I have a problem with getting the return type of Balance from "ink::env::call::build_call" and the contract keeps panicking when called

Question

let selector: [u8; 4] = [0xbd, 0x77, 0x15, 0xef];
let amount_out = build_call::<DefaultEnvironment>()
    .call_type(Call::new().callee(self.liquidity_pool_address))
    .exec_input(
        ExecutionInput::new(Selector::new(selector))
            .push_arg(amount)
    )
    .returns::<u128>()
    .fire();

match amount_out {
    Ok(output) => return output,
    Err(_) => {
        panic!("Failed to execute call")
    }
} 

The method with the selector: 0xbd7715ef returns a u128 (Balance) type. It doesn't ever have an Err variant, but instead returns 0. The liquidity_pool_address is also its deployed contract address And it takes one u128 argument

There are no error messages to help me debug the problem with the call.

Any clues?

Answer 1

A minimal reproducer would be helpful for answering the question in more depth. So ideally code for a message in contract A and a message in contract B.

That being said, the issue in this case is often that either the selector doesn't exist or the contract doesn't exist.

Try the following:

Instead of

let selector: [u8; 4] = [0xbd, 0x77, 0x15, 0xef];
...
ExecutionInput::new(Selector::new(selector))

you can write:

ExecutionInput::new(Selector::new(ink::selector_bytes!("my_message")))

This will automatically compute the selector bytes, ensuring that there was no mistake when transforming it manually to a byte array.

For self.liquidity_pool_address: Check if you do any castings to AccountId here. Sometimes I see contracts that do some weird stuff to get a String into AccountId.

You could try having a message fn test(&self, acc_id: AccountId) that contains the code you posted above, but instead of self.liquidity_pool_address it would use the message argument acc_id. This way you can test it with a properly typed AccountId; polkadot-js, Contracts UI and cargo-contract will automatically transform the supplied account id to the correct type.