Pay EVM gas fees with tokens via HydraDX pallet

[4meta5]

Some changes must be made to safely config HydraDX-node/pallet-transaction-multi-payment for evm-template

HydraDX/tx-multi usage blockers

evm-template EVM config violates key assumptions built into the current version of HydraDX-node/pallet-transaction-multi-payment. The configurations that violate these assumptions include:

1. setting the native currency as the EVM currency
2. setting Ethereum Accounts as the main AccountId type
3. setting ECDSA as the main Signature scheme

These settings were chosen intentionally to maximize Ethereum compatibility for developers building and using the EVM. They are not subject to change.

Unfortunately, HydraDX-node/pallet-transaction-multi-payment does not expect this config and, moreover, has hardcoded assumptions to the contrary that lead to unexpected behavior:

1. reset_payment_currency extrinsic incorrectly routes native balance operations to the foreign asset handler because it assumes the EvmAssetId != NativeAssetId.
2. Config::MultiCurrency has bounds not satisfied by pallet-assets (tried here to wrap it without luck). The only out of the box config for Config::MultiCurrency is orml-tokens or orml-currencies, the latter of the two still to use these pallets as is because pallet-assets is not supported.

orml-currencies usage blockers

orml-currencies is a pallet that allows ORML users to route native asset execution to a separate path than foreign asset execution. It supports pallet-balances + orml-tokens but does not support out of the box pallet-balances + pallet-assets.

Making orml-currencies work with pallet-assets is the same work required to resolve the problem outlined in HydraDX/tx-multi. By enabling pallet-assets to replace orml-tokens in the orml-currencies config, it would enable pallet-assets to be used in HydraDX/tx-multi as originally intended.

Code Changes

• Split out DeFi configs into evm-template/runtime/src/defi.rs
• Chose ecosystem pallet to enable paying EVM gas fees with any registered/governance-approved token: HydraDX-node/transaction-multi-payment. Additional approaches were compared and contrasted in an internal doc titled "Choosing an Implementation to Pay Gas Fees with Any Token".
• Fork HydraDX-node && open-runtime-module-library to use HydraDX-Node/pallet-transaction-multi-payment
• Match HydraDX-node, open-runtime-module-library fork dependencies to polkadot-sdk and frontier version used locally (polkadot-v1.7.0 when last updated). Import HydraDX-Node/transacton_multi_payment into deps.
• Configured orml-tokens, orml-currencies to satisfy transaction-multi-payment::Config::MultiCurrency trait bounds. Justification: https://substrate.stackexchange.com/questions/8410/orml-tokens-vs-pallet-assets
• Summarized blockers encountered configuring HydraDX/transaction-multi-payment for the evm-template runtime at the top of the PR description.

Next Steps

Following steps are sequential and should not be pursued in parallel:

• implement pallet to enable using pallet-assets + pallet-balances by tx-multi-payment instead of orml-tokens nor orml-currencies
• make issue & upstream changes required to tx-multi-payment to support EvmCurrency = NativeCurrencyId (so that reset_payment does not incorrectly route execution away from pallet-balances, could be solved by the write pallet impl in the top TODO)
• write local precompile that uses ECDSA for tx-multi-payment precompile
• make issue & upstream for tx-multi-payment precompile generic over signature scheme HydraDX-node

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[4meta5]

Chose to use orml_tokens instead of adding pallet-multi-asset (which required implementing all the necessary MultiCurrency traits using pallet-assets). That work was saved on a separate branch before proceeding with orml_tokens configuration.

[ggonzalez94]

@4meta5 I removed this from EVM milestone since we are not shipping this. We can include as part of a later milestone if we decide to ship this

[4meta5]

Closed because extremely stale at this point, blockers are documented clearly in the PR description for anyone wishing to take up this work in the future.