assertion failed !ty::type_needs_infer when infering type of closure with a reference argument

[huonw]

fn main() {
    let mut p: proc(&()) = match () {
        _ => proc(_) {}
    };
}

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: !ty::type_needs_infer(ty)', /home/rustbuild/src/rust-buildbot/slave/nightly-linux/build/src/librustc/middle/typeck/mod.rs:251
stack backtrace:
   1:     0x7f5ab0346240 - rt::backtrace::imp::write::h47fe109ac3049adffza::v0.11.pre
   2:     0x7f5ab02975d0 - rt::unwind::begin_unwind_inner::h6061c949133dceeek99::v0.11.pre
   3:     0x7f5ab0297250 - rt::unwind::begin_unwind_fmt::h40112ecebfab41f4u89::v0.11.pre
   4:     0x7f5ab11aa940 - middle::typeck::write_ty_to_tcx::hf3e3ebe0cc028e99JNv::v0.11.pre
   5:     0x7f5ab11a4f50 - middle::typeck::check::writeback::resolve_type_vars_for_node::h05a8139df2037e2dcP2::v0.11.pre
   6:     0x7f5ab11ab890 - middle::typeck::check::writeback::visit_expr::hc3fe28c41c92bb09612::v0.11.pre
   7:     0x7f5ab11ad690 - middle::typeck::check::writeback::visit_local::hd2a7e1d446c15515w72::v0.11.pre
   8:     0x7f5ab11ab590 - middle::typeck::check::writeback::visit_stmt::h5a3eb6a3a123bc2bw12::v0.11.pre
   9:     0x7f5ab11ace40 - visit::walk_block::h774050335718882335::v0.11.pre
  10:     0x7f5ab11b0380 - middle::typeck::check::writeback::resolve_type_vars_in_fn::h14075a7c48abb418Fk3::v0.11.pre
  11:     0x7f5ab12035a0 - middle::typeck::check::check_bare_fn::h276d49bccf79d6cbib8::v0.11.pre
  12:     0x7f5ab11fb3e0 - middle::typeck::check::check_item::hf4303c618e67640ejI8::v0.11.pre
  13:     0x7f5ab12033a0 - middle::typeck::check::check_item_types::h3a12f8481de3c645Aa8::v0.11.pre
  14:     0x7f5ab134fe70 - util::common::time::h14771813586294062655::v0.11.pre
  15:     0x7f5ab134ebd0 - middle::typeck::check_crate::ha64d37049d8764a6L7v::v0.11.pre
  16:     0x7f5ab177a1d0 - driver::driver::phase_3_run_analysis_passes::hfcc0f62a0837a3f1ZDh::v0.11.pre
  17:     0x7f5ab177fa80 - driver::driver::compile_input::h109dae099456ee6aO3h::v0.11.pre
  18:     0x7f5ab17a4da0 - run_compiler::h05fa0a47a6b6f28bzwp::v0.11.pre
  19:     0x7f5ab17c13d0 - main_args::closure.93793
  20:     0x7f5ab17bf8d0 - monitor::closure.93668
  21:     0x7f5ab17ba090 - task::TaskBuilder::try::closure.93434
  22:     0x7f5ab09e10b0 - task::spawn_opts::closure.7161
  23:     0x7f5ab033bc70 - rt::task::Task::run::closure.40355
  24:     0x7f5ab034c5b0 - rust_try
  25:     0x7f5ab033bab0 - rt::task::Task::run::hf886fab2982b08c7nZ7::v0.11.pre
  26:     0x7f5ab09e0e80 - task::spawn_opts::closure.7134
  27:     0x7f5ab0344d80 - rt::thread::thread_start::h7d20e7f4bce06592AE8::v0.11.pre
  28:     0x7f5aae020fa0 - start_thread
  29:     0x7f5aaff6ba09 - __clone
  30:                0x0 - <unknown>

See #14037 for a similar scenario with let (this one also works when changing the argument type to something without a reference).

cc @nikomatsakis @pnkfelix

[kmcallister]

In Rust master this would be something like

#![feature(default_type_params)]

use std::thunk::Thunk;

fn main() {
    let mut p: Thunk<&()> = match () {
        _ => Thunk::with_arg(move |_| {})
    };
}

which compiles without error.

[steveklabnik]

Yes, with proc gone, this seems resolved.