Erc4626 extension

[Ifechukwudaniel]

Resolves #356

PR Checklist

• Tests
• Documentation
• Changelog

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[Ifechukwudaniel]

I just stared this

[0xNeshi]

I'll convert this to a draft, so that the team does not invest time reviewing a WIP

[0xNeshi]

Be careful, you should not be calling _mint on the asset, but on the contract itself (see Solidity version).

Maybe it would be helpful to take inspiration from the Erc20FlashMint extension PR, as it has a similar design problem as ERC4626, namely that you need to extend ERC20, but still leverage ERC20's functions (which is a problem in Stylus due to lack of proper inheritance).

One way to solve this is to make each ERC4626 function that needs to call base contract's functions (e.g. _mint) accept an erc20: &mut Erc20 parameter, which acts as a reference to the base/parent contract.

Note that you'll still need _asset: Erc20 as a storage field. But you can make it a generic IErc20 type, so that users of the library are free to define their own Erc20 implementation (as is done in Solidity) (@bidzyyys @qalisander wdyt about this approach?):

#[storage] // this is the new convention we use for defining storage
#[allow(clippy::pub_underscore_fields)]
pub struct ERC4626<T: IErc20 + StorageType> {
    pub _asset: T, 
    pub _underlying_decimals: StorageU8,
}

NOTE: although _asset and _underlying_decimals should be private, we're making them public for the purposes of testing. This will be changed at some point.

[Ifechukwudaniel]

Thanks you

[Ifechukwudaniel]

@0xNeshi
The Solidity implementation uses safe transfer

SafeERC20.safeTransferFrom(_asset, caller, address(this), assets);

In the Solidity implementation, SafeERC20 is a utility library. However, in the Stylus implementation, SafeTransfer is a contract. What do you think

[0xNeshi]

@0xNeshi The Solidity implementation uses safe transfer

SafeERC20.safeTransferFrom(_asset, caller, address(this), assets);

In the Solidity implementation, SafeERC20 is a utility library. However, in the Stylus implementation, SafeTransfer is a contract. What do you think

See how VestingWallet handles this

[Ifechukwudaniel]

Should I implement something like mulDiv for U256 MATH?

function _convertToShares(uint256 assets, Math.Rounding rounding) internal view virtual returns (uint256) {
        return assets.mulDiv(totalSupply() + 10 ** _decimalsOffset(), totalAssets() + 1, rounding);
    }

@0xNeshi

[Ifechukwudaniel]

Should I add the security concerns like docs erc4626