Contract binding generator: Wrong handling of multiple return values

[lukasz-zimnoch]

During the work on threshold-network/keep-core#3427, we noticed a problem with a generated contract binding that maps the WalletRegistry contract. That contract defines the following function:

function isDkgResultValid(DKG.Result calldata result) external view returns (bool, string memory)

which is covered by the WalletRegistry.go binding as:

func (wr *WalletRegistry) IsDkgResultValid(
    arg_result abi.EcdsaDkgResult,
) (isDkgResultValid, error) {
    ...
}

type isDkgResultValid struct {
	bool
	string
}

The isDkgResultValid is package-private and contains anonymous fields that can't be accessed outside. The only possible workaround is by using Go's reflection. This should be improved by making the returned values accessible.