Regression in type inference of casting in constants

[jethrogb]

This works in stable, beta and nightly:

let x: *mut () = (0 as *const usize) as *const _ as *mut _;

This only works in stable:

const x: *mut () = (0 as *const usize) as *const _ as *mut _;

But in beta and nightly results in:

<anon>:2:47: 2:55 error: unable to infer enough type information about `_`; type annotations or generic parameter binding required [E0282]
<anon>:2     const x: *mut () = (0 as *const usize) as *const _ as *mut _;

[alexcrichton]

triage: I-nominated

[arielb1]

This compiles with rustc 1.5.0-nightly (168a23ebe 2015-10-01) and 1.3.0, but not 1.4.0 Should we bisect?

[arielb1]

This looks to be fixed by #28131. Should I beta-nominate that?

[alexcrichton]

@arielb1 yeah I'll beta-nominate that, thanks for the investigation!

[alexcrichton]

Also removing I-nominated as this should be dealt with by the beta-nomination

[alexcrichton]

Thanks for the report again @jethrogb! I'm gonna close this in favor of the beta nomination over at #28131 now.