ICE

[o11c]

What I'm trying to do is turn a Box into a *mut c_void. I've hit this with several variants of the following code:

        unsafe
        {
            let fun = Some(pen_lively_callback);
            let data = box LivelyPenData{pen: self.pen, cb: cb};
            let mut id: c_int = 0;
            {
                let raw_data_ptr: *const *const LivelyPenData = std::mem::transmute(&data);
                let raw_data = *raw_data_ptr;
                let raw_data: *mut c_void = std::mem::transmute(raw_data);
                id = c::tickit_pen_bind_event(self.pen, ev, fun, raw_data);
            };
            LivelyPenEvent{id: id, data: data}
        }

error: internal compiler error: unexpected failure
note: the compiler hit an unexpected failure path. this is a bug.
note: we would appreciate a bug report: http://doc.rust-lang.org/complement-bugreport.html
note: run with `RUST_BACKTRACE=1` for a backtrace
task 'rustc' failed at 'index out of bounds: the len is 0 but the index is 0', /build/buildd/rust-nightly-201407010407~90ab2f8~trusty/src/librustc/lib.rs:1

stack backtrace:
   1:     0x7f40f48f9f10 - rt::backtrace::imp::write::h20ea790cd11512b89Hp::v0.11.0.pre
   2:     0x7f40f4900a40 - <unknown>
   3:     0x7f40f50c5330 - unwind::begin_unwind_inner::h6989cca23ac32950cZd::v0.11.0.pre
   4:     0x7f40f50c4de0 - unwind::begin_unwind_fmt::hed325abc04af5cbbFWd::v0.11.0.pre
   5:     0x7f40f50c4da0 - rust_begin_unwind
   6:     0x7f40f5107180 - failure::begin_unwind::h04dff981da03c579xiw::v0.11.0.pre
   7:     0x7f40f5108ea0 - failure::fail_bounds_check::h48f92529758f7c44Jgw::v0.11.0.pre
   8:     0x7f40f57f32d0 - middle::subst::SubstFolder<'a>.TypeFolder::fold_region::ha4c49cfb8c9c0c98wFU::v0.11.0.pre
   9:     0x7f40f57f3250 - <unknown>
  10:     0x7f40f57f2670 - <unknown>
  11:     0x7f40f57f24c0 - <unknown>
  12:     0x7f40f579b8c0 - middle::subst::SubstFolder<'a>.TypeFolder::fold_ty::h4677d2be2ed197995FU::v0.11.0.pre
  13:     0x7f40f579b8c0 - middle::subst::SubstFolder<'a>.TypeFolder::fold_ty::h4677d2be2ed197995FU::v0.11.0.pre
  14:     0x7f40f579b7d0 - <unknown>
  15:     0x7f40f5920d40 - middle::ty::lookup_field_type::hcf295e3c01ace151ugS::v0.11.0.pre
  16:     0x7f40f57da3e0 - middle::ty::struct_fields::h750a5e3c9ba03de9LoS::v0.11.0.pre
  17:     0x7f40f594d5e0 - <unknown>
  18:     0x7f40f58e7d70 - middle::ty::type_contents::h04f981e1d4907a10rvP::v0.11.0.pre
  19:     0x7f40f5caad40 - <unknown>
  20:     0x7f40f5cadba0 - middle::kind::check_crate::h9276be46bc90db1fS0P::v0.11.0.pre
  21:     0x7f40f6093050 - driver::driver::phase_3_run_analysis_passes::h7a1b0f2c50043fdfTdq::v0.11.0.pre
  22:     0x7f40f608e600 - driver::driver::compile_input::h8cab87c201bb9a18R0p::v0.11.0.pre
  23:     0x7f40f615b410 - <unknown>
  24:     0x7f40f615b320 - <unknown>
  25:     0x7f40f6170430 - <unknown>
  26:     0x7f40f6170050 - <unknown>
  27:     0x7f40f821cc90 - <unknown>
  28:     0x7f40f511d4d0 - rust_try
  29:     0x7f40f50c1940 - unwind::try::h31ede991d064db63BNd::v0.11.0.pre
  30:     0x7f40f50c1620 - task::Task::run::h4e89f6317d5d7de3XYc::v0.11.0.pre
  31:     0x7f40f821ca50 - <unknown>
  32:     0x7f40f50c41e0 - <unknown>
  33:     0x7f40f4368000 - start_thread
  34:     0x7f40f4d86039 - __clone
  35:                0x0 - <unknown>

[huonw]

Could you post a reproducing example? (Even if it's not minimal, although that would be nice. :) )

Just substituting best-guess definitions in naively doesn't reproduce the ICE:

extern crate libc;

use libc::{c_void, c_int};

struct LivelyPenData { pen: uint, cb: extern "C" fn() }
struct LivelyPenEvent { id: c_int, data: Box<LivelyPenData> }

extern "C" fn pen_lively_callback() {}
extern "C" fn cb() {}

mod c {
    extern {
        pub fn tickit_pen_bind_event(x: uint, ev: (), fun: Option<extern "C" fn()>, ptr: *mut ::libc::c_void) -> ::libc::c_int;
    }
}

fn main() {
    let ev = ();

        unsafe
        {
            let fun = Some(pen_lively_callback);
            let data = box LivelyPenData{pen: 0, cb: cb};
            let mut id: c_int = 0;
            {
                let raw_data_ptr: *const *const LivelyPenData = std::mem::transmute(&data);
                let raw_data = *raw_data_ptr;
                let raw_data: *mut c_void = std::mem::transmute(raw_data);
                id = c::tickit_pen_bind_event(0, ev, fun, raw_data);
            };
            LivelyPenEvent{id: id, data: data}
        };

}

That compiles (on the playpen) with a pile of warnings and a linkage error, but no ICE.

[o11c]

Looks like the external C functions needing the data pointer was a red herring.

#![crate_type = "dylib"]

struct Boxee<'a> {
    cb: ||: 'a,
}

pub struct Boxer<'a> {
    data: Box<Boxee<'a>>,
}

impl<'a> Drop for Boxer<'a> {
    fn drop(&mut self) {
        println!("dropping boxer");
    }
}

pub fn build_it<'a>(cb: ||: 'a) -> Boxer<'a> {
    let data = box Boxee{cb: cb};
    Boxer{data: data}
}

The ICE appeared once I added the Drop impl, but the fact that I'm taking a lifetime'd closure is also relevant. If I change the closure to 'static, I get an error (regardless of whether I leave the unused 'a lifetime on everything else):

ice.rs:11:15: 11:20 error: cannot implement a destructor on a structure that does not satisfy Send
ice.rs:11 impl Drop for Boxer {
                        ^~~~~
ice.rs:11:15: 11:20 note: use "#[unsafe_destructor]" on the implementation to force the compiler to allow this
ice.rs:11 impl Drop for Boxer {
                        ^~~~~
error: aborting due to previous error

If I replace the closure with an extern fn(), then I get the ICE if the unused lifetime is left in, and I get no error if the unused lifetime is removed.

If I impl Drop for Boxee instead of Boxer, there is no change.

[o11c]

If I follow the error's suggestion and use #[unsafe_destructor], then both my minimal testcase and my real code compile just fine.

[luqmana]

Dupe of #14889.