DST coercions do not work in slices

[huonw]

fn main() {
    let x: &[uint] = &[1u];
    let _y = &[x, &[1, 2]];
}

<anon>:3:19: 3:26 error: mismatched types: expected `&[uint]`, found `&[uint, .. 2]` (expected vector, found vector)
<anon>:3     let _y = &[x, &[1, 2]];
                           ^~~~~~~

This may not be a bug, but it does mean that slices constructed like this need to have type annotations.

[steveklabnik]

Triage: this is still true. Also not sure if it's a bug. @nikomatsakis ?

[eddyb]

This is because we propagate the expected type downwards but not rightwards (from x to &[1, 2]).
We probably should do this by taking x's type after applying the outer expected type on it (and repeat this for any array element, so they can each add more information for the next one).

[Mark-Simulacrum]

With the code updated, this no longer causes an error. Closing.

fn main() {
    let x: &[u32] = &[1u32];
    let _y = &[x, &[1, 2]];
}