editor: Fix panic in text_layout_details pre layout (#55816)

Fixes a panic at `Editor::text_layout_details` when called against an
editor whose element has never been laid out (i.e., `set_style` has
never been called, so the cached `style` is still `None`).

We've seen this crash once through a helix motion. The exact production
sequence isn't clear — for the editor to receive a vim action without
ever having been drawn, the active item would have to have changed
inside the same update tick that ends with the deferred `search_submit`,
which is narrow but not impossible (since it's dispatched by the
workspace, not the editor).

Release Notes:

- Fixed a rare panic when invoking helix motions on an editor that had
not yet been laid out.

crates/editor/src/editor.rs

@@ -5985,7 +5985,7 @@ impl Editor {
     pub fn text_layout_details(&self, window: &mut Window, cx: &mut App) -> TextLayoutDetails {
         TextLayoutDetails {
             text_system: window.text_system().clone(),
-            editor_style: self.style.clone().unwrap(),
+            editor_style: self.style.clone().unwrap_or_else(|| self.create_style(cx)),
             rem_size: window.rem_size(),
             scroll_anchor: self.scroll_manager.shared_scroll_anchor(cx),
             visible_rows: self.visible_line_count(),

crates/vim/src/helix.rs

@@ -2960,6 +2960,61 @@ mod test {
         cx.assert_state("«ˇone» two three", Mode::HelixSelect);
     }
 
+    // Regression test for ZED-758: helix motions called
+    // `Editor::text_layout_details` on an editor whose `style` had never
+    // been set, panicking on `unwrap()`.
+    #[gpui::test]
+    async fn test_helix_motion_on_unrendered_editor(cx: &mut gpui::TestAppContext) {
+        use editor::{Editor, EditorMode, SelectionEffects};
+        use multi_buffer::{MultiBuffer, MultiBufferOffset};
+
+        VimTestContext::init(cx);
+        cx.update(|cx| {
+            VimTestContext::init_keybindings(true, cx);
+            SettingsStore::update_global(cx, |store, cx| {
+                store.update_user_settings(cx, |s| {
+                    s.vim_mode = Some(true);
+                    s.helix_mode = Some(true);
+                });
+            });
+        });
+
+        let cx = cx.add_empty_window();
+
+        let editor = cx.update(|window, cx| {
+            use gpui::AppContext as _;
+            let buffer = MultiBuffer::build_simple("one two three", cx);
+            cx.new(|cx| {
+                let mut editor = Editor::new(EditorMode::full(), buffer, None, window, cx);
+                editor.change_selections(SelectionEffects::no_scroll(), window, cx, |s| {
+                    s.select_ranges([MultiBufferOffset(4)..MultiBufferOffset(4)])
+                });
+                editor
+            })
+        });
+
+        let vim = editor
+            .read_with(cx, |editor, _| editor.addon::<VimAddon>().cloned())
+            .expect("VimAddon should be auto-attached to new editors when vim mode is enabled");
+
+        cx.update(|window, cx| {
+            vim.entity.update(cx, |vim, cx| {
+                vim.switch_mode(Mode::HelixNormal, true, window, cx);
+                vim.helix_move_and_collapse(crate::motion::Motion::Left, None, window, cx);
+            });
+        });
+
+        let cursor_offset = cx.update(|_, cx| {
+            editor.update(cx, |editor, cx| {
+                editor
+                    .selections
+                    .newest::<MultiBufferOffset>(&editor.display_snapshot(cx))
+                    .head()
+            })
+        });
+        assert_eq!(cursor_offset, MultiBufferOffset(3));
+    }
+
     #[gpui::test]
     async fn test_helix_select_regex(cx: &mut gpui::TestAppContext) {
         let mut cx = VimTestContext::new(cx, true).await;