action_sheet: Have "Share" button give feedback on sharing failure

Or at least, on `ShareResultStatus.unavailable`, which the plugin
just defines as "The status can not be determined".

assets/l10n/app_en.arb

@@ -124,6 +124,10 @@
       "message": {"type": "String", "example": "Invalid format"}
     }
   },
+  "errorSharingFailed": "Sharing failed",
+  "@errorSharingFailed": {
+    "description": "Error message when sharing a message failed."
+  },
   "successLinkCopied": "Link copied",
   "@successLinkCopied": {
     "description": "Success message after copy link action completed."

lib/widgets/action_sheet.dart

@@ -76,19 +76,20 @@ class ShareButton extends MessageActionSheetMenuItemButton {
 
   @override get onPressed => (BuildContext context) async {
     // Close the message action sheet; we're about to show the share
-    // sheet. (We could do this after the sharing Future settles, but
-    // on iOS I get impatient with how slowly our action sheet
-    // dismisses in that case.)
+    // sheet. (We could do this after the sharing Future settles
+    // with [ShareResultStatus.success], but on iOS I get impatient with
+    // how slowly our action sheet dismisses in that case.)
     // TODO(#24): Fix iOS bug where this call causes the keyboard to
     //   reopen (if it was open at the time of this
     //   `showMessageActionSheet` call) and cover a large part of the
     //   share sheet.
     Navigator.of(context).pop();
+    final zulipLocalizations = ZulipLocalizations.of(messageListContext);
 
     final rawContent = await fetchRawContentWithFeedback(
       context: messageListContext,
       messageId: message.id,
-      errorDialogTitle: 'Sharing failed',
+      errorDialogTitle: zulipLocalizations.errorSharingFailed,
     );
 
     if (rawContent == null) return;
@@ -100,7 +101,19 @@ class ShareButton extends MessageActionSheetMenuItemButton {
     //     https://pub.dev/packages/share_plus#ipad
     //   Perhaps a wart in the API; discussion:
     //     https://github.com/zulip/zulip-flutter/pull/12#discussion_r1130146231
-    await Share.shareWithResult(rawContent);
+    final result = await Share.shareWithResult(rawContent);
+
+    switch (result.status) {
+      // The plugin isn't very helpful: "The status can not be determined".
+      // Until we learn otherwise, assume something wrong happened.
+      case ShareResultStatus.unavailable:
+        if (!messageListContext.mounted) return;
+        await showErrorDialog(context: messageListContext,
+          title: zulipLocalizations.errorSharingFailed);
+      case ShareResultStatus.success:
+      case ShareResultStatus.dismissed:
+        // nothing to do
+    }
   };
 }
 

test/test_share_plus.dart

@@ -1,8 +1,12 @@
 import 'package:flutter/services.dart';
+import 'package:share_plus/share_plus.dart';
 
 class MockSharePlus {
   MockSharePlus();
 
+  /// The mock [ShareResult.raw] that `shareWithResult` should give.
+  String resultString = 'some-success-response';
+
   /// The last string that `shareWithResult` was called with.
   String? sharedString;
 
@@ -13,7 +17,7 @@ class MockSharePlus {
         // `arguments`'s type; logging runtimeType gives _Map<Object?, Object?>.
         final arguments = methodCall.arguments as Map;
         sharedString = arguments['text'] as String;
-        return 'some-success-response';
+        return resultString;
       default:
         throw UnimplementedError();
     }

test/widgets/action_sheet_test.dart

@@ -116,7 +116,7 @@ void main() {
       await tester.pump(); // [MenuItemButton.onPressed] called in a post-frame callback: flutter/flutter@e4a39fa2e
     }
 
-    testWidgets('success', (WidgetTester tester) async {
+    testWidgets('request succeeds; sharing succeeds', (WidgetTester tester) async {
       final mockSharePlus = setupMockSharePlus();
       final message = eg.streamMessage();
       await setupToMessageActionSheet(tester, message: message, narrow: TopicNarrow.ofMessage(message));
@@ -128,6 +128,22 @@ void main() {
       check(mockSharePlus.sharedString).equals('Hello world');
     });
 
+    testWidgets('request succeeds; sharing fails', (WidgetTester tester) async {
+      final mockSharePlus = setupMockSharePlus();
+      final message = eg.streamMessage();
+      await setupToMessageActionSheet(tester, message: message, narrow: TopicNarrow.ofMessage(message));
+      final store = await TestZulipBinding.instance.globalStore.perAccount(eg.selfAccount.id);
+
+      prepareRawContentResponseSuccess(store, message: message, rawContent: 'Hello world');
+      mockSharePlus.resultString = 'dev.fluttercommunity.plus/share/unavailable';
+      await tapShareButton(tester);
+      await tester.pump(Duration.zero);
+      check(mockSharePlus.sharedString).equals('Hello world');
+      await tester.pump();
+      await tester.tap(find.byWidget(checkErrorDialog(tester,
+        expectedTitle: 'Sharing failed')));
+    });
+
     testWidgets('request has an error', (WidgetTester tester) async {
       final mockSharePlus = setupMockSharePlus();
       final message = eg.streamMessage();