editor: Fix git-hunk toggling for adjacent hunks (#43187)

Closes #42934 

Release Notes:

- Fix toggling adjacent git-diff hunks based on the reported behaviour
in #42934

---------

Co-authored-by: Jakub Konka <kubkon@jakubkonka.com>

crates/editor/src/editor_tests.rs

@@ -20880,6 +20880,36 @@ async fn test_toggling_adjacent_diff_hunks(cx: &mut TestAppContext) {
         .to_string(),
     );
 
+    cx.update_editor(|editor, window, cx| {
+        editor.move_up(&MoveUp, window, cx);
+        editor.toggle_selected_diff_hunks(&Default::default(), window, cx);
+    });
+    cx.assert_state_with_diff(
+        indoc! { "
+        ˇone
+      - two
+        three
+        five
+    "}
+        .to_string(),
+    );
+
+    cx.update_editor(|editor, window, cx| {
+        editor.move_down(&MoveDown, window, cx);
+        editor.move_down(&MoveDown, window, cx);
+        editor.toggle_selected_diff_hunks(&Default::default(), window, cx);
+    });
+    cx.assert_state_with_diff(
+        indoc! { "
+        one
+      - two
+        ˇthree
+      - four
+        five
+    "}
+        .to_string(),
+    );
+
     cx.set_state(indoc! { "
         one
         ˇTWO
@@ -20919,6 +20949,66 @@ async fn test_toggling_adjacent_diff_hunks(cx: &mut TestAppContext) {
     );
 }
 
+#[gpui::test]
+async fn test_toggling_adjacent_diff_hunks_2(
+    executor: BackgroundExecutor,
+    cx: &mut TestAppContext,
+) {
+    init_test(cx, |_| {});
+
+    let mut cx = EditorTestContext::new(cx).await;
+
+    let diff_base = r#"
+        lineA
+        lineB
+        lineC
+        lineD
+        "#
+    .unindent();
+
+    cx.set_state(
+        &r#"
+        ˇlineA1
+        lineB
+        lineD
+        "#
+        .unindent(),
+    );
+    cx.set_head_text(&diff_base);
+    executor.run_until_parked();
+
+    cx.update_editor(|editor, window, cx| {
+        editor.toggle_selected_diff_hunks(&ToggleSelectedDiffHunks, window, cx);
+    });
+    executor.run_until_parked();
+    cx.assert_state_with_diff(
+        r#"
+        - lineA
+        + ˇlineA1
+          lineB
+          lineD
+        "#
+        .unindent(),
+    );
+
+    cx.update_editor(|editor, window, cx| {
+        editor.move_down(&MoveDown, window, cx);
+        editor.move_right(&MoveRight, window, cx);
+        editor.toggle_selected_diff_hunks(&ToggleSelectedDiffHunks, window, cx);
+    });
+    executor.run_until_parked();
+    cx.assert_state_with_diff(
+        r#"
+        - lineA
+        + lineA1
+          lˇineB
+        - lineC
+          lineD
+        "#
+        .unindent(),
+    );
+}
+
 #[gpui::test]
 async fn test_edits_around_expanded_deletion_hunks(
     executor: BackgroundExecutor,

crates/multi_buffer/src/multi_buffer.rs

@@ -2610,9 +2610,8 @@ impl MultiBuffer {
         for range in ranges {
             let range = range.to_point(&snapshot);
             let start = snapshot.point_to_offset(Point::new(range.start.row, 0));
-            let end = snapshot.point_to_offset(Point::new(range.end.row + 1, 0));
-            let start = start.saturating_sub_usize(1);
-            let end = snapshot.len().min(end + 1usize);
+            let end = (snapshot.point_to_offset(Point::new(range.end.row + 1, 0)) + 1usize)
+                .min(snapshot.len());
             cursor.seek(&start, Bias::Right);
             while let Some(item) = cursor.item() {
                 if *cursor.start() >= end {