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Erik JohnstonandGitHub
be511b22a2
If presence is disabled after having been enabled, the presence states in the database (and hence on clients) are frozen at whatever they were when presence was last enabled: nothing writes to the presence stream any more and /sync omits the presence section entirely, so clients show the old presence states forever. Fix this in two parts: 1. At startup, if presence is disabled but the database still contains non-offline presence states, the presence writer sends out one final round of updates marking those users as offline. 2. /sync no longer unconditionally omits presence when presence is disabled: incremental syncs whose since token is behind the presence stream still get the straggling updates. As the stream doesn't advance while presence is disabled, clients catch up once and the check then short-circuits to a token comparison. Remote servers already handle this themselves by timing out our users ([`FEDERATION_TIMEOUT`](https://github.com/element-hq/synapse/blob/4d8905a15a417ed0054ec2533d243932d890bbbd/synapse/handlers/presence.py#L194-L198)), so no federation changes are needed. Note that this only fixes the issue if presence is fully disabled. If set to `untracked` we still have the same issue, however since modules would still write to presence we can't just clobber everything like we do in this patch.