[feature request] Add voting hooks

[enthusiastmartin]

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Motivation

We, in HydraDX, would need to execute additional custom logic when referendum vote is added or removed.

Currently, there does not seem to be a way where we can easily add a hook which would execute when a vote is added or removed.

Request

We would like to propose adding hooks into “old” democracy pallet as well as to conviction-voting pallet.

We can easily prepare a PR with such change, but i figured i would open an issue first to discuss if this is something that can be added and/or hear anything against it.

Solution

We would imagine having a trait similar to this one:

pub trait VotingHooks<AccountId, Balance> {
	fn on_vote(who: &AccountId, ref_index: ReferendumIndex, vote: AccountVote<Balance>) -> DispatchResult;
	fn on_remove_vote(who: &AccountId, ref_index: ReferendumIndex) -> DispatchResult;
}

// Pallet's Config

/// Hooks are actions that are executed on certain events - on_vote, on_remove_vote
type VotingHooks: VotingHooks<Self::AccountId, BalanceOf<Self>>;

The hooks would be executed in try_vote and try_remove_vote.

Perhaps , ReferendumIndex would need to be generic as well, to have only one trait used in both democracy pallet and conviction-voting pallet.

Regarding benchmarking and weights - special trait functions can be added to prepare worst case scenario.

Are you willing to help with this request?

Yes!