[c-lightning] Towards atomic multipath payments

[ZmnSCPxj]

Good morning Rusty,

> > Good morning c-lightningers,
> > I would like to propose a JSON-RPC interface for low-level atomic multipath payments.
>
> Sorry I've been MIA on this thread, but I was in the middle of moving
> `pay` out to a plugin.

At least you are actually working on code, unlike I who am now mostly "theoretically a c-lightning developer".

>
> A result of that is a new `paystatus` command which details all payment
> attempts in full detail (not yet persistent across restarts).
>
> I agree that we need to change the APIs, but I think we should do it
> differently: have the pay plugin provide `listpays` which merges
> `listpayments` back into whole payments.
>

I worry as this is a breaking change for existing systems.
Currently, if we use `pay` we use `listpayments` to determine status of each `pay` payment.
This will change once we enable bass amp and we should instead use `listpays`.

I suppose as we are at "beta" level (pre 1.0), we can do:

1.  Introduce `listpays` as an alias of `listpayments`,
2.  Inform everyone to use `listpays` for `pay` attempts and `listpayments` for `sendpay` attempts.
    Also add this warning strongly to release notes.
3.  Make a release *before* AMP is implemented with this `listpays == listpayments` initial implementation with this strong warning to move to using `listpays` for use of `pay`.

Regards,
ZmnSCPxj