buttons: Add support for old format for narrow links.

This commit provides support for narrow links in message content
containing 'subject' instead of 'topic', which may be present in
messages before server version 2.1.0.

Test cases added.

Fixes #1422.

tests/ui_tools/test_buttons.py

@@ -677,6 +677,15 @@ def test__decode_message_id(
                 ),
                 id="topic_narrow_link",
             ),
+            case(
+                "/#narrow/stream/1-Stream-1/subject/foo.20bar",
+                ParsedNarrowLink(
+                    narrow="stream:topic",
+                    topic_name="foo bar",
+                    stream=DecodedStream(stream_id=1, stream_name=None),
+                ),
+                id="subject_narrow_link",
+            ),
             case(
                 "/#narrow/stream/1-Stream-1/near/1",
                 ParsedNarrowLink(
@@ -696,6 +705,16 @@ def test__decode_message_id(
                 ),
                 id="topic_near_narrow_link",
             ),
+            case(
+                "/#narrow/stream/1-Stream-1/subject/foo/near/1",
+                ParsedNarrowLink(
+                    narrow="stream:topic:near",
+                    topic_name="foo",
+                    message_id=1,
+                    stream=DecodedStream(stream_id=1, stream_name=None),
+                ),
+                id="subject_near_narrow_link",
+            ),
             case(
                 "/#narrow/foo",
                 ParsedNarrowLink(),
@@ -712,15 +731,25 @@ def test__decode_message_id(
                 id="invalid_narrow_link_3",
             ),
             case(
-                "/#narrow/stream/1-Stream-1//near/",
+                "/#narrow/stream/1-Stream-1/subject/",
                 ParsedNarrowLink(),
                 id="invalid_narrow_link_4",
             ),
             case(
-                "/#narrow/stream/1-Stream-1/topic/foo/near/",
+                "/#narrow/stream/1-Stream-1//near/",
                 ParsedNarrowLink(),
                 id="invalid_narrow_link_5",
             ),
+            case(
+                "/#narrow/stream/1-Stream-1/topic/foo/near/",
+                ParsedNarrowLink(),
+                id="invalid_narrow_link_6",
+            ),
+            case(
+                "/#narrow/stream/1-Stream-1/subject/foo/near/",
+                ParsedNarrowLink(),
+                id="invalid_narrow_link_7",
+            ),
         ],
     )
     def test__parse_narrow_link(

zulipterminal/ui_tools/buttons.py

@@ -493,12 +493,17 @@ def _parse_narrow_link(cls, link: str) -> ParsedNarrowLink:
         """
         # NOTE: The optional stream_id link version is deprecated. The extended
         # support is for old messages.
+        # NOTE: Support for narrow links with subject instead of topic is also added
         # We expect the fragment to be one of the following types:
         # a. narrow/stream/[{stream_id}-]{stream-name}
         # b. narrow/stream/[{stream_id}-]{stream-name}/near/{message_id}
         # c. narrow/stream/[{stream_id}-]{stream-name}/topic/
         #    {encoded.20topic.20name}
-        # d. narrow/stream/[{stream_id}-]{stream-name}/topic/
+        # d. narrow/stream/[{stream_id}-]{stream-name}/subject/
+        #    {encoded.20topic.20name}
+        # e. narrow/stream/[{stream_id}-]{stream-name}/topic/
+        #    {encoded.20topic.20name}/near/{message_id}
+        # f. narrow/stream/[{stream_id}-]{stream-name}/subject/
         #    {encoded.20topic.20name}/near/{message_id}
         fragments = urlparse(link.rstrip("/")).fragment.split("/")
         len_fragments = len(fragments)
@@ -509,7 +514,9 @@ def _parse_narrow_link(cls, link: str) -> ParsedNarrowLink:
             parsed_link = dict(narrow="stream", stream=stream_data)
 
         elif (
-            len_fragments == 5 and fragments[1] == "stream" and fragments[3] == "topic"
+            len_fragments == 5
+            and fragments[1] == "stream"
+            and (fragments[3] == "topic" or fragments[3] == "subject")
         ):
             stream_data = cls._decode_stream_data(fragments[2])
             topic_name = hash_util_decode(fragments[4])
@@ -527,7 +534,7 @@ def _parse_narrow_link(cls, link: str) -> ParsedNarrowLink:
         elif (
             len_fragments == 7
             and fragments[1] == "stream"
-            and fragments[3] == "topic"
+            and (fragments[3] == "topic" or fragments[3] == "subject")
             and fragments[5] == "near"
         ):
             stream_data = cls._decode_stream_data(fragments[2])