Toolbar items may not act on the proper target (jupyterlab#12368)

* Notebook toolbar buttons do not respect context
Fixes jupyterlab#12177

* Make sure main area widget focuses its content in bubble phase of mousedown (#4)

Co-authored-by: Afshin Taylor Darian <[email protected]>

galata/test/jupyterlab/notebook-toolbar.test.ts

@@ -12,7 +12,6 @@ async function populateNotebook(page: IJupyterLabPageFixture) {
     '## This is **bold** and *italic* [link to jupyter.org!](http://jupyter.org)'
   );
   await page.notebook.addCell('code', '2 ** 3');
-  // await page.notebook.runCell(2, true);
 }
 
 test.describe('Notebook Toolbar', () => {
@@ -99,3 +98,44 @@ test.describe('Notebook Toolbar', () => {
     expect(await nbPanel.screenshot()).toMatchSnapshot(imageName);
   });
 });
+
+test('Toolbar items act on owner widget', async ({ page }) => {
+  // Given two side-by-side notebooks and the second being active
+  const file1 = 'notebook1.ipynb';
+  await page.notebook.createNew(file1);
+  const panel1 = await page.activity.getPanel(file1);
+  const tab1 = await page.activity.getTab(file1);
+
+  // FIXME Calling a second time `page.notebook.createNew` is not robust
+  await page.menu.clickMenuItem('File>New>Notebook');
+  try {
+    await page.waitForSelector('.jp-Dialog', { timeout: 5000 });
+    await page.click('.jp-Dialog .jp-mod-accept');
+  } catch (reason) {
+    // no-op
+  }
+
+  const tab2 = await page.activity.getTab();
+
+  const tab2BBox = await tab2.boundingBox();
+  await page.mouse.move(
+    tab2BBox.x + 0.5 * tab2BBox.width,
+    tab2BBox.y + 0.5 * tab2BBox.height
+  );
+  await page.mouse.down();
+  await page.mouse.move(900, tab2BBox.y + tab2BBox.height + 200);
+  await page.mouse.up();
+
+  const classlist = await tab1.getAttribute('class');
+  expect(classlist.split(' ')).not.toContain('jp-mod-current');
+
+  // When clicking on toolbar item of the first file
+  await (
+    await panel1.$('button[data-command="notebook:insert-cell-below"]')
+  ).click();
+
+  // Then the first file is activated and the action is performed
+  const classlistEnd = await tab1.getAttribute('class');
+  expect(classlistEnd.split(' ')).toContain('jp-mod-current');
+  expect(await page.notebook.getCellCount()).toEqual(2);
+});

packages/apputils/src/mainareawidget.ts

@@ -8,6 +8,11 @@ import { BoxLayout, BoxPanel, Widget } from '@lumino/widgets';
 import { DOMUtils } from './domutils';
 import { Printing } from './printing';
 
+/**
+ * A flag to indicate that event handlers are caught in the capture phase.
+ */
+const USE_CAPTURE = true;
+
 /**
  * A widget meant to be contained in the JupyterLab main area.
  *
@@ -163,14 +168,32 @@ export class MainAreaWidget<T extends Widget = Widget>
    */
   protected onActivateRequest(msg: Message): void {
     if (this._isRevealed) {
-      if (this._content) {
-        this._focusContent();
-      }
+      this._focusContent();
     } else {
       this._spinner.node.focus();
     }
   }
 
+  /**
+   * Handle `after-attach` messages for the widget.
+   */
+  protected onAfterAttach(msg: Message): void {
+    super.onAfterAttach(msg);
+    // Focus content in capture phase to ensure relevant commands operate on the
+    // current main area widget.
+    // Add the event listener directly instead of using `handleEvent` in order
+    // to save sub-classes from needing to reason about calling it as well.
+    this.node.addEventListener('mousedown', this._evtMouseDown, USE_CAPTURE);
+  }
+
+  /**
+   * Handle `before-detach` messages for the widget.
+   */
+  protected onBeforeDetach(msg: Message): void {
+    this.node.removeEventListener('mousedown', this._evtMouseDown, USE_CAPTURE);
+    super.onBeforeDetach(msg);
+  }
+
   /**
    * Handle `'close-request'` messages.
    */
@@ -266,6 +289,11 @@ export class MainAreaWidget<T extends Widget = Widget>
 
   private _isRevealed = false;
   private _revealed: Promise<void>;
+  private _evtMouseDown = () => {
+    if (!this.node.contains(document.activeElement)) {
+      this._focusContent();
+    }
+  };
 }
 
 /**