Associated type not found for type parameter when using `where` keyword

[aldanor]

This compiles fine (Decoder is serialize::Decoder trait):

fn read_field<D: Decoder, T>(d: &mut D, field: &str) -> Result<T, D::Error> 
where T: Decodable

while this doesn't:

fn read_field<D, T>(d: &mut D, field: &str) -> Result<T, D::Error> 
where D: Decoder, T: Decodable

yielding the following error:

src/main.rs:149:58: 149:66 error: associated type `Error` not found for type parameter `D` [E0220]
src/main.rs:149 fn read_field<D, T>(d: &mut D, field: &str) -> Result<T, D::Error>

[edwardw]

Right now one has to write:

fn read_field<D, T>(d: &mut D, field: &str) -> Result<T, <D as Decoder>::Error> 
where D: Decoder, T: Decodable

It is a known issue being actively worked on. See #20300. So this issue probably could be closed.

[apasel422]

This is fixed. I don't know if we need to add a run-pass test for it, but:

trait Decoder {
    type Error;
}

trait Decodable {}

fn read_field<D, T>(d: &mut D, field: &str) -> Result<T, D::Error> where
    D: Decoder,
    T: Decodable,
{
    unimplemented!()
}

fn main() {}