editor: Fix sticky headers not accounting for deleted diff hunks (#49296)

Release Notes:

- Fixed sticky headers sometimes disappearing when dealing with expanded
deleted diff hunks

crates/editor/src/editor.rs

@@ -200,7 +200,7 @@ use std::{
     time::{Duration, Instant},
 };
 use task::{ResolvedTask, RunnableTag, TaskTemplate, TaskVariables};
-use text::{BufferId, FromAnchor, OffsetUtf16, Rope, ToOffset as _};
+use text::{BufferId, FromAnchor, OffsetUtf16, Rope, ToOffset as _, ToPoint as _};
 use theme::{
     AccentColors, ActiveTheme, GlobalTheme, PlayerColor, StatusColors, SyntaxTheme, Theme,
     ThemeSettings, observe_buffer_font_size_adjustment,
@@ -1992,20 +1992,21 @@ impl Editor {
             return;
         }
         let multi_buffer = display_snapshot.buffer_snapshot();
-        let multi_buffer_visible_start = self
+        let scroll_anchor = self
             .scroll_manager
             .native_anchor(display_snapshot, cx)
-            .anchor
-            .to_point(&multi_buffer);
-        let max_row = multi_buffer.max_point().row;
-
-        let start_row = (multi_buffer_visible_start.row).min(max_row);
-        let end_row = (multi_buffer_visible_start.row + 10).min(max_row);
+            .anchor;
         let Some((excerpt_id, _, buffer)) = multi_buffer.as_singleton() else {
             return;
         };
         let buffer = buffer.clone();
         let &excerpt_id = excerpt_id;
+
+        let buffer_visible_start = scroll_anchor.text_anchor.to_point(&buffer);
+        let max_row = buffer.max_point().row;
+        let start_row = buffer_visible_start.row.min(max_row);
+        let end_row = (buffer_visible_start.row + 10).min(max_row);
+
         let syntax = self.style(cx).syntax.clone();
         let background_task = cx.background_spawn(async move {
             buffer

crates/editor/src/editor_tests.rs

@@ -29058,6 +29058,95 @@ async fn test_sticky_scroll(cx: &mut TestAppContext) {
     assert_eq!(sticky_headers(10.0), vec![]);
 }
 
+#[gpui::test]
+async fn test_sticky_scroll_with_expanded_deleted_diff_hunks(
+    executor: BackgroundExecutor,
+    cx: &mut TestAppContext,
+) {
+    init_test(cx, |_| {});
+    let mut cx = EditorTestContext::new(cx).await;
+
+    let diff_base = indoc! {"
+        fn foo() {
+            let a = 1;
+            let b = 2;
+            let c = 3;
+            let d = 4;
+            let e = 5;
+        }
+    "};
+
+    let buffer = indoc! {"
+        ˇfn foo() {
+        }
+    "};
+
+    cx.set_state(&buffer);
+
+    cx.update_editor(|e, _, cx| {
+        e.buffer()
+            .read(cx)
+            .as_singleton()
+            .unwrap()
+            .update(cx, |buffer, cx| {
+                buffer.set_language(Some(rust_lang()), cx);
+            })
+    });
+
+    cx.set_head_text(diff_base);
+    executor.run_until_parked();
+
+    cx.update_editor(|editor, window, cx| {
+        editor.expand_all_diff_hunks(&ExpandAllDiffHunks, window, cx);
+    });
+    executor.run_until_parked();
+
+    // After expanding, the display should look like:
+    //   row 0: fn foo() {
+    //   row 1: -    let a = 1;   (deleted)
+    //   row 2: -    let b = 2;   (deleted)
+    //   row 3: -    let c = 3;   (deleted)
+    //   row 4: -    let d = 4;   (deleted)
+    //   row 5: -    let e = 5;   (deleted)
+    //   row 6: }
+    //
+    // fn foo() spans display rows 0-6. Scrolling into the deleted region
+    // (rows 1-5) should still show fn foo() as a sticky header.
+
+    let fn_foo = Point { row: 0, column: 0 };
+
+    let mut sticky_headers = |offset: ScrollOffset| {
+        cx.update_editor(|e, window, cx| {
+            e.scroll(gpui::Point { x: 0., y: offset }, None, window, cx);
+        });
+        cx.run_until_parked();
+        cx.update_editor(|e, window, cx| {
+            EditorElement::sticky_headers(&e, &e.snapshot(window, cx))
+                .into_iter()
+                .map(
+                    |StickyHeader {
+                         start_point,
+                         offset,
+                         ..
+                     }| { (start_point, offset) },
+                )
+                .collect::<Vec<_>>()
+        })
+    };
+
+    assert_eq!(sticky_headers(0.0), vec![]);
+    assert_eq!(sticky_headers(0.5), vec![(fn_foo, 0.0)]);
+    assert_eq!(sticky_headers(1.0), vec![(fn_foo, 0.0)]);
+    // Scrolling into deleted lines: fn foo() should still be a sticky header.
+    assert_eq!(sticky_headers(2.0), vec![(fn_foo, 0.0)]);
+    assert_eq!(sticky_headers(3.0), vec![(fn_foo, 0.0)]);
+    assert_eq!(sticky_headers(4.0), vec![(fn_foo, 0.0)]);
+    assert_eq!(sticky_headers(5.0), vec![(fn_foo, 0.0)]);
+    assert_eq!(sticky_headers(5.5), vec![(fn_foo, -0.5)]);
+    // Past the closing brace: no more sticky header.
+    assert_eq!(sticky_headers(6.0), vec![]);
+}
+
 #[gpui::test]
 fn test_relative_line_numbers(cx: &mut TestAppContext) {
     init_test(cx, |_| {});