alert_words: Fix case-sensitivity of alert words.

Previously, alert words were case-insensitive in practice, by which I
mean the Markdown logic had always been case-insensitive; but the data
model was not, so you could create "duplicate" alert words with the
same words in different cases.  We fix this inconsistency by making
the database model case-insensitive.

I'd prefer to be using the Postgres `citext` extension to have
postgres take care of case-insensitive logic for us, but that requires
installing a postgres extension as root on the postgres server, which
is a pain and perhaps not worth the effort to arrange given that we
can achieve our goals with transaction when adding alert words.

We take advantage of the migrate_alert_words migration we're already
doing for all users to effect this transition.

Fixes #12563.

zerver/lib/alert_words.py

@@ -1,3 +1,5 @@
+from django.db import transaction
+
 from zerver.models import UserProfile, Realm, AlertWord
 from zerver.lib.cache import cache_with_key, realm_alert_words_cache_key, \
     realm_alert_words_automaton_cache_key
@@ -38,22 +40,29 @@ def get_alert_word_automaton(realm: Realm) -> ahocorasick.Automaton:
 def user_alert_words(user_profile: UserProfile) -> List[str]:
     return list(AlertWord.objects.filter(user_profile=user_profile).values_list("word", flat=True))
 
-def add_user_alert_words(user_profile: UserProfile, alert_words: Iterable[str]) -> List[str]:
-    words = user_alert_words(user_profile)
+@transaction.atomic
+def add_user_alert_words(user_profile: UserProfile, new_words: Iterable[str]) -> List[str]:
+    existing_words_lower = {word.lower() for word in user_alert_words(user_profile)}
 
-    new_words = [w for w in alert_words if w not in words]
-
-    # to avoid duplication of words
-    new_words = list(set(new_words))
+    # Keeping the case, use a dictionary to get the set of
+    # case-insensitive distinct, new alert words
+    word_dict: Dict[str, str] = {}
+    for word in new_words:
+        if word.lower() in existing_words_lower:
+            continue
+        word_dict[word.lower()] = word
 
     AlertWord.objects.bulk_create(
-        AlertWord(user_profile=user_profile, word=word, realm=user_profile.realm) for word in new_words)
-
-    return words+new_words
-
-def remove_user_alert_words(user_profile: UserProfile, alert_words: Iterable[str]) -> List[str]:
-    words = user_alert_words(user_profile)
-    delete_words = [w for w in alert_words if w in words]
-    AlertWord.objects.filter(user_profile=user_profile, word__in=delete_words).delete()
+        AlertWord(user_profile=user_profile, word=word, realm=user_profile.realm)
+        for word in word_dict.values()
+    )
 
     return user_alert_words(user_profile)
+
+@transaction.atomic
+def remove_user_alert_words(user_profile: UserProfile, delete_words: Iterable[str]) -> List[str]:
+    # TODO: Ideally, this would be a bulk query, but Django doesn't have a `__iexact`.
+    # We can clean this up if/when Postgres has more native support for case-insensitive fields.
+    for delete_word in delete_words:
+        AlertWord.objects.filter(user_profile=user_profile, word__iexact=delete_word).delete()
+    return user_alert_words(user_profile)

zerver/migrations/0277_migrate_alert_word.py

@@ -11,10 +11,17 @@ def move_to_seperate_table(apps: StateApps, schema_editor: DatabaseSchemaEditor)
     AlertWord = apps.get_model('zerver', 'AlertWord')
 
     for user_profile in UserProfile.objects.all():
-
         list_of_words = ujson.loads(user_profile.alert_words)
+
+        # Remove duplicates with our case-insensitive model.
+        word_dict: Dict[str, str] = {}
+        for word in list_of_words:
+            word_dict[word.lower()] = word
+
         AlertWord.objects.bulk_create(
-            AlertWord(user_profile=user_profile, word=word, realm=user_profile.realm) for word in list_of_words)
+            AlertWord(user_profile=user_profile, word=word, realm=user_profile.realm)
+            for word in word_dict.values()
+        )
 
 def move_back_to_user_profile(apps: StateApps, schema_editor: DatabaseSchemaEditor) -> None:
     AlertWord = apps.get_model('zerver', 'AlertWord')

zerver/models.py

@@ -2894,6 +2894,7 @@ class AlertWord(models.Model):
     # all the alert words in a realm.
     realm = models.ForeignKey(Realm, db_index=True, on_delete=CASCADE)  # type: Realm
     user_profile = models.ForeignKey(UserProfile, on_delete=CASCADE)  # type: UserProfile
+    # Case-insensitive name for the alert word.
     word = models.TextField()   # type: str
 
     class Meta:

zerver/tests/test_alert_words.py

@@ -56,6 +56,16 @@ class AlertWordTests(ZulipTestCase):
         words = user_alert_words(user)
         self.assertEqual(set(words), set(self.interesting_alert_word_list))
 
+        # Test the case-insensitivity of adding words
+        add_user_alert_words(user, set(["ALert", "ALERT"]))
+        words = user_alert_words(user)
+        self.assertEqual(set(words), set(self.interesting_alert_word_list))
+
+        # Test the case-insensitivity of removing words
+        remove_user_alert_words(user, set(["ALert"]))
+        words = user_alert_words(user)
+        self.assertEqual(set(words), set(self.interesting_alert_word_list) - {'alert'})
+
     def test_remove_word(self) -> None:
         """
         Removing alert words works via remove_user_alert_words, even