output

✗ RUST_BACKTRACE=1 ./test
failed at 'called `Option::get_mut_ref()` on a `None` value', /home/rustbuild/src/rust-buildbot/slave/nightly-linux/build/src/libcore/option.rs:469
stack backtrace:
   1:           0x47bd80 - rt::backtrace::imp::write::h6bc482a91e850a6bWrx::v0.11.0.pre
   2:           0x45f830 - rt::unwind::begin_unwind_inner::h0c987df59e660255X1w::v0.11.0.pre
   3:           0x45eb60 - rt::unwind::begin_unwind_fmt::hab4ea20b6306f10470w::v0.11.0.pre
   4:           0x47bc90 - rust_begin_unwind
   5:           0x4bfc80 - failure::begin_unwind::h274c645ee0d8103btZv::v0.11.0.pre
   6:           0x472030 - rt::rtio::LocalIo<'a>::borrow::h842cb4f2d84fdb8b5bv::v0.11.0.pre
   7:           0x4723d0 - io::stdio::src::h11364002286917177819::v0.11.0.pre
   8:           0x4729a0 - io::stdio::with_task_stdout::hb01b740306898b1eALp::v0.11.0.pre
   9:           0x4764a0 - io::stdio::println_args::h924873875200ca8aRQp::v0.11.0.pre
  10:           0x407420 - testing::h2e53314e7edb7f5eoga::v0.0
  11:           0x407360 - main::closure.2145
  12:           0x4772d0 - rt::task::Task::run::closure.25247
  13:           0x4855a0 - rust_try
  14:           0x477220 - rt::task::Task::run::hda8101fd3672740eAQu::v0.11.0.pre
  15:           0x404f60 - main::h61e0dc92ec131703Tea::v0.0
  16:           0x45ea10 - start::closure.7884
  17:           0x4772d0 - rt::task::Task::run::closure.25247
  18:           0x4855a0 - rust_try
  19:           0x477220 - rt::task::Task::run::hda8101fd3672740eAQu::v0.11.0.pre
  20:           0x45e650 - start::h3ff5ebe13c0e357eqqe::v0.11.0.pre
  21:           0x45e5c0 - lang_start::h8e81b66aa034d05bKpe::v0.11.0.pre
  22:           0x405600 - main
  23:     0x7fd662087cf0 - __libc_start_main
  24:           0x402fbd - <unknown>
  25:                0x0 - <unknown>
[1]    51012 illegal hardware instruction  RUST_BACKTRACE=1 ./test

test.rs

extern crate debug;

use std::mem::transmute;
use std::rt::task::Task;
use std::rt::local::Local;
use std::any::Any;

struct RawUnwinder {
    unwinding: bool,
    cause: Option<Box<Any:Send>>
}

#[deriving(Show)]
struct Inner {
    text: String
}

#[deriving(Show)]
struct Args<'a> {
    fail: bool,
    first: String,
    second: Vec<&'static str>,
    reference: Option<&'a Inner>
}

fn main() {
    let inner = Inner { text: "Heyo".to_str() };
    let mut args = Some(box Args { fail: false, first: "hello".to_str(), second: vec!("world", "and", "stuff"), reference: Some(&inner) });
    let mut fail = Some(box Args { fail: true, first: "hello".to_str(), second: vec!(), reference: None });

    (box Task::new()).run(|| testing(args.take_unwrap()));
    (box Task::new()).run(|| testing(fail.take_unwrap()));

    //local_unwinder_try(|| testing(args.take_unwrap()));
    //local_unwinder_try(|| testing(fail.take_unwrap())).map_err(|e| println!("{}", e));
}

fn testing(args: &Args) {
    if args.fail { fail!("YOLO BROLO"); }

    println!("{}", args);
}

fn local_task_handle() -> *mut Task {
    let task: Box<Task> = Local::take();
    let handle: *mut Task = unsafe { *transmute::<&Box<Task>, &*mut Task>(&task) };
    Local::put(task);
    handle
}

fn unwinder_for_handle(handle: *mut Task) -> &mut std::rt::unwind::Unwinder {
    unsafe { &mut ((*handle).unwinder) }
}

fn local_unwinder_try(closure: ||) -> Result<(), String> {
    let handle = local_task_handle();
    let unwinder = unwinder_for_handle(handle);

    unwinder.try(closure);

    match unwinder_result(unwinder) {
        Some(string) => Err(string),
        None => Ok(())
    }
}

fn unwinder_result(unwinder: &mut std::rt::unwind::Unwinder) -> Option<String> {
    let raw: &RawUnwinder = unsafe { transmute(unwinder) };

    raw.cause.as_ref().map(|err| cause_str(err))
}

fn cause_str(reason: &Box<Any:Send>) -> String {
    use std::any::AnyRefExt;

    match reason.as_ref::<&'static str>() {
        Some(s) => *s,
        None => match reason.as_ref::<String>() {
             Some(s) => s.as_slice(),
             None => "Box<Any>",
        }
    }.to_str()
}