casting in a static breaks type inference

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.

1. See https://github.com/rust-lang/rfcs/pull/259

   mahkoh at 2014-10-04 00:00:41

2. This works on 1.1+:

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

   Ariel Ben-Yehuda at 2015-06-29 17:10:58

3. Regression test added in #26668

   Corey Farwell at 2015-06-30 00:12:13