ignore! macro doesn't seem to work

[erickt]

ignore!( foo bar )

fn main() {
}

Errors out with:

test.rs:1:0: 1:6 error: expected item but found `ignore`
test.rs:1 ignore!( foo bar )
          ^~~~~~

[nikomatsakis]

Like any macro, it can only be used in expr position. Dup of #3086.

[graydon]

Yeah. I'd quite like to fix/finish this.