pallet-xcm: enhance reserve_transfer_assets to support remote reserves (#1672)

## Motivation

`pallet-xcm` is the main user-facing interface for XCM functionality,
including assets manipulation functions like `teleportAssets()` and
`reserve_transfer_assets()` calls.

While `teleportAsset()` works both ways, `reserve_transfer_assets()`
works only for sending reserve-based assets to a remote destination and
beneficiary when the reserve is the _local chain_.

## Solution

This PR enhances `pallet_xcm::(limited_)reserve_withdraw_assets` to
support transfers when reserves are other chains.
This will allow complete, **bi-directional** reserve-based asset
transfers user stories using `pallet-xcm`.

Enables following scenarios:
- transferring assets with local reserve (was previously supported iff
asset used as fee also had local reserve - now it works in all cases),
- transferring assets with reserve on destination,
- transferring assets with reserve on remote/third-party chain (iff
assets and fees have same remote reserve),
- transferring assets with reserve different than the reserve of the
asset to be used as fees - meaning can be used to transfer random asset
with local/dest reserve while using DOT for fees on all involved chains,
even if DOT local/dest reserve doesn't match asset reserve,
- transferring assets with any type of local/dest reserve while using
fees which can be teleported between involved chains.

All of the above is done by pallet inner logic without the user having
to specify which scenario/reserves/teleports/etc. The correct scenario
and corresponding XCM programs are identified, and respectively, built
automatically based on runtime configuration of trusted teleporters and
trusted reserves.

#### Current limitations:
- while `fees` and "non-fee" `assets` CAN have different reserves (or
fees CAN be teleported), the remaining "non-fee" `assets` CANNOT, among
themselves, have different reserve locations (this is also implicitly
enforced by `MAX_ASSETS_FOR_TRANSFER=2`, but this can be safely
increased in the future).
- `fees` and "non-fee" `assets` CANNOT have **different remote**
reserves (this could also be supported in the future, but adds even more
complexity while possibly not being worth it - we'll see what the future
holds).

Fixes https://github.com/paritytech/polkadot-sdk/issues/1584
Fixes https://github.com/paritytech/polkadot-sdk/issues/2055

---------

Co-authored-by: Francisco Aguirre <franciscoaguirreperez@gmail.com>
Co-authored-by: Branislav Kontur <bkontur@gmail.com>

cumulus/parachains/integration-tests/emulated/chains/parachains/assets/asset-hub-rococo/src/lib.rs

@@ -21,7 +21,7 @@ use frame_support::traits::OnInitialize;
 // Cumulus
 use emulated_integration_tests_common::{
 	impl_accounts_helpers_for_parachain, impl_assert_events_helpers_for_parachain,
-	impl_assets_helpers_for_system_parachain, xcm_emulator::decl_test_parachains,
+	impl_assets_helpers_for_parachain, xcm_emulator::decl_test_parachains,
 };
 use rococo_emulated_chain::Rococo;
 
@@ -51,5 +51,5 @@ decl_test_parachains! {
 
 // AssetHubRococo implementation
 impl_accounts_helpers_for_parachain!(AssetHubRococo);
-impl_assert_events_helpers_for_parachain!(AssetHubRococo);
-impl_assets_helpers_for_system_parachain!(AssetHubRococo, Rococo);
+impl_assert_events_helpers_for_parachain!(AssetHubRococo, false);
+impl_assets_helpers_for_parachain!(AssetHubRococo, Rococo);

cumulus/parachains/integration-tests/emulated/chains/parachains/assets/asset-hub-westend/src/lib.rs

@@ -21,7 +21,7 @@ use frame_support::traits::OnInitialize;
 // Cumulus
 use emulated_integration_tests_common::{
 	impl_accounts_helpers_for_parachain, impl_assert_events_helpers_for_parachain,
-	impl_assets_helpers_for_system_parachain, xcm_emulator::decl_test_parachains,
+	impl_assets_helpers_for_parachain, xcm_emulator::decl_test_parachains,
 };
 use westend_emulated_chain::Westend;
 
@@ -51,5 +51,5 @@ decl_test_parachains! {
 
 // AssetHubWestend implementation
 impl_accounts_helpers_for_parachain!(AssetHubWestend);
-impl_assert_events_helpers_for_parachain!(AssetHubWestend);
-impl_assets_helpers_for_system_parachain!(AssetHubWestend, Westend);
+impl_assert_events_helpers_for_parachain!(AssetHubWestend, false);
+impl_assets_helpers_for_parachain!(AssetHubWestend, Westend);

cumulus/parachains/integration-tests/emulated/chains/parachains/assets/asset-hub-wococo/src/lib.rs

@@ -19,7 +19,7 @@ use frame_support::traits::OnInitialize;
 // Cumulus
 use emulated_integration_tests_common::{
 	impl_accounts_helpers_for_parachain, impl_assert_events_helpers_for_parachain,
-	impl_assets_helpers_for_system_parachain, xcm_emulator::decl_test_parachains,
+	impl_assets_helpers_for_parachain, xcm_emulator::decl_test_parachains,
 };
 use wococo_emulated_chain::Wococo;
 
@@ -49,5 +49,5 @@ decl_test_parachains! {
 
 // AssetHubWococo implementation
 impl_accounts_helpers_for_parachain!(AssetHubWococo);
-impl_assert_events_helpers_for_parachain!(AssetHubWococo);
-impl_assets_helpers_for_system_parachain!(AssetHubWococo, Wococo);
+impl_assert_events_helpers_for_parachain!(AssetHubWococo, false);
+impl_assets_helpers_for_parachain!(AssetHubWococo, Wococo);

cumulus/parachains/integration-tests/emulated/chains/parachains/bridges/bridge-hub-rococo/src/lib.rs

@@ -46,4 +46,4 @@ decl_test_parachains! {
 
 // BridgeHubRococo implementation
 impl_accounts_helpers_for_parachain!(BridgeHubRococo);
-impl_assert_events_helpers_for_parachain!(BridgeHubRococo);
+impl_assert_events_helpers_for_parachain!(BridgeHubRococo, false);

cumulus/parachains/integration-tests/emulated/chains/parachains/bridges/bridge-hub-westend/src/lib.rs

@@ -46,4 +46,4 @@ decl_test_parachains! {
 
 // BridgeHubWestend implementation
 impl_accounts_helpers_for_parachain!(BridgeHubWestend);
-impl_assert_events_helpers_for_parachain!(BridgeHubWestend);
+impl_assert_events_helpers_for_parachain!(BridgeHubWestend, false);

cumulus/parachains/integration-tests/emulated/chains/parachains/bridges/bridge-hub-wococo/src/lib.rs

@@ -44,4 +44,4 @@ decl_test_parachains! {
 
 // BridgeHubWococo implementation
 impl_accounts_helpers_for_parachain!(BridgeHubWococo);
-impl_assert_events_helpers_for_parachain!(BridgeHubWococo);
+impl_assert_events_helpers_for_parachain!(BridgeHubWococo, false);

cumulus/parachains/integration-tests/emulated/chains/parachains/testing/penpal/Cargo.toml

@@ -22,3 +22,4 @@ parachains-common = { path = "../../../../../../../parachains/common" }
 cumulus-primitives-core = { path = "../../../../../../../primitives/core", default-features = false }
 emulated-integration-tests-common = { path = "../../../../common", default-features = false }
 penpal-runtime = { path = "../../../../../../runtimes/testing/penpal" }
+rococo-emulated-chain = { path = "../../../relays/rococo" }

cumulus/parachains/integration-tests/emulated/chains/parachains/testing/penpal/src/lib.rs

@@ -21,8 +21,10 @@ use frame_support::traits::OnInitialize;
 
 // Cumulus
 use emulated_integration_tests_common::{
-	impl_assert_events_helpers_for_parachain, xcm_emulator::decl_test_parachains,
+	impl_accounts_helpers_for_parachain, impl_assert_events_helpers_for_parachain,
+	impl_assets_helpers_for_parachain, xcm_emulator::decl_test_parachains,
 };
+use rococo_emulated_chain::Rococo;
 
 // Penpal Parachain declaration
 decl_test_parachains! {
@@ -40,6 +42,7 @@ decl_test_parachains! {
 		pallets = {
 			PolkadotXcm: penpal_runtime::PolkadotXcm,
 			Assets: penpal_runtime::Assets,
+			Balances: penpal_runtime::Balances,
 		}
 	},
 	pub struct PenpalB {
@@ -56,10 +59,13 @@ decl_test_parachains! {
 		pallets = {
 			PolkadotXcm: penpal_runtime::PolkadotXcm,
 			Assets: penpal_runtime::Assets,
+			Balances: penpal_runtime::Balances,
 		}
 	},
 }
 
 // Penpal implementation
-impl_assert_events_helpers_for_parachain!(PenpalA);
-impl_assert_events_helpers_for_parachain!(PenpalB);
+impl_accounts_helpers_for_parachain!(PenpalA);
+impl_assets_helpers_for_parachain!(PenpalA, Rococo);
+impl_assert_events_helpers_for_parachain!(PenpalA, true);
+impl_assert_events_helpers_for_parachain!(PenpalB, true);