Use multibuffer to fix symbol search when diff is present (#52268)

Steven created 5 days ago

## Context

<!-- What does this PR do, and why? How is it expected to impact users?
     Not just what changed, but what motivated it and why this approach.

Link to Linear issue (e.g., ENG-123) or GitHub issue (e.g., Closes #456)
     if one exists — helps with traceability. -->
     
Fixes a bug where project symbol search navigates to the wrong position
when diff hunks are expanded. The cursor would land offset by the number
of lines added by the expanded diffs (Closes #51331). Now, users
navigating to symbols via project symbol search will land on the correct
position even when diff hunks are expanded in the editor.

The fix converts the buffer position to a `multi_buffer::Anchor` before
passing it to `select_ranges`, so it resolves correctly through the diff
transform layer instead of being interpreted as a literal MultiBuffer
coordinate.

Previously, the symbol's position was passed as a raw coordinate to the
editor, which interpreted it relative to what's displayed on screen
(including expanded diff lines). The fix converts the position to an
anchor, which is tied to the actual content in the file rather than a
screen position.

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- All changes are in `crates/project_symbols/src/project_symbols.rs`.
Most of the changes are in `confirm()` method (Lines 142-154).
  - There's also one change on the first line of the file.

## Self-Review Checklist

<!-- Check before requesting review: -->
- [x] I've reviewed my own diff for quality, security, and reliability
- [ ] Unsafe blocks (if any) have justifying comments
- [x] The content is consistent with the [UI/UX
checklist](https://github.com/zed-industries/zed/blob/main/CONTRIBUTING.md#uiux-checklist)
- [x] Tests cover the new/changed behavior
- [x] Performance impact has been considered and is acceptable

Release Notes:

- Fixed a bug where project symbols did not take you to the correct
location when diffs are expanded.

Change summary

crates/project_symbols/src/project_symbols.rs | 14 ++++++++++++--
1 file changed, 12 insertions(+), 2 deletions(-)

Detailed changes

crates/project_symbols/src/project_symbols.rs

@@ -1,4 +1,6 @@
-use editor::{Bias, Editor, SelectionEffects, scroll::Autoscroll, styled_runs_for_code_label};
+use editor::{
+    Anchor, Bias, Editor, SelectionEffects, scroll::Autoscroll, styled_runs_for_code_label,
+};
 use fuzzy::{StringMatch, StringMatchCandidate};
 use gpui::{
     App, Context, DismissEvent, Entity, HighlightStyle, ParentElement, StyledText, Task, TextStyle,
@@ -140,11 +142,19 @@ impl PickerDelegate for ProjectSymbolsDelegate {
                     );
 
                     editor.update(cx, |editor, cx| {
+                        let multibuffer_snapshot = editor.buffer().read(cx).snapshot(cx);
+                        let Some((excerpt_id, _, buffer_snapshot)) =
+                            multibuffer_snapshot.as_singleton()
+                        else {
+                            return;
+                        };
+                        let text_anchor = buffer_snapshot.anchor_before(position);
+                        let anchor = Anchor::in_buffer(excerpt_id, text_anchor);
                         editor.change_selections(
                             SelectionEffects::scroll(Autoscroll::center()),
                             window,
                             cx,
-                            |s| s.select_ranges([position..position]),
+                            |s| s.select_ranges([anchor..anchor]),
                         );
                     });
                 })?;