fix: status-iterator won't swallow legitimate modification during 'racy-git'.

When a modification is marked as being racy, then previously the iterator would have
kept the whole modification even though it should just have tracked the single change.

This made the legitimate modification disappear.

Author: Byron

gix/src/status/iter/mod.rs

@@ -19,6 +19,20 @@ where
     ///
     /// * `patterns`
     ///     - Optional patterns to use to limit the paths to look at. If empty, all paths are considered.
+    ///
+    /// ### Important: Undefined ordering
+    ///
+    /// When compiled with the `parallel` feature, three operations are run at once:
+    ///
+    /// * a dirwalk to find untracked and possibly ignored files
+    /// * an entry-by-entry check to see which of the tracked files changed, and how
+    /// * a tree-index comparison
+    ///
+    /// All of these generate distinct events which may now happen in any order, so consumers
+    /// that are ordering dependent have to restore their desired order.
+    ///
+    /// This isn't feasible to do here as it would mean that returned items would have to be delayed,
+    /// degrading performance for everyone who isn't order-dependent.
     #[doc(alias = "diff_index_to_workdir", alias = "git2")]
     pub fn into_iter(
         self,
@@ -274,12 +288,15 @@ impl Iter {
 
 impl Iter {
     fn maybe_keep_index_change(&mut self, item: Item) -> Option<Item> {
-        let change = match item {
+        match item {
             Item::IndexWorktree(index_worktree::Item::Modification {
                 status: EntryStatus::NeedsUpdate(stat),
                 entry_index,
                 ..
-            }) => (entry_index, ApplyChange::NewStat(stat)),
+            }) => {
+                self.index_changes.push((entry_index, ApplyChange::NewStat(stat)));
+                return None;
+            }
             Item::IndexWorktree(index_worktree::Item::Modification {
                 status:
                     EntryStatus::Change(Change::Modification {
@@ -288,12 +305,12 @@ impl Iter {
                     }),
                 entry_index,
                 ..
-            }) if set_entry_stat_size_zero => (entry_index, ApplyChange::SetSizeToZero),
-            _ => return Some(item),
+            }) if set_entry_stat_size_zero => {
+                self.index_changes.push((entry_index, ApplyChange::SetSizeToZero));
+            }
+            _ => {}
         };
-
-        self.index_changes.push(change);
-        None
+        Some(item)
     }
 }
 

gix/tests/fixtures/generated-archives/make_status_repos.tar

@@ -21,3 +21,12 @@ git init git-mv
 
   git mv file renamed
 )
+
+git init racy-git
+(cd racy-git
+  echo hi >file
+  git add file && git commit -m "init"
+
+  echo ho >file && git add file
+  echo ha >file
+)

gix/tests/fixtures/make_status_repos.sh

@@ -73,6 +73,16 @@ mod into_iter {
         Ok(())
     }
 
+    #[test]
+    fn tree_index_modification_worktree_modification_racy_git() -> crate::Result {
+        let repo = repo("racy-git")?;
+        let mut status = repo.status(gix::progress::Discard)?.into_iter(None)?;
+        let mut items: Vec<_> = status.by_ref().filter_map(Result::ok).collect();
+        items.sort_by(|a, b| a.location().cmp(b.location()));
+        assert_eq!(items.len(), 2, "1 modified in index, the same in worktree");
+        Ok(())
+    }
+
     #[test]
     fn error_during_tree_traversal_causes_failure() -> crate::Result {
         let repo = repo("untracked-only")?;