improve: show whole-diff totals alongside file stats

src/diff.rs

@@ -135,6 +135,8 @@ pub struct ChangedFile {
     pub status: FileStatus,
     /// False means text, EOF flags, hunks and notices have not been prepared.
     pub loaded: bool,
+    /// Frozen (added, removed) counts for catalog entries whose text is unloaded.
+    pub stats: Option<(usize, usize)>,
     pub before: Vec<String>,
     pub after: Vec<String>,
     pub before_eof: bool,
@@ -142,6 +144,17 @@ pub struct ChangedFile {
     pub hunks: Vec<Hunk>,
     pub notice: Option<String>,
 }
+impl ChangedFile {
+    pub(crate) fn line_counts(&self) -> Option<(usize, usize)> {
+        if self.loaded {
+            Some(self.hunks.iter().fold((0, 0), |(added, removed), hunk| {
+                (added + hunk.after_len, removed + hunk.before_len)
+            }))
+        } else {
+            self.stats
+        }
+    }
+}
 #[derive(Clone, Debug, PartialEq, Eq)]
 pub struct BlameRevision {
     pub store: PathBuf,
@@ -690,6 +703,7 @@ impl DiffState {
         comparison.root = root.clone();
         comparison.files.resize_with(paths.len(), || ChangedFile {
             review_revisions: None,
+            stats: None,
             path: PathBuf::new(),
             old_path: None,
             status: FileStatus::Modified,