Fix warning messages

[positiveblue]

Stop casting warnings to errors before passing it to the service handling the message. BOLT1 talks about error and warning messages so I created a new interface called ErrorLike.

Warning messages for pending channels are now handled by the funding manager. Until now they were simply ignored.

Currently, the only action triggered by a warning messages sent by our peers is logging.

Fixes #6801

[Crypt-iQ]

I don't really see the benefit of this - I dislike changing the peer/brontide code more than it has to be changed. I think it is better if Warning does not embed Error and either:

• handleError is duplicated with a handleWarning function
• handleError handles both a Warning or an Error without an interface, and is renamed to handleErrorOrWarning or something similar

[positiveblue]

I chose option A 👍

[saubyk]

Cleared the milestone for the pr as the issue (#6801) is tagged now

[Crypt-iQ]

i think the link test should be added back and that a fundingmanager test should be added

[Crypt-iQ]

is this called anywhere?

[Roasbeef]

I think we can actually also just fall through to the case below.

[positiveblue]

No, and the method will be removed soon* (YY comment). However, I added in case someone is using lnwire.WriteElement outside the lnd code base for completeness.

[Roasbeef]

IIRC, you had a test that you used to repro the behavior in the first place? If we modified SendCustomMessage to allow sending messages below the custom message range w/ a build tag (for itests) then we can test this out in the wild to ensure that sending a warning doesn't lead to a force close. This should help catch any future regressions in the future.

[Roasbeef]

I think we can actually also just fall through to the case below.

[Roasbeef]

If we keep the existing Error method, then we can pass it around as a normal error. Not sure if we 100% want that behavior though...

[positiveblue]

I would leave it like this so we do not have any error in the future using the Error interface for warnings.

[lightninglabs-deploy]

@Roasbeef: review reminder
@Crypt-iQ: review reminder

[Crypt-iQ]

needs rebase

[Roasbeef]

LGTM ❄️

[guggero]

@positiveblue the new linter rules seem to cause a few new complaints.