From bf78c1655b7e49503a11cb070235089ea1e2455e Mon Sep 17 00:00:00 2001
From: Guillaume Thiolliere <gui.thiolliere@gmail.com>
Date: Mon, 9 Nov 2020 20:26:24 +0100
Subject: [PATCH] refactor subtrait/elevated trait as not needed (#7497)

---
 frame/balances/src/lib.rs | 74 +++++----------------------------------
 1 file changed, 9 insertions(+), 65 deletions(-)

diff --git a/frame/balances/src/lib.rs b/frame/balances/src/lib.rs
index 7ca6fd1e78091..141a360f7e180 100644
--- a/frame/balances/src/lib.rs
+++ b/frame/balances/src/lib.rs
@@ -704,7 +704,7 @@ impl<T: Trait<I>, I: Instance> Module<T, I> {
 // of the inner member.
 mod imbalances {
 	use super::{
-		result, Subtrait, DefaultInstance, Imbalance, Trait, Zero, Instance, Saturating,
+		result, DefaultInstance, Imbalance, Trait, Zero, Instance, Saturating,
 		StorageValue, TryDrop,
 	};
 	use sp_std::mem;
@@ -712,9 +712,9 @@ mod imbalances {
 	/// Opaque, move-only struct with private fields that serves as a token denoting that
 	/// funds have been created without any equal and opposite accounting.
 	#[must_use]
-	pub struct PositiveImbalance<T: Subtrait<I>, I: Instance=DefaultInstance>(T::Balance);
+	pub struct PositiveImbalance<T: Trait<I>, I: Instance=DefaultInstance>(T::Balance);
 
-	impl<T: Subtrait<I>, I: Instance> PositiveImbalance<T, I> {
+	impl<T: Trait<I>, I: Instance> PositiveImbalance<T, I> {
 		/// Create a new positive imbalance from a balance.
 		pub fn new(amount: T::Balance) -> Self {
 			PositiveImbalance(amount)
@@ -724,9 +724,9 @@ mod imbalances {
 	/// Opaque, move-only struct with private fields that serves as a token denoting that
 	/// funds have been destroyed without any equal and opposite accounting.
 	#[must_use]
-	pub struct NegativeImbalance<T: Subtrait<I>, I: Instance=DefaultInstance>(T::Balance);
+	pub struct NegativeImbalance<T: Trait<I>, I: Instance=DefaultInstance>(T::Balance);
 
-	impl<T: Subtrait<I>, I: Instance> NegativeImbalance<T, I> {
+	impl<T: Trait<I>, I: Instance> NegativeImbalance<T, I> {
 		/// Create a new negative imbalance from a balance.
 		pub fn new(amount: T::Balance) -> Self {
 			NegativeImbalance(amount)
@@ -835,81 +835,25 @@ mod imbalances {
 		}
 	}
 
-	impl<T: Subtrait<I>, I: Instance> Drop for PositiveImbalance<T, I> {
+	impl<T: Trait<I>, I: Instance> Drop for PositiveImbalance<T, I> {
 		/// Basic drop handler will just square up the total issuance.
 		fn drop(&mut self) {
-			<super::TotalIssuance<super::ElevatedTrait<T, I>, I>>::mutate(
+			<super::TotalIssuance<T, I>>::mutate(
 				|v| *v = v.saturating_add(self.0)
 			);
 		}
 	}
 
-	impl<T: Subtrait<I>, I: Instance> Drop for NegativeImbalance<T, I> {
+	impl<T: Trait<I>, I: Instance> Drop for NegativeImbalance<T, I> {
 		/// Basic drop handler will just square up the total issuance.
 		fn drop(&mut self) {
-			<super::TotalIssuance<super::ElevatedTrait<T, I>, I>>::mutate(
+			<super::TotalIssuance<T, I>>::mutate(
 				|v| *v = v.saturating_sub(self.0)
 			);
 		}
 	}
 }
 
-// TODO: #2052
-// Somewhat ugly hack in order to gain access to module's `increase_total_issuance_by`
-// using only the Subtrait (which defines only the types that are not dependent
-// on Positive/NegativeImbalance). Subtrait must be used otherwise we end up with a
-// circular dependency with Trait having some types be dependent on PositiveImbalance<Trait>
-// and PositiveImbalance itself depending back on Trait for its Drop impl (and thus
-// its type declaration).
-// This works as long as `increase_total_issuance_by` doesn't use the Imbalance
-// types (basically for charging fees).
-// This should eventually be refactored so that the type item that
-// depends on the Imbalance type (DustRemoval) is placed in its own pallet.
-struct ElevatedTrait<T: Subtrait<I>, I: Instance>(T, I);
-impl<T: Subtrait<I>, I: Instance> Clone for ElevatedTrait<T, I> {
-	fn clone(&self) -> Self { unimplemented!() }
-}
-impl<T: Subtrait<I>, I: Instance> PartialEq for ElevatedTrait<T, I> {
-	fn eq(&self, _: &Self) -> bool { unimplemented!() }
-}
-impl<T: Subtrait<I>, I: Instance> Eq for ElevatedTrait<T, I> {}
-impl<T: Subtrait<I>, I: Instance> frame_system::Trait for ElevatedTrait<T, I> {
-	type BaseCallFilter = T::BaseCallFilter;
-	type Origin = T::Origin;
-	type Call = T::Call;
-	type Index = T::Index;
-	type BlockNumber = T::BlockNumber;
-	type Hash = T::Hash;
-	type Hashing = T::Hashing;
-	type AccountId = T::AccountId;
-	type Lookup = T::Lookup;
-	type Header = T::Header;
-	type Event = ();
-	type BlockHashCount = T::BlockHashCount;
-	type MaximumBlockWeight = T::MaximumBlockWeight;
-	type DbWeight = T::DbWeight;
-	type BlockExecutionWeight = T::BlockExecutionWeight;
-	type ExtrinsicBaseWeight = T::ExtrinsicBaseWeight;
-	type MaximumExtrinsicWeight = T::MaximumBlockWeight;
-	type MaximumBlockLength = T::MaximumBlockLength;
-	type AvailableBlockRatio = T::AvailableBlockRatio;
-	type Version = T::Version;
-	type PalletInfo = T::PalletInfo;
-	type OnNewAccount = T::OnNewAccount;
-	type OnKilledAccount = T::OnKilledAccount;
-	type AccountData = T::AccountData;
-	type SystemWeightInfo = T::SystemWeightInfo;
-}
-impl<T: Subtrait<I>, I: Instance> Trait<I> for ElevatedTrait<T, I> {
-	type Balance = T::Balance;
-	type Event = ();
-	type DustRemoval = ();
-	type ExistentialDeposit = T::ExistentialDeposit;
-	type AccountStore = T::AccountStore;
-	type WeightInfo = <T as Subtrait<I>>::WeightInfo;
-	type MaxLocks = T::MaxLocks;
-}
-
 impl<T: Trait<I>, I: Instance> Currency<T::AccountId> for Module<T, I> where
 	T::Balance: MaybeSerializeDeserialize + Debug
 {