dialog [nfc]: Wrap showErrorDialog's return value

As a result, showErrorDialog no longer returns a Future that can be
mistakenly awaited.  The wrapped return value offers clarity on how the
Future is supposed to be used.

There is no user visible change because existing callers (other than
lightbox's) that wait for its return value are all asynchronous
handlers for UI elements like buttons, and waits unnecessarily.

See also discussion
  zulip#937 (comment).

Signed-off-by: Zixuan James Li <zixuan@zulip.com>

Author: PIG208

lib/widgets/action_sheet.dart

@@ -120,7 +120,7 @@ class AddThumbsUpButton extends MessageActionSheetMenuItemButton {
         default:
       }
 
-      await showErrorDialog(context: context,
+      showErrorDialog(context: context,
         title: 'Adding reaction failed', message: errorMessage);
     }
   }
@@ -165,7 +165,7 @@ class StarButton extends MessageActionSheetMenuItemButton {
         default:
       }
 
-      await showErrorDialog(context: messageListContext,
+      showErrorDialog(context: messageListContext,
         title: switch(op) {
           UpdateMessageFlagsOp.remove => zulipLocalizations.errorUnstarMessageFailedTitle,
           UpdateMessageFlagsOp.add    => zulipLocalizations.errorStarMessageFailedTitle,
@@ -215,7 +215,7 @@ Future<String?> fetchRawContentWithFeedback({
       // TODO(?) give no feedback on error conditions we expect to
       //   flag centrally in event polling, like invalid auth,
       //   user/realm deactivated. (Support with reusable code.)
-      await showErrorDialog(context: context,
+      showErrorDialog(context: context,
         title: errorDialogTitle, message: errorMessage);
     }
 
@@ -423,7 +423,7 @@ class ShareButton extends MessageActionSheetMenuItemButton {
       // Until we learn otherwise, assume something wrong happened.
       case ShareResultStatus.unavailable:
         if (!messageListContext.mounted) return;
-        await showErrorDialog(context: messageListContext,
+        showErrorDialog(context: messageListContext,
           title: zulipLocalizations.errorSharingFailed);
       case ShareResultStatus.success:
       case ShareResultStatus.dismissed:

lib/widgets/actions.dart

@@ -27,7 +27,7 @@ Future<void> markNarrowAsRead(BuildContext context, Narrow narrow) async {
       return;
     } catch (e) {
       if (!context.mounted) return;
-      await showErrorDialog(context: context,
+      showErrorDialog(context: context,
         title: zulipLocalizations.errorMarkAsReadFailedTitle,
         message: e.toString()); // TODO(#741): extract user-facing message better
       return;

lib/widgets/content.dart

@@ -1195,7 +1195,7 @@ class GlobalTime extends StatelessWidget {
 }
 
 void _launchUrl(BuildContext context, String urlString) async {
-  Future<void> showError(BuildContext context, String? message) {
+  DialogStatusController showError(BuildContext context, String? message) {
     return showErrorDialog(context: context,
       title: 'Unable to open link',
       message: [
@@ -1207,7 +1207,7 @@ void _launchUrl(BuildContext context, String urlString) async {
   final store = PerAccountStoreWidget.of(context);
   final url = store.tryResolveUrl(urlString);
   if (url == null) { // TODO(log)
-    await showError(context, null);
+    showError(context, null);
     return;
   }
 
@@ -1236,7 +1236,7 @@ void _launchUrl(BuildContext context, String urlString) async {
   }
   if (!launched) { // TODO(log)
     if (!context.mounted) return;
-    await showError(context, errorMessage);
+    showError(context, errorMessage);
   }
 }
 

lib/widgets/dialog.dart

@@ -15,16 +15,33 @@ Widget _dialogActionText(String text) {
   );
 }
 
+/// A wrapper providing access to the status of an [AlertDialog].
+///
+/// See also:
+///  * [showDialog], whose return value this class is intended to wrap.
+class DialogStatusController {
+  const DialogStatusController(this._closed);
+
+  /// Resolves when the dialog is closed.
+  Future<void> get closed => _closed;
+  final Future<void> _closed;
+}
+
 /// Displays an [AlertDialog] with a dismiss button.
 ///
-/// Returns a [Future] that resolves when the dialog is closed.
-Future<void> showErrorDialog({
+/// Returns a [DialogStatusController]. Useful for checking if the dialog has
+/// been closed.
+// This API is inspired by [ScaffoldManager.showSnackBar].  We wrap
+// [showDialog]'s return value, a [Future], inside [DialogStatusController]
+// whose documentation can be accessed.  This helps avoid confusion when
+// intepreting the meaning of the [Future].
+DialogStatusController showErrorDialog({
   required BuildContext context,
   required String title,
   String? message,
 }) {
   final zulipLocalizations = ZulipLocalizations.of(context);
-  return showDialog(
+  final future = showDialog<void>(
     context: context,
     builder: (BuildContext context) => AlertDialog(
       title: Text(title),
@@ -34,6 +51,7 @@ Future<void> showErrorDialog({
           onPressed: () => Navigator.pop(context),
           child: _dialogActionText(zulipLocalizations.errorDialogContinue)),
       ]));
+  return DialogStatusController(future);
 }
 
 void showSuggestedActionDialog({

lib/widgets/lightbox.dart

@@ -476,11 +476,11 @@ class _VideoLightboxPageState extends State<VideoLightboxPage> with PerAccountSt
       assert(debugLog("VideoPlayerController.initialize failed: $error"));
       if (!mounted) return;
       final zulipLocalizations = ZulipLocalizations.of(context);
-      // Wait until the dialog is closed
-      await showErrorDialog(
+      final dialog = showErrorDialog(
         context: context,
         title: zulipLocalizations.errorDialogTitle,
         message: zulipLocalizations.errorVideoPlayerFailed);
+      await dialog.closed;
       if (!mounted) return;
       Navigator.pop(context); // Pops the lightbox
     }

lib/widgets/login.dart

@@ -307,7 +307,7 @@ class _LoginPageState extends State<LoginPage> {
       if (e is PlatformException && e.message != null) {
         message = e.message!;
       }
-      await showErrorDialog(context: context,
+      showErrorDialog(context: context,
         title: zulipLocalizations.errorWebAuthOperationalErrorTitle,
         message: message);
     } finally {
@@ -351,7 +351,7 @@ class _LoginPageState extends State<LoginPage> {
       if (e is PlatformException && e.message != null) {
         message = e.message!;
       }
-      await showErrorDialog(context: context,
+      showErrorDialog(context: context,
         title: zulipLocalizations.errorWebAuthOperationalErrorTitle,
         message: message);
     }