import: Replace data-stream-id in rendered_content.

See the data-user-id commit for details.

zerver/lib/import_realm.py

@@ -253,6 +253,15 @@ def fix_message_rendered_content(realm: Realm,
                     if old_user_id in user_id_map:
                         mention["data-user-id"] = str(user_id_map[old_user_id])
                 message['rendered_content'] = str(soup)
+
+            stream_mentions = soup.findAll("a", {"class": "stream"})
+            if len(stream_mentions) != 0:
+                stream_id_map = ID_MAP["stream"]
+                for mention in stream_mentions:
+                    old_stream_id = int(mention["data-stream-id"])
+                    if old_stream_id in stream_id_map:
+                        mention["data-stream-id"] = str(stream_id_map[old_stream_id])
+                message['rendered_content'] = str(soup)
             continue
 
         message_object = FakeMessage()

zerver/tests/test_import_export.py

@@ -655,6 +655,9 @@ class ImportExportTest(ZulipTestCase):
         user_mention_message = '@**King Hamlet** Hello'
         self.send_stream_message(self.example_email("iago"), "Verona", user_mention_message)
 
+        stream_mention_message = 'Subscribe to #**Denmark**'
+        self.send_stream_message(self.example_email("hamlet"), "Verona", stream_mention_message)
+
         # data to test import of hotspots
         sample_user = self.example_user('hamlet')
 
@@ -896,6 +899,14 @@ class ImportExportTest(ZulipTestCase):
 
         assert_realm_values(get_user_mention)
 
+        def get_stream_mention(r: Realm) -> Set[Any]:
+            mentioned_stream = get_stream(u'Denmark', r)
+            data_stream_id = 'data-stream-id="{}"'.format(mentioned_stream.id)
+            mention_message = get_stream_messages(r).get(rendered_content__contains=data_stream_id)
+            return mention_message.content
+
+        assert_realm_values(get_stream_mention)
+
     def test_import_files_from_local(self) -> None:
 
         realm = Realm.objects.get(string_id='zulip')