Fix unhandled promise rejection in setupInitialUrlState (#5864)

dispatch(finalizeProfileView()) returns a Promise that was previously
discarded. Errors thrown synchronously inside it (e.g. from selectors
like computeReferenceCPUDeltaPerMs) were converted to rejected promises
by the async function, then escaped as "Uncaught (in promise)" instead
of being routed to the FATAL_ERROR state.

Adding .catch() dispatches fatalError() on failure so the error UI is
shown correctly. finalizeProfileView is still intentionally not awaited
since it handles long-running work like symbolication in the background.

Author: canova

src/actions/app.ts

@@ -169,7 +169,15 @@ export function setupInitialUrlState(
     // load process.
     withHistoryReplaceStateSync(() => {
       dispatch(updateUrlState(urlState));
-      dispatch(finalizeProfileView(browserConnection));
+      // finalizeProfileView is intentionally not awaited: it kicks off
+      // long-running async work like symbolication that should run in the
+      // background without blocking this action. The .catch() ensures that any
+      // synchronous errors thrown before the first await (e.g. from selectors)
+      // are still routed to the FATAL_ERROR state rather than escaping as
+      // unhandled promise rejections.
+      dispatch(finalizeProfileView(browserConnection)).catch((error) => {
+        dispatch(fatalError(error));
+      });
       dispatch(urlSetupDone());
     });
   };

src/test/components/UrlManager.test.tsx

@@ -8,6 +8,7 @@ import { render, act } from 'firefox-profiler/test/fixtures/testing-library';
 import { getView, getUrlSetupPhase } from '../../selectors/app';
 import { UrlManager } from '../../components/app/UrlManager';
 import { blankStore } from '../fixtures/stores';
+import * as receiveProfileModule from 'firefox-profiler/actions/receive-profile';
 import {
   getDataSource,
   getHash,
@@ -61,7 +62,13 @@ describe('UrlManager', function () {
         waitUntilState(store, (state) => getUrlSetupPhase(state) === phase)
       );
 
-    return { dispatch, getState, createUrlManager, waitUntilUrlSetupPhase };
+    return {
+      store,
+      dispatch,
+      getState,
+      createUrlManager,
+      waitUntilUrlSetupPhase,
+    };
   }
 
   beforeEach(function () {
@@ -184,6 +191,35 @@ describe('UrlManager', function () {
     expect(window.location.search).toBe(searchString);
   });
 
+  it('routes errors thrown in finalizeProfileView to the FATAL_ERROR state', async function () {
+    window.fetchMock.get('*', getSerializableProfile());
+
+    const error = new Error('Simulated error in finalizeProfileView');
+    jest
+      .spyOn(receiveProfileModule, 'finalizeProfileView')
+      .mockReturnValue(async () => {
+        throw error;
+      });
+
+    const urlPath = '/public/FAKE_HASH/calltree/';
+    const { store, getState, createUrlManager } = setup(
+      urlPath + '?v=' + CURRENT_URL_VERSION
+    );
+
+    createUrlManager();
+
+    // urlSetupDone() fires synchronously before the .catch() microtask runs,
+    // so we wait for the FATAL_ERROR view phase directly instead of waiting
+    // for the url setup phase.
+    await act(() =>
+      waitUntilState(store, (state) => getView(state).phase === 'FATAL_ERROR')
+    );
+
+    const view: any = getView(getState());
+    expect(view.phase).toBe('FATAL_ERROR');
+    expect(view.error).toBe(error);
+  });
+
   it(`fetches profile and sets the phase to done when everything works`, async function () {
     window.fetchMock.get('*', getSerializableProfile());