Callbacks for pallet-assets

[Dinonard]

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Description of bug

Hi there,

it would be very useful if we could register callback methods for when new assets in pallet-assets are created, destroyed or manipulated in some other way.
The motivation behind is making assets cross-chain compatible for EVM contracts - in order to do this automatically, we need to do some actions after a new asset has been created. Being able to do this just using what pallet-assets provides would be great.

E.g. introduce a trait like:

/// Callbacks for various asset manipulation functions
pub trait AssetsCallback<AssetId, AccountId> {

	/// Indicates that asset with `id` was successfully created by the `owner`
	fn created(id: &AssetId, owner: &AccountId);

	/// Indicates that asset with `id` has just been destroyed
    fn destroyed(id: &AssetId);
}

and have it as part of pallet-assets Config:

	pub trait Config<I: 'static = ()>: frame_system::Config {
                ....
		/// Callback methods for asset state change (e.g. asset created or destroyed)
		type Callback: AssetsCallback<Self::AssetId, Self::AccountId>;
	}

Then it's just a matter of calling it once create or destroy have been successfully executed.
This would be a lightweight change, no benchmarks would really need to be changed if user doesn't introduce any custom hooks.

Is this a feasible change for pallet-assets?
Or should it just be handled by another pallet in chains that require it?

Related to this discussion basically.

Steps to reproduce

No response

[joepetrowski]

Seems reasonable to me at first glance. @tonyalaribe - can you look into it more?

[kianenigma]

Should be an easy addition -- and a () impl does nothing.

[Dinonard]

Thanks for the feedback!

I'll prepare a PR during tomorrow and reference this issue.

[Polkadot-Forum]

This issue has been mentioned on Polkadot Forum. There might be relevant details there:

https://forum.polkadot.network/t/polkadot-release-analysis-v0-9-37/1736/1