Removing every member from a comminuty leaves behind a dead community

[dragetd]

If every member of a community leaves it, the community is still saved on the server and blocks the name. Like this (kind of accidental) test-community I created:
https://riot.im/app/#/group/+bobbycar:matrix.org

I could imagine that there are more ghost-communities on the servers. It would be nice if a community could be purged once it is empty.

[Kr4ken-9]

+1, created a test community: https://riot.im/app/#/group/+thanking:matrix.org and I can't reclaim the id.

[Matombo]

+1 Just updated my merge request #3401 that would help with this issue.

[Matombo]

There is now an api to remove a group https://github.com/matrix-org/synapse/blob/master/docs/admin_api/delete_group.md
What's missing is something that scans the server for empty groups and calls the api automatically.
At he Repo maintainers: Is there intresst in such an automation? Then i would try to code it.

[anoadragon453]

I would modify delete_group_summary_user to check whether there are any users left after deleting one, and if not then delete the group. Be aware that this function is called both from the CS API and the Federation API. Turns out this isn't where a user is actually removed. You'll want remove_user_from_group, which is what that admin servlet actually uses.

However, that would not cover the groups that are already dead and without users. For cleaning those up, I would create a delta file with a line of SQL to delete all groups without any remaining users in them. This will go when Synapse is first run after upgrade to a version containing this delta file.

[Matombo]

Just a quick addition, the correct function to modify would be

synapse/synapse/groups/groups_server.py

Line 745 in 54fef09

def remove_user_from_group(self, group_id, user_id, requester_user_id, content):

I will look into it

[Matombo]

Can be closed now can't it?

[dragetd]

Yep!