Trying to iterate over `&mut Iterator` using a for loop, results in lifetime error

[japaric]

STR

fn test(it: &mut Iterator<Item=()>) {
    for _ in it {}
}

fn main() {}

Output

for.rs:2:14: 2:16 error: cannot infer an appropriate lifetime for lifetime parameter `'a` due to conflicting requirements
for.rs:2     for _ in it {}
                      ^~
for.rs:2:14: 2:16 error: cannot infer an appropriate lifetime for lifetime parameter `'a` due to conflicting requirements
for.rs:2     for _ in it {}
                      ^~
for.rs:2:14: 2:16 error: cannot infer an appropriate lifetime for lifetime parameter `'a` due to conflicting requirements
for.rs:2     for _ in it {}
                      ^~
for.rs:1:1: 3:2 help: consider using an explicit lifetime parameter as shown: fn test<'a>(it: &'a mut Iterator<Item = ()>)
for.rs:1 fn test(it: &mut Iterator<Item=()>) {
for.rs:2     for _ in it {}
for.rs:3 }
error: aborting due to 3 previous errors

Version

rustc 1.0.0-nightly (458a6a2f6 2015-01-25 21:20:37 +0000)

cc @nikomatsakis

[japaric]

This compiles with the new for loops (#20790).

[bluss]

Isn't it the same with non-trait &mut T iterators? I'd use for elt in *it.

[japaric]

@bluss for _ in it when it: &mut Iterator results in an ICE (see #21379). Also this should just work, because &mut Iterator implements the Iterator trait.