Fix detection that a diff hunk is expanded (zed-industries#18302)

Release Notes:

- N/A

---------

Co-authored-by: Marshall <marshall@zed.dev>

Author: 2 people

crates/collab/src/tests/editor_tests.rs

@@ -2214,10 +2214,7 @@ struct Row10;"#};
         let snapshot = editor.snapshot(cx);
         let all_hunks = editor_hunks(editor, &snapshot, cx);
         let all_expanded_hunks = expanded_hunks(editor, &snapshot, cx);
-        assert_eq!(
-            expanded_hunks_background_highlights(editor, cx),
-            vec![DisplayRow(5)..=DisplayRow(5)]
-        );
+        assert_eq!(expanded_hunks_background_highlights(editor, cx), Vec::new());
         assert_eq!(
             all_hunks,
             vec![(

crates/editor/src/element.rs

@@ -1335,7 +1335,11 @@ impl EditorElement {
                         }
                         match status {
                             DiffHunkStatus::Added => {}
-                            DiffHunkStatus::Modified => {}
+                            DiffHunkStatus::Modified => {
+                                if is_expanded {
+                                    *status = DiffHunkStatus::Added;
+                                }
+                            }
                             DiffHunkStatus::Removed => {
                                 if is_expanded {
                                     return None;

crates/editor/src/hunk_diff.rs

@@ -279,8 +279,12 @@ impl Editor {
                                 ..Point::new(remaining_hunk.row_range.end.0, 0);
                         hunks_to_expand.push(HoveredHunk {
                             status: hunk_status(&remaining_hunk),
-                            multi_buffer_range: remaining_hunk_point_range
-                                .to_anchors(&snapshot.buffer_snapshot),
+                            multi_buffer_range: snapshot
+                                .buffer_snapshot
+                                .anchor_before(remaining_hunk_point_range.start)
+                                ..snapshot
+                                    .buffer_snapshot
+                                    .anchor_after(remaining_hunk_point_range.end),
                             diff_base_byte_range: remaining_hunk.diff_base_byte_range.clone(),
                         });
                     }