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

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

These particular allocations are not visible when profiling (as many files
in a typical repo don’t have a copy source). This change is "warm up"
for doing the same with paths of files themselves, which is more involved
since those paths are used as `HashMap` keys. This gets of the way the
addition of a lifetime parameter to several types.

Differential Revision: https://phab.mercurial-scm.org/D10559

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

@@ -1,618 +1,620 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,
+    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 = FastHashMap<WithBasename<HgPathBuf>, Node>;
+pub(super) type ChildNodes<'on_disk> =
+    FastHashMap<WithBasename<HgPathBuf>, Node<'on_disk>>;
 
 /// Represents a file or a directory
 #[derive(Default)]
-pub(super) struct Node {
+pub(super) struct Node<'on_disk> {
     /// `None` for directories
     pub(super) entry: Option<DirstateEntry>,
 
-    pub(super) copy_source: Option<HgPathBuf>,
+    pub(super) copy_source: Option<Cow<'on_disk, HgPath>>,
 
-    pub(super) children: ChildNodes,
+    pub(super) children: ChildNodes<'on_disk>,
 
     /// How many (non-inclusive) descendants of this node are tracked files
     tracked_descendants_count: usize,
 }
 
-impl Node {
+impl Node<'_> {
     pub(super) fn state(&self) -> Option<EntryState> {
         self.entry.as_ref().map(|entry| entry.state)
     }
 }
 
 /// `(full_path, entry, copy_source)`
-type NodeDataMut<'a> = (
-    &'a HgPath,
-    &'a mut Option<DirstateEntry>,
-    &'a mut Option<HgPathBuf>,
+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(
                     &mut self.root,
                     path,
                     |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(HgPath::to_owned);
+                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,
+        root: &'tree mut ChildNodes<'on_disk>,
         path: &HgPath,
-    ) -> Option<&'tree mut Node> {
+    ) -> 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,
+        root: &'tree mut ChildNodes<'on_disk>,
         path: &HgPath,
         mut each_ancestor: impl FnMut(&mut Node),
-    ) -> Option<&'tree 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>(
-        root: &'tree mut ChildNodes,
+        root: &'tree mut ChildNodes<'on_disk>,
         path: &HgPath,
-    ) -> &'tree mut Node {
+    ) -> &'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,
+        root: &'tree mut ChildNodes<'on_disk>,
         path: &HgPath,
         mut each_ancestor: impl FnMut(&mut Node),
-    ) -> &'tree 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();
             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(
             &mut self.root,
             path,
             |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<'a>(
-        &'a mut self,
-    ) -> impl Iterator<Item = NodeDataMut<'a>> + 'a {
+    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()
+            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);
         if node.copy_source.is_none() {
             self.nodes_with_copy_source_count += 1
         }
-        node.copy_source.replace(value)
+        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))
         }))
     }
 }