project_panel: Allow New File from an empty hidden-root project (#53947)

This fixes #53869.

Creating a new file from the project panel background menu failed when a
single local project was empty and its root was hidden. In that state
there are no visible entries to seed `expanded_dir_ids`, so the action
returned early before opening the filename editor.

This initializes that state lazily from the root entry when creating a
new item, and adds a regression test for the empty hidden-root path.

Release Notes:

- Fixed creating a new file from the project panel context menu in empty
local projects

crates/project_panel/src/project_panel.rs

@@ -2077,13 +2077,18 @@ impl ProjectPanel {
 
         let directory_id;
         let new_entry_id = self.resolve_entry(entry_id);
-        if let Some((worktree, expanded_dir_ids)) = self
-            .project
-            .read(cx)
-            .worktree_for_id(worktree_id, cx)
-            .zip(self.state.expanded_dir_ids.get_mut(&worktree_id))
-        {
+        if let Some(worktree) = self.project.read(cx).worktree_for_id(worktree_id, cx) {
             let worktree = worktree.read(cx);
+            let expanded_dir_ids = match self.state.expanded_dir_ids.entry(worktree_id) {
+                hash_map::Entry::Occupied(entry) => entry.into_mut(),
+                hash_map::Entry::Vacant(entry) => {
+                    let Some(root_entry_id) = worktree.root_entry().map(|entry| entry.id) else {
+                        return;
+                    };
+                    entry.insert(vec![root_entry_id])
+                }
+            };
+
             if let Some(mut entry) = worktree.entry_for_id(new_entry_id) {
                 loop {
                     if entry.is_dir() {

crates/project_panel/src/project_panel_tests.rs

@@ -8065,6 +8065,104 @@ async fn test_create_entries_without_selection_hide_root(cx: &mut gpui::TestAppC
     );
 }
 
+#[gpui::test]
+async fn test_context_menu_new_file_in_empty_hidden_root(cx: &mut gpui::TestAppContext) {
+    init_test(cx);
+
+    let fs = FakeFs::new(cx.executor());
+    fs.insert_tree(path!("/root"), json!({})).await;
+
+    let project = Project::test(fs.clone(), [path!("/root").as_ref()], cx).await;
+    let window = cx.add_window(|window, cx| MultiWorkspace::test_new(project.clone(), window, cx));
+    let workspace = window
+        .read_with(cx, |mw, _| mw.workspace().clone())
+        .unwrap();
+    let cx = &mut VisualTestContext::from_window(window.into(), cx);
+
+    cx.update(|_, cx| {
+        let settings = *ProjectPanelSettings::get_global(cx);
+        ProjectPanelSettings::override_global(
+            ProjectPanelSettings {
+                hide_root: true,
+                ..settings
+            },
+            cx,
+        );
+    });
+
+    let panel = workspace.update_in(cx, |workspace, window, cx| {
+        let panel = ProjectPanel::new(workspace, window, cx);
+        workspace.add_panel(panel.clone(), window, cx);
+        panel
+    });
+    cx.run_until_parked();
+
+    assert!(
+        visible_entries_as_strings(&panel, 0..20, cx).is_empty(),
+        "Empty worktree with hide_root=true should render no entries"
+    );
+
+    panel.update(cx, |panel, _| {
+        assert!(
+            panel.selection.is_none(),
+            "Project panel should start without a selection"
+        );
+        assert!(
+            panel.state.last_worktree_root_id.is_some(),
+            "Project panel should still track the hidden root entry"
+        );
+    });
+
+    panel.update_in(cx, |panel, window, cx| {
+        let root_entry_id = panel
+            .state
+            .last_worktree_root_id
+            .expect("hidden root should be available for background context menu actions");
+        panel.deploy_context_menu(
+            gpui::point(gpui::px(1.), gpui::px(1.)),
+            root_entry_id,
+            window,
+            cx,
+        );
+        panel.new_file(&NewFile, window, cx);
+    });
+    cx.run_until_parked();
+
+    panel.update_in(cx, |panel, window, cx| {
+        assert!(
+            panel.filename_editor.read(cx).is_focused(window),
+            "New File from the background context menu should open the filename editor"
+        );
+    });
+
+    assert_eq!(
+        visible_entries_as_strings(&panel, 0..20, cx),
+        &["  [EDITOR: '']  <== selected"],
+        "New file editor should appear at the hidden root level"
+    );
+
+    let confirm = panel.update_in(cx, |panel, window, cx| {
+        panel.filename_editor.update(cx, |editor, cx| {
+            editor.set_text("new_file_from_context_menu.txt", window, cx)
+        });
+        panel.confirm_edit(true, window, cx).unwrap()
+    });
+    confirm.await.unwrap();
+    cx.run_until_parked();
+
+    assert_eq!(
+        visible_entries_as_strings(&panel, 0..20, cx),
+        &["  new_file_from_context_menu.txt  <== selected  <== marked"],
+        "Confirmed file should appear at the hidden root level"
+    );
+
+    assert!(
+        fs.is_file(Path::new("/root/new_file_from_context_menu.txt"))
+            .await,
+        "File should be created in the empty root directory"
+    );
+}
+
 #[cfg(windows)]
 #[gpui::test]
 async fn test_create_entry_with_trailing_dot_windows(cx: &mut gpui::TestAppContext) {