rhg: fix race when an ambiguous file is deleted on disk stable

rhg: fix race when an ambiguous file is deleted on disk

There are two places in the status code where we handle files whose status
we are unsure of based off of metadata alone: this one is the first one to
actually disambiguate, and the second one is later in the code (but updated
in the previous commit) for files that are actually clean to update the
dirstate. Since there is a chance that the contents have changed between
those two moments, we need to stat the files again, since re-using the old
stat could lie about the clean state of the file.

--- a/rust/rhg/src/commands/status.rs	Mon Feb 27 15:18:50 2023 +0100
+++ b/rust/rhg/src/commands/status.rs	Tue Feb 28 16:19:21 2023 +0100
@@ -299,25 +299,45 @@
                 .unsure
                 .into_par_iter()
                 .map(|to_check| {
-                    unsure_is_modified(
+                    // The compiler seems to get a bit confused with complex
+                    // inference when using a parallel iterator + map
+                    // + map_err + collect, so let's just inline some of the
+                    // logic.
+                    match unsure_is_modified(
                         working_directory_vfs,
                         store_vfs,
                         &manifest,
                         &to_check.path,
-                    )
-                    .map(|modified| (to_check, modified))
+                    ) {
+                        Err(HgError::IoError { .. }) => {
+                            // IO errors most likely stem from the file being
+                            // deleted even though we know it's in the
+                            // dirstate.
+                            Ok((to_check, UnsureOutcome::Deleted))
+                        }
+                        Ok(outcome) => Ok((to_check, outcome)),
+                        Err(e) => Err(e),
+                    }
                 })
                 .collect::<Result<_, _>>()?;
-            for (status_path, is_modified) in res.into_iter() {
-                if is_modified {
-                    if display_states.modified {
-                        ds_status.modified.push(status_path);
+            for (status_path, outcome) in res.into_iter() {
+                match outcome {
+                    UnsureOutcome::Clean => {
+                        if display_states.clean {
+                            ds_status.clean.push(status_path.clone());
+                        }
+                        fixup.push(status_path.path.into_owned())
                     }
-                } else {
-                    if display_states.clean {
-                        ds_status.clean.push(status_path.clone());
+                    UnsureOutcome::Modified => {
+                        if display_states.modified {
+                            ds_status.modified.push(status_path);
+                        }
                     }
-                    fixup.push(status_path.path.into_owned())
+                    UnsureOutcome::Deleted => {
+                        if display_states.deleted {
+                            ds_status.deleted.push(status_path);
+                        }
+                    }
                 }
             }
         }
@@ -557,6 +577,16 @@
     }
 }
 
+/// Outcome of the additional check for an ambiguous tracked file
+enum UnsureOutcome {
+    /// The file is actually clean
+    Clean,
+    /// The file has been modified
+    Modified,
+    /// The file was deleted on disk (or became another type of fs entry)
+    Deleted,
+}
+
 /// Check if a file is modified by comparing actual repo store and file system.
 ///
 /// This meant to be used for those that the dirstate cannot resolve, due
@@ -566,7 +596,7 @@
     store_vfs: hg::vfs::Vfs,
     manifest: &Manifest,
     hg_path: &HgPath,
-) -> Result<bool, HgError> {
+) -> Result<UnsureOutcome, HgError> {
     let vfs = working_directory_vfs;
     let fs_path = hg_path_to_path_buf(hg_path).expect("HgPath conversion");
     let fs_metadata = vfs.symlink_metadata(&fs_path)?;
@@ -585,7 +615,7 @@
         .find_by_path(hg_path)?
         .expect("ambgious file not in p1");
     if entry.flags != fs_flags {
-        return Ok(true);
+        return Ok(UnsureOutcome::Modified);
     }
     let filelog = hg::filelog::Filelog::open_vfs(&store_vfs, hg_path)?;
     let fs_len = fs_metadata.len();
@@ -599,7 +629,7 @@
     if filelog_entry.file_data_len_not_equal_to(fs_len) {
         // No need to read file contents:
         // it cannot be equal if it has a different length.
-        return Ok(true);
+        return Ok(UnsureOutcome::Modified);
     }
 
     let p1_filelog_data = filelog_entry.data()?;
@@ -607,7 +637,7 @@
     if p1_contents.len() as u64 != fs_len {
         // No need to read file contents:
         // it cannot be equal if it has a different length.
-        return Ok(true);
+        return Ok(UnsureOutcome::Modified);
     }
 
     let fs_contents = if is_symlink {
@@ -615,7 +645,12 @@
     } else {
         vfs.read(fs_path)?
     };
-    Ok(p1_contents != &*fs_contents)
+
+    Ok(if p1_contents != &*fs_contents {
+        UnsureOutcome::Modified
+    } else {
+        UnsureOutcome::Clean
+    })
 }
 
 fn print_pattern_file_warning(