[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:

#[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.

[dastansam]

macro is now always auto inserting system supertrait with a RuntimeEvent bound if it detects the valid #[pallet::event] and simply ignoring the deprecated RuntimeEvent. it now looks bit different and much smaller than the initial PR, so I guess reviewing from scratch would be easier)
@gui1117

[gui1117]

Some minor comments, then it looks good to me.