Segfault when casting owned structs to owned traits (double free?)

[bstrie]

This compiles, but segfaults when run:

pub enum Thing {
    A(~Foo)
}

pub trait Foo {}

pub struct Struct;

impl Foo for Struct {}

fn main() {
    match A(~Struct as ~Foo) {
        A(a) => 0,
    };
}

The segfault goes away when you do the following:

• Convert A(a) => 0 to A(_) => 0
• Change all the unique pointers to managed pointers
• Change the tag from A(~Foo) to A(~Struct) (and remove the cast)

[wilkie]

I've been looking at this one as I originally discovered it. I've been looking in the wrong place though... it is not just sum-types, but any cast of a unique struct to a unique trait. This also segfaults:

pub trait Foo {}

pub struct Struct;

impl Foo for Struct {}

fn func(thing: ~Foo) {}

fn main() {
  let a = ~Struct as ~Foo;
  let b = func(a);
}

It segfaults on a glue_drop function in both examples. I'm not too certain about the invariants of the takes and drops. I'm assuming they are done in mirror. Is it dropping something twice by mistake?

[bstrie]

Good catch, I've updated the title.

[emberian]

This no longer segfaults; needs a testcase.

[emberian]

(well, testcases arleady exist, just need their way into the suite)

[wilkie]

@cmr yay! that's awesome. :) I'll try and pull the fixed code and try it out with my original breaking code later today.

[wilkie]

Awesome. All of the cases I came up with all compile and run as expected. Thanks. :)