wip reportErrorToUserBriefly; TODO doc, test

Author: gnprice

lib/log.dart

@@ -30,3 +30,13 @@ bool debugLog(String message) {
   }());
   return true;
 }
+
+void Function(String message) reportErrorToUserBriefly = _defaultReportErrorToUserBriefly;
+
+void _defaultReportErrorToUserBriefly(String message) {
+  // If this callback is still in place, then the app's widget tree
+  // hasn't mounted yet even as far as the [Navigator].
+  // So there's not much we can do to tell the user;
+  // just log, in case the user is actually a developer watching the console.
+  assert(debugLog(message));
+}

lib/widgets/app.dart

@@ -5,6 +5,7 @@ import 'package:flutter/material.dart';
 import 'package:flutter/scheduler.dart';
 import 'package:flutter_gen/gen_l10n/zulip_localizations.dart';
 
+import '../log.dart';
 import '../model/localizations.dart';
 import '../model/narrow.dart';
 import 'about_zulip.dart';
@@ -92,9 +93,14 @@ class ZulipApp extends StatefulWidget {
   /// Useful in tests.
   final List<NavigatorObserver>? navigatorObservers;
 
+  static void _reportErrorToUserBriefly(String message) {
+    scaffoldMessenger?.showSnackBar(SnackBar(content: Text(message)));
+  }
+
   void _declareReady() {
     assert(navigatorKey.currentContext != null);
     _ready.value = true;
+    reportErrorToUserBriefly = _reportErrorToUserBriefly;
   }
 
   @override