editor: Add in_preview boolean context for keybindings (#61777)

# Objective

- Add an `in_preview` context that is available when the current editor
is in preview mode (opened from project panel or go to definition).
- closes https://github.com/zed-industries/zed/discussions/61765

## Solution

- In `editor.rs`, added a check in `key_context()` that detects if the
editor is the active preview item in its pane, and if so, adds
`"in_preview"` to the key context.
- Uses existing `workspace.pane_for_item_id()` and
`pane.is_active_preview_item()` methods — no new APIs introduced.

## Testing

- Added two tests in `editor_tests.rs`:
- `test_in_preview_context_added_when_in_preview_mode` — verifies
`in_preview` is present when editor is set as preview item.
- `test_in_preview_context_not_added_when_not_in_preview_mode` —
verifies `in_preview` is absent for regular (non-preview) tabs.
- Tested on Linux.

## Self-Review Checklist:

- [x] I've reviewed my own diff for quality, security, and reliability
- [x] Unsafe blocks (if any) have justifying comments
- [x] The content adheres to Zed's UI standards
([UX/UI](https://github.com/zed-industries/zed/blob/main/CONTRIBUTING.md#uiux-checklist)
and
[icon](https://github.com/zed-industries/zed/blob/main/crates/icons/README.md)
guidelines)
- [x] Tests cover the new/changed behavior
- [x] Performance impact has been considered and is acceptable

---

Release Notes:

- Added `in_preview` keybinding context for when an editor is in preview
mode.

crates/editor/src/editor.rs

@@ -2787,6 +2787,14 @@ impl Editor {
             key_context.add("diffs_expanded");
         }
 
+        if self
+            .nav_history
+            .as_ref()
+            .is_some_and(ItemNavHistory::is_preview_item)
+        {
+            key_context.add("in_preview");
+        }
+
         key_context
     }
 

crates/editor/src/editor_tests.rs

@@ -43364,3 +43364,74 @@ async fn test_select_delimiters_expansion(cx: &mut TestAppContext) {
     cx.dispatch_action(SelectInsideDelimiters);
     cx.assert_editor_state("foo(«x, { a: 1 }ˇ»);");
 }
+
+#[gpui::test]
+async fn test_in_preview_key_context(cx: &mut TestAppContext) {
+    init_test(cx, |_| {});
+    cx.update(|cx| {
+        SettingsStore::update_global(cx, |store, cx| {
+            store.update_user_settings(cx, |settings: &mut SettingsContent| {
+                settings.preview_tabs.get_or_insert_default().enabled = Some(true);
+            });
+        });
+    });
+
+    let fs = FakeFs::new(cx.executor());
+    fs.insert_tree(
+        path!("/root"),
+        serde_json::json!({
+            "test.txt": "hello",
+        }),
+    )
+    .await;
+    let project = Project::test(fs, [path!("/root").as_ref()], cx).await;
+    let (multi_workspace, cx) =
+        cx.add_window_view(|window, cx| MultiWorkspace::test_new(project.clone(), window, cx));
+    let workspace = multi_workspace.read_with(cx, |mw, _| mw.workspace().clone());
+    let worktree_id = workspace.update(cx, |workspace, cx| {
+        workspace.project().update(cx, |project, cx| {
+            project.worktrees(cx).next().unwrap().read(cx).id()
+        })
+    });
+
+    let editor = workspace
+        .update_in(cx, |workspace, window, cx| {
+            workspace.open_path_preview(
+                (worktree_id, rel_path("test.txt")),
+                None,
+                true,
+                true,
+                true,
+                window,
+                cx,
+            )
+        })
+        .unwrap()
+        .await
+        .downcast::<Editor>()
+        .unwrap();
+
+    let pane = workspace.update(cx, |workspace, _| workspace.active_pane().clone());
+    pane.read_with(cx, |pane, _| {
+        assert!(pane.is_active_preview_item(editor.entity_id()));
+    });
+
+    cx.focus(&editor);
+    editor.update_in(cx, |editor, window, cx| {
+        assert!(
+            editor.key_context(window, cx).contains("in_preview"),
+            "Expected 'in_preview' context when the editor is the pane's preview item"
+        );
+    });
+
+    pane.update(cx, |pane, _cx| {
+        pane.unpreview_item_if_preview(editor.entity_id());
+    });
+
+    editor.update_in(cx, |editor, window, cx| {
+        assert!(
+            !editor.key_context(window, cx).contains("in_preview"),
+            "Expected no 'in_preview' context after the tab is unpreviewed"
+        );
+    });
+}

crates/workspace/src/pane.rs

@@ -4661,6 +4661,10 @@ impl Render for Pane {
 }
 
 impl ItemNavHistory {
+    pub fn is_preview_item(&self) -> bool {
+        self.history.0.lock().preview_item_id == Some(self.item.id())
+    }
+
     pub fn push<D: 'static + Any + Send + Sync>(
         &mut self,
         data: Option<D>,
@@ -4672,19 +4676,18 @@ impl ItemNavHistory {
             .upgrade()
             .is_some_and(|item| item.include_in_nav_history())
         {
-            let is_preview_item = self.history.0.lock().preview_item_id == Some(self.item.id());
+            let is_preview_item = self.is_preview_item();
             self.history
                 .push(data, self.item.clone(), is_preview_item, row, cx);
         }
     }
 
     pub fn navigation_entry(&self, data: Option<Arc<dyn Any + Send + Sync>>) -> NavigationEntry {
-        let is_preview_item = self.history.0.lock().preview_item_id == Some(self.item.id());
         NavigationEntry {
             item: self.item.clone(),
             data,
             timestamp: 0,
-            is_preview: is_preview_item,
+            is_preview: self.is_preview_item(),
             row: None,
         }
     }