dirstate-tree: Borrow paths from the "on disk" bytes

Use std::borrow::Cow to avoid some memory allocations and copying.

Differential Revision: https://phab.mercurial-scm.org/D10560

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

@@ -1,620 +1,623 b''
 use bytes_cast::BytesCast;
 use micro_timer::timed;
 use std::borrow::Cow;
 use std::convert::TryInto;
 use std::path::PathBuf;
 
 use super::path_with_basename::WithBasename;
 use crate::dirstate::parsers::clear_ambiguous_mtime;
 use crate::dirstate::parsers::pack_entry;
 use crate::dirstate::parsers::packed_entry_size;
 use crate::dirstate::parsers::parse_dirstate_entries;
 use crate::dirstate::parsers::Timestamp;
 use crate::matchers::Matcher;
 use crate::utils::hg_path::{HgPath, HgPathBuf};
 use crate::CopyMapIter;
 use crate::DirstateEntry;
 use crate::DirstateError;
 use crate::DirstateMapError;
 use crate::DirstateParents;
 use crate::DirstateStatus;
 use crate::EntryState;
 use crate::FastHashMap;
 use crate::PatternFileWarning;
 use crate::StateMapIter;
 use crate::StatusError;
 use crate::StatusOptions;
 
 pub struct DirstateMap<'on_disk> {
     /// Contents of the `.hg/dirstate` file
     on_disk: &'on_disk [u8],
 
     pub(super) root: ChildNodes<'on_disk>,
 
     /// Number of nodes anywhere in the tree that have `.entry.is_some()`.
     nodes_with_entry_count: usize,
 
     /// Number of nodes anywhere in the tree that have
     /// `.copy_source.is_some()`.
     nodes_with_copy_source_count: usize,
 }
 
 /// 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 `BTreeMap` would waste time always re-comparing the same
 /// string prefix.
 pub(super) type ChildNodes<'on_disk> =
-    FastHashMap<WithBasename<HgPathBuf>, Node<'on_disk>>;
+    FastHashMap<WithBasename<Cow<'on_disk, HgPath>>, Node<'on_disk>>;
 
 /// Represents a file or a directory
 #[derive(Default)]
 pub(super) struct Node<'on_disk> {
     /// `None` for directories
     pub(super) entry: Option<DirstateEntry>,
 
     pub(super) copy_source: Option<Cow<'on_disk, HgPath>>,
 
     pub(super) children: ChildNodes<'on_disk>,
 
     /// How many (non-inclusive) descendants of this node are tracked files
     tracked_descendants_count: usize,
 }
 
 impl Node<'_> {
     pub(super) fn state(&self) -> Option<EntryState> {
         self.entry.as_ref().map(|entry| entry.state)
     }
 }
 
 /// `(full_path, entry, copy_source)`
 type NodeDataMut<'tree, 'on_disk> = (
     &'tree HgPath,
     &'tree mut Option<DirstateEntry>,
     &'tree mut Option<Cow<'on_disk, HgPath>>,
 );
 
 impl<'on_disk> DirstateMap<'on_disk> {
     pub fn new(
         on_disk: &'on_disk [u8],
     ) -> Result<(Self, Option<DirstateParents>), DirstateError> {
         let mut map = Self {
             on_disk,
             root: ChildNodes::default(),
             nodes_with_entry_count: 0,
             nodes_with_copy_source_count: 0,
         };
         let parents = map.read()?;
         Ok((map, parents))
     }
 
     /// Should only be called in `new`
     #[timed]
     fn read(&mut self) -> Result<Option<DirstateParents>, DirstateError> {
         if self.on_disk.is_empty() {
             return Ok(None);
         }
 
         let parents = parse_dirstate_entries(
             self.on_disk,
             |path, entry, copy_source| {
                 let tracked = entry.state.is_tracked();
-                let node = Self::get_or_insert_node_tracing_ancestors(
+                let node = Self::get_or_insert_node(
                     &mut self.root,
                     path,
+                    WithBasename::to_cow_borrowed,
                     |ancestor| {
                         if tracked {
                             ancestor.tracked_descendants_count += 1
                         }
                     },
                 );
                 assert!(
                     node.entry.is_none(),
                     "duplicate dirstate entry in read"
                 );
                 assert!(
                     node.copy_source.is_none(),
                     "duplicate dirstate entry in read"
                 );
                 node.entry = Some(*entry);
                 node.copy_source = copy_source.map(Cow::Borrowed);
                 self.nodes_with_entry_count += 1;
                 if copy_source.is_some() {
                     self.nodes_with_copy_source_count += 1
                 }
             },
         )?;
 
         Ok(Some(parents.clone()))
     }
 
     fn get_node(&self, path: &HgPath) -> Option<&Node> {
         let mut children = &self.root;
         let mut components = path.components();
         let mut component =
             components.next().expect("expected at least one components");
         loop {
             let child = children.get(component)?;
             if let Some(next_component) = components.next() {
                 component = next_component;
                 children = &child.children;
             } else {
                 return Some(child);
             }
         }
     }
 
     /// 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>(
         root: &'tree mut ChildNodes<'on_disk>,
         path: &HgPath,
     ) -> Option<&'tree mut Node<'on_disk>> {
         Self::get_node_mut_tracing_ancestors(root, path, |_| {})
     }
 
     /// Same as `get_node_mut`, and calls `each_ancestor` for each ancestor of
     /// the node.
     ///
     /// Note that `each_ancestor` may be called (with what would be ancestors)
     /// even if it turns out there is no node at `path`.
     fn get_node_mut_tracing_ancestors<'tree>(
         root: &'tree mut ChildNodes<'on_disk>,
         path: &HgPath,
         mut each_ancestor: impl FnMut(&mut Node),
     ) -> Option<&'tree mut Node<'on_disk>> {
         let mut children = root;
         let mut components = path.components();
         let mut component =
             components.next().expect("expected at least one components");
         loop {
             let child = children.get_mut(component)?;
             if let Some(next_component) = components.next() {
                 each_ancestor(child);
                 component = next_component;
                 children = &mut child.children;
             } else {
                 return Some(child);
             }
         }
     }
 
-    fn get_or_insert_node<'tree>(
+    fn get_or_insert_node<'tree, 'path>(
         root: &'tree mut ChildNodes<'on_disk>,
-        path: &HgPath,
-    ) -> &'tree mut Node<'on_disk> {
-        Self::get_or_insert_node_tracing_ancestors(root, path, |_| {})
-    }
-
-    fn get_or_insert_node_tracing_ancestors<'tree>(
-        root: &'tree mut ChildNodes<'on_disk>,
-        path: &HgPath,
+        path: &'path HgPath,
+        to_cow: impl Fn(
+            WithBasename<&'path HgPath>,
+        ) -> WithBasename<Cow<'on_disk, HgPath>>,
         mut each_ancestor: impl FnMut(&mut Node),
     ) -> &'tree mut Node<'on_disk> {
         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.entry(ancestor_path.to_owned()).or_default();
+                child_nodes.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 child_node;
             }
         }
     }
 
     fn add_or_remove_file(
         &mut self,
         path: &HgPath,
         old_state: EntryState,
         new_entry: DirstateEntry,
     ) {
         let tracked_count_increment =
             match (old_state.is_tracked(), new_entry.state.is_tracked()) {
                 (false, true) => 1,
                 (true, false) => -1,
                 _ => 0,
             };
 
-        let node = Self::get_or_insert_node_tracing_ancestors(
+        let node = Self::get_or_insert_node(
             &mut self.root,
             path,
+            WithBasename::to_cow_owned,
             |ancestor| {
                 // 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 node.entry.is_none() {
             self.nodes_with_entry_count += 1
         }
         node.entry = Some(new_entry)
     }
 
     fn iter_nodes<'a>(
         &'a self,
     ) -> impl Iterator<Item = (&'a HgPath, &'a Node)> + 'a {
         // 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.iter();
         std::iter::from_fn(move || {
             while let Some((key, child_node)) = iter.next() {
                 // Pseudo-recursion
                 let new_iter = child_node.children.iter();
                 let old_iter = std::mem::replace(&mut iter, new_iter);
                 let key = &**key.full_path();
                 stack.push((key, child_node, old_iter));
             }
             // Found the end of a `children.iter()` iterator.
             if let Some((key, child_node, next_iter)) = stack.pop() {
                 // "Return" from pseudo-recursion by restoring state from the
                 // explicit stack
                 iter = next_iter;
 
                 Some((key, child_node))
             } else {
                 // Reached the bottom of the stack, we’re done
                 None
             }
         })
     }
 
     /// Mutable iterator for the `(entry, copy source)` of each node.
     ///
     /// It would not be safe to yield mutable references to nodes themeselves
     /// with `-> impl Iterator<Item = &mut Node>` since child nodes are
     /// reachable from their ancestor nodes, potentially creating multiple
     /// `&mut` references to a given node.
     fn iter_node_data_mut<'tree>(
         &'tree mut self,
     ) -> impl Iterator<Item = NodeDataMut<'tree, 'on_disk>> + 'tree {
         // Explict stack for pseudo-recursion, see `iter_nodes` above.
         let mut stack = Vec::new();
         let mut iter = self.root.iter_mut();
         std::iter::from_fn(move || {
             while let Some((key, child_node)) = iter.next() {
                 // Pseudo-recursion
                 let data = (
                     &**key.full_path(),
                     &mut child_node.entry,
                     &mut child_node.copy_source,
                 );
                 let new_iter = child_node.children.iter_mut();
                 let old_iter = std::mem::replace(&mut iter, new_iter);
                 stack.push((data, old_iter));
             }
             // Found the end of a `children.values_mut()` iterator.
             if let Some((data, next_iter)) = stack.pop() {
                 // "Return" from pseudo-recursion by restoring state from the
                 // explicit stack
                 iter = next_iter;
 
                 Some(data)
             } else {
                 // Reached the bottom of the stack, we’re done
                 None
             }
         })
     }
 }
 
 impl<'on_disk> super::dispatch::DirstateMapMethods for DirstateMap<'on_disk> {
     fn clear(&mut self) {
         self.root.clear();
         self.nodes_with_entry_count = 0;
         self.nodes_with_copy_source_count = 0;
     }
 
     fn add_file(
         &mut self,
         filename: &HgPath,
         old_state: EntryState,
         entry: DirstateEntry,
     ) -> Result<(), DirstateMapError> {
         self.add_or_remove_file(filename, old_state, entry);
         Ok(())
     }
 
     fn remove_file(
         &mut self,
         filename: &HgPath,
         old_state: EntryState,
         size: i32,
     ) -> Result<(), DirstateMapError> {
         let entry = DirstateEntry {
             state: EntryState::Removed,
             mode: 0,
             size,
             mtime: 0,
         };
         self.add_or_remove_file(filename, old_state, entry);
         Ok(())
     }
 
     fn drop_file(
         &mut self,
         filename: &HgPath,
         old_state: EntryState,
     ) -> Result<bool, DirstateMapError> {
         let was_tracked = old_state.is_tracked();
         if let Some(node) = Self::get_node_mut_tracing_ancestors(
             &mut self.root,
             filename,
             |ancestor| {
                 if was_tracked {
                     ancestor.tracked_descendants_count -= 1
                 }
             },
         ) {
             let had_entry = node.entry.is_some();
             let had_copy_source = node.copy_source.is_some();
 
             // TODO: this leaves in the tree a "non-file" node. Should we
             // remove the node instead, together with ancestor nodes for
             // directories that become empty?
             node.entry = None;
             node.copy_source = None;
 
             if had_entry {
                 self.nodes_with_entry_count -= 1
             }
             if had_copy_source {
                 self.nodes_with_copy_source_count -= 1
             }
             Ok(had_entry)
         } else {
             assert!(!was_tracked);
             Ok(false)
         }
     }
 
     fn clear_ambiguous_times(&mut self, filenames: Vec<HgPathBuf>, now: i32) {
         for filename in filenames {
             if let Some(node) = Self::get_node_mut(&mut self.root, &filename) {
                 if let Some(entry) = node.entry.as_mut() {
                     clear_ambiguous_mtime(entry, now);
                 }
             }
         }
     }
 
     fn non_normal_entries_contains(&mut self, key: &HgPath) -> bool {
         self.get_node(key)
             .and_then(|node| node.entry.as_ref())
             .map_or(false, DirstateEntry::is_non_normal)
     }
 
     fn non_normal_entries_remove(&mut self, _key: &HgPath) {
         // Do nothing, this `DirstateMap` does not have a separate "non normal
         // entries" set that need to be kept up to date
     }
 
     fn non_normal_or_other_parent_paths(
         &mut self,
     ) -> Box<dyn Iterator<Item = &HgPath> + '_> {
         Box::new(self.iter_nodes().filter_map(|(path, node)| {
             node.entry
                 .as_ref()
                 .filter(|entry| {
                     entry.is_non_normal() || entry.is_from_other_parent()
                 })
                 .map(|_| path)
         }))
     }
 
     fn set_non_normal_other_parent_entries(&mut self, _force: bool) {
         // Do nothing, this `DirstateMap` does not have a separate "non normal
         // entries" and "from other parent" sets that need to be recomputed
     }
 
     fn iter_non_normal_paths(
         &mut self,
     ) -> Box<dyn Iterator<Item = &HgPath> + Send + '_> {
         self.iter_non_normal_paths_panic()
     }
 
     fn iter_non_normal_paths_panic(
         &self,
     ) -> Box<dyn Iterator<Item = &HgPath> + Send + '_> {
         Box::new(self.iter_nodes().filter_map(|(path, node)| {
             node.entry
                 .as_ref()
                 .filter(|entry| entry.is_non_normal())
                 .map(|_| path)
         }))
     }
 
     fn iter_other_parent_paths(
         &mut self,
     ) -> Box<dyn Iterator<Item = &HgPath> + Send + '_> {
         Box::new(self.iter_nodes().filter_map(|(path, node)| {
             node.entry
                 .as_ref()
                 .filter(|entry| entry.is_from_other_parent())
                 .map(|_| path)
         }))
     }
 
     fn has_tracked_dir(
         &mut self,
         directory: &HgPath,
     ) -> Result<bool, DirstateMapError> {
         if let Some(node) = self.get_node(directory) {
             // A node without a `DirstateEntry` was created to hold child
             // nodes, and is therefore a directory.
             Ok(node.entry.is_none() && node.tracked_descendants_count > 0)
         } else {
             Ok(false)
         }
     }
 
     fn has_dir(
         &mut self,
         directory: &HgPath,
     ) -> Result<bool, DirstateMapError> {
         if let Some(node) = self.get_node(directory) {
             // A node without a `DirstateEntry` was created to hold child
             // nodes, and is therefore a directory.
             Ok(node.entry.is_none())
         } else {
             Ok(false)
         }
     }
 
     fn pack(
         &mut self,
         parents: DirstateParents,
         now: Timestamp,
     ) -> Result<Vec<u8>, DirstateError> {
         // Optizimation (to be measured?): pre-compute size to avoid `Vec`
         // reallocations
         let mut size = parents.as_bytes().len();
         for (path, node) in self.iter_nodes() {
             if node.entry.is_some() {
                 size += packed_entry_size(
                     path,
                     node.copy_source.as_ref().map(|p| &**p),
                 )
             }
         }
 
         let mut packed = Vec::with_capacity(size);
         packed.extend(parents.as_bytes());
 
         let now: i32 = now.0.try_into().expect("time overflow");
         for (path, opt_entry, copy_source) in self.iter_node_data_mut() {
             if let Some(entry) = opt_entry {
                 clear_ambiguous_mtime(entry, now);
                 pack_entry(
                     path,
                     entry,
                     copy_source.as_ref().map(|p| &**p),
                     &mut packed,
                 );
             }
         }
         Ok(packed)
     }
 
     fn set_all_dirs(&mut self) -> Result<(), DirstateMapError> {
         // Do nothing, this `DirstateMap` does not a separate `all_dirs` that
         // needs to be recomputed
         Ok(())
     }
 
     fn set_dirs(&mut self) -> Result<(), DirstateMapError> {
         // Do nothing, this `DirstateMap` does not a separate `dirs` that needs
         // to be recomputed
         Ok(())
     }
 
     fn status<'a>(
         &'a mut self,
         matcher: &'a (dyn Matcher + Sync),
         root_dir: PathBuf,
         ignore_files: Vec<PathBuf>,
         options: StatusOptions,
     ) -> Result<(DirstateStatus<'a>, Vec<PatternFileWarning>), StatusError>
     {
         super::status::status(self, matcher, root_dir, ignore_files, options)
     }
 
     fn copy_map_len(&self) -> usize {
         self.nodes_with_copy_source_count
     }
 
     fn copy_map_iter(&self) -> CopyMapIter<'_> {
         Box::new(self.iter_nodes().filter_map(|(path, node)| {
             node.copy_source
                 .as_ref()
                 .map(|copy_source| (path, &**copy_source))
         }))
     }
 
     fn copy_map_contains_key(&self, key: &HgPath) -> bool {
         if let Some(node) = self.get_node(key) {
             node.copy_source.is_some()
         } else {
             false
         }
     }
 
     fn copy_map_get(&self, key: &HgPath) -> Option<&HgPath> {
         self.get_node(key)?.copy_source.as_ref().map(|p| &**p)
     }
 
     fn copy_map_remove(&mut self, key: &HgPath) -> Option<HgPathBuf> {
         let count = &mut self.nodes_with_copy_source_count;
         Self::get_node_mut(&mut self.root, key).and_then(|node| {
             if node.copy_source.is_some() {
                 *count -= 1
             }
             node.copy_source.take().map(Cow::into_owned)
         })
     }
 
     fn copy_map_insert(
         &mut self,
         key: HgPathBuf,
         value: HgPathBuf,
     ) -> Option<HgPathBuf> {
-        let node = Self::get_or_insert_node(&mut self.root, &key);
+        let node = Self::get_or_insert_node(
+            &mut self.root,
+            &key,
+            WithBasename::to_cow_owned,
+            |_ancestor| {},
+        );
         if node.copy_source.is_none() {
             self.nodes_with_copy_source_count += 1
         }
         node.copy_source.replace(value.into()).map(Cow::into_owned)
     }
 
     fn len(&self) -> usize {
         self.nodes_with_entry_count
     }
 
     fn contains_key(&self, key: &HgPath) -> bool {
         self.get(key).is_some()
     }
 
     fn get(&self, key: &HgPath) -> Option<&DirstateEntry> {
         self.get_node(key)?.entry.as_ref()
     }
 
     fn iter(&self) -> StateMapIter<'_> {
         Box::new(self.iter_nodes().filter_map(|(path, node)| {
             node.entry.as_ref().map(|entry| (path, entry))
         }))
     }
 }

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

@@ -1,165 +1,172 b''
 use crate::utils::hg_path::HgPath;
-use std::borrow::Borrow;
+use std::borrow::{Borrow, Cow};
 
 /// Wraps `HgPath` or `HgPathBuf` to make it behave "as" its last path
 /// component, a.k.a. its base name (as in Python’s `os.path.basename`), but
 /// also allow recovering the full path.
 ///
 /// "Behaving as" means that equality and comparison consider only the base
 /// name, and `std::borrow::Borrow` is implemented to return only the base
 /// name. This allows using the base name as a map key while still being able
 /// to recover the full path, in a single memory allocation.
 #[derive(Debug)]
 pub struct WithBasename<T> {
     full_path: T,
 
     /// The position after the last slash separator in `full_path`, or `0`
     /// if there is no slash.
     base_name_start: usize,
 }
 
 impl<T> WithBasename<T> {
     pub fn full_path(&self) -> &T {
         &self.full_path
     }
 }
 
 impl<T: AsRef<HgPath>> WithBasename<T> {
     pub fn new(full_path: T) -> Self {
         let base_name_start = if let Some(last_slash_position) = full_path
             .as_ref()
             .as_bytes()
             .iter()
             .rposition(|&byte| byte == b'/')
         {
             last_slash_position + 1
         } else {
             0
         };
         Self {
             base_name_start,
             full_path,
         }
     }
 
     pub fn base_name(&self) -> &HgPath {
         HgPath::new(
             &self.full_path.as_ref().as_bytes()[self.base_name_start..],
         )
     }
 }
 
 impl<T: AsRef<HgPath>> Borrow<HgPath> for WithBasename<T> {
     fn borrow(&self) -> &HgPath {
         self.base_name()
     }
 }
 
 impl<T: AsRef<HgPath>> std::hash::Hash for WithBasename<T> {
     fn hash<H: std::hash::Hasher>(&self, hasher: &mut H) {
         self.base_name().hash(hasher)
     }
 }
 
 impl<T: AsRef<HgPath> + PartialEq> PartialEq for WithBasename<T> {
     fn eq(&self, other: &Self) -> bool {
         self.base_name() == other.base_name()
     }
 }
 
 impl<T: AsRef<HgPath> + Eq> Eq for WithBasename<T> {}
 
 impl<T: AsRef<HgPath> + PartialOrd> PartialOrd for WithBasename<T> {
     fn partial_cmp(&self, other: &Self) -> Option<std::cmp::Ordering> {
         self.base_name().partial_cmp(other.base_name())
     }
 }
 
 impl<T: AsRef<HgPath> + Ord> Ord for WithBasename<T> {
     fn cmp(&self, other: &Self) -> std::cmp::Ordering {
         self.base_name().cmp(other.base_name())
     }
 }
 
-impl<T: ?Sized + ToOwned> WithBasename<&'_ T> {
-    pub fn to_owned(&self) -> WithBasename<T::Owned> {
+impl<'a> WithBasename<&'a HgPath> {
+    pub fn to_cow_borrowed(self) -> WithBasename<Cow<'a, HgPath>> {
         WithBasename {
-            full_path: self.full_path.to_owned(),
+            full_path: Cow::Borrowed(self.full_path),
+            base_name_start: self.base_name_start,
+        }
+    }
+
+    pub fn to_cow_owned<'b>(self) -> WithBasename<Cow<'b, HgPath>> {
+        WithBasename {
+            full_path: Cow::Owned(self.full_path.to_owned()),
             base_name_start: self.base_name_start,
         }
     }
 }
 
 impl<'a> WithBasename<&'a HgPath> {
     /// Returns an iterator of `WithBasename<&HgPath>` for the ancestor
     /// directory paths of the given `path`, as well as `path` itself.
     ///
     /// For example, the full paths of inclusive ancestors of "a/b/c" are "a",
     /// "a/b", and "a/b/c" in that order.
     pub fn inclusive_ancestors_of(
         path: &'a HgPath,
     ) -> impl Iterator<Item = WithBasename<&'a HgPath>> {
         let mut slash_positions =
             path.as_bytes().iter().enumerate().filter_map(|(i, &byte)| {
                 if byte == b'/' {
                     Some(i)
                 } else {
                     None
                 }
             });
         let mut opt_next_component_start = Some(0);
         std::iter::from_fn(move || {
             opt_next_component_start.take().map(|next_component_start| {
                 if let Some(slash_pos) = slash_positions.next() {
                     opt_next_component_start = Some(slash_pos + 1);
                     Self {
                         full_path: HgPath::new(&path.as_bytes()[..slash_pos]),
                         base_name_start: next_component_start,
                     }
                 } else {
                     // Not setting `opt_next_component_start` here: there will
                     // be no iteration after this one because `.take()` set it
                     // to `None`.
                     Self {
                         full_path: path,
                         base_name_start: next_component_start,
                     }
                 }
             })
         })
     }
 }
 
 #[test]
 fn test() {
     let a = WithBasename::new(HgPath::new("a").to_owned());
     assert_eq!(&**a.full_path(), HgPath::new(b"a"));
     assert_eq!(a.base_name(), HgPath::new(b"a"));
 
     let cba = WithBasename::new(HgPath::new("c/b/a").to_owned());
     assert_eq!(&**cba.full_path(), HgPath::new(b"c/b/a"));
     assert_eq!(cba.base_name(), HgPath::new(b"a"));
 
     assert_eq!(a, cba);
     let borrowed: &HgPath = cba.borrow();
     assert_eq!(borrowed, HgPath::new("a"));
 }
 
 #[test]
 fn test_inclusive_ancestors() {
     let mut iter = WithBasename::inclusive_ancestors_of(HgPath::new("a/bb/c"));
 
     let next = iter.next().unwrap();
     assert_eq!(*next.full_path(), HgPath::new("a"));
     assert_eq!(next.base_name(), HgPath::new("a"));
 
     let next = iter.next().unwrap();
     assert_eq!(*next.full_path(), HgPath::new("a/bb"));
     assert_eq!(next.base_name(), HgPath::new("bb"));
 
     let next = iter.next().unwrap();
     assert_eq!(*next.full_path(), HgPath::new("a/bb/c"));
     assert_eq!(next.base_name(), HgPath::new("c"));
 
     assert!(iter.next().is_none());
 }