Error type of FunctionMiddleware::feed is private

[webmaster128]

Describe the bug

The error type of the FunctionMiddleware::feed is BinaryReaderError:

use wasmparser::{BinaryReader, Operator, Result as WpResult, Type};

// …

/// A function middleware specialized for a single function.
pub trait FunctionMiddleware: Debug {
    /// Processes the given operator.
    fn feed<'a>(
        &mut self,
        operator: Operator<'a>,
        state: &mut MiddlewareReaderState<'a>,
    ) -> WpResult<()> {
        state.push_operator(operator);
        Ok(())
    }
}

and

pub type Result<T, E = BinaryReaderError> = result::Result<T, E>;

However, BinaryReaderError is a type in the wasmparser crate with no public constructor. So if I understand correctly, a user of Wasmer cannot implement a FunctionMiddleware that errors.

Steps to reproduce

–

Expected behavior

The error type is either constructible or can be defined by the user (as in Wasmer 0.17).

Actual behavior

The error type is fixed to wasmparser::BinaryReaderError, which is not constructible.

Additional context

I'm trying rewrite a the Deterministic middleware, orginally created here: https://github.com/spacemeshos/svm/blob/5df80288c8b9a5ab3665297251c283cb614ebb81/crates/svm-compiler/src/middleware/validation.rs.

[syrusakbary]

We should improve that, so middlewares can report errors!

Would you like to work on a PR for it @webmaster128 ?

[webmaster128]

I'm happy to help where I can. However, in this case I'm a bit clueless what a desired API would look like. I tried the associated error type from Wasmer 0.17, but this leads to all kind of new generic in the code that uses the middleware. So if I don't a brilliant idea magically, it would be cool if someone from the team could look into it.

[webmaster128]

Okay, I got some ideas now that I realized everthing is converted to WasmError at the end of the day.