rustc stackoverflow

[yshui]

Offending program: http://is.gd/uNH2bk

[bluss]

Reduced testcase (only cleanup, not really significant)

use std::cell::{Cell, RefCell};
struct A<T: Fn()> {
    x: RefCell<Option<T>>,
    b: Cell<i32>,
}

fn main() {
    let mut p = A{x: RefCell::new(None), b: Cell::new(4i32)};
    let q = || p.b.set(5i32);
    *(p.x.borrow_mut()) = Some(q);
}

[mitaa]

Further reduced:

struct B<F: Fn()> (F);

fn main() {
    let mut p = B(std::mem::zeroed());
    p.0 = ||{p.0;} ;
}

[bluss]

😊 nice

[bluss]

The recursion is inside check::regionck::type_must_outlive

[nikomatsakis]

I'm curious what is the origin of this example?

[nikomatsakis]

So the core problem is that closure types can contain themselves. In PR #27087, I changed how closures are desugared, preventing cyclic closures and thus sidestepping this problem.