internal_links: Always include a "/" after hostname

Fixes: #845

Signed-off-by: Zixuan James Li <[email protected]>

lib/model/internal_link.dart

@@ -96,7 +96,14 @@ Uri narrowLink(PerAccountStore store, Narrow narrow, {int? nearMessageId}) {
     fragment.write('/near/$nearMessageId');
   }
 
-  return store.realmUrl.replace(fragment: fragment.toString());
+  Uri result = store.realmUrl.replace(fragment: fragment.toString());
+  if (result.path.isEmpty) {
+    // Always ensure that there is a '/' right after the hostname.
+    // A generated URL without '/' looks odd and does not linkify.
+    result = result.replace(path: '/');
+  }
+  assert(result.path.startsWith('/'));
+  return result;
 }
 
 /// A [Narrow] from a given URL, on `store`'s realm.

test/model/compose_test.dart

@@ -314,6 +314,28 @@ hello
         '#narrow/dm/1,2-dm/near/12345',
         '#narrow/pm-with/1,2-pm/near/12345');
     });
+
+    test('normalize links to always include a "/" after hostname', () {
+      void checkGeneratedLink({required String realmUrl, required String expectedLink}) {
+        final account = eg.selfAccount.copyWith(realmUrl: Uri.parse(realmUrl));
+        final store = eg.store(account: account);
+        check(narrowLink(store, const CombinedFeedNarrow()))
+          .equals(Uri.parse(expectedLink));
+      }
+
+      checkGeneratedLink(
+        realmUrl:     'http://chat.example.com',
+        expectedLink: 'http://chat.example.com/#narrow');
+      checkGeneratedLink(
+        realmUrl:     'http://chat.example.com/',
+        expectedLink: 'http://chat.example.com/#narrow');
+      checkGeneratedLink(
+        realmUrl:     'http://chat.example.com/path',
+        expectedLink: 'http://chat.example.com/path#narrow');
+      checkGeneratedLink(
+        realmUrl:     'http://chat.example.com/path/',
+        expectedLink: 'http://chat.example.com/path/#narrow');
+    });
   });
 
   group('mention', () {