Initial mechanics for 80:20 fee split (#2912)

* Initial mechanics for 80:20 fee split

Also:
- Introduce extra functions for Imbalance manipulation;
- Store treasury pot in an account, letting total issuance account for
  it.

* Fix some tests

* Fix some tests

* Minor cleanups

* Update parity-codec version (#2855)

* Update parity-codec version

* Update grandpa, rhododendron and trie-bench

* Use primitive-types from crates.io

* Bump impl version

* Fix trie-bench version

* Fix lock files

* Fix versions

* Update codec to 4.1

* merge fix

* Revert merge

* More reversions

* Remove accidental code

* Update locks

* Bump runtime

* Update locks

* Tweaks and label TODO

* Update srml/treasury/src/lib.rs

Co-Authored-By: DemiMarie-parity <48690212+DemiMarie-parity@users.noreply.github.com>

* Update issue number

* Update core/sr-primitives/src/traits.rs

Co-Authored-By: Robert Habermeier <rphmeier@gmail.com>

* Fix wasm build

* Fix subkey build

substrate/Cargo.lock

@@ -2268,6 +2268,7 @@ dependencies = [
  "sr-std 2.0.0",
  "sr-version 2.0.0",
  "srml-aura 2.0.0",
+ "srml-authorship 0.1.0",
  "srml-balances 2.0.0",
  "srml-contracts 2.0.0",
  "srml-council 2.0.0",
@@ -3772,6 +3773,7 @@ dependencies = [
  "srml-support-procedural 2.0.0",
  "srml-system 2.0.0",
  "substrate-inherents 2.0.0",
+ "substrate-primitives 2.0.0",
 ]
 
 [[package]]

substrate/core/sr-primitives/src/lib.rs

@@ -69,6 +69,14 @@ pub type Justification = Vec<u8>;
 
 use traits::{Verify, Lazy};
 
+/// A module identifier. These are per module and should be stored in a registry somewhere.
+#[derive(Clone, Copy, Eq, PartialEq, Encode, Decode)]
+pub struct ModuleId(pub [u8; 8]);
+
+impl traits::TypeId for ModuleId {
+	const TYPE_ID: [u8; 4] = *b"modl";
+}
+
 /// A String that is a `&'static str` on `no_std` and a `Cow<'static, str>` on `std`.
 #[cfg(feature = "std")]
 pub type RuntimeString = ::std::borrow::Cow<'static, str>;

substrate/core/sr-primitives/src/traits.rs

@@ -830,6 +830,110 @@ pub trait OpaqueKeys: Clone {
 	fn ownership_proof_is_valid(&self, _proof: &[u8]) -> bool { true }
 }
 
+struct TrailingZeroInput<'a>(&'a [u8]);
+impl<'a> codec::Input for TrailingZeroInput<'a> {
+	fn read(&mut self, into: &mut [u8]) -> usize {
+		let len = into.len().min(self.0.len());
+		into[..len].copy_from_slice(&self.0[..len]);
+		for i in &mut into[len..] {
+			*i = 0;
+		}
+		self.0 = &self.0[len..];
+		into.len()
+	}
+}
+
+/// This type can be converted into and possibly from an AccountId (which itself is generic).
+pub trait AccountIdConversion<AccountId>: Sized {
+	/// Convert into an account ID. This is infallible.
+	fn into_account(&self) -> AccountId;
+
+	/// Try to convert an account ID into this type. Might not succeed.
+	fn try_from_account(a: &AccountId) -> Option<Self>;
+}
+
+/// Provide a simply 4 byte identifier for a type.
+pub trait TypeId {
+	/// Simple 4 byte identifier.
+	const TYPE_ID: [u8; 4];
+}
+
+/// Format is TYPE_ID ++ encode(parachain ID) ++ 00.... where 00... is indefinite trailing zeroes to fill AccountId.
+impl<T: Encode + Decode + Default, Id: Encode + Decode + TypeId> AccountIdConversion<T> for Id {
+	fn into_account(&self) -> T {
+		(Id::TYPE_ID, self).using_encoded(|b|
+			T::decode(&mut TrailingZeroInput(b))
+		).unwrap_or_default()
+	}
+
+	fn try_from_account(x: &T) -> Option<Self> {
+		x.using_encoded(|d| {
+			if &d[0..4] != Id::TYPE_ID { return None }
+			let mut cursor = &d[4..];
+			let result = Decode::decode(&mut cursor)?;
+			if cursor.iter().all(|x| *x == 0) {
+				Some(result)
+			} else {
+				None
+			}
+		})
+	}
+}
+
+#[cfg(test)]
+mod tests {
+	use super::AccountIdConversion;
+	use crate::codec::{Encode, Decode};
+
+	#[derive(Encode, Decode, Default, PartialEq, Debug)]
+	struct U32Value(u32);
+	impl super::TypeId for U32Value {
+		const TYPE_ID: [u8; 4] = [0x0d, 0xf0, 0xfe, 0xca];
+	}
+	// cafef00d
+
+	#[derive(Encode, Decode, Default, PartialEq, Debug)]
+	struct U16Value(u16);
+	impl super::TypeId for U16Value {
+		const TYPE_ID: [u8; 4] = [0xfe, 0xca, 0x0d, 0xf0];
+	}
+	// f00dcafe
+
+	type AccountId = u64;
+
+	#[test]
+	fn into_account_should_work() {
+		let r: AccountId = U32Value::into_account(&U32Value(0xdeadbeef));
+		assert_eq!(r, 0x_deadbeef_cafef00d);
+	}
+
+	#[test]
+	fn try_from_account_should_work() {
+		let r = U32Value::try_from_account(&0x_deadbeef_cafef00d_u64);
+		assert_eq!(r.unwrap(), U32Value(0xdeadbeef));
+	}
+
+	#[test]
+	fn into_account_with_fill_should_work() {
+		let r: AccountId = U16Value::into_account(&U16Value(0xc0da));
+		assert_eq!(r, 0x_0000_c0da_f00dcafe);
+	}
+
+	#[test]
+	fn try_from_account_with_fill_should_work() {
+		let r = U16Value::try_from_account(&0x0000_c0da_f00dcafe_u64);
+		assert_eq!(r.unwrap(), U16Value(0xc0da));
+	}
+
+	#[test]
+	fn bad_try_from_account_should_fail() {
+		let r = U16Value::try_from_account(&0x0000_c0de_baadcafe_u64);
+		assert!(r.is_none());
+		let r = U16Value::try_from_account(&0x0100_c0da_f00dcafe_u64);
+		assert!(r.is_none());
+	}
+}
+
 /// Calls a given macro a number of times with a set of fixed params and an incrementing numeral.
 /// e.g.
 /// ```nocompile

substrate/core/test-runtime/wasm/Cargo.lock

@@ -2397,6 +2397,7 @@ dependencies = [
  "srml-metadata 2.0.0",
  "srml-support-procedural 2.0.0",
  "substrate-inherents 2.0.0",
+ "substrate-primitives 2.0.0",
 ]
 
 [[package]]

substrate/node-template/runtime/wasm/Cargo.lock

@@ -2521,6 +2521,7 @@ dependencies = [
  "srml-metadata 2.0.0",
  "srml-support-procedural 2.0.0",
  "substrate-inherents 2.0.0",
+ "substrate-primitives 2.0.0",
 ]
 
 [[package]]

substrate/node/executor/src/lib.rs

@@ -54,7 +54,7 @@ mod tests {
 	use system::{EventRecord, Phase};
 	use node_runtime::{Header, Block, UncheckedExtrinsic, CheckedExtrinsic, Call, Runtime, Balances,
 		BuildStorage, GenesisConfig, BalancesConfig, SessionConfig, StakingConfig, System,
-		SystemConfig, GrandpaConfig, IndicesConfig, Event, SessionKeys};
+		SystemConfig, GrandpaConfig, IndicesConfig, Event, SessionKeys, Treasury};
 	use wabt;
 	use primitives::map;
 
@@ -566,6 +566,34 @@ mod tests {
 					event: Event::system(system::Event::ExtrinsicSuccess),
 					topics: vec![],
 				},
+				EventRecord {
+					phase: Phase::ApplyExtrinsic(1),
+					event: Event::indices(
+						indices::RawEvent::NewAccountIndex(Treasury::account_id(), 6)
+					),
+					topics: vec![],
+				},
+				EventRecord {
+					phase: Phase::ApplyExtrinsic(1),
+					event: Event::balances(
+						balances::RawEvent::NewAccount(Treasury::account_id(), 0)
+					),
+					topics: vec![],
+				},
+				EventRecord {
+					phase: Phase::ApplyExtrinsic(1),
+					event: Event::indices(
+						indices::RawEvent::NewAccountIndex(Default::default(), 7)
+					),
+					topics: vec![],
+				},
+				EventRecord {
+					phase: Phase::ApplyExtrinsic(1),
+					event: Event::balances(
+						balances::RawEvent::NewAccount(Default::default(), 1)
+					),
+					topics: vec![],
+				},
 				EventRecord {
 					phase: Phase::ApplyExtrinsic(1),
 					event: Event::balances(balances::RawEvent::Transfer(

substrate/node/runtime/Cargo.toml

@@ -16,6 +16,7 @@ offchain-primitives = { package = "substrate-offchain-primitives", path = "../..
 version = { package = "sr-version", path = "../../core/sr-version", default-features = false }
 support = { package = "srml-support", path = "../../srml/support", default-features = false }
 aura = { package = "srml-aura", path = "../../srml/aura", default-features = false }
+authorship = { package = "srml-authorship", path = "../../srml/authorship", default-features = false }
 balances = { package = "srml-balances", path = "../../srml/balances", default-features = false }
 contracts = { package = "srml-contracts", path = "../../srml/contracts", default-features = false }
 council = { package = "srml-council", path = "../../srml/council", default-features = false }
@@ -48,6 +49,7 @@ std = [
 	"runtime_primitives/std",
 	"support/std",
 	"aura/std",
+	"authorship/std",
 	"balances/std",
 	"contracts/std",
 	"council/std",

substrate/node/runtime/src/lib.rs

@@ -21,7 +21,9 @@
 #![recursion_limit="256"]
 
 use rstd::prelude::*;
-use support::{construct_runtime, parameter_types};
+use support::{
+	construct_runtime, parameter_types, traits::{SplitTwoWays, Currency, OnUnbalanced}
+};
 use substrate_primitives::u32_trait::{_1, _2, _3, _4};
 use node_primitives::{
 	AccountId, AccountIndex, Balance, BlockNumber, Hash, Index, Signature, AuraId
@@ -58,8 +60,8 @@ pub const VERSION: RuntimeVersion = RuntimeVersion {
 	spec_name: create_runtime_str!("node"),
 	impl_name: create_runtime_str!("substrate-node"),
 	authoring_version: 10,
-	spec_version: 99,
-	impl_version: 106,
+	spec_version: 100,
+	impl_version: 100,
 	apis: RUNTIME_API_VERSIONS,
 };
 
@@ -72,6 +74,23 @@ pub fn native_version() -> NativeVersion {
 	}
 }
 
+type NegativeImbalance = <Balances as Currency<AccountId>>::NegativeImbalance;
+
+pub struct Author;
+
+impl OnUnbalanced<NegativeImbalance> for Author {
+	fn on_unbalanced(amount: NegativeImbalance) {
+		Balances::resolve_creating(&Authorship::author(), amount);
+	}
+}
+
+pub type DealWithFees = SplitTwoWays<
+	Balance,
+	NegativeImbalance,
+	_4, Treasury,   // 4 parts (80%) goes to the treasury.
+	_1, Author,     // 1 part (20%) goes to the block author.
+>;
+
 pub struct CurrencyToVoteHandler;
 
 impl CurrencyToVoteHandler {
@@ -115,7 +134,7 @@ impl balances::Trait for Runtime {
 	type OnFreeBalanceZero = ((Staking, Contracts), Session);
 	type OnNewAccount = Indices;
 	type Event = Event;
-	type TransactionPayment = ();
+	type TransactionPayment = DealWithFees;
 	type DustRemoval = ();
 	type TransferPayment = ();
 }
@@ -125,6 +144,18 @@ impl timestamp::Trait for Runtime {
 	type OnTimestampSet = Aura;
 }
 
+parameter_types! {
+	pub const UncleGenerations: u64 = 0;
+}
+
+// TODO: #2986 implement this properly
+impl authorship::Trait for Runtime {
+	type FindAuthor = ();
+	type UncleGenerations = UncleGenerations;
+	type FilterUncle = ();
+	type EventHandler = ();
+}
+
 parameter_types! {
 	pub const Period: BlockNumber = 10 * MINUTES;
 	pub const Offset: BlockNumber = 0;
@@ -250,6 +281,7 @@ construct_runtime!(
 		System: system::{Module, Call, Storage, Config, Event},
 		Aura: aura::{Module, Config<T>, Inherent(Timestamp)},
 		Timestamp: timestamp::{Module, Call, Storage, Config<T>, Inherent},
+		Authorship: authorship::{Module, Call, Storage},
 		Indices: indices,
 		Balances: balances,
 		Session: session::{Module, Call, Storage, Event, Config<T>},

substrate/node/runtime/wasm/Cargo.lock

@@ -1499,6 +1499,7 @@ dependencies = [
  "sr-std 2.0.0",
  "sr-version 2.0.0",
  "srml-aura 2.0.0",
+ "srml-authorship 0.1.0",
  "srml-balances 2.0.0",
  "srml-contracts 2.0.0",
  "srml-council 2.0.0",
@@ -2452,6 +2453,19 @@ dependencies = [
  "substrate-primitives 2.0.0",
 ]
 
+[[package]]
+name = "srml-authorship"
+version = "0.1.0"
+dependencies = [
+ "parity-codec 4.1.1 (registry+https://github.com/rust-lang/crates.io-index)",
+ "sr-io 2.0.0",
+ "sr-primitives 2.0.0",
+ "sr-std 2.0.0",
+ "srml-support 2.0.0",
+ "srml-system 2.0.0",
+ "substrate-primitives 2.0.0",
+]
+
 [[package]]
 name = "srml-balances"
 version = "2.0.0"
@@ -2642,6 +2656,7 @@ dependencies = [
  "srml-metadata 2.0.0",
  "srml-support-procedural 2.0.0",
  "substrate-inherents 2.0.0",
+ "substrate-primitives 2.0.0",
 ]
 
 [[package]]

substrate/srml/authorship/src/lib.rs

@@ -18,6 +18,8 @@
 //!
 //! This tracks the current author of the block and recent uncles.
 
+#![cfg_attr(not(feature = "std"), no_std)]
+
 use rstd::prelude::*;
 use rstd::collections::btree_set::BTreeSet;
 use srml_support::{decl_module, decl_storage, for_each_tuple, StorageValue};
@@ -102,6 +104,15 @@ pub trait FilterUncle<Header, Author> {
 		-> Result<(Option<Author>, Self::Accumulator), &'static str>;
 }
 
+impl<H, A> FilterUncle<H, A> for () {
+	type Accumulator = ();
+	fn filter_uncle(_: &H, acc: Self::Accumulator)
+		-> Result<(Option<A>, Self::Accumulator), &'static str>
+	{
+		Ok((None, acc))
+	}
+}
+
 /// A filter on uncles which verifies seals and does no additional checks.
 /// This is well-suited to consensus modes such as PoW where the cost of
 /// equivocating is high.
@@ -201,8 +212,8 @@ decl_module! {
 
 		fn on_finalize() {
 			// ensure we never go to trie with these values.
-			let _ = <Self as Store>::Author::take();
-			let _ = <Self as Store>::DidSetUncles::take();
+			<Self as Store>::Author::kill();
+			<Self as Store>::DidSetUncles::kill();
 		}
 
 		/// Provide a set of uncles.

substrate/srml/balances/src/lib.rs

@@ -161,7 +161,7 @@ use srml_support::traits::{
 use srml_support::dispatch::Result;
 use primitives::traits::{
 	Zero, SimpleArithmetic, StaticLookup, Member, CheckedAdd, CheckedSub,
-	MaybeSerializeDebug, Saturating
+	MaybeSerializeDebug, Saturating, Bounded
 };
 use system::{IsDeadAccount, OnNewAccount, ensure_signed};
 
@@ -313,7 +313,9 @@ decl_storage! {
 		///
 		/// `system::AccountNonce` is also deleted if `ReservedBalance` is also zero (it also gets
 		/// collapsed to zero if it ever becomes less than `ExistentialDeposit`.
-		pub FreeBalance get(free_balance) build(|config: &GenesisConfig<T, I>| config.balances.clone()): map T::AccountId => T::Balance;
+		pub FreeBalance get(free_balance)
+			build(|config: &GenesisConfig<T, I>| config.balances.clone()):
+			map T::AccountId => T::Balance;
 
 		/// The amount of the balance of a given account that is externally reserved; this can still get
 		/// slashed, but gets slashed last of all.
@@ -735,6 +737,26 @@ where
 		<FreeBalance<T, I>>::get(who)
 	}
 
+	fn burn(mut amount: Self::Balance) -> Self::PositiveImbalance {
+		<TotalIssuance<T, I>>::mutate(|issued|
+			issued.checked_sub(&amount).unwrap_or_else(|| {
+				amount = *issued;
+				Zero::zero()
+			})
+		);
+		PositiveImbalance::new(amount)
+	}
+
+	fn issue(mut amount: Self::Balance) -> Self::NegativeImbalance {
+		<TotalIssuance<T, I>>::mutate(|issued|
+			*issued = issued.checked_add(&amount).unwrap_or_else(|| {
+				amount = Self::Balance::max_value() - *issued;
+				Self::Balance::max_value()
+			})
+		);
+		NegativeImbalance::new(amount)
+	}
+
 	// # <weight>
 	// Despite iterating over a list of locks, they are limited by the number of
 	// lock IDs, which means the number of runtime modules that intend to use and create locks.

substrate/srml/support/Cargo.toml

@@ -11,6 +11,7 @@ srml-metadata = { path = "../metadata", default-features = false }
 sr-std = { path = "../../core/sr-std", default-features = false }
 runtime_io = { package = "sr-io", path = "../../core/sr-io", default-features = false }
 sr-primitives = { path = "../../core/sr-primitives", default-features = false }
+substrate-primitives = { path = "../../core/primitives", default-features = false }
 inherents = { package = "substrate-inherents", path = "../../core/inherents", default-features = false }
 srml-support-procedural = { path = "./procedural" }
 paste = "0.1"

substrate/srml/support/src/traits.rs

@@ -18,10 +18,11 @@
 //!
 //! NOTE: If you're looking for `parameter_types`, it has moved in to the top-level module.
 
-use crate::rstd::result;
+use crate::rstd::{result, marker::PhantomData, ops::Div};
 use crate::codec::{Codec, Encode, Decode};
+use substrate_primitives::u32_trait::Value as U32;
 use crate::runtime_primitives::traits::{
-	MaybeSerializeDebug, SimpleArithmetic
+	MaybeSerializeDebug, SimpleArithmetic, Saturating
 };
 use crate::runtime_primitives::ConsensusEngineId;
 
@@ -111,6 +112,14 @@ pub trait FindAuthor<Author> {
 		where I: 'a + IntoIterator<Item=(ConsensusEngineId, &'a [u8])>;
 }
 
+impl<A> FindAuthor<A> for () {
+	fn find_author<'a, I>(_: I) -> Option<A>
+		where I: 'a + IntoIterator<Item=(ConsensusEngineId, &'a [u8])>
+	{
+		None
+	}
+}
+
 /// A trait for verifying the seal of a header and returning the author.
 pub trait VerifySeal<Header, Author> {
 	/// Verify a header and return the author, if any.
@@ -270,6 +279,34 @@ impl<
 	}
 }
 
+/// Split an unbalanced amount two ways between a common divisor.
+pub struct SplitTwoWays<
+	Balance,
+	Imbalance,
+	Part1,
+	Target1,
+	Part2,
+	Target2,
+>(PhantomData<(Balance, Imbalance, Part1, Target1, Part2, Target2)>);
+
+impl<
+	Balance: From<u32> + Saturating + Div<Output=Balance>,
+	I: Imbalance<Balance>,
+	Part1: U32,
+	Target1: OnUnbalanced<I>,
+	Part2: U32,
+	Target2: OnUnbalanced<I>,
+> OnUnbalanced<I> for SplitTwoWays<Balance, I, Part1, Target1, Part2, Target2>
+{
+	fn on_unbalanced(amount: I) {
+		let total: u32 = Part1::VALUE + Part2::VALUE;
+		let amount1 = amount.peek().saturating_mul(Part1::VALUE.into()) / total.into();
+		let (imb1, imb2) = amount.split(amount1);
+		Target1::on_unbalanced(imb1);
+		Target2::on_unbalanced(imb2);
+	}
+}
+
 /// Abstraction over a fungible assets system.
 pub trait Currency<AccountId> {
 	/// The balance of an account.
@@ -299,6 +336,21 @@ pub trait Currency<AccountId> {
 	/// `ExistentialDeposit`.
 	fn minimum_balance() -> Self::Balance;
 
+	/// Reduce the total issuance by `amount` and return the according imbalance. The imbalance will
+	/// typically be used to reduce an account by the same amount with e.g. `settle`.
+	///
+	/// This is infallible, but doesn't guarantee that the entire `amount` is burnt, for example
+	/// in the case of underflow.
+	fn burn(amount: Self::Balance) -> Self::PositiveImbalance;
+
+	/// Increase the total issuance by `amount` and return the according imbalance. The imbalance
+	/// will typically be used to increase an account by the same amount with e.g.
+	/// `resolve_into_existing` or `resolve_creating`.
+	///
+	/// This is infallible, but doesn't guarantee that the entire `amount` is issued, for example
+	/// in the case of overflow.
+	fn issue(amount: Self::Balance) -> Self::NegativeImbalance;
+
 	/// The 'free' balance of a given account.
 	///
 	/// This is the only balance that matters in terms of most operations on tokens. It alone
@@ -355,17 +407,18 @@ pub trait Currency<AccountId> {
 		value: Self::Balance
 	) -> result::Result<Self::PositiveImbalance, &'static str>;
 
-	/// Removes some free balance from `who` account for `reason` if possible. If `liveness` is `KeepAlive`,
-	/// then no less than `ExistentialDeposit` must be left remaining.
-	///
-	/// This checks any locks, vesting, and liquidity requirements. If the removal is not possible, then it
-	/// returns `Err`.
-	fn withdraw(
+	/// Similar to deposit_creating, only accepts a `NegativeImbalance` and returns nothing on
+	/// success.
+	fn resolve_into_existing(
 		who: &AccountId,
-		value: Self::Balance,
-		reason: WithdrawReason,
-		liveness: ExistenceRequirement,
-	) -> result::Result<Self::NegativeImbalance, &'static str>;
+		value: Self::NegativeImbalance,
+	) -> result::Result<(), Self::NegativeImbalance> {
+		let v = value.peek();
+		match Self::deposit_into_existing(who, v) {
+			Ok(opposite) => Ok(drop(value.offset(opposite))),
+			_ => Err(value),
+		}
+	}
 
 	/// Adds up to `value` to the free balance of `who`. If `who` doesn't exist, it is created.
 	///
@@ -375,6 +428,45 @@ pub trait Currency<AccountId> {
 		value: Self::Balance,
 	) -> Self::PositiveImbalance;
 
+	/// Similar to deposit_creating, only accepts a `NegativeImbalance` and returns nothing on
+	/// success.
+	fn resolve_creating(
+		who: &AccountId,
+		value: Self::NegativeImbalance,
+	) {
+		let v = value.peek();
+		drop(value.offset(Self::deposit_creating(who, v)));
+	}
+
+	/// Removes some free balance from `who` account for `reason` if possible. If `liveness` is
+	/// `KeepAlive`, then no less than `ExistentialDeposit` must be left remaining.
+	///
+	/// This checks any locks, vesting, and liquidity requirements. If the removal is not possible,
+	/// then it returns `Err`.
+	///
+	/// If the operation is successful, this will return `Ok` with a `NegativeImbalance` whose value
+	/// is `value`.
+	fn withdraw(
+		who: &AccountId,
+		value: Self::Balance,
+		reason: WithdrawReason,
+		liveness: ExistenceRequirement,
+	) -> result::Result<Self::NegativeImbalance, &'static str>;
+
+	/// Similar to withdraw, only accepts a `PositiveImbalance` and returns nothing on success.
+	fn settle(
+		who: &AccountId,
+		value: Self::PositiveImbalance,
+		reason: WithdrawReason,
+		liveness: ExistenceRequirement,
+	) -> result::Result<(), Self::PositiveImbalance> {
+		let v = value.peek();
+		match Self::withdraw(who, v, reason, liveness) {
+			Ok(opposite) => Ok(drop(value.offset(opposite))),
+			_ => Err(value),
+		}
+	}
+
 	/// Ensure an account's free balance equals some value; this will create the account
 	/// if needed.
 	///

substrate/srml/treasury/src/lib.rs

@@ -70,11 +70,14 @@
 #[cfg(feature = "std")]
 use serde::{Serialize, Deserialize};
 use rstd::prelude::*;
-use srml_support::{StorageValue, StorageMap, decl_module, decl_storage, decl_event, ensure};
-use srml_support::traits::{Currency, ReservableCurrency, OnDilution, OnUnbalanced, Imbalance};
-use runtime_primitives::{Permill,
-	traits::{Zero, EnsureOrigin, StaticLookup, Saturating, CheckedSub, CheckedMul}
+use srml_support::{StorageValue, StorageMap, decl_module, decl_storage, decl_event, ensure, print};
+use srml_support::traits::{
+	Currency, ReservableCurrency, OnDilution, OnUnbalanced, Imbalance, WithdrawReason,
+	ExistenceRequirement
 };
+use runtime_primitives::{Permill, ModuleId, traits::{
+	Zero, EnsureOrigin, StaticLookup, CheckedSub, CheckedMul, AccountIdConversion
+}};
 use parity_codec::{Encode, Decode};
 use system::ensure_signed;
 
@@ -82,6 +85,8 @@ type BalanceOf<T> = <<T as Trait>::Currency as Currency<<T as system::Trait>::Ac
 type PositiveImbalanceOf<T> = <<T as Trait>::Currency as Currency<<T as system::Trait>::AccountId>>::PositiveImbalance;
 type NegativeImbalanceOf<T> = <<T as Trait>::Currency as Currency<<T as system::Trait>::AccountId>>::NegativeImbalance;
 
+const MODULE_ID: ModuleId = ModuleId(*b"py/trsry");
+
 pub trait Trait: system::Trait {
 	/// The staking balance.
 	type Currency: Currency<Self::AccountId> + ReservableCurrency<Self::AccountId>;
@@ -135,12 +140,6 @@ decl_module! {
 			Self::deposit_event(RawEvent::Proposed(c));
 		}
 
-		/// Set the balance of funds available to spend.
-		fn set_pot(#[compact] new_pot: BalanceOf<T>) {
-			// Put the new value into storage.
-			<Pot<T>>::put(new_pot);
-		}
-
 		/// (Re-)configure this module.
 		fn configure(
 			#[compact] proposal_bond: Permill,
@@ -224,9 +223,6 @@ decl_storage! {
 
 		// State...
 
-		/// Total funds available to this module for spending.
-		Pot get(pot): BalanceOf<T>;
-
 		/// Number of proposals that have been made.
 		ProposalCount get(proposal_count): ProposalIndex;
 
@@ -260,6 +256,14 @@ decl_event!(
 impl<T: Trait> Module<T> {
 	// Add public immutables and private mutables.
 
+	/// The account ID of the treasury pot.
+	///
+	/// This actually does computation. If you need to keep using it, then make sure you cache the
+	/// value and only call this once.
+	pub fn account_id() -> T::AccountId {
+		MODULE_ID.into_account()
+	}
+
 	/// The needed bond for a proposal whose spend is `value`.
 	fn calculate_bond(value: BalanceOf<T>) -> BalanceOf<T> {
 		Self::proposal_bond_minimum().max(Self::proposal_bond() * value)
@@ -298,18 +302,36 @@ impl<T: Trait> Module<T> {
 			});
 		});
 
-		T::MintedForSpending::on_unbalanced(imbalance);
-
 		if !missed_any {
 			// burn some proportion of the remaining budget if we run a surplus.
 			let burn = (Self::burn() * budget_remaining).min(budget_remaining);
 			budget_remaining -= burn;
+			imbalance.subsume(T::Currency::burn(burn));
 			Self::deposit_event(RawEvent::Burnt(burn))
 		}
 
-		Self::deposit_event(RawEvent::Rollover(budget_remaining));
+		if let Err(problem) = T::Currency::settle(
+			&Self::account_id(),
+			imbalance,
+			WithdrawReason::Transfer,
+			ExistenceRequirement::KeepAlive
+		) {
+			print("Inconsistent state - couldn't settle imbalance for funds spent by treasury");
+			// Nothing else to do here.
+			drop(problem);
+		}
 
-		<Pot<T>>::put(budget_remaining);
+		Self::deposit_event(RawEvent::Rollover(budget_remaining));
+	}
+
+	fn pot() -> BalanceOf<T> {
+		T::Currency::free_balance(&Self::account_id())
+	}
+}
+
+impl<T: Trait> OnUnbalanced<NegativeImbalanceOf<T>> for Module<T> {
+	fn on_unbalanced(amount: NegativeImbalanceOf<T>) {
+		T::Currency::resolve_creating(&Self::account_id(), amount);
 	}
 }
 
@@ -322,7 +344,7 @@ impl<T: Trait> OnDilution<BalanceOf<T>> for Module<T> {
 			if let Some(funding) = total_issuance.checked_sub(&portion) {
 				let funding = funding / portion;
 				if let Some(funding) = funding.checked_mul(&minted) {
-					<Pot<T>>::mutate(|x| *x = x.saturating_add(funding));
+					Self::on_unbalanced(T::Currency::issue(funding));
 				}
 			}
 		}
@@ -519,6 +541,7 @@ mod tests {
 	fn accepted_spend_proposal_enacted_on_spend_period() {
 		with_externalities(&mut new_test_ext(), || {
 			Treasury::on_dilution(100, 100);
+			assert_eq!(Treasury::pot(), 100);
 
 			assert_ok!(Treasury::propose_spend(Origin::signed(0), 100, 3));
 			assert_ok!(Treasury::approve_proposal(Origin::ROOT, 0));
@@ -536,25 +559,27 @@ mod tests {
 	fn on_dilution_quantization_effects() {
 		with_externalities(&mut new_test_ext(), || {
 			// minted = 1% of total issuance for all cases
-			let _ = Treasury::set_pot(0);
 			assert_eq!(Balances::total_issuance(), 200);
 
 			Treasury::on_dilution(2, 66);   // portion = 33% of total issuance
 			assert_eq!(Treasury::pot(), 4); // should increase by 4 (200 - 66) / 66 * 2
+			Balances::make_free_balance_be(&Treasury::account_id(), 0);
 
 			Treasury::on_dilution(2, 67);   // portion = 33+eps% of total issuance
-			assert_eq!(Treasury::pot(), 6); // should increase by 2 (200 - 67) / 67 * 2
+			assert_eq!(Treasury::pot(), 2); // should increase by 2 (200 - 67) / 67 * 2
+			Balances::make_free_balance_be(&Treasury::account_id(), 0);
 
 			Treasury::on_dilution(2, 100);  // portion = 50% of total issuance
-			assert_eq!(Treasury::pot(), 8); // should increase by 2 (200 - 100) / 100 * 2
+			assert_eq!(Treasury::pot(), 2); // should increase by 2 (200 - 100) / 100 * 2
+			Balances::make_free_balance_be(&Treasury::account_id(), 0);
 
 			// If any more than 50% of the network is staked (i.e. (2 * portion) > total_issuance)
 			// then the pot will not increase.
 			Treasury::on_dilution(2, 101);  // portion = 50+eps% of total issuance
-			assert_eq!(Treasury::pot(), 8); // should increase by 0 (200 - 101) / 101 * 2
+			assert_eq!(Treasury::pot(), 0); // should increase by 0 (200 - 101) / 101 * 2
 
 			Treasury::on_dilution(2, 134);  // portion = 67% of total issuance
-			assert_eq!(Treasury::pot(), 8); // should increase by 0 (200 - 134) / 134 * 2
+			assert_eq!(Treasury::pot(), 0); // should increase by 0 (200 - 134) / 134 * 2
 		});
 	}
 
@@ -572,7 +597,7 @@ mod tests {
 			Treasury::on_dilution(100, 100);
 			<Treasury as OnFinalize<u64>>::on_finalize(4);
 			assert_eq!(Balances::free_balance(&3), 150);
-			assert_eq!(Treasury::pot(), 25);
+			assert_eq!(Treasury::pot(), 75);
 		});
 	}
 }