XCM precompile - transact

[Dinonard]

Pull Request Summary

Support for using Transact instruction remotely on other chains via EVM smart contracts.

This enables smart contracts to send an arbitrary call to any chain Astar/Shiden has an open channel with. User needs to specify a couple of arguments:

• destination - parachain Id or relay chain
• payment asset & amount - to use on the destination chain
  • user should have enough asset on the destination chain
• weight - total execution weight in the destination chain - sum of 4 XCM instructions executions + weight required to execute the encoded call via Transact
• call - remote encoded call - this is what will be executed on the destination chain

The template message being sent looks like this:

1. DescendOrigin
2. WithdrawAsset
3. BuyExecution
4. Transact

User doesn't have control over this, except for the aforementioned configurable parameters.

Open Questions

• Q1 - destination chain needs to support DescendOrigin and converting e.g. AccountId32 into appropriate local representation. Will this work with chains like Moonbeam where AccountKey20 is the default account representation type?
• A - yes because we don't control direct mapping of our address in the destination chain but most likely a mapping achieved by hashing our multilocation with additional fixed data to derive new address
• Q2 - should there be Refund and DepositAsset instructions? Or should user ensure they use the correct weight and payment amount? This DOES make the transaction more expensive so perhaps it's better to leave it for future improvement.

Check list

• [x] extend UTs or create an item to improve XCM precompile tests
• [x] added unit tests
• [x] updated documentation

[github-actions[bot]]

Package	Line Rate	Branch Rate	Health
primitives/xcm/src	88%	0%	✔
precompiles/dapps-staking/src	95%	0%	✔
chain-extensions/types/rmrk/src	0%	0%	❌
precompiles/utils/macro/src	0%	0%	❌
frame/block-reward/src	96%	0%	✔
frame/dapps-staking/src	94%	0%	✔
chain-extensions/xvm/src	0%	0%	❌
chain-extensions/types/dapps-staking/src	0%	0%	❌
frame/xc-asset-config/src	87%	0%	✔
precompiles/sr25519/src	78%	0%	➖
precompiles/utils/src	84%	0%	✔
precompiles/xcm/src	82%	0%	✔
precompiles/xvm/src	71%	0%	➖
frame/custom-signatures/src	81%	0%	✔
frame/dapps-staking/src/pallet	90%	0%	✔
frame/collator-selection/src	88%	0%	✔
precompiles/substrate-ecdsa/src	78%	0%	➖
chain-extensions/rmrk/src	0%	0%	❌
chain-extensions/types/xvm/src	0%	0%	❌
frame/pallet-xvm/src/pallet	37%	0%	❌
precompiles/utils/macro/tests	100%	0%	✔
precompiles/assets-erc20/src	91%	0%	✔
chain-extensions/dapps-staking/src	0%	0%	❌
frame/pallet-xvm/src	9%	0%	❌
precompiles/utils/src/data	72%	0%	➖
contracts/xvm/src	0%	0%	❌
frame/pallet-xcm/src	81%	0%	✔
chain-extensions/trait/src	0%	0%	❌
Summary	80% (7491 / 9366)	0% (0 / 0)	➖

Minimum allowed line rate is 60%