synapse returns undocumented device property from GET /_matrix/client/v3/pushrules/

[richvdh]

Synapse's response to a /pushrules query looks something like:

[
  "global": {
    "content": { /*... */ },
    "override": { /*... */ },
    "room": { /*... */ },
    "sender": { /*... */ },
    "underride": { /*... */ }
  },
  "device": {}
]

This device property is not specced and should be removed.

[DMRobertson]

I have asked the client developers' room to double-check that no-one is using this field. https://matrix.to/#/!XXSJTvRPInupfUgQVb:matrix.org/$0adIq-vLha08iT0Hx3Gj-3VGQltT8Db63MptF0FZ-90?via=pixie.town&via=matrix.org&via=element.io

Are clients using this field?

• Nheko: no
• Trixinity: no
• Quotient: no
• Hydrogen: no
• matrix-js-sdk: parsed, but considered optional.
  • matrix-react-sdk, Element Web: not used.
• Element iOS: no, though it used to be parsed per internal room

  I've just checked, looks like it used to be in the SDK but is commented out so we definitely don't use it: https://github.com/matrix-org/matrix-ios-sdk/blob/8ae45d250cf0714b37aa6abdb8bffa8c2a438606/MatrixSDK/JSONModels/MXJSONModels.h#L791

• Element Android: not used per internal room

  This is safe to remove it server side for existing code and this PR removes it from the Android SDK (the field was not used).