casting in a static breaks type inference

[porglezomp]

Writing the following works perfectly:

static count : uint = 2;
fn main() {
    let larger : [uint, ..count*2];
}

While the following:

static count : uint = 2 as uint;
fn main() {
    let larger : [uint, ..count*2];
}

Fails with error: expected constant expr for vector length: can't do this op on a uint and int. This looks like a problem with the type inference, and using 2u fixes this example, but breaks the one that previously worked.
When the array is being initialized rather than having the type set:

let larger = [0u, ..count*2];

The error is a much more cryptic error: expected constant integer for repeat count, found variable, and which one fails can again be swapped by multiplying by 2u instead of 2.

[mahkoh]

See rust-lang/rfcs#259

[arielb1]

This works on 1.1+:

const count : usize = 2 as usize;
fn main() {
    let larger : [usize; count*2];
}

[frewsxcv]

Regression test added in #26668