Calling Error messages when cross contract calling in ink

Question

I want to call Error messages from different contract I am calling in ink! using the '?' operator. However it gives me the following Error:

`?` couldn't convert the error to `contract::Error`
  --> lib.rs:77:107
   |
77 |   self.diff_contract.method(value_1, value_2)?;
   |                                   ^ the trait `std::convert::From<diff_contract::diff_contract::Error>` is not implemented for `contract::Error`
   |
   = note: the question mark operation (`?`) implicitly performs a conversion on the error value using the `From` trait
   = note: required because of the requirements on the impl of `std::ops::FromResidual<std::result::Result<std::convert::Infallible, diff_contract::diff_contract::Error>>` for `std::result::Result<[u8; 32], contract::Error>`

I guess I have to declare that I want to use the Error handling of the other contract in my original smart contract? If so, how can I do that?

Answer 1

If you have different errors inside the function's body, you need to define the rules for converting one error into another.

For example, if diff_contract.method(value_1, value_2) returns Resutl<(), DiffError>, and your function returns Result<(), MyCurrentError>, you need to convert DiffError into MyCurrentError.

If you define MyCurrentError, you can implement the From<DiffError> trait, and the Rust will convert your error under the hood. You can check the example here.

But if MyCurrentError is defined by someone else, you can't implement foreign traits for foreign types. In that case, you need manually map one error into another.