abigen! generates incorrect types for functions as arguments

[tomtau]

Version
0.17
Platform
macOS 12
Description
The generated method will have u8 as the type for the function, but according to https://docs.soliditylang.org/en/develop/abi-spec.html#types

function: an address (20 bytes) followed by a function selector (4 bytes). Encoded identical to bytes24.

Example ABI snippet:

	{
		"inputs": [
			{
				"internalType": "uint256[]",
				"name": "r",
				"type": "uint256[]"
			},
			{
				"internalType": "function (uint256) pure external returns (uint256)",
				"name": "f",
				"type": "function"
			}
		],
		"name": "map",
...

Example corresponding currently generated function by abigen!:

pub fn map(&self, r: ::std::vec::Vec<ethers::core::types::U256>, f: u8) -> ethers::contract::builders::ContractCall<M, ...>

Ideally, this should generate correct raw types or take a high-level type that will e.g. resolve the provided contract address+function name to the corresponding bytes24 argument.

[gakonst]

How are you calling this client side? I wouldn't expect a function that takes a function pointer to be exposed to the client?

[mattsse]

also raised here rust-ethereum/ethabi#273

there's currently no native support for Function types.

we could work around this by tracking function inputs separately. Similar to the existing workarounds that we're using to resolve all structs.

is definitely doable

[gakonst]

But how are you supposed to call this from Rust? Can you pass it a Function type?

[mattsse]

function: an address (20 bytes) followed by a function selector (4 bytes). Encoded identical to bytes24.

I think a function argument is something like a callback.

Something like this is possible:

contract Callback {

  Request[] requests;

  struct Request {
    bytes data;
    function(bytes memory) external callback;
  

  function request(bytes memory data, function(bytes memory) external callback) public {
    requests.push(Request(data, callback));
  }

  function reply(uint256 id, bytes memory response) public {
    requests[id].callback(response);
  }
}