compiler unexpectedly panicked

[dls]

I tried this code:

fn main() {
    let fib = {
        struct Recurrence {
            mem: [u64; 2],
            pos: usize,
        }

        impl Iterator for Recurrence {
            #[inline]
            fn next(&mut self) -> Option<u64> {
                if self.pos < 2 {
                    let next_val = self.mem[self.pos];
                    self.pos += 1;
                    Some(next_val)
                } else {
                    let next_val = (self.mem[0] + self.mem[1]);
                    self.mem[0] = self.mem[1];
                    self.mem[1] = next_val;
                    Some(next_val)
                }
            }
        }

        Recurrence { mem: [0, 1], pos: 0 }
    };

    for e in fib.take(10) {
        println!("{}", e)
    }
}

I expected to see this happen:

0
1
1
2
3
5
8
13
21
34

Instead, this happened:

$ RUST_BACKTRACE=1 cargo run
   Compiling hello_world v0.0.1 (file:///Users/dls/ac4/hello_world)
src/main.rs:27:5: 30:2 error: internal compiler error: cat_expr Errd
src/main.rs:27     for e in fib.take(10) {
src/main.rs:28         println!("{}", e)
src/main.rs:29     }
src/main.rs:30 }
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>', /Users/rustbuild/src/rust-buildbot/slave/nightly-dist-rustc-mac/build/src/libsyntax/diagnostic.rs:130

Meta

rustc 1.0.0-nightly (123a754 2015-03-24) (built 2015-03-25)
binary: rustc
commit-hash: 123a754
commit-date: 2015-03-24
build-date: 2015-03-25
host: x86_64-apple-darwin
release: 1.0.0-nightly

Backtrace:

stack backtrace:
   1:        0x108671ea4 - sys::backtrace::write::h78053bbfb550960cgjD
   2:        0x10869d358 - panicking::on_panic::hc4e82bbd2a46726dR8I
   3:        0x1085ba76e - rt::unwind::begin_unwind_inner::h5e8e19c0097ac0cdBRI
   4:        0x107dcbcbe - rt::unwind::begin_unwind::h8176364159252686369
   5:        0x107dcbc6b - diagnostic::SpanHandler::span_bug::hdcd6dc2adc048426AaB
   6:        0x1055bdcec - session::Session::span_bug::hd2e8d90e6e32fe5bTHn
   7:        0x104d624db - check::regionck::visit_expr::h67ec4d109373a14f2Dd
   8:        0x104d69e7a - visit::walk_expr::h4641389526047920594
   9:        0x104d61353 - check::regionck::visit_expr::h67ec4d109373a14f2Dd
  10:        0x104d610c1 - check::regionck::visit_expr::h67ec4d109373a14f2Dd
  11:        0x104d69ecb - visit::walk_expr::h4641389526047920594
  12:        0x104d61353 - check::regionck::visit_expr::h67ec4d109373a14f2Dd
  13:        0x104d62e41 - check::regionck::visit_local::hd93c3707d09d90fd7Ad
  14:        0x104d69f5c - visit::walk_expr::h4641389526047920594
  15:        0x104d61783 - check::regionck::visit_expr::h67ec4d109373a14f2Dd
  16:        0x104d5d3c5 - check::regionck::Rcx<'a, 'tcx>::visit_fn_body::h91b65695e5e98981fgd
  17:        0x104dee2da - check::check_bare_fn::h4d8e30b5b0012b734jn
  18:        0x104de6184 - check::check_item::h4b4a2b730b65c17cMCn
  19:        0x104ebd782 - check_crate::closure.35881
  20:        0x104eb83da - check_crate::h4e5a2f60ebec7dccblC
  21:        0x104bf9417 - driver::phase_3_run_analysis_passes::h00707ed732905e83rGa
  22:        0x104bdf816 - driver::compile_input::h22976530edbb8120Rba
  23:        0x104c99313 - run_compiler::h6f6a07f7c4e7d147s2b
  24:        0x104c96ea5 - thunk::F.Invoke<A, R>::invoke::h5399241532089372082
  25:        0x104c96267 - rt::unwind::try::try_fn::h14095088624371570858
  26:        0x108723468 - rust_try_inner
  27:        0x108723455 - rust_try
  28:        0x104c96605 - thunk::F.Invoke<A, R>::invoke::h14770910994046267349
  29:        0x10868825d - sys::thread::create::thread_start::h3a4e0027cd5d22bdqPH
  30:     0x7fff902a9267 - _pthread_body
  31:     0x7fff902a91e4 - _pthread_start

[dls]

if you add:

            type Item = u64;

To the iterator declaration the compiler no longer panics.

        impl Iterator for Recurrence {
            type Item = u64;

            #[inline]
            fn next(&mut self) -> Option<u64> {
                if self.pos < 2 {
                    let next_val = self.mem[self.pos];
                    self.pos += 1;
                    Some(next_val)
                } else {
                    let next_val = (self.mem[0] + self.mem[1]);
                    self.mem[0] = self.mem[1];
                    self.mem[1] = next_val;
                    Some(next_val)
                }
            }
        }