result<&'tree mut Node<'on_disk>, DirstateV2ParseError> {
        let mut child_nodes = root;
        let mut inclusive_ancestor_paths =
            WithBasename::inclusive_ancestors_of(path);
        let mut ancestor_path = inclusive_ancestor_paths
            .next()
            .expect("expected at least one inclusive ancestor");
        loop {
            // TODO: can we avoid allocating an owned key in cases where the
            // map already contains that key, without introducing double
            // lookup?
            let child_node = child_nodes
                .make_mut(on_disk, unreachable_bytes)?
                .entry(to_cow(ancestor_path))
                .or_default();
            if let Some(next) = inclusive_ancestor_paths.next() {
                each_ancestor(child_node);
                ancestor_path = next;
                child_nodes = &mut child_node.children;
            } else {
                return Ok(child_node);
            }
        }
    }

    fn add_or_remove_file(
        &mut self,
        path: &HgPath,
        old_state: Option<EntryState>,
        new_entry: DirstateEntry,
    ) -> Result<(), DirstateV2ParseError> {
        let had_entry = old_state.is_some();
        let was_tracked = old_state.map_or(false, |s| s.is_tracked());
        let tracked_count_increment =
            match (was_tracked, new_entry.state().is_tracked()) {
                (false, true) => 1,
                (true, false) => -1,
                _ => 0,
            };

        let node = Self::get_or_insert_node(
            self.on_disk,
            &mut self.unreachable_bytes,
            &mut self.root,
            path,
            WithBasename::to_cow_owned,
            |ancestor| {
                if !had_entry {
                    ancestor.descendants_with_entry_count += 1;
                }

                // We can’t use `+= increment` because the counter is unsigned,
                // and we want debug builds to detect accidental underflow
                // through zero
                match tracked_count_increment {
                    1 => ancestor.tracked_descendants_count += 1,
                    -1 => ancestor.tracked_descendants_count -= 1,
                    _ => {}
                }
            },
        )?;
        if !had_entry {
            self.nodes_with_entry_count += 1
        }
        node.data = NodeData::Entry(new_entry);
        Ok(())
    }

    fn iter_nodes<'tree>(
        &'tree self,
    ) -> impl Iterator<
        Item = Result<NodeRef<'tree, 'on_disk>, DirstateV2ParseError>,
    > + 'tree {
        // Depth first tree traversal.
        //
        // If we could afford internal iteration and recursion,
        // this would look like:
        //
        // ```
        // fn traverse_children(
        //     children: &ChildNodes,
        //     each: &mut impl FnMut(&Node),
        // ) {
        //     for child in children.values() {
        //         traverse_children(&child.children, each);
        //         each(child);
        //     }
        // }
        // ```
        //
        // However we want an external iterator and therefore can’t use the
        // call stack. Use an explicit stack instead:
        let mut stack = Vec::new();
        let mut iter = self.root.as_ref().iter();
        std::iter::from_fn(move || {
            while let Some(child_node) = iter.next() {
                let children = match child_node.children(self.on_disk) {
                    Ok(children) => children,
                    Err(error) => return Some(Err(error)),
                };
                // Pseudo-recursion
                let new_iter = children.iter();
                let old_iter = std::mem::replace(&mut iter, new_iter);
                stack.push((child_node, old_iter));
            }
            // Found the end of a `children.iter()` iterator.
            if let Some((child_node, next_iter)) = stack.pop() {
                // "Return" from pseudo-recursion by restoring state from the
                // explicit stack
                iter = next_iter;

                Some(Ok(child_node))
            } else {
                // Reached the bottom of the stack, we’re done
                None
            }
        })
    }

    fn count_dropped_path(unreachable_bytes: &mut u32, path: &Cow<HgPath>) {
        if let Cow::Borrowed(path) = path {
            *unreachable_bytes += path.len() as u32
        }
    }
}

/// Like `Iterator::filter_map`, but over a fallible iterator of `Result`s.
///
/// The callback is only called for incoming `Ok` values. Errors are passed
/// through as-is. In order to let it use the `?` operator the callback is
/// expected to return a `Result` of `Option`, instead of an `Option` of
/// `Result`.
fn filter_map_results<'a, I, F, A, B, E>(
    iter: I,
    f: F,
) -> impl Iterator<Item = Result<B, E>> + 'a
where
    I: Iterator<Item = Result<A, E>> + 'a,
    F: Fn(A) -> Result<Option<B>, E> + 'a,
{
    iter.filter_map(move |result| match result {
        Ok(node) => f(node).transpose(),
        Err(e) => Some(Err(e)),
    })
}

impl OwningDirstateMap {
    pub fn clear(&mut self) {
        self.with_dmap_mut(|map| {
            map.root = Default::default();
            map.nodes_with_entry_count = 0;
            map.nodes_with_copy_source_count = 0;
        });
    }

    pub fn set_entry(
        &mut self,
        filename: &HgPath,
        entry: DirstateEntry,
    ) -> Result<(), DirstateV2ParseError> {
        self.with_dmap_mut(|map| {
            map.get_or_insert(&filename)?.data = NodeData::Entry(entry);
            Ok(())
        })
    }

    pub fn add_file(
        &mut self,
        filename: &HgPath,
        entry: DirstateEntry,
    ) -> Result<(), DirstateError> {
        let old_state = self.get(filename)?.map(|e| e.state());
        self.with_dmap_mut(|map| {
            Ok(map.add_or_remove_file(filename, old_state, entry)?)
        })
    }

    pub fn remove_file(
        &mut self,
        filename: &HgPath,
        in_merge: bool,
    ) -> Result<(), DirstateError> {
        let old_entry_opt = self.get(filename)?;
        let old_state = old_entry_opt.map(|e| e.state());
        let mut size = 0;
        if in_merge {
            // XXX we should not be able to have 'm' state and 'FROM_P2' if not
            // during a merge. So I (marmoute) am not sure we need the
            // conditionnal at all. Adding double checking this with assert
            // would be nice.
            if let Some(old_entry) = old_entry_opt {
                // backup the previous state
                if old_entry.state() == EntryState::Merged {
                    size = SIZE_NON_NORMAL;
                } else if old_entry.state() == EntryState::Normal
                    && old_entry.size() == SIZE_FROM_OTHER_PARENT
                {
                    // other parent
                    size = SIZE_FROM_OTHER_PARENT;
                }
            }
        }
        if size == 0 {
            self.copy_map_remove(filename)?;
        }
        self.with_dmap_mut(|map| {
            let entry = DirstateEntry::new_removed(size);
            Ok(map.add_or_remove_file(filename, old_state, entry)?)
        })
    }

    pub fn drop_entry_and_copy_source(
        &mut self,
        filename: &HgPath,
    ) -> Result<(), DirstateError> {
        let was_tracked = self
            .get(filename)?
            .map_or(false, |e| e.state().is_tracked());
        struct Dropped {
            was_tracked: bool,
            had_entry: bool,
            had_copy_source: bool,
        }

        /// If this returns `Ok(Some((dropped, removed)))`, then
        ///
        /// * `dropped` is about the leaf node that was at `filename`
        /// * `removed` is whether this particular level of recursion just
        ///   removed a node in `nodes`.
        fn recur<'on_disk>(
            on_disk: &'on_disk [u8],
            unreachable_bytes: &mut u32,
            nodes: &mut ChildNodes<'on_disk>,
            path: &HgPath,
        ) -> Result<Option<(Dropped, bool)>, DirstateV2ParseError> {
            let (first_path_component, rest_of_path) =
                path.split_first_component();
            let nodes = nodes.make_mut(on_disk, unreachable_bytes)?;
            let node = if let Some(node) = nodes.get_mut(first_path_component)
            {
                node
            } else {
                return Ok(None);
            };
            let dropped;
            if let Some(rest) = rest_of_path {
                if let Some((d, removed)) = recur(
                    on_disk,
                    unreachable_bytes,
                    &mut node.children,
                    rest,
                )? {
                    dropped = d;
                    if dropped.had_entry {
                        node.descendants_with_entry_count -= 1;
                    }
                    if dropped.was_tracked {
                        node.tracked_descendants_count -= 1;
                    }

                    // Directory caches must be invalidated when removing a
                    // child node
                    if removed {
                        if let NodeData::CachedDirectory { .. } = &node.data {
                            node.data = NodeData::None
                        }
                    }
                } else {
                    return Ok(None);
                }
            } else {
                let had_entry = node.data.has_entry();
                if had_entry {
                    node.data = NodeData::None
                }
                if let Some(source) = &node.copy_source {
                    DirstateMap::count_dropped_path(unreachable_bytes, source);
                    node.copy_source = None
                }
                dropped = Dropped {
                    was_tracked: node
                        .data
                        .as_entry()
                        .map_or(false, |entry| entry.state().is_tracked()),
                    had_entry,
                    had_copy_source: node.copy_source.take().is_some(),
                };
            }
            // After recursion, for both leaf (rest_of_path is None) nodes and
            // parent nodes, remove a node if it just became empty.
            let remove = !node.data.has_entry()
                && node.copy_source.is_none()
                && node.children.is_empty();
            if remove {
                let (key, _) =
                    nodes.remove_entry(first_path_component).unwrap();
                DirstateMap::count_dropped_path(
                    unreachable_bytes,
                    key.full_path(),
                )
            }
            Ok(Some((dropped, remove)))
        }

        self.with_dmap_mut(|map| {
            if let Some((dropped, _removed)) = recur(
                map.on_disk,
                &mut map.unreachable_bytes,
                &mut map.root,
                filename,
            )? {
                if dropped.had_entry {
                    map.nodes_with_entry_count -= 1
                }
                if dropped.had_copy_source {
                    map.nodes_with_copy_source_count -= 1
                }
            } else {
                debug_assert!(!was_tracked);
            }
            Ok(())
        })
    }

    pub fn has_tracked_dir(
        &mut self,
        directory: &HgPath,
    ) -> Result<bool, DirstateError> {
        self.with_dmap_mut(|map| {
            if let Some(node) = map.get_node(directory)? {
                // A node without a `DirstateEntry` was created to hold child
                // nodes, and is therefore a directory.
                let state = node.state()?;
                Ok(state.is_none() && node.tracked_descendants_count() > 0)
            } else {
                Ok(false)
            }
        })
    }

    pub fn has_dir(
        &mut self,
        directory: &HgPath,
    ) -> Result<bool, DirstateError> {
        self.with_dmap_mut(|map| {
            if let Some(node) = map.get_node(directory)? {
                // A node without a `DirstateEntry` was created to hold child
                // nodes, and is therefore a directory.
                let state = node.state()?;
                Ok(state.is_none() && node.descendants_with_entry_count() > 0)
            } else {
                Ok(false)
            }
        })
    }

    #[timed]
    pub fn pack_v1(
        &self,
        parents: DirstateParents,
    ) -> Result<Vec<u8>, DirstateError> {
        let map = self.get_map();
        // Optizimation (to be measured?): pre-compute size to avoid `Vec`
        // reallocations
        let mut size = parents.as_bytes().len();
        for node in map.iter_nodes() {
            let node = node?;
            if node.entry()?.is_some() {
                size += packed_entry_size(
                    node.full_path(map.on_disk)?,
                    node.copy_source(map.on_disk)?,
                );
            }
        }

        let mut packed = Vec::with_capacity(size);
        packed.extend(parents.as_bytes());

        for node in map.iter_nodes() {
            let node = node?;
            if let Some(entry) = node.entry()? {
                pack_entry(
                    node.full_path(map.on_disk)?,
                    &entry,
                    node.copy_source(map.on_disk)?,
                    &mut packed,
                );
            }
        }
        Ok(packed)
    }

    /// Returns new data and metadata together with whether that data should be
    /// appended to the existing data file whose content is at
    /// `map.on_disk` (true), instead of written to a new data file
    /// (false).
    #[timed]
    pub fn pack_v2(
        &self,
        can_append: bool,
    ) -> Result<(Vec<u8>, on_disk::TreeMetadata, bool), DirstateError> {
        let map = self.get_map();
        on_disk::write(map, can_append)
    }

    /// `callback` allows the caller to process and do something with the
    /// results of the status. This is needed to do so efficiently (i.e.
    /// without cloning the `DirstateStatus` object with its paths) because
    /// we need to borrow from `Self`.
    pub fn with_status<R>(
        &mut self,
        matcher: &(dyn Matcher + Sync),
        root_dir: PathBuf,
        ignore_files: Vec<PathBuf>,
        options: StatusOptions,
        callback: impl for<'r> FnOnce(
            Result<(DirstateStatus<'r>, Vec<PatternFileWarning>), StatusError>,
        ) -> R,
    ) -> R {
        self.with_dmap_mut(|map| {
            callback(super::status::status(
                map,
                matcher,
                root_dir,
                ignore_files,
                options,
            ))
        })
    }

    pub fn copy_map_len(&self) -> usize {
        let map = self.get_map();
        map.nodes_with_copy_source_count as usize
    }

    pub fn copy_map_iter(&self) -> CopyMapIter<'_> {
        let map = self.get_map();
        Box::new(filter_map_results(map.iter_nodes(), move |node| {
            Ok(if let Some(source) = node.copy_source(map.on_disk)? {
                Some((node.full_path(map.on_disk)?, source))
            } else {
                None
            })
        }))
    }

    pub fn copy_map_contains_key(
        &self,
        key: &HgPath,
    ) -> Result<bool, DirstateV2ParseError> {
        let map = self.get_map();
        Ok(if let Some(node) = map.get_node(key)? {
            node.has_copy_source()
        } else {
            false
        })
    }

    pub fn copy_map_get(
        &self,
        key: &HgPath,
    ) -> Result<Option<&HgPath>, DirstateV2ParseError> {
        let map = self.get_map();
        if let Some(node) = map.get_node(key)? {
            if let Some(source) = node.copy_source(map.on_disk)? {
                return Ok(Some(source));
            }
        }
        Ok(None)
    }

    pub fn copy_map_remove(
        &mut self,
        key: &HgPath,
    ) -> Result<Option<HgPathBuf>, DirstateV2ParseError> {
        self.with_dmap_mut(|map| {
            let count = &mut map.nodes_with_copy_source_count;
            let unreachable_bytes = &mut map.unreachable_bytes;
            Ok(DirstateMap::get_node_mut(
                map.on_disk,
                unreachable_bytes,
                &mut map.root,
                key,
            )?
            .and_then(|node| {
                if let Some(source) = &node.copy_source {
                    *count -= 1;
                    DirstateMap::count_dropped_path(unreachable_bytes, source);
                }
                node.copy_source.take().map(Cow::into_owned)
            }))
        })
    }

    pub fn copy_map_insert(
        &mut self,
        key: HgPathBuf,
        value: HgPathBuf,
    ) -> Result<Option<HgPathBuf>, DirstateV2ParseError> {
        self.with_dmap_mut(|map| {
            let node = DirstateMap::get_or_insert_node(
                map.on_disk,
                &mut map.unreachable_bytes,
                &mut map.root,
                &key,
                WithBasename::to_cow_owned,
                |_ancestor| {},
            )?;
            if node.copy_source.is_none() {
                map.nodes_with_copy_source_count += 1
            }
            Ok(node.copy_source.replace(value.into()).map(Cow::into_owned))
        })
    }

    pub fn len(&self) -> usize {
        let map = self.get_map();
        map.nodes_with_entry_count as usize
    }

    pub fn contains_key(
        &self,
        key: &HgPath,
    ) -> Result<bool, DirstateV2ParseError> {
        Ok(self.get(key)?.is_some())
    }

    pub fn get(
        &self,
        key: &HgPath,
    ) -> Result<Option<DirstateEntry>, DirstateV2ParseError> {
        let map = self.get_map();
        Ok(if let Some(node) = map.get_node(key)? {
            node.entry()?
        } else {
            None
        })
    }

    pub fn iter(&self) -> StateMapIter<'_> {
        let map = self.get_map();
        Box::new(filter_map_results(map.iter_nodes(), move |node| {
            Ok(if let Some(entry) = node.entry()? {
                Some((node.full_path(map.on_disk)?, entry))
            } else {
                None
            })
        }))
    }

    pub fn iter_tracked_dirs(
        &mut self,
    ) -> Result<
        Box<
            dyn Iterator<Item = Result<&HgPath, DirstateV2ParseError>>
                + Send
                + '_,
        >,
        DirstateError,
    > {
        let map = self.get_map();
        let on_disk = map.on_disk;
        Ok(Box::new(filter_map_results(
            map.iter_nodes(),
            move |node| {
                Ok(if node.tracked_descendants_count() > 0 {
                    Some(node.full_path(on_disk)?)
                } else {
                    None
                })
            },
        )))
    }

    pub fn debug_iter(
        &self,
        all: bool,
    ) -> Box<
        dyn Iterator<
                Item = Result<
                    (&HgPath, (u8, i32, i32, i32)),
                    DirstateV2ParseError,
                >,
            > + Send
            + '_,
    > {
        let map = self.get_map();
        Box::new(filter_map_results(map.iter_nodes(), move |node| {
            let debug_tuple = if let Some(entry) = node.entry()? {
                entry.debug_tuple()
            } else if !all {
                return Ok(None);
            } else if let Some(mtime) = node.cached_directory_mtime()? {
                (b' ', 0, -1, mtime.truncated_seconds() as i32)
            } else {
                (b' ', 0, -1, -1)
            };
            Ok(Some((node.full_path(map.on_disk)?, debug_tuple)))
        }))
    }
}