error: internal compiler error: unexpected panic

[withkittens]

error: internal compiler error: unexpected panic
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 'called `Option::unwrap()` on a `None` value', ../src/libcore\option.rs:362

I tried this code:

#![feature(iter_arith)]

fn main() {
    println!("avg1 = {}", avg::<isize>( (1..11) ));
    println!("avg1 = {}", avg::<isize>( (1..11).filter(|&x| x % 2 == 0) ));
}

fn avg<S, T=T::Item>(x: T) -> f64
    where T: IntoIterator<Item=isize> {

    let it = x.into_iter();
    match it.size_hint() {
        (lower, Some(upper)) if lower == upper => {
            println!("exact len");
            it.sum::<S>() as f64 / lower as f64
        }
        _ => {
            let mut sum = 0;
            let mut count = 0;

            for i in it {
                sum = sum + i;
                count += 1;
            }

            sum as f64 / count as f64
        }
    }
}

I expected to see this happen: code should compile or the compiler should report an error.

Instead, this happened: the compiler panicked.

Meta

rustc --version --verbose:

rustc 1.3.0-nightly (cb7d06215 2015-06-26)
binary: rustc
commit-hash: cb7d0621556fabcdcc36d0da279305ad285ec662
commit-date: 2015-06-26
host: x86_64-pc-windows-gnu
release: 1.3.0-nightly

Backtrace:

   1:         0x61df90f5 - sys::backtrace::write::h025f886ce4157216LAs
   2:         0x61e0289c - rt::unwind::register::h5ad63c24fb31bf08qfw
   3:         0x61dc561f - rt::unwind::begin_unwind_inner::hfc1332db90d09e50zcw
   4:         0x61dc5f9a - rt::unwind::begin_unwind_fmt::ha3ff9e0dc1fa5705Fbw
   5:         0x61e022b3 - rust_begin_unwind
   6:         0x61e1ead9 - panicking::panic_fmt::h9bd2cfb05a12923fH8B
   7:         0x61e19121 - panicking::panic::hacb4eddea015f0f3e7B
   8:         0x62ded9de - middle::ty::ctxt<'tcx>::type_parameter_def::hda01cc044215acd1rU6
   9:           0xc32659 - check::TupleArgumentsFlag...std..clone..Clone::clone::h1be2a27edcea5bafSDq
  10:           0xbf2459 - check::FnCtxt<'a, 'tcx>::require_type_meets::h64f5de27ee30a606zjp
  11:           0xc714a9 - collect::ast..Generics.GetTypeParameterBounds<'tcx>::get_type_parameter_bounds::h08e9b997e941d802Oxx
  12:           0xc6e276 - collect::ast..Generics.GetTypeParameterBounds<'tcx>::get_type_parameter_bounds::h08e9b997e941d802Oxx
  13:           0xc6519d - collect::ast..Generics.GetTypeParameterBounds<'tcx>::get_type_parameter_bounds::h08e9b997e941d802Oxx
  14:           0xc4d100 - collect::AstConvRequest...std..clone..Clone::clone::hcbd1e5932dbd5c05o7w
  15:           0xc4a0a7 - collect::collect_item_types::h832ec93e81779425R0w
  16:           0xc98b72 - check_crate::hc0757b7883cfbf0b08C
  17:         0x71068b49 - driver::assign_node_ids_and_map::h19857398bfcdab684Da
  18:         0x71066f94 - driver::assign_node_ids_and_map::h19857398bfcdab684Da
  19:         0x71061489 - driver::assign_node_ids_and_map::h19857398bfcdab684Da
  20:         0x71042a66 - driver::compile_input::h4f87ae57d3ecc9bdTba
  21:         0x7112483d - run_compiler::h2ed758d21912ca6fx7b
  22:         0x711224c5 - run::h53e8d74dd390297dd7b
  23:         0x71121e09 - run::h53e8d74dd390297dd7b
  24:         0x61e3d54c - rust_try
  25:         0x61e3d529 - rust_try
  26:         0x61ded4c5 - rt::unwind::try::inner_try::hbdd1fe1d49ddad43s8v
  27:         0x71121fc7 - run::h53e8d74dd390297dd7b
  28:         0x61e003f4 - sys::process::Command::cwd::h4194821e987e71efwUu
  29:     0x7ffa49102ef2 - BaseThreadInitThunk

[mitaa]

Reduced test case:

fn avg<T=T::Item>(_: T) {}