Rococo: add dispatchable call to transfer ROC/DOT/KSM to parachains

[shaunxw]

Relay chain tokens will be used in parachains, currently there is no way to send ROC/DOT/KSM to parachains. Adding a dispatchable call is needed to do this. It was supported in rococo v0 but not in v1.

Along with the dispatchable call to transfer tokens, a "registry" would be helpful to indicate if a parachain can handle receiving transfer, since not every parachain actually does. If not, the call should fail early to prevent loss. I know it's common design to just let tokens be gone if recipient address doesn't handles it, but in this case we could do better and make token holders less likely to make mistakes.

The above "registry" could be generalized into categories, to not only guard tokens transfer from relay chain to parachains, but also all XCM assets transfer.

cc @shawntabrizi @xlc

[brenzi]

Encointer needs this feature in order to fulfill its common good parachain manifesto

[riusricardo]

cc: @bertstachios
Looping you in to track it.

[brenzi]

What's the state and priority of this? I reckon this is a crucial feature for Statemint too @joepetrowski?

[joepetrowski]

Can we close based on #2995 ?

[xlc]

No. #2995 only enable teleport to trusted chain. It doesn't work for other parachains.

[clangenb]

Is there any roadmap to alleviate the trusted requirement, or to add trusted parachains with a root call or something the like?

[brenzi]

So "trusted" means that #2995 doesn't ensure that the parachain respects its DOT balance and doesn't create new DOT?

[xlc]

will be closed by #3010