topic_link_util: Support message links in backend.

This commit adds support for message link
(#**stream>topic@message_id**) syntax in the
backend `topic_link_util` module.

zerver/lib/topic_link_util.py

@@ -45,10 +45,10 @@ def encode_hash_component(s: str) -> str:
 
 
 def get_fallback_markdown_link(
-    stream_id: int, stream_name: str, topic_name: str | None = None
+    stream_id: int, stream_name: str, topic_name: str | None = None, message_id: int | None = None
 ) -> str:
     """
-    Generates the markdown link syntax for a stream or topic link.
+    Generates the markdown link syntax for a stream/topic/message link.
     """
     escape = escape_invalid_stream_topic_characters
     link = f"#narrow/channel/{stream_id}-{encode_hash_component(stream_name.replace(' ', '-'))}"
@@ -59,9 +59,26 @@ def get_fallback_markdown_link(
             topic_name = Message.EMPTY_TOPIC_FALLBACK_NAME
         text += f" > {escape(topic_name)}"
 
+    if message_id is not None:
+        link += f"/near/{message_id}"
+        text += " @ 💬"
+
     return f"[{text}]({link})"
 
 
+def get_message_link_syntax(
+    stream_id: int, stream_name: str, topic_name: str, message_id: int
+) -> str:
+    # If the stream/topic name is such that it will
+    # generate an invalid #**stream>topic@message_id** syntax,
+    # we revert to generating the normal markdown syntax for a link.
+    if will_produce_broken_stream_topic_link(topic_name) or will_produce_broken_stream_topic_link(
+        stream_name
+    ):
+        return get_fallback_markdown_link(stream_id, stream_name, topic_name, message_id)
+    return f"#**{stream_name}>{topic_name}@{message_id}**"
+
+
 def get_stream_topic_link_syntax(stream_id: int, stream_name: str, topic_name: str) -> str:
     # If the stream/topic name is such that it will generate an invalid #**stream>topic** syntax,
     # we revert to generating the normal markdown syntax for a link.

zerver/tests/test_topic_link_util.py

@@ -1,5 +1,9 @@
 from zerver.lib.test_classes import ZulipTestCase
-from zerver.lib.topic_link_util import get_stream_link_syntax, get_stream_topic_link_syntax
+from zerver.lib.topic_link_util import (
+    get_message_link_syntax,
+    get_stream_link_syntax,
+    get_stream_topic_link_syntax,
+)
 
 
 class TestTopicLinkUtil(ZulipTestCase):
@@ -76,3 +80,22 @@ class TestTopicLinkUtil(ZulipTestCase):
             get_stream_topic_link_syntax(sweden_id, "Sw*den", ""),
             f"[#Sw*den > general chat](#narrow/channel/{sweden_id}-Sw*den/topic/)",
         )
+
+    def test_message_link_syntax(self) -> None:
+        sweden_id = self.make_stream("Sweden").id
+        self.assertEqual(
+            get_message_link_syntax(sweden_id, "Sweden", "topic", 123),
+            "#**Sweden>topic@123**",
+        )
+        self.assertEqual(
+            get_message_link_syntax(sweden_id, "Sweden", "", 123),
+            "#**Sweden>@123**",
+        )
+        self.assertEqual(
+            get_message_link_syntax(sweden_id, "Sw*den", "topic", 123),
+            f"[#Sw*den > topic @ 💬](#narrow/channel/{sweden_id}-Sw*den/topic/topic/near/123)",
+        )
+        self.assertEqual(
+            get_message_link_syntax(sweden_id, "Sw*den", "", 123),
+            f"[#Sw*den > general chat @ 💬](#narrow/channel/{sweden_id}-Sw*den/topic//near/123)",
+        )