How should m.room.canonical_alias be handled on room upgrade

[olivia-fl]

Link to problem area: https://spec.matrix.org/v1.14/client-server-api/#server-behaviour-19

Issue

Step 4 of server behavior on the room upgrade endpoint is:

Moves any local aliases to the new room.

The spec does not mention what should happen with m.room.canonical_alias explicitly. On synapse, it appears that local aliases are removed from m.room.canonical_alias on the old room, and added to m.room.canonical_alias on the new room.

[richvdh]

A subset of #1906 ?

[olivia-fl]

Yeah, looks like it