Refactor SignedExtension

[athei]

polkadot companion: paritytech/polkadot#979

This PR refactors the trait SignedExtension. The following changes where applied:

Move the DispatchInfo associated type to Dispatchable::Info

This information logically belongs to the Dispatchable. Not having it there requires consuming types to duplicate this as an associated type (SignedExtension, Applyable).

Bound Call: Dispatchable

This is a requirement for the first change. Because the DispatchInfo type is now an associated type on Dispatchable.

Pass Dispatchable::PostInfo to SignedExtension::post_dispatch

This is a followup of #5458 that passes this new information to the SignedExtension where it can then be used to accomplish weight refund (in a followup PR).

Pass Dispatchable::Info by reference

There was no apparent reason (or is there one?) for having DispatchInfo to be cloned into every SignedExtension.

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[tomusdrw]

on the right track, but we need to reduce boilerplate

[kianenigma]

I realised something:

I don't think it actually makes sense for dispatchInfo to be generic at the moment. Maybe we can make it generic, but currently it isn't.
otherwise, it doesn't even make sense for it to be generic as it is since it is kinda hard-coded in frame-support::dispatch. Your weight annotation must return weight + pays_fee + class and then they get bundled into this type DispatchInfo.

Yes, you can use any type to compute these 3, but they are fixed themselves. From this PoV I think this work needs to be refactored again.

I recommend merging this PR leniently just to unblock weight refund and I can make a follow up asap and my goal would be actually to either rethink the whole process or make it un-generic, as it used to be.

[athei]

An alternative approach would be that I pass the Dispatchable::PostInfo as an additional associated type of SignedExtension. Then the refactor can happen after getting the refund merged. However, this would clash with how we want to do it eventually (move associated types way from SignedExtension. @tomusdrw what do you think?

[tomusdrw]

I don't think it actually makes sense for dispatchInfo to be generic at the moment. Maybe we can make it generic, but currently it isn't.

Yes, I think @athei is fully aware of that, but it making it a fixed type would require moving Dispatchable to sp_runtime (which might be another big task).

An alternative approach would be that I pass the Dispatchable::PostInfo as an additional associated type of SignedExtension. Then the refactor can happen after getting the refund merged. However, this would clash with how we want to do it eventually (move associated types way from SignedExtension. @tomusdrw what do you think?

I think this PR looks good and is a bit nicer than current approach, so I think we should merge it as is (especially that it unlocks stuff). We can further change it in the future if needed.

[athei]

Yes, I think @athei is fully aware of that, but it making it a fixed type would require moving Dispatchable to sp_runtime (which might be another big task).

Dispatchableis in sp_runtime. Do you mean FRAME?

[tomusdrw]

Dispatchableis in sp_runtime. Do you mean FRAME?

Ugh, yes. So it's now generic, since weight is frame-specific, right?

[athei]

Yes Dispatchable is generic since #5458.

[athei]

I think this PR looks good and is a bit nicer than current approach, so I think we should merge it as is (especially that it unlocks stuff). We can further change it in the future if needed.

That would be nice. I think I addressed all raised concerns now. Praying to CI gods.

[athei]

I added the Polkadot companion and tested it against this PR locally.