markdown: Fix invalid mention bug for user mention.

Modifies `UserMentionPattern` to inherit from InlineProcessor
instead of Pattern. This change is done because Pattern
stopped checking for matching patterns as soon as it found
a match which was not a valid user. Due to this all the
subsequent user mention failed. This bug was only present in
backend renderring due to markdown.inlinepatterns.Pattern.

This was reported as issue #17535.

These changes were tested locally in dev server and by adding
some new markdown tests to test these.

zerver/lib/markdown/__init__.py

@@ -1796,8 +1796,10 @@ class RealmFilterPattern(markdown.inlinepatterns.Pattern):
         )
 
 
-class UserMentionPattern(markdown.inlinepatterns.Pattern):
-    def handleMatch(self, m: Match[str]) -> Optional[Element]:
+class UserMentionPattern(markdown.inlinepatterns.InlineProcessor):
+    def handleMatch(  # type: ignore[override] # supertype incompatible with supersupertype
+        self, m: Match[str], data: str
+    ) -> Union[Tuple[None, None, None], Tuple[Element, int, int]]:
         match = m.group("match")
         silent = m.group("silent") == "_"
 
@@ -1806,7 +1808,7 @@ class UserMentionPattern(markdown.inlinepatterns.Pattern):
             if match.startswith("**") and match.endswith("**"):
                 name = match[2:-2]
             else:
-                return None
+                return None, None, None
 
             wildcard = mention.user_mention_matches_wildcard(name)
 
@@ -1827,7 +1829,7 @@ class UserMentionPattern(markdown.inlinepatterns.Pattern):
                 user_id = str(user["id"])
             else:
                 # Don't highlight @mentions that don't refer to a valid user
-                return None
+                return None, None, None
 
             el = Element("span")
             el.set("data-user-id", user_id)
@@ -1838,8 +1840,8 @@ class UserMentionPattern(markdown.inlinepatterns.Pattern):
                 el.set("class", "user-mention")
                 text = f"@{text}"
             el.text = markdown.util.AtomicString(text)
-            return el
-        return None
+            return el, m.start(), m.end()
+        return None, None, None
 
 
 class UserGroupMentionPattern(markdown.inlinepatterns.Pattern):

zerver/tests/test_markdown.py

@@ -1845,6 +1845,36 @@ class MarkdownTest(ZulipTestCase):
         )
         self.assertEqual(msg.mentions_user_ids, set())
 
+    def test_mention_invalid_followed_by_valid(self) -> None:
+        sender_user_profile = self.example_user("othello")
+        user_profile = self.example_user("hamlet")
+        msg = Message(sender=sender_user_profile, sending_client=get_client("test"))
+        user_id = user_profile.id
+
+        content = "@**Invalid user** and @**King Hamlet**"
+        self.assertEqual(
+            render_markdown(msg, content),
+            '<p>@<strong>Invalid user</strong> and <span class="user-mention" '
+            f'data-user-id="{user_id}">'
+            "@King Hamlet</span></p>",
+        )
+        self.assertEqual(msg.mentions_user_ids, {user_profile.id})
+
+    def test_silent_mention_invalid_followed_by_valid(self) -> None:
+        sender_user_profile = self.example_user("othello")
+        user_profile = self.example_user("hamlet")
+        msg = Message(sender=sender_user_profile, sending_client=get_client("test"))
+        user_id = user_profile.id
+
+        content = "@_**Invalid user** and @_**King Hamlet**"
+        self.assertEqual(
+            render_markdown(msg, content),
+            '<p>@_<strong>Invalid user</strong> and <span class="user-mention silent" '
+            f'data-user-id="{user_id}">'
+            "King Hamlet</span></p>",
+        )
+        self.assertEqual(msg.mentions_user_ids, set())
+
     def test_possible_mentions(self) -> None:
         def assert_mentions(content: str, names: Set[str], has_wildcards: bool = False) -> None:
             self.assertEqual(possible_mentions(content), (names, has_wildcards))