Add assets in pool with native to query_acceptable_payment_assets's r…

…eturn (#5599)

`XcmPaymentApi::query_acceptable_payment_assets` is an API that returns
the assets that can be used to pay fees on the runtime where it's
called.
For relays and most system chains this was configured only as the native
asset: ROC and WND.
However, the asset hubs have the asset conversion pallet, which allows
fees to be paid in any asset in a pool with the native one.
This PR adds the list of assets in a pool with the native one to the
return value of this API for the asset hubs.

---------

Co-authored-by: Branislav Kontur <bkontur@gmail.com>
(cherry picked from commit d2ba567)

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

@@ -1325,7 +1325,23 @@ impl_runtime_apis! {
 
 	impl xcm_runtime_apis::fees::XcmPaymentApi<Block> for Runtime {
 		fn query_acceptable_payment_assets(xcm_version: xcm::Version) -> Result<Vec<VersionedAssetId>, XcmPaymentApiError> {
-			let acceptable_assets = vec![AssetId(xcm_config::TokenLocation::get())];
+			let native_token = xcm_config::TokenLocation::get();
+			// We accept the native token to pay fees.
+			let mut acceptable_assets = vec![AssetId(native_token.clone())];
+			// We also accept all assets in a pool with the native token.
+			acceptable_assets.extend(
+				pallet_asset_conversion::Pools::<Runtime>::iter_keys().filter_map(
+					|(asset_1, asset_2)| {
+						if asset_1 == native_token {
+							Some(asset_2.clone().into())
+						} else if asset_2 == native_token {
+							Some(asset_1.clone().into())
+						} else {
+							None
+						}
+					},
+				),
+			);
 			PolkadotXcm::query_acceptable_payment_assets(xcm_version, acceptable_assets)
 		}
 

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

@@ -1358,7 +1358,23 @@ impl_runtime_apis! {
 
 	impl xcm_runtime_apis::fees::XcmPaymentApi<Block> for Runtime {
 		fn query_acceptable_payment_assets(xcm_version: xcm::Version) -> Result<Vec<VersionedAssetId>, XcmPaymentApiError> {
-			let acceptable_assets = vec![AssetId(xcm_config::WestendLocation::get())];
+			let native_token = xcm_config::WestendLocation::get();
+			// We accept the native token to pay fees.
+			let mut acceptable_assets = vec![AssetId(native_token.clone())];
+			// We also accept all assets in a pool with the native token.
+			acceptable_assets.extend(
+				pallet_asset_conversion::Pools::<Runtime>::iter_keys().filter_map(
+					|(asset_1, asset_2)| {
+						if asset_1 == native_token {
+							Some(asset_2.clone().into())
+						} else if asset_2 == native_token {
+							Some(asset_1.clone().into())
+						} else {
+							None
+						}
+					},
+				),
+			);
 			PolkadotXcm::query_acceptable_payment_assets(xcm_version, acceptable_assets)
 		}
 

prdoc/pr_5599.prdoc

@@ -0,0 +1,19 @@
+# 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: Add assets in pool with native to query_acceptable_payment_assets
+
+doc:
+  - audience: Runtime Dev
+    description: |
+      The `XcmPaymentApi::query_acceptable_payment_assets` API can be used to get a list of all
+      the assets that can be used for fee payment.
+      This is usually just the native asset, but the asset hubs have the asset conversion pallet.
+      In the case of the asset hubs, this list now includes all assets in a liquidity pool with
+      the native one.
+
+crates:
+  - name: asset-hub-rococo-runtime
+    bump: minor
+  - name: asset-hub-westend-runtime
+    bump: minor