internal_links: Add "/" before fragment identifier

lib/model/internal_link.dart

@@ -96,7 +96,11 @@ Uri narrowLink(PerAccountStore store, Narrow narrow, {int? nearMessageId}) {
     fragment.write('/near/$nearMessageId');
   }
 
-  return store.realmUrl.replace(fragment: fragment.toString());
+  final realmUrlWithSlash = store.realmUrl.path.isNotEmpty
+      ? store.realmUrl
+      : store.realmUrl.replace(path: '${store.realmUrl.path}/');
+
+  return realmUrlWithSlash.replace(fragment: fragment.toString());
 }
 
 /// A [Narrow] from a given URL, on `store`'s realm.

test/widgets/action_sheet_test.dart

@@ -38,11 +38,14 @@ late FakeApiConnection connection;
 Future<void> setupToMessageActionSheet(WidgetTester tester, {
   required Message message,
   required Narrow narrow,
+  Account? account,
 }) async {
   addTearDown(testBinding.reset);
 
-  await testBinding.globalStore.add(eg.selfAccount, eg.initialSnapshot());
-  final store = await testBinding.globalStore.perAccount(eg.selfAccount.id);
+  account ??= eg.selfAccount;
+  final initialSnapshot = eg.initialSnapshot();
+  await testBinding.globalStore.add(account, initialSnapshot);
+  final store = await testBinding.globalStore.perAccount(account.id);
   await store.addUser(eg.user(userId: message.senderId));
   if (message is StreamMessage) {
     final stream = eg.stream(streamId: message.streamId);
@@ -61,7 +64,7 @@ Future<void> setupToMessageActionSheet(WidgetTester tester, {
     messages: [message],
   ).toJson());
 
-  await tester.pumpWidget(TestZulipApp(accountId: eg.selfAccount.id,
+  await tester.pumpWidget(TestZulipApp(accountId: account.id,
     child: MessageListPage(initNarrow: narrow)));
 
   // global store, per-account store, and message list get loaded
@@ -553,6 +556,82 @@ void main() {
     });
   });
 
+  group('Message link verbatim URL tests', () {
+    Future<void> tapCopyMessageLinkButton(WidgetTester tester) async {
+      await tester.ensureVisible(find.byIcon(Icons.link, skipOffstage: false));
+      await tester.tap(find.byIcon(Icons.link));
+      await tester.pump(); // [MenuItemButton.onPressed] called in a post-frame callback: flutter/flutter@e4a39fa2e
+    }
+
+    Future<void> testMessageLink({
+      required WidgetTester tester,
+      required String realmUrl,
+      required String topic,
+      required String expectedLink,
+    }) async {
+      final stream = eg.stream(streamId: 42, name: 'stream 42');
+      final message = eg.streamMessage(id: 12345, stream: stream, topic: topic);
+      final narrow = TopicNarrow.ofMessage(message);
+      final account = eg.selfAccount.copyWith(realmUrl: Uri.parse(realmUrl));
+      await setupToMessageActionSheet(
+      tester, message: message, narrow: narrow, account: account);
+
+      final store = await testBinding.globalStore.perAccount(account.id);
+      if (!store.streams.containsKey(stream.streamId)) {
+       await store.addStream(stream);
+      }
+
+      await tapCopyMessageLinkButton(tester);
+      await tester.pump(Duration.zero);
+      check(await Clipboard.getData('text/plain')).isNotNull().text.equals(expectedLink);
+    }
+
+    testWidgets('Copies link with custom realm path', (tester) async {
+      await testMessageLink(
+      tester: tester,
+      realmUrl: 'https://chat.example/foo',
+      topic: 'test topic',
+      expectedLink: 'https://chat.example/foo#narrow/stream/42-stream-42/topic/test.20topic/near/12345',
+      );
+    });
+
+    testWidgets('Copies link with realm URL without path', (tester) async {
+      await testMessageLink(
+      tester: tester,
+      realmUrl: 'https://chat.zulip.org',
+      topic: 'test topic',
+      expectedLink: 'https://chat.zulip.org/#narrow/stream/42-stream-42/topic/test.20topic/near/12345',
+      );
+    });
+
+    testWidgets('Copies link with special characters in topic', (tester) async {
+      await testMessageLink(
+      tester: tester,
+      realmUrl: 'https://chat.zulip.org',
+      topic: 'What\'s up? 123!',
+      expectedLink: 'https://chat.zulip.org/#narrow/stream/42-stream-42/topic/What\'s.20up.3F.20123!/near/12345',
+      );
+    });
+
+    testWidgets('Copies link with realm URL ending in path', (tester) async {
+      await testMessageLink(
+      tester: tester,
+      realmUrl: 'https://chat.zulip.org/path',
+      topic: 'Numbers & Symbols: 100%',
+      expectedLink: 'https://chat.zulip.org/path#narrow/stream/42-stream-42/topic/Numbers.20.26.20Symbols.3A.20100.25/near/12345',
+      );
+    });
+
+    testWidgets('Copies link with realm URL ending in slash', (tester) async {
+      await testMessageLink(
+      tester: tester,
+      realmUrl: 'https://chat.zulip.org/',
+      topic: 'Regular topic',
+      expectedLink: 'https://chat.zulip.org/#narrow/stream/42-stream-42/topic/Regular.20topic/near/12345',
+      );
+    });
+  });
+
   group('ShareButton', () {
     // Tests should call this.
     MockSharePlus setupMockSharePlus() {