dirstate-v2: Drop cached read_dir results after .hgignore changes

Soon we’ll want the status algorithm to be able to skip `std::fs::read_dir` in
more cases, notabling when listing unknown files but not ignored files.

When ignore patterns change (which we detect by their hash, added to the
dirstate-v2 format in a previous changeset), a formerly-ignored file could
become unknown without changing its parent directory’s modification time.
Therefore we remove any directory mtime from the dirstate, effictively
invalidating the existing caches.

Differential Revision: https://phab.mercurial-scm.org/D10907

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

@@ -495,6 +495,19 b" impl<'on_disk> DirstateMap<'on_disk> {"
         }
     }
 
+    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.root,
+            path,
+            WithBasename::to_cow_owned,
+            |_| {},
+        )
+    }
+
     pub(super) fn get_or_insert_node<'tree, 'path>(
         on_disk: &'on_disk [u8],
         root: &'tree mut ChildNodes<'on_disk>,

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

@@ -6,7 +6,6 b' use crate::dirstate_tree::dirstate_map::'
 use crate::dirstate_tree::dirstate_map::NodeRef;
 use crate::dirstate_tree::on_disk::DirstateV2ParseError;
 use crate::dirstate_tree::on_disk::Timestamp;
-use crate::dirstate_tree::path_with_basename::WithBasename;
 use crate::matchers::get_ignore_function;
 use crate::matchers::Matcher;
 use crate::utils::files::get_bytes_from_os_string;
@@ -70,6 +69,7 b" pub fn status<'tree, 'on_disk: 'tree>("
         outcome: Default::default(),
         ignore_patterns_have_changed: patterns_changed,
         new_cachable_directories: Default::default(),
+        outated_cached_directories: Default::default(),
         filesystem_time_at_status_start: filesystem_now(&root_dir).ok(),
     };
     let is_at_repo_root = true;
@@ -91,18 +91,22 b" pub fn status<'tree, 'on_disk: 'tree>("
     )?;
     let mut outcome = common.outcome.into_inner().unwrap();
     let new_cachable = common.new_cachable_directories.into_inner().unwrap();
+    let outdated = common.outated_cached_directories.into_inner().unwrap();
 
     outcome.dirty = common.ignore_patterns_have_changed == Some(true)
+        || !outdated.is_empty()
         || !new_cachable.is_empty();
 
+    // Remove outdated mtimes before adding new mtimes, in case a given
+    // directory is both
+    for path in &outdated {
+        let node = dmap.get_or_insert(path)?;
+        if let NodeData::CachedDirectory { .. } = &node.data {
+            node.data = NodeData::None
+        }
+    }
     for (path, mtime) in &new_cachable {
-        let node = DirstateMap::get_or_insert_node(
-            dmap.on_disk,
-            &mut dmap.root,
-            path,
-            WithBasename::to_cow_owned,
-            |_| {},
-        )?;
+        let node = dmap.get_or_insert(path)?;
         match &node.data {
             NodeData::Entry(_) => {} // Don’t overwrite an entry
             NodeData::CachedDirectory { .. } | NodeData::None => {
@@ -123,6 +127,7 b" struct StatusCommon<'a, 'tree, 'on_disk:"
     ignore_fn: IgnoreFnType<'a>,
     outcome: Mutex<DirstateStatus<'on_disk>>,
     new_cachable_directories: Mutex<Vec<(Cow<'on_disk, HgPath>, Timestamp)>>,
+    outated_cached_directories: Mutex<Vec<Cow<'on_disk, HgPath>>>,
 
     /// Whether ignore files like `.hgignore` have changed since the previous
     /// time a `status()` call wrote their hash to the dirstate. `None` means
@@ -155,6 +160,22 b" impl<'a, 'tree, 'on_disk> StatusCommon<'"
             .push((hg_path.to_owned().into(), BadMatch::OsError(errno)))
     }
 
+    fn check_for_outdated_directory_cache(
+        &self,
+        dirstate_node: &NodeRef<'tree, 'on_disk>,
+    ) -> Result<(), DirstateV2ParseError> {
+        if self.ignore_patterns_have_changed == Some(true)
+            && dirstate_node.cached_directory_mtime().is_some()
+        {
+            self.outated_cached_directories.lock().unwrap().push(
+                dirstate_node
+                    .full_path_borrowed(self.dmap.on_disk)?
+                    .detach_from_tree(),
+            )
+        }
+        Ok(())
+    }
+
     /// If this returns true, we can get accurate results by only using
     /// `symlink_metadata` for child nodes that exist in the dirstate and don’t
     /// need to call `read_dir`.
@@ -304,6 +325,7 b" impl<'a, 'tree, 'on_disk> StatusCommon<'"
         dirstate_node: NodeRef<'tree, 'on_disk>,
         has_ignored_ancestor: bool,
     ) -> Result<(), DirstateV2ParseError> {
+        self.check_for_outdated_directory_cache(&dirstate_node)?;
         let hg_path = &dirstate_node.full_path_borrowed(self.dmap.on_disk)?;
         let file_type = fs_metadata.file_type();
         let file_or_symlink = file_type.is_file() || file_type.is_symlink();
@@ -521,6 +543,7 b" impl<'a, 'tree, 'on_disk> StatusCommon<'"
         &self,
         dirstate_node: NodeRef<'tree, 'on_disk>,
     ) -> Result<(), DirstateV2ParseError> {
+        self.check_for_outdated_directory_cache(&dirstate_node)?;
         self.mark_removed_or_deleted_if_file(
             &dirstate_node.full_path_borrowed(self.dmap.on_disk)?,
             dirstate_node.state()?,