[Telepathy] Telepathy-based favorites system

[Travis Reitter]

Hi everyone,

I'm designing and implementing a portable "favorites" system for use in
Empathy (and any other client that wants to use it). Danielle Madeley
came up with the extra-portable idea of implementing this as a Telepathy
contact list, with a fallback to a magic group for protocols/CMs that
don't support favorites natively.

Here are the general ideas:

* Make a magic favorites group (eg, "favourite contacts")

    * multiple instances of this group across multiple accounts will be
      merged automatically by the client

    * the name will be localized by the clients and/or displayed
      specially (eg, with a star toggle switch next to each contact)

    * since this is just a Group channel, most of the infrastructure is
      already there -- we'd just want to define a constant for the magic
      group name, and clients can add and remove contacts with whatever
      UI they'd like

    * for any clients unaware of it, it will still degrade fairly well
      (there's a corner case where the user doesn't speak English and
      logs into the account on an unfamiliar client, but it's pretty
      much the same as filesystems that don't localize special directory
      names)

* Advanced work: use protocol-native annotation for favorites (eg, MSN
  and GTalk), and have the CM create a special "favourites" contact list
  (alongside "subscribe", etc.), which would be preferred over a
  "favourite contacts" group

One concern is the group-based fallback would be clunky or require ugly
group membership mangling for any protocols that that don't support
contacts being members of multiple groups. But the only example a few of
us could come up with is MSN, and apparently it's got a native concept
of favorites, so it shouldn't be a problem.

Also, link-local XMPP doesn't support groups, but we'd just skip
implementing favorites for them, since it's not terribly useful anyhow.

Does anyone know of any protocols where this scheme would be
problematic?

Thanks,
-Travis