1.11 returns a different error code for /initialSync than 1.10

[turt2live]

For years (decades?) Synapse has always returned M_GUEST_ACCESS_FORBIDDEN for /initialSync when the room isn't peekable, however 1.11 changed that to be M_FORBIDDEN .

The spec is, per usual, not very helpful here. Guest access errors seem most relevant given you aren't in the room yet and are in fact acting as a guest.

[richvdh]

yeah, this fell out of #6949. Note that peeking (https://matrix.org/docs/spec/client_server/r0.6.0#id116) and being a guest user (https://matrix.org/docs/spec/client_server/r0.6.0#guest-access) are different things, so I consider the new behaviour correcter.

[richvdh]

(in particular: it's possible for a room to permit guest access and not peeking, in which case it becomes obvious that M_GUEST_ACCESS_FORBIDDEN is a silly error code for this situation.)

[turt2live]

oh right, guest accounts. I wonder how I forgot about that...

It's a bit confusing how a change to aliases changed peeking, but I imagine it's something to do with shared code? Either way it kinda just helps justify why we need/should have CI that runs regression tests in Riot against current+develop Synapse: element-hq/element-web#12545