Associated Types Regression

[dylanmckay]

When implementing a trait with more than one associated type, the compiler complains:

note: the trait `Device` must be implemented because it is required by `Device`

This problem is fairly recent; the code used to compile several weeks ago on Rust master.

The problem does not occur when the trait Device has only one associated type. Note that the error occurs on the same line as the trait implementation.

Also on the Playpen

#![feature(associated_types)]

// using one associated type compiles fine
// using two causes an error

// a trait using associated types
pub trait Device
{
    type Program;

    // error: ###comment this next line out ###
    type Viewport;
}

// a struct which implemented the trait
pub struct TestDevice(u32);

impl Device for TestDevice
{
    type Program = u32;

    // error: ###comment this next line out ###
    type Viewport = i64;
}

fn main() { }

This issue is linked with #19058, which is caused by the same snippet of code.

[huonw]

Closing as a dupe of #19058. Entirely my fault, I was not clear at all on IRC: I was suggesting filing another bug about this version (i.e. only commenting out one use of Viewport) but didn't describe things well, in any case that ICE is covered by #17359.

Thanks!