Segfault when calling a method on an owned box cast to a trait and passed to another task

[mzabaluev]

This program compiles successfully, but segfaults:

trait A {
    fn f(&self);
}

struct B;

impl A for B {
    fn f(&self) {
    }
}

fn main() {
    let a = ~B as ~A;
    do spawn {
        a.f();
    }
}

The crash occurs in a generated thunk opaque to gdb:

#0  0x080494cb in glue_drop_2597 ()
#1  0x08048bc4 in main () at unsafe-owned.rs:15
#2  0x08048c10 in _rust_main () at unsafe-owned.rs:15
#3  0xb7495d01 in task_start_wrapper (a=0x9c4663c)
    at /home/mzabaluev/src/rust/src/rt/rust_task.cpp:162

[alexcrichton]

Nominating for production-ready.

This code today actually produces an LLVM assertion as well:

Assertion failed: (Ty && "Invalid GetElementPtrInst indices for type!"), function checkGEPType, file /Users/alex/code/rust-opt/src/llvm/include/llvm/IR/Instructions.h, line 704.
zsh: abort      rust run foo.rs

[huonw]

This fails with the same error with 63417da (but I don't think it fails with 803c12d):

trait A {}
fn main() {
  let a: ~[~A] = ~[];
}

[Aatch]

This is actually more general, with the assertion happening on pretty much any instance of an owned trait object.

I would suggest this be feature-complete, since trait objects are a feature, and clearly this is not complete.