ICE when using `typeof`

[jFransham]

Obviously typeof isn't used in the current version of Rust, but if you do try to use it you get some strange behaviour. rustc correctly reports that typeof is unimplemented, and the error message is sensible if used with a constant expression, but using it with local variables causes an ICE.

Minimum code sample:

fn main() {
    let thing = ();
    let other: typeof(thing) = thing;
}

I'd expect this to return the same error as doing typeof(5), which is:

rustc 1.17.0 (56124baa9 2017-04-24)
error[E0516]: `typeof` is a reserved keyword but unimplemented
 --> <anon>:3:16
  |
3 |     let other: typeof(5) = thing;
  |                ^^^^^^^^^ reserved keyword

error: aborting due to previous error

But instead I get this:

rustc 1.17.0 (56124baa9 2017-04-24)
error[E0516]: `typeof` is a reserved keyword but unimplemented
 --> <anon>:3:16
  |
3 |     let other: typeof(thing) = thing;
  |                ^^^^^^^^^^^^^ reserved keyword

error: internal compiler error: /checkout/src/librustc_typeck/check/mod.rs:1527: no type for local variable local thing (id=8)
 --> <anon>:3:23
  |
3 |     let other: typeof(thing) = thing;
  |                       ^^^^^

note: the compiler unexpectedly panicked. this is a bug.

note: we would appreciate a bug report: https://github.com/rust-lang/rust/blob/master/CONTRIBUTING.md#bug-reports

thread 'rustc' panicked at 'Box<Any>', /checkout/src/librustc_errors/lib.rs:377
note: Run with `RUST_BACKTRACE=1` for a backtrace.

[eddyb]

cc @nikomatsakis I think we'll have to make typeof work like closures if we want it to have access to variables in scope. Either that or we could ban this example in rustc_resolve.

[nikomatsakis]

@eddyb I don't quite know what you mean by "work like closures"? Work like closures in which respect?

[eddyb]

In terms of sharing inference, which would fix this ICE.

[nikomatsakis]

@eddyb I see. That seems ok. I thought you meant upvar inference or something.

[nikomatsakis]

triage: P-medium

[vi]

Another ICE case: fn f(){let q=1;<typeof(q)>::N}