Asset Conversion: Pool Touch Call (#3251)

Introduce `touch` call designed to address operational prerequisites
before providing liquidity to a pool.

This function ensures that essential requirements, such as the presence
of the pool's accounts, are fulfilled. It is particularly beneficial in
scenarios where a pool creator removes the pool's accounts without
providing liquidity.

---------

Co-authored-by: command-bot <>

cumulus/parachains/runtimes/assets/asset-hub-rococo/src/weights/pallet_asset_conversion.rs

@@ -154,4 +154,26 @@ impl<T: frame_system::Config> pallet_asset_conversion::WeightInfo for WeightInfo
 			.saturating_add(T::DbWeight::get().writes(4))
 			.saturating_add(Weight::from_parts(0, 393).saturating_mul(n.into()))
 	}
+	/// Storage: `AssetConversion::Pools` (r:1 w:0)
+	/// Proof: `AssetConversion::Pools` (`max_values`: None, `max_size`: Some(30), added: 2505, mode: `MaxEncodedLen`)
+	/// Storage: `Assets::Asset` (r:2 w:2)
+	/// Proof: `Assets::Asset` (`max_values`: None, `max_size`: Some(210), added: 2685, mode: `MaxEncodedLen`)
+	/// Storage: `Assets::Account` (r:2 w:2)
+	/// Proof: `Assets::Account` (`max_values`: None, `max_size`: Some(134), added: 2609, mode: `MaxEncodedLen`)
+	/// Storage: `PoolAssets::Asset` (r:1 w:1)
+	/// Proof: `PoolAssets::Asset` (`max_values`: None, `max_size`: Some(210), added: 2685, mode: `MaxEncodedLen`)
+	/// Storage: `PoolAssets::Account` (r:1 w:1)
+	/// Proof: `PoolAssets::Account` (`max_values`: None, `max_size`: Some(134), added: 2609, mode: `MaxEncodedLen`)
+	/// The range of component `n` is `[0, 3]`.
+	fn touch(n: u32, ) -> Weight {
+		// Proof Size summary in bytes:
+		//  Measured:  `1571`
+		//  Estimated: `6360`
+		// Minimum execution time: 381_000_000 picoseconds.
+		Weight::from_parts(398_540_909, 6360)
+			// Standard Error: 1_330_283
+			.saturating_add(Weight::from_parts(209_463_636, 0).saturating_mul(n.into()))
+			.saturating_add(T::DbWeight::get().reads(7_u64))
+			.saturating_add(T::DbWeight::get().writes((2_u64).saturating_mul(n.into())))
+	}
 }

cumulus/parachains/runtimes/assets/asset-hub-westend/src/weights/pallet_asset_conversion.rs

@@ -153,4 +153,26 @@ impl<T: frame_system::Config> pallet_asset_conversion::WeightInfo for WeightInfo
 			.saturating_add(T::DbWeight::get().writes(4))
 			.saturating_add(Weight::from_parts(0, 393).saturating_mul(n.into()))
 	}
+	/// Storage: `AssetConversion::Pools` (r:1 w:0)
+	/// Proof: `AssetConversion::Pools` (`max_values`: None, `max_size`: Some(30), added: 2505, mode: `MaxEncodedLen`)
+	/// Storage: `Assets::Asset` (r:2 w:2)
+	/// Proof: `Assets::Asset` (`max_values`: None, `max_size`: Some(210), added: 2685, mode: `MaxEncodedLen`)
+	/// Storage: `Assets::Account` (r:2 w:2)
+	/// Proof: `Assets::Account` (`max_values`: None, `max_size`: Some(134), added: 2609, mode: `MaxEncodedLen`)
+	/// Storage: `PoolAssets::Asset` (r:1 w:1)
+	/// Proof: `PoolAssets::Asset` (`max_values`: None, `max_size`: Some(210), added: 2685, mode: `MaxEncodedLen`)
+	/// Storage: `PoolAssets::Account` (r:1 w:1)
+	/// Proof: `PoolAssets::Account` (`max_values`: None, `max_size`: Some(134), added: 2609, mode: `MaxEncodedLen`)
+	/// The range of component `n` is `[0, 3]`.
+	fn touch(n: u32, ) -> Weight {
+		// Proof Size summary in bytes:
+		//  Measured:  `1571`
+		//  Estimated: `6360`
+		// Minimum execution time: 381_000_000 picoseconds.
+		Weight::from_parts(398_540_909, 6360)
+			// Standard Error: 1_330_283
+			.saturating_add(Weight::from_parts(209_463_636, 0).saturating_mul(n.into()))
+			.saturating_add(T::DbWeight::get().reads(7_u64))
+			.saturating_add(T::DbWeight::get().writes((2_u64).saturating_mul(n.into())))
+	}
 }

prdoc/pr_3251.prdoc

@@ -0,0 +1,14 @@
+# Schema: Polkadot SDK PRDoc Schema (prdoc) v1.0.0
+# See doc at https://raw.githubusercontent.com/paritytech/polkadot-sdk/master/prdoc/schema_user.json
+
+title: "Asset Conversion: Pool Touch Call"
+
+doc:
+  - audience: Runtime Dev
+    description: |
+      Introduce `touch` call designed to address operational prerequisites before providing liquidity to a pool.
+      This function ensures that essential requirements, such as the presence of the pool's accounts, are fulfilled.
+      It is particularly beneficial in scenarios where a pool creator removes the pool's accounts without providing liquidity.
+
+crates: 
+  - name: pallet-asset-conversion

substrate/frame/asset-conversion/src/benchmarking.rs

@@ -24,7 +24,7 @@ use frame_support::{
 	assert_ok,
 	traits::{
 		fungible::NativeOrWithId,
-		fungibles::{Create, Inspect, Mutate},
+		fungibles::{Create, Inspect, Mutate, Refund},
 	},
 };
 use frame_system::RawOrigin as SystemOrigin;
@@ -75,12 +75,21 @@ where
 }
 
 /// Create the `asset` and mint the `amount` for the `caller`.
-fn create_asset<T: Config>(caller: &T::AccountId, asset: &T::AssetKind, amount: T::Balance)
-where
+fn create_asset<T: Config>(
+	caller: &T::AccountId,
+	asset: &T::AssetKind,
+	amount: T::Balance,
+	is_sufficient: bool,
+) where
 	T::Assets: Create<T::AccountId> + Mutate<T::AccountId>,
 {
 	if !T::Assets::asset_exists(asset.clone()) {
-		assert_ok!(T::Assets::create(asset.clone(), caller.clone(), true, T::Balance::one()));
+		assert_ok!(T::Assets::create(
+			asset.clone(),
+			caller.clone(),
+			is_sufficient,
+			T::Balance::one()
+		));
 	}
 	assert_ok!(T::Assets::mint_into(
 		asset.clone(),
@@ -141,8 +150,8 @@ where
 		T::Assets::minimum_balance(asset1.clone()),
 		T::Assets::minimum_balance(asset2.clone()),
 	);
-	create_asset::<T>(caller, asset1, liquidity1);
-	create_asset::<T>(caller, asset2, liquidity2);
+	create_asset::<T>(caller, asset1, liquidity1, true);
+	create_asset::<T>(caller, asset2, liquidity2, true);
 	let lp_token = AssetConversion::<T>::get_next_pool_asset_id();
 
 	mint_setup_fee_asset::<T>(caller, asset1, asset2, &lp_token);
@@ -172,8 +181,8 @@ mod benchmarks {
 	fn create_pool() {
 		let caller: T::AccountId = whitelisted_caller();
 		let (asset1, asset2) = T::BenchmarkHelper::create_pair(0, 1);
-		create_asset::<T>(&caller, &asset1, T::Assets::minimum_balance(asset1.clone()));
-		create_asset::<T>(&caller, &asset2, T::Assets::minimum_balance(asset2.clone()));
+		create_asset::<T>(&caller, &asset1, T::Assets::minimum_balance(asset1.clone()), true);
+		create_asset::<T>(&caller, &asset2, T::Assets::minimum_balance(asset2.clone()), true);
 
 		let lp_token = AssetConversion::<T>::get_next_pool_asset_id();
 		create_fee_asset::<T>(&caller);
@@ -358,5 +367,47 @@ mod benchmarks {
 		assert_eq!(actual_balance, init_caller_balance + T::Balance::one());
 	}
 
+	#[benchmark]
+	fn touch(n: Linear<0, 3>) {
+		let caller: T::AccountId = whitelisted_caller();
+		let (asset1, asset2) = T::BenchmarkHelper::create_pair(0, 1);
+		let pool_id = T::PoolLocator::pool_id(&asset1, &asset2).unwrap();
+		let pool_account = T::PoolLocator::address(&pool_id).unwrap();
+
+		create_fee_asset::<T>(&caller);
+		create_asset::<T>(&caller, &asset1, <T as Config>::Balance::one(), false);
+		create_asset::<T>(&caller, &asset2, <T as Config>::Balance::one(), false);
+		let lp_token = AssetConversion::<T>::get_next_pool_asset_id();
+		mint_setup_fee_asset::<T>(&caller, &asset1, &asset2, &lp_token);
+
+		assert_ok!(AssetConversion::<T>::create_pool(
+			SystemOrigin::Signed(caller.clone()).into(),
+			Box::new(asset1.clone()),
+			Box::new(asset2.clone())
+		));
+
+		if n > 0 &&
+			<T as Config>::Assets::deposit_held(asset1.clone(), pool_account.clone()).is_some()
+		{
+			let _ = <T as Config>::Assets::refund(asset1.clone(), pool_account.clone());
+		}
+		if n > 1 &&
+			<T as Config>::Assets::deposit_held(asset2.clone(), pool_account.clone()).is_some()
+		{
+			let _ = <T as Config>::Assets::refund(asset2.clone(), pool_account.clone());
+		}
+		if n > 2 &&
+			<T as Config>::PoolAssets::deposit_held(lp_token.clone(), pool_account.clone())
+				.is_some()
+		{
+			let _ = <T as Config>::PoolAssets::refund(lp_token, pool_account);
+		}
+
+		#[extrinsic_call]
+		_(SystemOrigin::Signed(caller.clone()), Box::new(asset1.clone()), Box::new(asset2.clone()));
+
+		assert_last_event::<T>(Event::Touched { pool_id, who: caller }.into());
+	}
+
 	impl_benchmark_test_suite!(AssetConversion, crate::mock::new_test_ext(), crate::mock::Test);
 }

substrate/frame/asset-conversion/src/lib.rs

@@ -98,7 +98,10 @@ use sp_std::{boxed::Box, collections::btree_set::BTreeSet, vec::Vec};
 #[frame_support::pallet]
 pub mod pallet {
 	use super::*;
-	use frame_support::pallet_prelude::*;
+	use frame_support::{
+		pallet_prelude::{DispatchResult, *},
+		traits::fungibles::Refund,
+	};
 	use frame_system::pallet_prelude::*;
 	use sp_arithmetic::{traits::Unsigned, Permill};
 
@@ -130,7 +133,8 @@ pub mod pallet {
 		type Assets: Inspect<Self::AccountId, AssetId = Self::AssetKind, Balance = Self::Balance>
 			+ Mutate<Self::AccountId>
 			+ AccountTouch<Self::AssetKind, Self::AccountId, Balance = Self::Balance>
-			+ Balanced<Self::AccountId>;
+			+ Balanced<Self::AccountId>
+			+ Refund<Self::AccountId, AssetId = Self::AssetKind>;
 
 		/// Liquidity pool identifier.
 		type PoolId: Parameter + MaxEncodedLen + Ord;
@@ -149,7 +153,8 @@ pub mod pallet {
 		type PoolAssets: Inspect<Self::AccountId, AssetId = Self::PoolAssetId, Balance = Self::Balance>
 			+ Create<Self::AccountId>
 			+ Mutate<Self::AccountId>
-			+ AccountTouch<Self::PoolAssetId, Self::AccountId, Balance = Self::Balance>;
+			+ AccountTouch<Self::PoolAssetId, Self::AccountId, Balance = Self::Balance>
+			+ Refund<Self::AccountId, AssetId = Self::PoolAssetId>;
 
 		/// A % the liquidity providers will take of every swap. Represents 10ths of a percent.
 		#[pallet::constant]
@@ -281,6 +286,13 @@ pub mod pallet {
 			/// E.g. (A, amount_in) -> (Dot, amount_out) -> (B, amount_out)
 			path: BalancePath<T>,
 		},
+		/// Pool has been touched in order to fulfill operational requirements.
+		Touched {
+			/// The ID of the pool.
+			pool_id: T::PoolId,
+			/// The account initiating the touch.
+			who: T::AccountId,
+		},
 	}
 
 	#[pallet::error]
@@ -391,7 +403,9 @@ pub mod pallet {
 			NextPoolAssetId::<T>::set(Some(next_lp_token_id));
 
 			T::PoolAssets::create(lp_token.clone(), pool_account.clone(), false, 1u32.into())?;
-			T::PoolAssets::touch(lp_token.clone(), &pool_account, &sender)?;
+			if T::PoolAssets::should_touch(lp_token.clone(), &pool_account) {
+				T::PoolAssets::touch(lp_token.clone(), &pool_account, &sender)?
+			};
 
 			let pool_info = PoolInfo { lp_token: lp_token.clone() };
 			Pools::<T>::insert(pool_id.clone(), pool_info);
@@ -656,6 +670,49 @@ pub mod pallet {
 			)?;
 			Ok(())
 		}
+
+		/// Touch an existing pool to fulfill prerequisites before providing liquidity, such as
+		/// ensuring that the pool's accounts are in place. It is typically useful when a pool
+		/// creator removes the pool's accounts and does not provide a liquidity. This action may
+		/// involve holding assets from the caller as a deposit for creating the pool's accounts.
+		///
+		/// The origin must be Signed.
+		///
+		/// - `asset1`: The asset ID of an existing pool with a pair (asset1, asset2).
+		/// - `asset2`: The asset ID of an existing pool with a pair (asset1, asset2).
+		///
+		/// Emits `Touched` event when successful.
+		#[pallet::call_index(5)]
+		#[pallet::weight(T::WeightInfo::touch(3))]
+		pub fn touch(
+			origin: OriginFor<T>,
+			asset1: Box<T::AssetKind>,
+			asset2: Box<T::AssetKind>,
+		) -> DispatchResultWithPostInfo {
+			let who = ensure_signed(origin)?;
+
+			let pool_id = T::PoolLocator::pool_id(&asset1, &asset2)
+				.map_err(|_| Error::<T>::InvalidAssetPair)?;
+			let pool = Pools::<T>::get(&pool_id).ok_or(Error::<T>::PoolNotFound)?;
+			let pool_account =
+				T::PoolLocator::address(&pool_id).map_err(|_| Error::<T>::InvalidAssetPair)?;
+
+			let mut refunds_number: u32 = 0;
+			if T::Assets::should_touch(*asset1.clone(), &pool_account) {
+				T::Assets::touch(*asset1, &pool_account, &who)?;
+				refunds_number += 1;
+			}
+			if T::Assets::should_touch(*asset2.clone(), &pool_account) {
+				T::Assets::touch(*asset2, &pool_account, &who)?;
+				refunds_number += 1;
+			}
+			if T::PoolAssets::should_touch(pool.lp_token.clone(), &pool_account) {
+				T::PoolAssets::touch(pool.lp_token, &pool_account, &who)?;
+				refunds_number += 1;
+			}
+			Self::deposit_event(Event::Touched { pool_id, who });
+			Ok(Some(T::WeightInfo::touch(refunds_number)).into())
+		}
 	}
 
 	impl<T: Config> Pallet<T> {