rust-dirstatemap: add unit tests

These were missing and have already proven valuable since they have found
two bugs (fixed in previous patches).

There may be other behavior to test, but this gives us a decent coverage.

Differential Revision: https://phab.mercurial-scm.org/D12524

rust/hg-core/src/dirstate_tree/dirstate_map.rs

@@ -1,1435 +1,1849 b''
 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::DirstateV2Data;
 use crate::dirstate::ParentFileData;
 use crate::dirstate::StateMapIter;
 use crate::dirstate::TruncatedTimestamp;
 use crate::matchers::Matcher;
 use crate::utils::hg_path::{HgPath, HgPathBuf};
 use crate::DirstateEntry;
 use crate::DirstateError;
 use crate::DirstateMapError;
 use crate::DirstateParents;
 use crate::DirstateStatus;
 use crate::EntryState;
 use crate::FastHashbrownMap as 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;
 
 #[derive(Debug)]
 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.
 #[derive(Debug)]
 pub(super) enum BorrowedPath<'tree, 'on_disk> {
     InMemory(&'tree HgPathBuf),
     OnDisk(&'on_disk HgPath),
 }
 
 #[derive(Debug)]
 pub(super) enum ChildNodes<'on_disk> {
     InMemory(FastHashMap<NodeKey<'on_disk>, Node<'on_disk>>),
     OnDisk(&'on_disk [on_disk::Node]),
 }
 
 #[derive(Debug)]
 pub(super) enum ChildNodesRef<'tree, 'on_disk> {
     InMemory(&'tree FastHashMap<NodeKey<'on_disk>, Node<'on_disk>>),
     OnDisk(&'on_disk [on_disk::Node]),
 }
 
 #[derive(Debug)]
 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()?.and_then(|e| {
             if e.any_tracked() {
                 Some(e.state())
             } else {
                 None
             }
         }))
     }
 
     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, Debug)]
 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,
 }
 
 #[derive(Debug)]
 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,
         }
     }
 
     fn as_entry_mut(&mut self) -> Option<&mut 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 {
             let (_, child_node) = child_nodes
                 .make_mut(on_disk, unreachable_bytes)?
                 .raw_entry_mut()
                 .from_key(ancestor_path.base_name())
                 .or_insert_with(|| (to_cow(ancestor_path), Node::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 reset_state(
         &mut self,
         filename: &HgPath,
         old_entry_opt: Option<DirstateEntry>,
         wc_tracked: bool,
         p1_tracked: bool,
         p2_info: bool,
         has_meaningful_mtime: bool,
         parent_file_data_opt: Option<ParentFileData>,
     ) -> Result<(), DirstateError> {
         let (had_entry, was_tracked) = match old_entry_opt {
             Some(old_entry) => (true, old_entry.tracked()),
             None => (false, false),
         };
         let node = Self::get_or_insert_node(
             self.on_disk,
             &mut self.unreachable_bytes,
             &mut self.root,
             filename,
             WithBasename::to_cow_owned,
             |ancestor| {
                 if !had_entry {
                     ancestor.descendants_with_entry_count += 1;
                 }
                 if was_tracked {
                     if !wc_tracked {
                         ancestor.tracked_descendants_count = ancestor
                             .tracked_descendants_count
                             .checked_sub(1)
                             .expect("tracked count to be >= 0");
                     }
                 } else {
                     if wc_tracked {
                         ancestor.tracked_descendants_count += 1;
                     }
                 }
             },
         )?;
 
         let v2_data = if let Some(parent_file_data) = parent_file_data_opt {
             DirstateV2Data {
                 wc_tracked,
                 p1_tracked,
                 p2_info,
                 mode_size: parent_file_data.mode_size,
                 mtime: if has_meaningful_mtime {
                     parent_file_data.mtime
                 } else {
                     None
                 },
                 ..Default::default()
             }
         } else {
             DirstateV2Data {
                 wc_tracked,
                 p1_tracked,
                 p2_info,
                 ..Default::default()
             }
         };
         if !had_entry {
             self.nodes_with_entry_count += 1;
         }
         node.data = NodeData::Entry(DirstateEntry::from_v2_data(v2_data));
         Ok(())
     }
 
     fn set_tracked(
         &mut self,
         filename: &HgPath,
         old_entry_opt: Option<DirstateEntry>,
     ) -> Result<bool, DirstateV2ParseError> {
         let was_tracked = old_entry_opt.map_or(false, |e| e.tracked());
         let had_entry = old_entry_opt.is_some();
         let tracked_count_increment = if was_tracked { 0 } else { 1 };
         let mut new = false;
 
         let node = Self::get_or_insert_node(
             self.on_disk,
             &mut self.unreachable_bytes,
             &mut self.root,
             filename,
             WithBasename::to_cow_owned,
             |ancestor| {
                 if !had_entry {
                     ancestor.descendants_with_entry_count += 1;
                 }
 
                 ancestor.tracked_descendants_count += tracked_count_increment;
             },
         )?;
         let new_entry = if let Some(old_entry) = old_entry_opt {
             let mut e = old_entry.clone();
             if e.tracked() {
                 // XXX
                 // This is probably overkill for more case, but we need this to
                 // fully replace the `normallookup` call with `set_tracked`
                 // one. Consider smoothing this in the future.
                 e.set_possibly_dirty();
             } else {
                 new = true;
                 e.set_tracked();
             }
             e
         } else {
             self.nodes_with_entry_count += 1;
             new = true;
             DirstateEntry::new_tracked()
         };
         node.data = NodeData::Entry(new_entry);
         Ok(new)
     }
 
     /// It is the responsibility of the caller to know that there was an entry
     /// there before. Does not handle the removal of copy source
     fn set_untracked(
         &mut self,
         filename: &HgPath,
         old_entry: DirstateEntry,
     ) -> Result<(), DirstateV2ParseError> {
         let node = Self::get_or_insert_node(
             self.on_disk,
             &mut self.unreachable_bytes,
             &mut self.root,
             filename,
             WithBasename::to_cow_owned,
             |ancestor| {
                 ancestor.tracked_descendants_count = ancestor
                     .tracked_descendants_count
                     .checked_sub(1)
                     .expect("tracked_descendants_count should be >= 0");
             },
         )?;
         let mut new_entry = old_entry.clone();
         new_entry.set_untracked();
         node.data = NodeData::Entry(new_entry);
         Ok(())
     }
 
     fn set_clean(
         &mut self,
         filename: &HgPath,
         old_entry: DirstateEntry,
         mode: u32,
         size: u32,
         mtime: TruncatedTimestamp,
     ) -> Result<(), DirstateError> {
         let node = Self::get_or_insert_node(
             self.on_disk,
             &mut self.unreachable_bytes,
             &mut self.root,
             filename,
             WithBasename::to_cow_owned,
             |ancestor| {
                 if !old_entry.tracked() {
                     ancestor.tracked_descendants_count += 1;
                 }
             },
         )?;
         let mut new_entry = old_entry.clone();
         new_entry.set_clean(mode, size, mtime);
         node.data = NodeData::Entry(new_entry);
         Ok(())
     }
 
     fn set_possibly_dirty(
         &mut self,
         filename: &HgPath,
     ) -> Result<(), DirstateError> {
         let node = Self::get_or_insert_node(
             self.on_disk,
             &mut self.unreachable_bytes,
             &mut self.root,
             filename,
             WithBasename::to_cow_owned,
             |_ancestor| {},
         )?;
         let entry = node.data.as_entry_mut().expect("entry should exist");
         entry.set_possibly_dirty();
         node.data = NodeData::Entry(*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_tracked(
         &mut self,
         filename: &HgPath,
     ) -> Result<bool, DirstateV2ParseError> {
         let old_entry_opt = self.get(filename)?;
         self.with_dmap_mut(|map| map.set_tracked(filename, old_entry_opt))
     }
 
     pub fn set_untracked(
         &mut self,
         filename: &HgPath,
     ) -> Result<bool, DirstateError> {
         let old_entry_opt = self.get(filename)?;
         match old_entry_opt {
             None => Ok(false),
             Some(old_entry) => {
                 if !old_entry.tracked() {
                     // `DirstateMap::set_untracked` is not a noop if
                     // already not tracked as it will decrement the
                     // tracked counters while going down.
                     return Ok(true);
                 }
                 if old_entry.added() {
                     // Untracking an "added" entry will just result in a
                     // worthless entry (and other parts of the code will
                     // complain about it), just drop it entirely.
                     self.drop_entry_and_copy_source(filename)?;
                     return Ok(true);
                 }
                 if !old_entry.p2_info() {
                     self.copy_map_remove(filename)?;
                 }
 
                 self.with_dmap_mut(|map| {
                     map.set_untracked(filename, old_entry)?;
                     Ok(true)
                 })
             }
         }
     }
 
     pub fn set_clean(
         &mut self,
         filename: &HgPath,
         mode: u32,
         size: u32,
         mtime: TruncatedTimestamp,
     ) -> Result<(), DirstateError> {
         let old_entry = match self.get(filename)? {
             None => {
                 return Err(
                     DirstateMapError::PathNotFound(filename.into()).into()
                 )
             }
             Some(e) => e,
         };
         self.copy_map_remove(filename)?;
         self.with_dmap_mut(|map| {
             map.set_clean(filename, old_entry, mode, size, mtime)
         })
     }
 
     pub fn set_possibly_dirty(
         &mut self,
         filename: &HgPath,
     ) -> Result<(), DirstateError> {
         if self.get(filename)?.is_none() {
             return Err(DirstateMapError::PathNotFound(filename.into()).into());
         }
         self.with_dmap_mut(|map| map.set_possibly_dirty(filename))
     }
 
     pub fn reset_state(
         &mut self,
         filename: &HgPath,
         wc_tracked: bool,
         p1_tracked: bool,
         p2_info: bool,
         has_meaningful_mtime: bool,
         parent_file_data_opt: Option<ParentFileData>,
     ) -> Result<(), DirstateError> {
         if !(p1_tracked || p2_info || wc_tracked) {
             self.drop_entry_and_copy_source(filename)?;
             return Ok(());
         }
         self.copy_map_remove(filename)?;
         let old_entry_opt = self.get(filename)?;
         self.with_dmap_mut(|map| {
             map.reset_state(
                 filename,
                 old_entry_opt,
                 wc_tracked,
                 p1_tracked,
                 p2_info,
                 has_meaningful_mtime,
                 parent_file_data_opt,
             )
         })
     }
 
     pub fn drop_entry_and_copy_source(
         &mut self,
         filename: &HgPath,
     ) -> Result<(), DirstateError> {
         let was_tracked = self.get(filename)?.map_or(false, |e| e.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 = node
                             .descendants_with_entry_count
                             .checked_sub(1)
                             .expect(
                                 "descendants_with_entry_count should be >= 0",
                             );
                     }
                     if dropped.was_tracked {
                         node.tracked_descendants_count = node
                             .tracked_descendants_count
                             .checked_sub(1)
                             .expect(
                                 "tracked_descendants_count should be >= 0",
                             );
                     }
 
                     // 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 entry = node.data.as_entry();
                 let was_tracked = entry.map_or(false, |entry| entry.tracked());
                 let had_entry = entry.is_some();
                 if had_entry {
                     node.data = NodeData::None
                 }
                 let mut had_copy_source = false;
                 if let Some(source) = &node.copy_source {
                     DirstateMap::count_dropped_path(unreachable_bytes, source);
                     had_copy_source = true;
                     node.copy_source = None
                 }
                 dropped = Dropped {
                     was_tracked,
                     had_entry,
                     had_copy_source,
                 };
             }
             // 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 = map
                         .nodes_with_entry_count
                         .checked_sub(1)
                         .expect("nodes_with_entry_count should be >= 0");
                 }
                 if dropped.had_copy_source {
                     map.nodes_with_copy_source_count = map
                         .nodes_with_copy_source_count
                         .checked_sub(1)
                         .expect("nodes_with_copy_source_count should be >= 0");
                 }
             } 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: &HgPath,
         value: &HgPath,
     ) -> 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.to_owned().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
                 })
             },
         )))
     }
 
     /// Only public because it needs to be exposed to the Python layer.
     /// It is not the full `setparents` logic, only the parts that mutate the
     /// entries.
     pub fn setparents_fixup(
         &mut self,
     ) -> Result<Vec<(HgPathBuf, HgPathBuf)>, DirstateV2ParseError> {
         // XXX
         // All the copying and re-querying is quite inefficient, but this is
         // still a lot better than doing it from Python.
         //
         // The better solution is to develop a mechanism for `iter_mut`,
         // which will be a lot more involved: we're dealing with a lazy,
         // append-mostly, tree-like data structure. This will do for now.
         let mut copies = vec![];
         let mut files_with_p2_info = vec![];
         for res in self.iter() {
             let (path, entry) = res?;
             if entry.p2_info() {
                 files_with_p2_info.push(path.to_owned())
             }
         }
         self.with_dmap_mut(|map| {
             for path in files_with_p2_info.iter() {
                 let node = map.get_or_insert(path)?;
                 let entry =
                     node.data.as_entry_mut().expect("entry should exist");
                 entry.drop_merge_data();
                 if let Some(source) = node.copy_source.take().as_deref() {
                     copies.push((path.to_owned(), source.to_owned()));
                 }
             }
             Ok(copies)
         })
     }
 
     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)))
         }))
     }
 }
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    /// Shortcut to return tracked descendants of a path.
+    /// Panics if the path does not exist.
+    fn tracked_descendants(map: &OwningDirstateMap, path: &[u8]) -> u32 {
+        let path = dbg!(HgPath::new(path));
+        let node = map.get_map().get_node(path);
+        node.unwrap().unwrap().tracked_descendants_count()
+    }
+
+    /// Shortcut to return descendants with an entry.
+    /// Panics if the path does not exist.
+    fn descendants_with_an_entry(map: &OwningDirstateMap, path: &[u8]) -> u32 {
+        let path = dbg!(HgPath::new(path));
+        let node = map.get_map().get_node(path);
+        node.unwrap().unwrap().descendants_with_entry_count()
+    }
+
+    fn assert_does_not_exist(map: &OwningDirstateMap, path: &[u8]) {
+        let path = dbg!(HgPath::new(path));
+        let node = map.get_map().get_node(path);
+        assert!(node.unwrap().is_none());
+    }
+
+    /// Shortcut for path creation in tests
+    fn p(b: &[u8]) -> &HgPath {
+        HgPath::new(b)
+    }
+
+    /// Test the very simple case a single tracked file
+    #[test]
+    fn test_tracked_descendants_simple() -> Result<(), DirstateError> {
+        let mut map = OwningDirstateMap::new_empty(vec![]);
+        assert_eq!(map.len(), 0);
+
+        map.set_tracked(p(b"some/nested/path"))?;
+
+        assert_eq!(map.len(), 1);
+        assert_eq!(tracked_descendants(&map, b"some"), 1);
+        assert_eq!(tracked_descendants(&map, b"some/nested"), 1);
+        assert_eq!(tracked_descendants(&map, b"some/nested/path"), 0);
+
+        map.set_untracked(p(b"some/nested/path"))?;
+        assert_eq!(map.len(), 0);
+        assert!(map.get_map().get_node(p(b"some"))?.is_none());
+
+        Ok(())
+    }
+
+    /// Test the simple case of all tracked, but multiple files
+    #[test]
+    fn test_tracked_descendants_multiple() -> Result<(), DirstateError> {
+        let mut map = OwningDirstateMap::new_empty(vec![]);
+
+        map.set_tracked(p(b"some/nested/path"))?;
+        map.set_tracked(p(b"some/nested/file"))?;
+        // one layer without any files to test deletion cascade
+        map.set_tracked(p(b"some/other/nested/path"))?;
+        map.set_tracked(p(b"root_file"))?;
+        map.set_tracked(p(b"some/file"))?;
+        map.set_tracked(p(b"some/file2"))?;
+        map.set_tracked(p(b"some/file3"))?;
+
+        assert_eq!(map.len(), 7);
+        assert_eq!(tracked_descendants(&map, b"some"), 6);
+        assert_eq!(tracked_descendants(&map, b"some/nested"), 2);
+        assert_eq!(tracked_descendants(&map, b"some/other"), 1);
+        assert_eq!(tracked_descendants(&map, b"some/other/nested"), 1);
+        assert_eq!(tracked_descendants(&map, b"some/nested/path"), 0);
+
+        map.set_untracked(p(b"some/nested/path"))?;
+        assert_eq!(map.len(), 6);
+        assert_eq!(tracked_descendants(&map, b"some"), 5);
+        assert_eq!(tracked_descendants(&map, b"some/nested"), 1);
+        assert_eq!(tracked_descendants(&map, b"some/other"), 1);
+        assert_eq!(tracked_descendants(&map, b"some/other/nested"), 1);
+
+        map.set_untracked(p(b"some/nested/file"))?;
+        assert_eq!(map.len(), 5);
+        assert_eq!(tracked_descendants(&map, b"some"), 4);
+        assert_eq!(tracked_descendants(&map, b"some/other"), 1);
+        assert_eq!(tracked_descendants(&map, b"some/other/nested"), 1);
+        assert_does_not_exist(&map, b"some_nested");
+
+        map.set_untracked(p(b"some/other/nested/path"))?;
+        assert_eq!(map.len(), 4);
+        assert_eq!(tracked_descendants(&map, b"some"), 3);
+        assert_does_not_exist(&map, b"some/other");
+
+        map.set_untracked(p(b"root_file"))?;
+        assert_eq!(map.len(), 3);
+        assert_eq!(tracked_descendants(&map, b"some"), 3);
+        assert_does_not_exist(&map, b"root_file");
+
+        map.set_untracked(p(b"some/file"))?;
+        assert_eq!(map.len(), 2);
+        assert_eq!(tracked_descendants(&map, b"some"), 2);
+        assert_does_not_exist(&map, b"some/file");
+
+        map.set_untracked(p(b"some/file2"))?;
+        assert_eq!(map.len(), 1);
+        assert_eq!(tracked_descendants(&map, b"some"), 1);
+        assert_does_not_exist(&map, b"some/file2");
+
+        map.set_untracked(p(b"some/file3"))?;
+        assert_eq!(map.len(), 0);
+        assert_does_not_exist(&map, b"some/file3");
+
+        Ok(())
+    }
+
+    /// Check with a mix of tracked and non-tracked items
+    #[test]
+    fn test_tracked_descendants_different() -> Result<(), DirstateError> {
+        let mut map = OwningDirstateMap::new_empty(vec![]);
+
+        // A file that was just added
+        map.set_tracked(p(b"some/nested/path"))?;
+        // This has no information, the dirstate should ignore it
+        map.reset_state(p(b"some/file"), false, false, false, false, None)?;
+        assert_does_not_exist(&map, b"some/file");
+
+        // A file that was removed
+        map.reset_state(
+            p(b"some/nested/file"),
+            false,
+            true,
+            false,
+            false,
+            None,
+        )?;
+        assert!(!map.get(p(b"some/nested/file"))?.unwrap().tracked());
+        // Only present in p2
+        map.reset_state(p(b"some/file3"), false, false, true, false, None)?;
+        assert!(!map.get(p(b"some/file3"))?.unwrap().tracked());
+        // A file that was merged
+        map.reset_state(p(b"root_file"), true, true, true, false, None)?;
+        assert!(map.get(p(b"root_file"))?.unwrap().tracked());
+        // A file that is added, with info from p2
+        // XXX is that actually possible?
+        map.reset_state(p(b"some/file2"), true, false, true, false, None)?;
+        assert!(map.get(p(b"some/file2"))?.unwrap().tracked());
+        // A clean file
+        // One layer without any files to test deletion cascade
+        map.reset_state(
+            p(b"some/other/nested/path"),
+            true,
+            true,
+            false,
+            false,
+            None,
+        )?;
+        assert!(map.get(p(b"some/other/nested/path"))?.unwrap().tracked());
+
+        assert_eq!(map.len(), 6);
+        assert_eq!(tracked_descendants(&map, b"some"), 3);
+        assert_eq!(descendants_with_an_entry(&map, b"some"), 5);
+        assert_eq!(tracked_descendants(&map, b"some/other/nested"), 1);
+        assert_eq!(descendants_with_an_entry(&map, b"some/other/nested"), 1);
+        assert_eq!(tracked_descendants(&map, b"some/other/nested/path"), 0);
+        assert_eq!(
+            descendants_with_an_entry(&map, b"some/other/nested/path"),
+            0
+        );
+        assert_eq!(tracked_descendants(&map, b"some/nested"), 1);
+        assert_eq!(descendants_with_an_entry(&map, b"some/nested"), 2);
+
+        // might as well check this
+        map.set_untracked(p(b"path/does/not/exist"))?;
+        assert_eq!(map.len(), 6);
+
+        map.set_untracked(p(b"some/other/nested/path"))?;
+        // It is set untracked but not deleted since it held other information
+        assert_eq!(map.len(), 6);
+        assert_eq!(tracked_descendants(&map, b"some"), 2);
+        assert_eq!(descendants_with_an_entry(&map, b"some"), 5);
+        assert_eq!(descendants_with_an_entry(&map, b"some/other"), 1);
+        assert_eq!(descendants_with_an_entry(&map, b"some/other/nested"), 1);
+        assert_eq!(tracked_descendants(&map, b"some/nested"), 1);
+        assert_eq!(descendants_with_an_entry(&map, b"some/nested"), 2);
+
+        map.set_untracked(p(b"some/nested/path"))?;
+        // It is set untracked *and* deleted since it was only added
+        assert_eq!(map.len(), 5);
+        assert_eq!(tracked_descendants(&map, b"some"), 1);
+        assert_eq!(descendants_with_an_entry(&map, b"some"), 4);
+        assert_eq!(tracked_descendants(&map, b"some/nested"), 0);
+        assert_eq!(descendants_with_an_entry(&map, b"some/nested"), 1);
+        assert_does_not_exist(&map, b"some/nested/path");
+
+        map.set_untracked(p(b"root_file"))?;
+        // Untracked but not deleted
+        assert_eq!(map.len(), 5);
+        assert!(map.get(p(b"root_file"))?.is_some());
+
+        map.set_untracked(p(b"some/file2"))?;
+        assert_eq!(map.len(), 5);
+        assert_eq!(tracked_descendants(&map, b"some"), 0);
+        assert!(map.get(p(b"some/file2"))?.is_some());
+
+        map.set_untracked(p(b"some/file3"))?;
+        assert_eq!(map.len(), 5);
+        assert_eq!(tracked_descendants(&map, b"some"), 0);
+        assert!(map.get(p(b"some/file3"))?.is_some());
+
+        Ok(())
+    }
+
+    /// Check that copies counter is correctly updated
+    #[test]
+    fn test_copy_source() -> Result<(), DirstateError> {
+        let mut map = OwningDirstateMap::new_empty(vec![]);
+
+        // Clean file
+        map.reset_state(p(b"files/clean"), true, true, false, false, None)?;
+        // Merged file
+        map.reset_state(p(b"files/from_p2"), true, true, true, false, None)?;
+        // Removed file
+        map.reset_state(p(b"removed"), false, true, false, false, None)?;
+        // Added file
+        map.reset_state(p(b"files/added"), true, false, false, false, None)?;
+        // Add copy
+        map.copy_map_insert(p(b"files/clean"), p(b"clean_copy_source"))?;
+        assert_eq!(map.copy_map_len(), 1);
+
+        // Copy override
+        map.copy_map_insert(p(b"files/clean"), p(b"other_clean_copy_source"))?;
+        assert_eq!(map.copy_map_len(), 1);
+
+        // Multiple copies
+        map.copy_map_insert(p(b"removed"), p(b"removed_copy_source"))?;
+        assert_eq!(map.copy_map_len(), 2);
+
+        map.copy_map_insert(p(b"files/added"), p(b"added_copy_source"))?;
+        assert_eq!(map.copy_map_len(), 3);
+
+        // Added, so the entry is completely removed
+        map.set_untracked(p(b"files/added"))?;
+        assert_does_not_exist(&map, b"files/added");
+        assert_eq!(map.copy_map_len(), 2);
+
+        // Removed, so the entry is kept around, so is its copy
+        map.set_untracked(p(b"removed"))?;
+        assert!(map.get(p(b"removed"))?.is_some());
+        assert_eq!(map.copy_map_len(), 2);
+
+        // Clean, so the entry is kept around, but not its copy
+        map.set_untracked(p(b"files/clean"))?;
+        assert!(map.get(p(b"files/clean"))?.is_some());
+        assert_eq!(map.copy_map_len(), 1);
+
+        map.copy_map_insert(p(b"files/from_p2"), p(b"from_p2_copy_source"))?;
+        assert_eq!(map.copy_map_len(), 2);
+
+        // Info from p2, so its copy source info is kept around
+        map.set_untracked(p(b"files/from_p2"))?;
+        assert!(map.get(p(b"files/from_p2"))?.is_some());
+        assert_eq!(map.copy_map_len(), 2);
+
+        Ok(())
+    }
+
+    /// Test with "on disk" data. For the sake of this test, the "on disk" data
+    /// does not actually come from the disk, but it's opaque to the code being
+    /// tested.
+    #[test]
+    fn test_on_disk() -> Result<(), DirstateError> {
+        // First let's create some data to put "on disk"
+        let mut map = OwningDirstateMap::new_empty(vec![]);
+
+        // A file that was just added
+        map.set_tracked(p(b"some/nested/added"))?;
+        map.copy_map_insert(p(b"some/nested/added"), p(b"added_copy_source"))?;
+
+        // A file that was removed
+        map.reset_state(
+            p(b"some/nested/removed"),
+            false,
+            true,
+            false,
+            false,
+            None,
+        )?;
+        // Only present in p2
+        map.reset_state(
+            p(b"other/p2_info_only"),
+            false,
+            false,
+            true,
+            false,
+            None,
+        )?;
+        map.copy_map_insert(
+            p(b"other/p2_info_only"),
+            p(b"other/p2_info_copy_source"),
+        )?;
+        // A file that was merged
+        map.reset_state(p(b"merged"), true, true, true, false, None)?;
+        // A file that is added, with info from p2
+        // XXX is that actually possible?
+        map.reset_state(
+            p(b"other/added_with_p2"),
+            true,
+            false,
+            true,
+            false,
+            None,
+        )?;
+        // One layer without any files to test deletion cascade
+        // A clean file
+        map.reset_state(
+            p(b"some/other/nested/clean"),
+            true,
+            true,
+            false,
+            false,
+            None,
+        )?;
+
+        let (packed, metadata, _should_append) = map.pack_v2(false)?;
+        let packed_len = packed.len();
+        assert!(packed_len > 0);
+
+        // Recreate "from disk"
+        let mut map = OwningDirstateMap::new_v2(
+            packed,
+            packed_len,
+            metadata.as_bytes(),
+        )?;
+
+        // Check that everything is accounted for
+        assert!(map.contains_key(p(b"some/nested/added"))?);
+        assert!(map.contains_key(p(b"some/nested/removed"))?);
+        assert!(map.contains_key(p(b"merged"))?);
+        assert!(map.contains_key(p(b"other/p2_info_only"))?);
+        assert!(map.contains_key(p(b"other/added_with_p2"))?);
+        assert!(map.contains_key(p(b"some/other/nested/clean"))?);
+        assert_eq!(
+            map.copy_map_get(p(b"some/nested/added"))?,
+            Some(p(b"added_copy_source"))
+        );
+        assert_eq!(
+            map.copy_map_get(p(b"other/p2_info_only"))?,
+            Some(p(b"other/p2_info_copy_source"))
+        );
+        assert_eq!(tracked_descendants(&map, b"some"), 2);
+        assert_eq!(descendants_with_an_entry(&map, b"some"), 3);
+        assert_eq!(tracked_descendants(&map, b"other"), 1);
+        assert_eq!(descendants_with_an_entry(&map, b"other"), 2);
+        assert_eq!(tracked_descendants(&map, b"some/other"), 1);
+        assert_eq!(descendants_with_an_entry(&map, b"some/other"), 1);
+        assert_eq!(tracked_descendants(&map, b"some/other/nested"), 1);
+        assert_eq!(descendants_with_an_entry(&map, b"some/other/nested"), 1);
+        assert_eq!(tracked_descendants(&map, b"some/nested"), 1);
+        assert_eq!(descendants_with_an_entry(&map, b"some/nested"), 2);
+        assert_eq!(map.len(), 6);
+        assert_eq!(map.get_map().unreachable_bytes, 0);
+        assert_eq!(map.copy_map_len(), 2);
+
+        // Shouldn't change anything since it's already not tracked
+        map.set_untracked(p(b"some/nested/removed"))?;
+        assert_eq!(map.get_map().unreachable_bytes, 0);
+
+        match map.get_map().root {
+            ChildNodes::InMemory(_) => {
+                panic!("root should not have been mutated")
+            }
+            _ => (),
+        }
+        // We haven't mutated enough (nothing, actually), we should still be in
+        // the append strategy
+        assert!(map.get_map().write_should_append());
+
+        // But this mutates the structure, so there should be unreachable_bytes
+        assert!(map.set_untracked(p(b"some/nested/added"))?);
+        let unreachable_bytes = map.get_map().unreachable_bytes;
+        assert!(unreachable_bytes > 0);
+
+        match map.get_map().root {
+            ChildNodes::OnDisk(_) => panic!("root should have been mutated"),
+            _ => (),
+        }
+
+        // This should not mutate the structure either, since `root` has
+        // already been mutated along with its direct children.
+        map.set_untracked(p(b"merged"))?;
+        assert_eq!(map.get_map().unreachable_bytes, unreachable_bytes);
+
+        match map.get_map().get_node(p(b"other/added_with_p2"))?.unwrap() {
+            NodeRef::InMemory(_, _) => {
+                panic!("'other/added_with_p2' should not have been mutated")
+            }
+            _ => (),
+        }
+        // But this should, since it's in a different path
+        // than `<root>some/nested/add`
+        map.set_untracked(p(b"other/added_with_p2"))?;
+        assert!(map.get_map().unreachable_bytes > unreachable_bytes);
+
+        match map.get_map().get_node(p(b"other/added_with_p2"))?.unwrap() {
+            NodeRef::OnDisk(_) => {
+                panic!("'other/added_with_p2' should have been mutated")
+            }
+            _ => (),
+        }
+
+        // We have rewritten most of the tree, we should create a new file
+        assert!(!map.get_map().write_should_append());
+
+        Ok(())
+    }
+}