Locally-rejected invites don't get passed on to the client over SSS

[richvdh]

Description

[in fairness I have not validated if this is a server-side or client-side problem]

Background: When a user rejects an invite, we generate a "leave" event to update their membership state. For an invite received from a remote server, we normally ask the remote server to generate the leave event for us. However, there is a fallback case for when the remote server is unreachable: we will generate an "outlier" event locally, which is then only sent to the invited user.

It appears that such locally-generated leave events are not passed down SSS.

In other words: this is a regression of https://github.com/matrix-org/synapse/issues/2181, but applies only to SSS.

Steps to reproduce

• Receive an invite from a user on a remote server
• The remote server goes offline
• On (say) Element-Web, reject the invite
• On EX, observe that you still have a pending invite

Homeserver

sw1v.org

Synapse Version

v1.115.0

Installation Method

pip (from PyPI)

Database

postgres. no. yes. yes.

Workers

Single process

Platform

-

Configuration

-

Relevant log output

-

Anything else that would be useful to know?

-

[Andoriax]

I have something like this going on with EX, but it cleared up after rejecting Invites in Element then logging out on EX and back in on EX to find the Invites list updated and cleared up,