ICE for closure / proc confusion

[wackywendell]

Here is a minimal program:

fn main() {
    let nums = range(0,20);
    let tasks = nums.map(proc(n) {n * 2});
}

The map function takes a closure, not a proc, but attempting to compile this results in an internal compiler error instead of a nice error message:

% rustc fail-minimal.rs                                                                                   :(
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://static.rust-lang.org/doc/master/complement-bugreport.html
note: run with `RUST_BACKTRACE=1` for a backtrace
task 'rustc' failed at 'assertion failed: `(left == right) && (right == left)` (left: `many`, right: `once`)', /build/rust-git/src/rust/src/librustc/util/ppaux.rs:288
stack backtrace:
   1:     0x7f097a174840 - rt::backtrace::imp::write::h225c71396cf30389qRa::v0.11.pre
   2:     0x7f097a0d6080 - rt::unwind::begin_unwind_inner::hf394975089b9a10eTra::v0.11.pre
   3:     0x7f097a0d5d00 - rt::unwind::begin_unwind_fmt::h22fcbc95e0e545013qa::v0.11.pre
   4:     0x7f097adbfdc0 - util::ppaux::ty_to_str::hb592748f8815eef7Kqh::v0.11.pre
   5:     0x7f097b034bf0 - middle::typeck::infer::InferCtxt$LT$$x27a$GT$::type_error_message::hffb9b35c27d4e338a3o::v0.11.pre
   6:     0x7f097b034dd0 - middle::typeck::infer::InferCtxt$LT$$x27a$GT$::report_mismatched_types::h45758484dd0f6fe8h4o::v0.11.pre
   7:     0x7f097affc5f0 - middle::typeck::check::demand::coerce::hd054c5403efa6f47b64::v0.11.pre
   8:     0x7f097b03ede0 - <unknown>
   9:     0x7f097b035740 - <unknown>
  10:     0x7f097b03f500 - <unknown>
  11:     0x7f097b03f0d0 - <unknown>
  12:     0x7f097b035740 - <unknown>
  13:     0x7f097b051820 - middle::typeck::check::check_decl_local::h81452c953e041c17Zzb::v0.11.pre
  14:     0x7f097b051aa0 - middle::typeck::check::check_stmt::h65a68c6329bac3deVBb::v0.11.pre
  15:     0x7f097b018040 - middle::typeck::check::check_block_with_expected::hf05f59868eb31121SFb::v0.11.pre
  16:     0x7f097b013730 - <unknown>
  17:     0x7f097b0134d0 - <unknown>
  18:     0x7f097b00e830 - middle::typeck::check::check_item::h7712d586a1e77a108w7::v0.11.pre
  19:     0x7f097b0133b0 - middle::typeck::check::check_item_types::hb0c38d033c99a851Ae7::v0.11.pre
  20:     0x7f097b153720 - <unknown>
  21:     0x7f097b152100 - middle::typeck::check_crate::h518ccce325ef460746t::v0.11.pre
  22:     0x7f097b591aa0 - driver::driver::phase_3_run_analysis_passes::h23bc51a4fd4272a46qe::v0.11.pre
  23:     0x7f097b5984b0 - driver::driver::compile_input::heeaf2ac59f6fbbc71Pe::v0.11.pre
  24:     0x7f097b5bc9a0 - run_compiler::h81631b1befd18d82lom::v0.11.pre
  25:     0x7f097b5d40a0 - <unknown>
  26:     0x7f097b5d29d0 - <unknown>
  27:     0x7f097b5ce2b0 - <unknown>
  28:     0x7f097a803b00 - <unknown>
  29:     0x7f097a16f870 - <unknown>
  30:     0x7f097a17b430 - rust_try
  31:     0x7f097a16f6b0 - rt::task::Task::run::h19b19c7dd158dbfefi8::v0.11.pre
  32:     0x7f097a8038d0 - <unknown>
  33:     0x7f097a173380 - <unknown>
  34:     0x7f09779abfe0 - start_thread
  35:     0x7f0979daace9 - clone
  36:                0x0 - <unknown>

This looks superficially similar to #8516 and #9400, but AFAICT they aren't the same.