delete_realm: Add command to completely remove realms.

This will need some tweaking in upcoming commits.

zerver/management/commands/delete_realm.py

@@ -0,0 +1,49 @@
+import os
+import subprocess
+from argparse import ArgumentParser
+from typing import Any
+
+from django.conf import settings
+from django.core.management.base import CommandError
+
+from zerver.lib.management import ZulipBaseCommand
+from zerver.models import Message, UserProfile
+
+
+class Command(ZulipBaseCommand):
+    help = """Script to permanently delete a realm. Recommended only for removing
+realms used for testing; consider using deactivate_realm instead."""
+
+    def add_arguments(self, parser: ArgumentParser) -> None:
+        self.add_realm_args(parser, True)
+
+    def handle(self, *args: Any, **options: str) -> None:
+        realm = self.get_realm(options)
+        assert realm is not None  # Should be ensured by parser
+
+        user_count = UserProfile.objects.filter(
+            realm_id=realm.id,
+            is_active=True,
+            is_bot=False,
+        ).count()
+
+        message_count = Message.objects.filter(
+            sender__realm=realm
+        ).count()
+
+        print(f"This realm has {user_count} users and {message_count} messages.\n")
+
+        print("This command will \033[91mPERMANENTLY DELETE\033[0m all data for this realm.  "
+              "Most use cases will be better served by scrub_realm and/or deactivate_realm.")
+
+        confirmation = input("Type the name of the realm to confirm: ")
+        if confirmation != realm.string_id:
+            raise CommandError("Aborting!")
+
+        # TODO: This approach leaks Recipient and Huddle objects,
+        # because those don't have a foreign key to the Realm or any
+        # other model it cascades to (Realm/Stream/UserProfile/etc.).
+        realm.delete()
+        subprocess.check_call([os.path.join(settings.DEPLOY_ROOT, "scripts", "setup", "flush-memcached")])
+
+        print("Realm has been successfully permanently deleted.")