commands: Add delete_user management command and document it.

docs/production/management-commands.md

@@ -126,6 +126,12 @@ There are dozens of useful management commands under
   export tools](../production/export-and-import.md) containing just
   the messages accessible by a single user.
 * `./manage.py reactivate_realm`: Reactivates a realm.
+* `./manage.py deactivate_user`: Deactivates a user. This can be done
+  more easily in Zulip's organization administrator UI.
+* `./manage.py delete_user`: Completely delete a user from the database.
+  For most purposes, deactivating users is preferred, since that does not
+  alter message history for other users.
+  See the `./manage.py delete_user --help` documentation for details.
 
 All of our management commands have internal documentation available
 via `manage.py command_name --help`.

zerver/management/commands/delete_user.py

@@ -0,0 +1,70 @@
+from argparse import ArgumentParser
+from typing import Any
+
+from zerver.lib.actions import do_delete_user
+from zerver.lib.management import CommandError, ZulipBaseCommand
+from zerver.models import UserProfile
+
+
+class Command(ZulipBaseCommand):
+    help = """
+
+Delete a user or users, including all messages sent by them and
+personal messages received by them, and audit records, like what
+streams they had been subscribed to. Deactivating users is generally
+recommended over this tool, but deletion can be useful if you
+specifically to completely delete an account created for testing.
+This will:
+
+* Delete the user's account, including metadata like name, email
+  address, custom profile fields, historical subscriptions, etc.
+
+* Delete any messages they've sent and any non-group private messages
+  they've received.
+
+* Group private messages in which the user participated won't be
+  deleted (with the exceptions of those message the deleted user
+  sent). An inactive, inaccessible dummy user account named "Deleted
+  User <id>" is created to replace the deleted user as a recipient in
+  group private message conversations, in order to somewhat preserve
+  their integrity.
+
+* Delete other records of the user's activity, such as emoji reactions.
+
+* Deactivate all bots owned by the user, without deleting them or
+  their data.  If you want to delete the bots and the message
+  sent/received by them, you can use the command on them individually.
+"""
+
+    def add_arguments(self, parser: ArgumentParser) -> None:
+        parser.add_argument(
+            "-f",
+            "--for-real",
+            action="store_true",
+            help="Actually delete the user(s). Default is a dry run.",
+        )
+        self.add_realm_args(parser)
+        self.add_user_list_args(parser)
+
+    def handle(self, *args: Any, **options: Any) -> None:
+        realm = self.get_realm(options)
+        user_profiles = self.get_users(options, realm)
+
+        for user_profile in user_profiles:
+            print(
+                "{} has {} active bots that will be deactivated as a result of the user's deletion.".format(
+                    user_profile.delivery_email,
+                    UserProfile.objects.filter(
+                        is_bot=True,
+                        is_active=True,
+                        bot_owner=user_profile,
+                    ).count(),
+                )
+            )
+
+        if not options["for_real"]:
+            raise CommandError("This was a dry run. Pass -f to actually delete.")
+
+        for user_profile in user_profiles:
+            do_delete_user(user_profile)
+            print(f"Successfully deleted user {user_profile.delivery_email}.")