assertion failed: !borrow_list.is_empty()

[metajack]

@kmcallister found this bug in some Servo code.

The following code compiles but triggers an internal assertion and crashes:

struct Foo {
  bar: @mut Bar,
}

struct Bar {
  x: int,
}

fn main() {
  let foo1 = @mut Foo { bar: @mut Bar { x: 1 } };
  let foo2 = @mut Foo { bar: @mut Bar { x: 2 } };
  let foos = ~[foo1, foo2];

  for &@Foo { bar: ref bar } in foos.iter() {
  }
}

If you remove the ref in the pattern match, the code works.

[metajack]

nominating production ready

[kmcallister]

It's worth noting that the symptom in Servo was not an assertion but rather memory corruption and an eventual segfault.

[catamorphism]

Accepted for production-ready

[nikomatsakis]

cc me

[pnkfelix]

P-low, not a 1.0 blocker.

[alexcrichton]

I can't reproduce this now, and it likely had to do with the interaction of @mut and @ patterns, both of which have been removed. Closing due to being unable to reproduce.