ICE during coherence check when impl'ing on the same type twice: "Asked to compute kind of a type variable"

[bstrie]

fn main() {}

trait MyAdd<RHS,Result> {
    pure fn add(&self, rhs: &RHS) -> Result;
}

impl<T: Copy> ~[T] : MyAdd<&[T],~[T]> {
    pure fn add(&self, rhs: & &self/[T]) -> ~[T] {}
}

impl<T: Copy> ~[T] : MyAdd<&[T],~[T]> {
    pure fn add(&self, rhs: & &self/[T]) -> ~[T] {}
}

$ rustc vectest.rs 
error: internal compiler error: Asked to compute kind of a type variable

[Aatch]

This still happens with updated syntax:

fn main() {}

trait MyAdd<RHS,Result> {
    fn add(&self, rhs: &RHS) -> Result;
}

impl<'self, T: Copy> MyAdd<&'self [T],~[T]> for ~[T] {
    fn add(&self, rhs: & &'self [T]) -> ~[T] {}
}

impl<'self, T: Copy> MyAdd<&'self [T],~[T]> for ~[T] {
    fn add(&self, rhs: & &'self [T]) -> ~[T] {}
}

Though I'm not sure if it should stay on 0.7. This is presumably still an error, right?

[bstrie]

Updated once more, this no longer causes an ICE:

fn main() {}

trait MyAdd<RHS,Result> {
    fn add(&self, rhs: &RHS) -> Result;
}

impl<'self, T: Copy> MyAdd<&'self [T],~[T]> for ~[T] {
    fn add(&self, rhs: & &'self [T]) -> ~[T] { rhs.to_owned() }
}

impl<'self, T: Copy> MyAdd<&'self [T],~[T]> for ~[T] {
    fn add(&self, rhs: & &'self [T]) -> ~[T] { rhs.to_owned() }
}

In fact it compiles and runs fine. Closing this bug, and I'll open another one for the fact that you can impl twice on the same type.

[bstrie]

Opened #7555 for the double-impl issue.