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

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## 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>
This commit is contained in:
Adrian Catangiu
2023-11-13 17:16:55 +02:00
committed by GitHub
parent 29654a4d71
commit 18257373b3
80 changed files with 3679 additions and 1466 deletions
Download Patch File Download Diff File Expand all files Collapse all files
cumulus/parachains/runtimes/assets/test-utils/src/lib.rs
+15
View File
@@ -27,6 +27,21 @@ use std::fmt::Debug;
use xcm::latest::prelude::*;
use xcm_builder::{CreateMatcher, MatchXcm};
/// Given a message, a sender, and a destination, it returns the delivery fees
fn get_fungible_delivery_fees<S: SendXcm>(destination: MultiLocation, message: Xcm<()>) -> u128 {
let Ok((_, delivery_fees)) = validate_send::<S>(destination, message) else {
unreachable!("message can be sent; qed")
};
if let Some(delivery_fee) = delivery_fees.inner().first() {
let Fungible(delivery_fee_amount) = delivery_fee.fun else {
unreachable!("asset is fungible; qed");
};
delivery_fee_amount
} else {
0
}
}
/// Helper function to verify `xcm` contains all relevant instructions expected on destination
/// chain as part of a reserve-asset-transfer.
pub(crate) fn assert_matches_reserve_asset_deposited_instructions<RuntimeCall: Debug>(