dialog: Use "default" and "destructive" styles in iOS alert buttons

Fixes #1032.

See Apple's HIG document:
  https://developer.apple.com/design/human-interface-guidelines/alerts

And note that Android doesn't vary the button styles in these ways;
see the description of #1032.

Author: chrisbobbe

lib/widgets/action_sheet.dart

@@ -643,7 +643,7 @@ class UnsubscribeButton extends ActionSheetMenuItemButton {
       final dialog = showSuggestedActionDialog(context: pageContext,
         title: zulipLocalizations.unsubscribeConfirmationDialogTitle(subscription.name),
         message: zulipLocalizations.unsubscribeConfirmationDialogMessageMaybeCannotResubscribe,
-        // TODO(#1032) "destructive" style for action button
+        destructiveActionButton: true,
         actionButtonText: zulipLocalizations.unsubscribeConfirmationDialogConfirmButton);
       if (await dialog.result != true) return;
       if (!pageContext.mounted) return;

lib/widgets/app.dart

@@ -347,7 +347,7 @@ class ChooseAccountPage extends StatelessWidget {
                 final dialog = showSuggestedActionDialog(context: context,
                   title: zulipLocalizations.logOutConfirmationDialogTitle,
                   message: zulipLocalizations.logOutConfirmationDialogMessage,
-                  // TODO(#1032) "destructive" style for action button
+                  destructiveActionButton: true,
                   actionButtonText: zulipLocalizations.logOutConfirmationDialogConfirmButton);
                 if (await dialog.result == true) {
                   if (!context.mounted) return;

lib/widgets/compose_box.dart

@@ -2024,7 +2024,7 @@ class _ComposeBoxState extends State<ComposeBox> with PerAccountStoreAwareStateM
       final dialog = showSuggestedActionDialog(context: context,
         title: zulipLocalizations.discardDraftConfirmationDialogTitle,
         message: dialogMessage,
-        // TODO(#1032) "destructive" style for action button
+        destructiveActionButton: true,
         actionButtonText: zulipLocalizations.discardDraftConfirmationDialogConfirmButton);
       if (await dialog.result != true) return true;
     }

lib/widgets/dialog.dart

@@ -10,7 +10,15 @@ import 'content.dart';
 import 'store.dart';
 
 /// A platform-appropriate action for [AlertDialog.adaptive]'s [actions] param.
-Widget _adaptiveAction({required VoidCallback onPressed, required String text}) {
+///
+/// [isDefaultAction] and [isDestructiveAction] are ignored on Android
+/// because Material Design doesn't specify corresponding styles.
+Widget _adaptiveAction({
+  required VoidCallback onPressed,
+  required bool isDefaultAction,
+  bool isDestructiveAction = false,
+  required String text,
+}) {
   switch (defaultTargetPlatform) {
     case TargetPlatform.android:
     case TargetPlatform.fuchsia:
@@ -30,7 +38,11 @@ Widget _adaptiveAction({required VoidCallback onPressed, required String text})
 
     case TargetPlatform.iOS:
     case TargetPlatform.macOS:
-      return CupertinoDialogAction(onPressed: onPressed, child: Text(text));
+      return CupertinoDialogAction(
+        onPressed: onPressed,
+        isDefaultAction: isDefaultAction,
+        isDestructiveAction: isDestructiveAction,
+        child: Text(text));
   }
 }
 
@@ -112,9 +124,11 @@ DialogStatus<void> showErrorDialog({
         if (learnMoreButtonUrl != null)
           _adaptiveAction(
             onPressed: () => PlatformActions.launchUrl(context, learnMoreButtonUrl),
+            isDefaultAction: false,
             text: zulipLocalizations.errorDialogLearnMore),
         _adaptiveAction(
           onPressed: () => Navigator.pop(context),
+          isDefaultAction: true,
           text: zulipLocalizations.errorDialogContinue),
       ]));
   return DialogStatus(future);
@@ -133,6 +147,7 @@ DialogStatus<bool> showSuggestedActionDialog({
   required String title,
   required String message,
   required String? actionButtonText,
+  bool destructiveActionButton = false,
 }) {
   final zulipLocalizations = ZulipLocalizations.of(context);
   final future = showDialog<bool>(
@@ -143,9 +158,12 @@ DialogStatus<bool> showSuggestedActionDialog({
       actions: [
         _adaptiveAction(
           onPressed: () => Navigator.pop<bool>(context, null),
+          isDefaultAction: false,
           text: zulipLocalizations.dialogCancel),
         _adaptiveAction(
           onPressed: () => Navigator.pop<bool>(context, true),
+          isDefaultAction: true,
+          isDestructiveAction: destructiveActionButton,
           text: actionButtonText ?? zulipLocalizations.dialogContinue),
       ]));
   return DialogStatus(future);
@@ -213,6 +231,7 @@ class UpgradeWelcomeDialog extends StatelessWidget {
       actions: [
         _adaptiveAction(
           onPressed: () => Navigator.pop(context),
+          isDefaultAction: true,
           text: zulipLocalizations.upgradeWelcomeDialogDismiss)
       ]);
   }

test/widgets/action_sheet_test.dart

@@ -576,6 +576,7 @@ void main() {
         final (unsubscribeButton, cancelButton) = checkSuggestedActionDialog(tester,
           expectedTitle: 'Unsubscribe from ${channel.name}?',
           expectedMessage: 'Once you leave this channel, you might not be able to rejoin.',
+          expectDestructiveActionButton: true,
           expectedActionButtonText: 'Unsubscribe');
         await tester.tap(find.byWidget(unsubscribeButton));
         await tester.pump(Duration.zero);

test/widgets/app_test.dart

@@ -382,6 +382,7 @@ void main() {
         return checkSuggestedActionDialog(tester,
           expectedTitle: 'Log out?',
           expectedMessage: 'To use this account in the future, you will have to re-enter the URL for your organization and your account information.',
+          expectDestructiveActionButton: true,
           expectedActionButtonText: 'Log out');
       }
 

test/widgets/compose_box_test.dart

@@ -1645,6 +1645,7 @@ void main() {
     final (actionButton, cancelButton) = checkSuggestedActionDialog(tester,
       expectedTitle: 'Discard the message you’re writing?',
       expectedMessage: expectedMessage,
+      expectDestructiveActionButton: true,
       expectedActionButtonText: 'Discard');
     if (shouldContinue) {
       await tester.tap(find.byWidget(actionButton));

test/widgets/dialog_checks.dart

@@ -100,13 +100,18 @@ void checkNoDialog(WidgetTester tester) {
 /// Checks for a suggested-action dialog matching an expected title and message.
 /// Fails if none is found.
 ///
+/// Use [expectDestructiveActionButton] to check whether
+/// the button is "destructive" (see [showSuggestedActionDialog]).
+/// This has no effect on Android because the "destructive" style is iOS-only.
+///
 /// On success, returns a Record with the widget's action button first
 /// and its cancel button second.
 /// Tap the action button by calling `tester.tap(find.byWidget(actionButton))`.
 (Widget, Widget) checkSuggestedActionDialog(WidgetTester tester, {
   required String expectedTitle,
   required String expectedMessage,
   String? expectedActionButtonText,
+  bool expectDestructiveActionButton = false,
 }) {
   switch (defaultTargetPlatform) {
     case TargetPlatform.android:
@@ -133,8 +138,13 @@ void checkNoDialog(WidgetTester tester) {
       tester.widget(find.descendant(matchRoot: true,
         of: find.byWidget(dialog.content!), matching: find.text(expectedMessage)));
 
-      final actionButton = tester.widget(find.descendant(of: find.byWidget(dialog),
-        matching: find.widgetWithText(CupertinoDialogAction, expectedActionButtonText ?? 'Continue')));
+      final actionButton = tester.widget<CupertinoDialogAction>(
+        find.descendant(
+          of: find.byWidget(dialog),
+          matching: find.widgetWithText(
+            CupertinoDialogAction,
+            expectedActionButtonText ?? 'Continue')));
+      check(actionButton.isDestructiveAction).equals(expectDestructiveActionButton);
       final cancelButton = tester.widget(find.descendant(of: find.byWidget(dialog),
         matching: find.widgetWithText(CupertinoDialogAction, 'Cancel')));
       return (actionButton, cancelButton);