[FRAME] Simplify pallet config definition: remove RuntimeEvent associated type

[dastansam]

part of #3743

Motivation

This PR removes the need for defining RuntimeEvent in the Config trait of a pallet. It uses associated type bound feature under the hood to make sure that Event of the pallet is convertible to the aggregated runtime event type frame_system::RuntimeEvent.

This is an initial PR for RuntimeEvent type and will be followed with other types, e.g RuntimeCall. As a demo, example pallets' config definition is updated to use this feature.

With this change, we can do this (and have support for events):

#[pallet::config]
pub trait Config: frame_system::Config {
}

instead of this:

#[pallet::config]
pub trait Config: frame_system::Config {
        /// Overarching event type.
       type RuntimeEvent: From<Event<Self>> + IsType<<Self as frame_system::Config>::RuntimeEvent>;
}

The latter will emit deprecation warnings and is redundant.

polkadot address: 16FqwPZ8GRC5U5D4Fu7W33nA55ZXzXGWHwmbnE1eT6pxuqcT

[bkchr]

Ty for doing this!

[dastansam]

@bkchr bunch of CI is failing because they treat the RuntimeEvent deprecation warnings as error. Do you think it's worth fixing all those deprecation warnings in this PR? I thought it would be a lot of changes and also would feel more comfortable doing it once this change is carefully reviewed.

[gui1117]

Looks good to me, after the suggestion, and also a few comments

[gui1117]

As a note personally I would always bound the supertrait: frame_system::Config<RuntimeEvent: From<Event>>, always, except if there is the flag is_frame_system.
If user wants to write it, he can do, then it will still compile fine.
https://play.rust-lang.org/?version=stable&mode=debug&edition=2021&gist=7cfad8342293e593a0c8041cd4b5a958

But this is also ok.

[dastansam]

thanks for this tip, really helpful)

[dastansam]

@bkchr I replaced with proc macro warning but now I have to put the #[allow(deprecated)] above the mod pallet:

#[frame_support::pallet]
#[allow(deprecated)]
pub mod pallet {

but this way it would take a big span and we could ignore other deprecation warnings as well. Putting #[allow(deprecated)] above pallet config implementations is not ignoring the warning. what would you suggest? am I missing sth?

[bkchr]

Putting #[allow(deprecated)] above pallet config implementations is not ignoring the warning. what would you suggest? am I missing sth?

You need to detect the allow(deprecated) in the macro and then forward this to the usage of this item.

[bkchr]

And sometimes they have to define their own copy of it, since they want to assert more bounds on it.

Yeah and that is was this feature brings you! You can also extend and add more bounds. Most of the time RuntimeCall is only added if you need to add the From<LocalCall> bound.

[bkchr]

Also noting that for pallets that use #[pallet::disable_frame_system_supertrait_check] This won't work

Why will this not work? EVERY pallet needs to have the frame_system::Config as a super trait. This attribute is only if you don't have it as a direct super trait, but you for example require pallet_balances::Config as super trait. Still, frame_system::Config is reachable.

[kianenigma]

Yeah and that is was this feature brings you! You can also extend and add more bounds. Most of the time RuntimeCall is only added if you need to add the From bound.

Okay so I didn't fully understand how this was meant to be implemented for RuntimeCall.

Also noting that for pallets that use #[pallet::disable_frame_system_supertrait_check] This won't work

Yeah, I was wrong about this, sorry, it works now!

[dastansam]

Yeah and that is was this feature brings you! You can also extend and add more bounds. Most of the time RuntimeCall is only added if you need to add the From bound.

Okay so I didn't fully understand how this was meant to be implemented for RuntimeCall.

Also noting that for pallets that use #[pallet::disable_frame_system_supertrait_check] This won't work

Yeah, I was wrong about this, sorry, it works now!

yeah, it is more about automatically adding common RuntimeCall bounds to system supertrait to avoid having to declare them in the pallet's Config. I am still clarifying some things, but should open the PR with draft version soon