Invited users don't trigger device_list updates via /sync at the point of being invited.

[matrixbot]

This issue has been migrated from #3503.

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I implemented https://github.com/matrix-org/synapse/pull/3484 with the assumption that it would cause invited users to trigger a /device_list update via /sync (as joined users do).

In practice it doesn't work (but clients are okay anyway as they query the device list via /unstable/keys/query whenever the membership list changes anyway).

[richvdh]

This issue isn't very clear, but I think it's trying to say something like:

When you first join a room with a user, or a user joins a room with you, that user is listed under device_lists: changed in the /sync response (cf https://spec.matrix.org/v1.10/client-server-api/#e2e-extensions-to-sync). The suggestion is that should also happen when a user is invited to a room, since invited users also receive copies of the message keys in suitably-configured rooms.

In practice there are bigger problems around tracking the device lists of invited users: see #3504.