git_ui: Prevent crash when selecting collapsed sections (#63164)

## Summary

- Select the first Git panel entry from the visible row indices instead
of treating an entry index as a visible-row position
- Avoid selecting files hidden by collapsed sections in both tree and
flat views
- Add a regression test for collapsing the only populated section in
tree view with no active selection

Fixes ZED-AZ3
Fixes ZED-B0Z

Release Notes:

- Fixed a crash in the Git panel when collapsed sections were used in
tree view.

crates/git_ui/src/git_panel.rs

@@ -1764,18 +1764,21 @@ impl GitPanel {
         _window: &mut Window,
         cx: &mut Context<Self>,
     ) {
+        let is_selectable = |index| {
+            self.entries
+                .get(index)
+                .is_some_and(GitListEntry::is_selectable)
+        };
         let first_entry = match &self.view_mode {
             GitPanelViewMode::Flat => self
-                .entries
+                .visible_flat_entry_indices()
+                .into_iter()
+                .find(|&index| is_selectable(index)),
+            GitPanelViewMode::Tree(state) => state
+                .logical_indices
                 .iter()
-                .position(|entry| entry.status_entry().is_some()),
-            GitPanelViewMode::Tree(state) => {
-                let index = self.entries.iter().position(|entry| {
-                    entry.status_entry().is_some() || entry.directory_entry().is_some()
-                });
-
-                index.map(|index| state.logical_indices[index])
-            }
+                .copied()
+                .find(|&index| is_selectable(index)),
         };
 
         if let Some(first_entry) = first_entry {
@@ -12389,6 +12392,48 @@ mod tests {
         });
     }
 
+    #[gpui::test]
+    async fn test_tree_view_select_first_skips_collapsed_section(cx: &mut TestAppContext) {
+        init_test(cx);
+        cx.update(|cx| {
+            SettingsStore::update_global(cx, |store, cx| {
+                store.update_user_settings(cx, |settings| {
+                    settings.git_panel.get_or_insert_default().tree_view = Some(true);
+                })
+            });
+        });
+
+        let (_, _, _, panel, mut cx) = setup_git_panel_with_changes(
+            cx,
+            json!({
+                ".git": {},
+                "modified.rs": "fn main() {}",
+            }),
+            &[("modified.rs", StatusCode::Modified)],
+        )
+        .await;
+
+        panel.update_in(&mut cx, |panel, window, cx| {
+            panel.selected_entry = None;
+            panel.toggle_section_collapsed(Section::Tracked, window, cx);
+
+            let state = panel
+                .view_mode
+                .tree_state()
+                .expect("tree view state should exist");
+            assert_eq!(state.logical_indices, [0]);
+            assert!(panel.selected_entry.is_none());
+
+            panel.toggle_section_collapsed(Section::Tracked, window, cx);
+
+            let selected_entry = panel
+                .get_selected_entry()
+                .and_then(GitListEntry::status_entry)
+                .expect("the first visible file should be selected");
+            assert_eq!(selected_entry.repo_path, repo_path("modified.rs"));
+        });
+    }
+
     fn assert_entry_paths(entries: &[GitListEntry], expected_paths: &[Option<&str>]) {
         assert_eq!(entries.len(), expected_paths.len());
         for (entry, expected_path) in entries.iter().zip(expected_paths) {