ICE on harmless cast

[aji]

A cast from what should be an Rc<Box<Display>> to an Rc<Box<Display>> causes an ICE.

The following code triggers the bug:

use std::fmt::Display;
use std::rc::Rc;

fn main() {
    let x = Rc::new(Box::new(3) as Box<Display>) as Rc<Box<Display>>;
    println!("{}", x);
}

Removing the last cast fixes any problems, and the code works as expected. Attempts to compile the included version, however, produce the following ICE. I haven't investigated whether a simpler example still causes the error.

error: internal compiler error: translating unsupported cast: alloc::rc::Rc<Box<core::fmt::Display>> (cast_other) -> alloc::rc::Rc<Box<core::fmt::Display>> (cast_other)
note: the compiler unexpectedly panicked. this is a bug.
note: we would appreciate a bug report: https://github.com/rust-lang/rust/blob/master/CONTRIBUTING.md#bug-reports
note: run with `RUST_BACKTRACE=1` for a backtrace
thread 'rustc' panicked at 'Box<Any>', /home/rustbuild/src/rust-buildbot/slave/nightly-dist-rustc-linux/build/src/libsyntax/diagnostic.rs:230

stack backtrace:
   1: 0xb7334c02 - sys::backtrace::write::h77d4324d8f687479hhs
   2: 0xb733e003 - panicking::on_panic::h5991b51df6754021gXw
   3: 0xb72f9931 - rt::unwind::begin_unwind_inner::h0b9bf67a6c91c871qCw
   4: 0xb5a95e8a - rt::unwind::begin_unwind::h4590825210216012210
   5: 0xb5a965c0 - diagnostic::Handler::bug::he1b4d17bbf37c901a2B
   6: 0xb62b8348 - session::Session::bug::h8b813292dd414a3bLOq
   7: 0xb6be4894 - trans::expr::trans_imm_cast::hcf6b081c061414ceJvC
   8: 0xb6bd843d - trans::expr::trans_unadjusted::h101c41dfc231ce49qIA
   9: 0xb6baaff3 - trans::expr::trans_into::h7c16b2d01d4f4517gfA
  10: 0xb6c30307 - trans::_match::mk_binding_alloca::h2886231291812574490
  11: 0xb6b14c20 - trans::base::init_local::h734fdf8e95d40b8aa2g
  12: 0xb6b253d6 - trans::controlflow::trans_block::h78fbb82977d10ae0r9u
  13: 0xb6b23f4e - trans::base::trans_closure::h935c8521a0e70422PIh
  14: 0xb6b25b9f - trans::base::trans_fn::he0f1206d0de4f31fxTh
  15: 0xb6b290b0 - trans::base::trans_item::h5f1e3b5e6e824334Jhi
  16: 0xb6b384bd - trans::base::trans_crate::heff82322305e67c0w6i
  17: 0xb76825d6 - driver::phase_4_translate_to_llvm::h44883988e2377a0fnOa
  18: 0xb76587a9 - driver::compile_input::h99ee9c2483e6eaf5Qba
  19: 0xb77228e7 - run_compiler::hc5bd2bad8247cbab65b
  20: 0xb771fd0e - boxed::F.FnBox<A>::call_box::h4547696616703108986
  21: 0xb771f3a1 - rt::unwind::try::try_fn::h5119335400925169066
  22: 0xb73c1fca - rust_try_inner
  23: 0xb73c1fa3 - rust_try
  24: 0xb771f612 - boxed::F.FnBox<A>::call_box::h12972956424599656712
  25: 0xb733ccf4 - sys::thread::Thread::new::thread_start::hb309cf85ff61e58eMIv
  26: 0xb33991a5 - start_thread
  27: 0xb71a47cd - __clone
  28:        0x0 - <unknown>

theta ~$ rustc --version --verbose
rustc 1.1.0-nightly (435622028 2015-05-04) (built 2015-05-05)
binary: rustc
commit-hash: 435622028f37085819843f4ac8938557501f0468
commit-date: 2015-05-04
build-date: 2015-05-05
host: i686-unknown-linux-gnu
release: 1.1.0-nightly

[arielb1]

Should be fixed by #24333 (when it is merged). Should I add a test?

[JustAPerson]

No longer causes an ICE on 1.2 nightly