push_notifications: Adjust APNs tokens to be case-insensitive in the database.

APNs apparently treats its tokens case-insensitively; FCM does not.
Adjust the `unique_together` to instead be separate partial
constraints, keyed on the `kind` of the PushDeviceToken.

zerver/migrations/0740_pushdevicetoken_apns_case_insensitive.py

@@ -0,0 +1,71 @@
+import django.db.models.functions.text
+from django.db import migrations, models
+
+
+class Migration(migrations.Migration):
+    dependencies = [
+        ("zerver", "0739_alter_realm_can_set_delete_message_policy_group"),
+    ]
+
+    operations = [
+        # Update the last_updated to the max for any set of (user_id, kind=1, lower(token))
+        migrations.RunSQL(
+            """
+            WITH dups AS (
+              SELECT user_id, kind, LOWER(token) AS token, MAX(last_updated) AS max_last_updated
+                FROM zerver_pushdevicetoken
+               WHERE kind = 1
+               GROUP BY user_id, kind, LOWER(token)
+              HAVING COUNT(*) > 1
+            )
+            UPDATE zerver_pushdevicetoken
+               SET last_updated = dups.max_last_updated
+              FROM dups
+             WHERE zerver_pushdevicetoken.user_id = dups.user_id
+               AND zerver_pushdevicetoken.kind = dups.kind
+               AND LOWER(zerver_pushdevicetoken.token) = dups.token
+            """
+        ),
+        # And then delete all but the first of each of those sets
+        migrations.RunSQL(
+            """
+            WITH dups AS (
+              SELECT user_id, kind, LOWER(token) AS token, MIN(id) AS min_id
+                FROM zerver_pushdevicetoken
+               WHERE kind = 1
+               GROUP BY user_id, kind, LOWER(token)
+              HAVING COUNT(*) > 1
+            )
+            DELETE FROM zerver_pushdevicetoken
+             USING dups
+             WHERE zerver_pushdevicetoken.user_id = dups.user_id
+               AND zerver_pushdevicetoken.kind = dups.kind
+               AND LOWER(zerver_pushdevicetoken.token) = dups.token
+               AND zerver_pushdevicetoken.id != dups.min_id
+            """
+        ),
+        migrations.AddConstraint(
+            model_name="pushdevicetoken",
+            constraint=models.UniqueConstraint(
+                models.F("user_id"),
+                models.F("kind"),
+                django.db.models.functions.text.Lower(models.F("token")),
+                condition=models.Q(("kind", 1)),
+                name="zerver_pushdevicetoken_apns_user_kind_token",
+            ),
+        ),
+        migrations.AddConstraint(
+            model_name="pushdevicetoken",
+            constraint=models.UniqueConstraint(
+                models.F("user_id"),
+                models.F("kind"),
+                models.F("token"),
+                condition=models.Q(("kind", 2)),
+                name="zerver_pushdevicetoken_fcm_user_kind_token",
+            ),
+        ),
+        migrations.AlterUniqueTogether(
+            name="pushdevicetoken",
+            unique_together=set(),
+        ),
+    ]