home: Stop assuming account existence from loading page

We could pass realmUrl when initializing the `_LoadingPlaceholderPage`,
but that will still require a check for the existence of the account.

The loading page will contain a CircularLoadingIndicator when the
account does not exist. The user can't easily reach this page
because they can only logout from `ChooseAccountPage`, until we
start invalidating API keys. Even then, they will only see the
page briefly before getting navigated, so we should not show any
text at all.

Fixes: #1219

Signed-off-by: Zixuan James Li <[email protected]>

Author: PIG208

lib/widgets/home.dart

@@ -151,6 +151,11 @@ const kTryAnotherAccountWaitPeriod = Duration(seconds: 5);
 class _LoadingPlaceholderPage extends StatefulWidget {
   const _LoadingPlaceholderPage({required this.accountId});
 
+  /// The relevant account for this page.
+  ///
+  /// The account is not guaranteed to exist in the global store. This can
+  /// happen briefly when the account is removed from the database for logout,
+  /// but before [PerAccountStoreWidget.routeToRemoveOnLogout] is processed.
   final int accountId;
 
   @override
@@ -180,9 +185,15 @@ class _LoadingPlaceholderPageState extends State<_LoadingPlaceholderPage> {
   @override
   Widget build(BuildContext context) {
     final zulipLocalizations = ZulipLocalizations.of(context);
-    final realmUrl = GlobalStoreWidget.of(context)
-      // TODO(#1219) `!` is incorrect
-      .getAccount(widget.accountId)!.realmUrl;
+    final account = GlobalStoreWidget.of(context).getAccount(widget.accountId);
+
+    if (account == null) {
+      // We should only reach this state very briefly.
+      // See [_LoadingPlaceholderPage.accountId].
+      return Scaffold(
+        appBar: AppBar(),
+        body: const CircularProgressIndicator());
+    }
 
     return Scaffold(
       appBar: AppBar(),
@@ -201,7 +212,7 @@ class _LoadingPlaceholderPageState extends State<_LoadingPlaceholderPage> {
                 child: Column(
                   children: [
                     const SizedBox(height: 16),
-                    Text(zulipLocalizations.tryAnotherAccountMessage(realmUrl.toString())),
+                    Text(zulipLocalizations.tryAnotherAccountMessage(account.realmUrl.toString())),
                     const SizedBox(height: 8),
                     ElevatedButton(
                       onPressed: () => Navigator.push(context,

test/widgets/home_test.dart

@@ -6,6 +6,7 @@ import 'package:zulip/api/model/events.dart';
 import 'package:zulip/model/narrow.dart';
 import 'package:zulip/model/store.dart';
 import 'package:zulip/widgets/about_zulip.dart';
+import 'package:zulip/widgets/actions.dart';
 import 'package:zulip/widgets/app.dart';
 import 'package:zulip/widgets/app_bar.dart';
 import 'package:zulip/widgets/home.dart';
@@ -21,6 +22,7 @@ import '../api/fake_api.dart';
 import '../example_data.dart' as eg;
 import '../flutter_checks.dart';
 import '../model/binding.dart';
+import '../model/store_checks.dart';
 import '../model/test_store.dart';
 import '../test_navigation.dart';
 import 'message_list_checks.dart';
@@ -441,5 +443,23 @@ void main () {
       // No additional wait for loadPerAccount.
       checkOnHomePage(tester, expectedAccount: eg.selfAccount);
     });
+
+    testWidgets('logging out', (tester) async {
+      // Regression test for: https://github.com/zulip/zulip-flutter/issues/1219
+      addTearDown(testBinding.reset);
+      await testBinding.globalStore.add(eg.selfAccount, eg.initialSnapshot());
+      await tester.pumpWidget(const ZulipApp());
+      await tester.pump(); // wait for the loading page
+      await tester.pump(); // wait for store
+
+      final element = tester.element(find.byType(HomePage));
+      final future = logOutAccount(element, eg.selfAccount.id);
+      await tester.pump(TestGlobalStore.removeAccountDuration);
+      await future;
+      // No error expected from [_LoadingPlaceholderPage] briefly not having
+      // access to the account being logged out.
+      checkOnLoadingPage();
+      check(testBinding.globalStore).accountIds.isEmpty();
+    });
   });
 }