Refactor module & runtime error handing

[xlc]

Fixes #2246

This PR should:

• introduce module error type which declared by new macro decl_error.
• update construct_runtime macro to generate a runtime Error
• keep module source code compatibility. i.e. existing module does not need to be updated
• encode runtime error as a two byte value
• ensure backward compatibility (needs help from @bkchr ) (I don't think this is needed anymore)

Next stage (won't be in this PR) will :

• metadata for module errors
• introduce decl_error to each module and replace all the string error
• anything else?

cc @jacogr this introduces a new type DispatchError, without additional metadata, SDK won't be able to know the the meaning of the error code, but we can kind of solve it by duplicate the definition of the Error enum like other types.

[xlc]

@bkchr can you take a look when you have time? Just want to make sure I am on the right track.

[bkchr]

I think the general direction looks good :)

[bkchr]

@tomusdrw you maybe also want to take a first peek :)

[tomusdrw]

Awesome work! Looks really impressive and mostly good for me.

[xlc]

I cannot get it compile without modify every modules

[bkchr]

What would be the modifications? And in general I don't see the problem? Introducing a new feature some times requires to touch every module.

[xlc]

Every module will need Error type in Trait similar to Event. It is fine I guess but will make this PR very large.
I would like to have this merged and then do incremental improvements over change all the modules in one go.

[bkchr]

Why does it need Error in the trait? Can you explain this please?

And do you also support nesting errors? If yes, how is this solved? Theoretically you could have an infinite nesting, how do I find the root cause?

[xlc]

It is complicated...
In the impl_outer_error macro of my attempt, it has impl From<$module::Error> for Error. This means all the $module::Error needs to be different type (which many of them are &'static str in this PR). So I have to insert decl_error! { pub enum Error { } } if type Error is not included in decl_module. This introduces a new issue with ensure_signed which returns Result<(), system::Error>. One solution is add Error: From<system::Error> + From<Error> to handle the conversion. But it means every module Trait needs change, which is trivial but still a lot of changes.

Nesting error is not really supported.
The runtime Error type is like

pub enum Error {
  system(system::Error),
  balances(balances::Error),
  ...
}

and module Error type is like

pub enum Error {
  Other(&'static str),
  SomeError,
  AnotherError
  ...
}

One way to handle nested error is convert the underlying error to the module error type, by add variants to error enum. Or if the error is from another module, just add From<another_module::Error>bounds to the module Error type and it should be good.

[gavofyork]

i'm pretty happy to get this in pre-kusama; the &static str is a bit annoying, but i agree with @xlc that it's otherwise a bit too big to manage as a single PR as it'll get stuck in resolve-hell.

it would be handy to have this pre-based onto #3102

[gavofyork]

in any case will need resolving if it is to go in soon

[bkchr]

I'm currently looking into this. (JFYI)

[xlc]

I am going to do some refactor to make this work with sr_primitives::traits::DispatchError that introduced in #3102,

[bkchr]

Can you postpone this? I started to write some code already for this pr.

[xlc]

Sure. I just started it and got distracted. Will wait for your one instead.

[xlc]

@bkchr any updates?

[bkchr]

@bkchr any updates?

Yeah, after a lot of Kusama related task, I finally have time to work on this. I merged master and now try some things.

[bkchr]

Superseded by: #3433