Extract topic_match_sa() helper.

We'll also use this in zerver/views/messages.py, but
that's a bigger change.

tools/linter_lib/custom_check.py

@@ -276,7 +276,9 @@ def build_custom_checkers(by_lang):
          'description': 'avoid subject as a var',
          'good_lines': ['topic_name'],
          'bad_lines': ['subject="foo"', ' MAX_SUBJECT_LEN'],
-         'include_only': set(['zerver/lib/actions.py'])},
+         'include_only': set([
+             'zerver/lib/actions.py',
+             'zerver/lib/topic_mutes.py'])},
         {'pattern': '^(?!#)@login_required',
          'description': '@login_required is unsupported; use @zulip_login_required',
          'good_lines': ['@zulip_login_required', '# foo @login_required'],

zerver/lib/topic.py

@@ -4,6 +4,11 @@ from django.db import connection
 from django.db.models.query import QuerySet, Q
 from django.utils.timezone import now as timezone_now
 
+from sqlalchemy.sql import (
+    column,
+    func,
+)
+
 from zerver.models import (
     Message,
     Recipient,
@@ -18,6 +23,12 @@ TOPIC_NAME = "subject"
 TOPIC_LINKS = "subject_links"
 PREV_TOPIC = "prev_subject"
 
+def topic_match_sa(topic_name: str) -> Any:
+    # _sa is short for Sql Alchemy, which we use mostly for
+    # queries that search messages
+    topic_cond = func.upper(column("subject")) == func.upper(topic_name)
+    return topic_cond
+
 def filter_by_exact_message_topic(query: QuerySet, message: Message) -> QuerySet:
     topic_name = message.topic_name()
     return query.filter(subject=topic_name)

zerver/lib/topic_mutes.py

@@ -1,5 +1,8 @@
 from typing import Any, Callable, Dict, List, Optional
 
+from zerver.lib.topic import (
+    topic_match_sa,
+)
 from zerver.models import (
     get_stream_recipient,
     get_stream,
@@ -9,7 +12,6 @@ from zerver.models import (
 from sqlalchemy.sql import (
     and_,
     column,
-    func,
     not_,
     or_,
     Selectable
@@ -97,7 +99,7 @@ def exclude_topic_mutes(conditions: List[Selectable],
         recipient_id = row['recipient_id']
         topic_name = row['topic_name']
         stream_cond = column("recipient_id") == recipient_id
-        topic_cond = func.upper(column("subject")) == func.upper(topic_name)
+        topic_cond = topic_match_sa(topic_name)
         return and_(stream_cond, topic_cond)
 
     condition = not_(or_(*list(map(mute_cond, rows))))