Drop flags on the stack not reinitialized in loops

[alexcrichton]

It looks like that when a local variable is initialized in a loop and dropped in the same loop, the stack local drop flag for that local isn't reinitialized to "not dropped" when the loop runs after the first time.

Concretely, this test passes on stable and fails on nightly right now:

struct A<'a>(&'a mut i32);

impl<'a> Drop for A<'a> {
    fn drop(&mut self) {
        *self.0 += 1;
    }
}

fn main() {
    let mut cnt = 0;
    for i in 0..2 {
        let a = A(&mut cnt);
        if i == 1 {
            break
        }
        drop(a);
    }
    assert_eq!(cnt, 2);
}

cc @pnkfelix

[pnkfelix]

Interestingly this slight variation on the above code does drop twice as expected:

playpen

struct A<'a>(&'a mut i32);

impl<'a> Drop for A<'a> {
    fn drop(&mut self) {
        *self.0 += 1;
    }
}

fn main() {
    let mut cnt = 0;
    for i in 0..2 {
        let a; a = A(&mut cnt); // This was `let a = A(&mut cnt);` before
        if i == 1 {
            break
        }
        drop(a);
    }
    assert_eq!(cnt, 2);
}