Rustc scoping regression

[Rupsbant]

The following code does not compile with rustc 1.17.0-nightly (c0b7112ba 2017-03-02). Compiles with stable-x86_64-unknown-linux-gnu unchanged - rustc 1.14.0 (e8a012324 2016-12-16). Testing with updated stable release.

fn n(c: u64) -> u64 {
    c
}
pub fn main() {
    let v = vec![1,2,3];
    let mut it = v.iter();
    while let Some(n) = it.next() {
        println!("{}", n);
    }
    assert!(n(1) == 1);
}

[alexcrichton]

cc @jseyfried

[TimNN]

Slightly minified:

fn foo() {}

pub fn main() {
    while let Some(foo) = Some(1) {
        // break; // EDIT: the break is not neccessary
    }
    foo();
}

Introduced between nightly-2017-02-25 and nightly-2017-02-27 (changes).

After skimming the PR's merged during that time I guess this was caused by #39864.

[alexcrichton]

cc @cramertj

[cramertj]

I think the problem is this missing Ribs line (and its corresponding pop). I fixed it locally and am currently testing.

[cramertj]

Confirmed the fix and opened #40242.

[cramertj]

Somewhat interestingly, there was a successful crater run done on that PR. IIUC, that means that @Rupsbant's PR just happens to be the first time anyone has added code like this to a popular crate.

[Rupsbant]

@cramertj This bug originates from petgraph and was committed 5 months ago: petgraph/petgraph@c85e189. It was tested in the crater run and succeeded.