implement IERC20Metadata for pallet-assets-precompiles

[seunlanlege]

Summary

Implements the missing ERC20 metadata functions (name, symbol, decimals) for the pallet-assets precompile to provide full ERC20 compatibility. These functions were missing from the original implementation and are essential for proper EVM wallet and tooling integration.

Changes

Solidity Interface

• substrate/primitives/ethereum-standards/src/IERC20.sol
  • Added name() external view returns (string memory)
  • Added symbol() external view returns (string memory)
  • Added decimals() external view returns (uint8)

Precompile Implementation

• substrate/frame/assets/precompiles/src/lib.rs
  • Implemented name() - reads metadata from pallet-assets storage and returns UTF-8 string
  • Implemented symbol() - reads metadata from pallet-assets storage and returns UTF-8 string
  • Implemented decimals() - reads metadata from pallet-assets storage and returns uint8 value
  • All functions charge appropriate gas using dedicated weight functions
  • Proper error handling for missing metadata and invalid UTF-8 encoding

Benchmarks

• substrate/frame/assets/src/benchmarking.rs
  • Added get_name benchmark - measures metadata read for name field
  • Added get_symbol benchmark - measures metadata read for symbol field
  • Added get_decimals benchmark - measures metadata read for decimals field

Weight Functions

• substrate/frame/assets/src/weights.rs
  • Added get_name() -> Weight to WeightInfo trait
  • Added get_symbol() -> Weight to WeightInfo trait
  • Added get_decimals() -> Weight to WeightInfo trait
  • Implemented for both SubstrateWeight<T> and () (fallback)
  • Each function: 1 storage read from Assets::Metadata (~12-12.5ms, 2615 bytes proof size)

Closes #8658

[pgherveou]

fixes #8658

[pgherveou]

Looks good thanks 🙏

[0xRVE]

/cmd fmt

[0xRVE]

/cmd prdoc --audience runtime_dev --bump minor

[github-actions]

Command "fmt" has failed ❌! See logs here

[github-actions]

Command "prdoc --audience runtime_dev --bump minor" has failed ❌! See logs here

[seunlanlege]

Commands won't run because it's on my fork

[SoneVibe]

Thanks for the fast progress on #10949 metadata views are a big win!

This will fix frontend crashes and metadata UX for DEXes.

Just confirming: will standard ERC-20 events (Transfer/Approval) be added in a future PR?

For lending (Compound/Aave forks), full events are needed for accrual tracking, liquidations, and subgraphs.

Happy to test on testnet when available.

Thanks again this is accelerating DeFi adoption on Hub!