Add AdditionalIssuance config for inflation calcs (moonbeam-foundation#9

)

Allows injecting any additional planned issuance 
that isn't part of the currency pallet for calculating inflation

pallets/parachain-staking/src/inflation.rs

@@ -16,11 +16,13 @@
 
 //! Helper methods for computing issuance based on inflation
 use crate::pallet::{BalanceOf, Config, Pallet};
+use crate::traits::AdditionalIssuance;
 use frame_support::traits::Currency;
 use parity_scale_codec::{Decode, Encode, MaxEncodedLen};
 use scale_info::TypeInfo;
 #[cfg(feature = "std")]
 use serde::{Deserialize, Serialize};
+use sp_runtime::traits::Saturating;
 use sp_runtime::PerThing;
 use sp_runtime::{Perbill, RuntimeDebug};
 use substrate_fixed::transcendental::pow as floatpow;
@@ -91,7 +93,8 @@ pub fn annual_to_round<T: Config>(annual: Range<Perbill>) -> Range<Perbill> {
 
 /// Compute round issuance range from round inflation range and current total issuance
 pub fn round_issuance_range<T: Config>(round: Range<Perbill>) -> Range<BalanceOf<T>> {
-	let circulating = T::Currency::total_issuance();
+	let circulating =
+		T::Currency::total_issuance().saturating_add(T::AdditionalIssuance::additional_issuance());
 	Range {
 		min: round.min * circulating,
 		ideal: round.ideal * circulating,

pallets/parachain-staking/src/lib.rs

@@ -172,6 +172,9 @@ pub mod pallet {
 		type OnNewRound: OnNewRound;
 		/// Whether a given collator has completed required registration to be selected as block author
 		type CollatorRegistration: ValidatorRegistration<Self::AccountId>;
+		/// Any additional issuance that should be used for inflation calcs
+		/// If you don't need it, you can specify the type `()`.
+		type AdditionalIssuance: AdditionalIssuance<BalanceOf<Self>>;
 		/// Weight information for extrinsics in this pallet.
 		type WeightInfo: WeightInfo;
 	}

pallets/parachain-staking/src/mock.rs

@@ -141,6 +141,7 @@ impl Config for Test {
 	type OnCollatorPayout = ();
 	type OnNewRound = ();
 	type CollatorRegistration = ValidatorRegistrationMock<Self>;
+	type AdditionalIssuance = ();
 	type WeightInfo = ();
 }
 

pallets/parachain-staking/src/traits.rs

@@ -41,3 +41,13 @@ impl OnNewRound for () {
 		0
 	}
 }
+
+use sp_runtime::traits::Zero;
+pub trait AdditionalIssuance<Balance> {
+	fn additional_issuance() -> Balance;
+}
+impl<Balance: Zero> AdditionalIssuance<Balance> for () {
+	fn additional_issuance() -> Balance {
+		Zero::zero()
+	}
+}