feat: add syntax-aware diff backgrounds and diagonal gap shading

src/diff.rs

@@ -147,6 +147,7 @@ pub struct DiffState {
     pub loading: bool,
     pub error: Option<String>,
     pub comparison: Option<Comparison>,
+    pub comparison_id: Option<u64>,
     pub files: Option<FilePicker>,
     pub files_visible: bool,
     pub file: usize,
@@ -177,6 +178,7 @@ impl DiffState {
             loading: true,
             error: None,
             comparison: None,
+            comparison_id: None,
             files: None,
             files_visible: true,
             file: 0,
@@ -215,7 +217,7 @@ impl DiffState {
         self.error = None;
     }
 
-    pub(crate) fn apply_result(&mut self, result: Result<Outcome, String>) {
+    pub(crate) fn apply_result(&mut self, id: u64, result: Result<Outcome, String>) {
         let expected = self.request_kind.take();
         self.loading = false;
         self.pending = None;
@@ -254,6 +256,7 @@ impl DiffState {
                 }
                 self.files = Some(files);
                 self.comparison = Some(comparison);
+                self.comparison_id = Some(id);
                 self.phase = Phase::View;
                 self.focus = Focus::Files;
                 self.file = 0;
@@ -1236,6 +1239,24 @@ mod tests {
         assert_eq!(editor.diff().unwrap().file, 0);
     }
 
+    #[test]
+    fn comparison_identity_comes_from_accepted_requests_not_working_labels() {
+        let mut editor = editor();
+        open(&mut editor);
+        let first = choose_pair(&mut editor);
+        assert!(editor.apply_diff_result(first, Ok(Outcome::Comparison(comparison()))));
+        assert_eq!(editor.diff().unwrap().comparison_id, Some(first));
+        editor.handle(Input::Escape);
+        open(&mut editor);
+        assert_eq!(editor.diff().unwrap().comparison_id, None);
+        let second = choose_pair(&mut editor);
+        assert!(second > first);
+        assert!(!editor.apply_diff_result(first, Ok(Outcome::Comparison(comparison()))));
+        assert_eq!(editor.diff().unwrap().comparison_id, None);
+        assert!(editor.apply_diff_result(second, Ok(Outcome::Comparison(comparison()))));
+        assert_eq!(editor.diff().unwrap().comparison_id, Some(second));
+    }
+
     #[test]
     fn discovery_and_fetch_errors_are_retryable_and_stale_responses_cannot_reopen() {
         let mut editor = editor();