ICE when using an unconstrained typaram in a typaram constraint

[erickt]

(I accidentally submitted this incomplete)

I just just ran across this bug that may actually be #16562, but I had a different stack trace so I wasn't completely positive.

trait Serialize<S> { }

impl<S> Serialize<S> for () { }

struct State<W> {
    writer: W,
}

pub fn to_format_vec<W, T: Serialize<State<W>>>(_value: T) { }

fn main() {
    let _ = to_format_vec(());
}

produces:

baz2.rs:13:13: 13:26 error: cannot determine a type for this bounded type parameter: unconstrained type
baz2.rs:13     let _ = to_format_vec(());
                       ^~~~~~~~~~~~~
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://doc.rust-lang.org/complement-bugreport.html
note: run with `RUST_BACKTRACE=1` for a backtrace
task 'rustc' failed at 't_f should be a trait', /Users/erickt/rust/rust-master/src/librustc/middle/typeck/check/vtable.rs:572

stack backtrace:
   1:        0x107abfdf5 - rt::backtrace::imp::write::he623acc81864f201rGr
   2:        0x107ac2fc3 - failure::on_fail::h8f9f19a91c24052dkXr
   3:        0x107d8d695 - unwind::begin_unwind_inner::h5d3cfad59626c9bcufe
   4:        0x104578108 - unwind::begin_unwind::h12330958406929428788
   5:        0x104adad74 - middle::typeck::check::vtable::search_for_vtable::haef69332461a5688NyM
   6:        0x104ad75aa - middle::typeck::check::vtable::lookup_vtables_for_param::closure.122062
   7:        0x104a9d27d - middle::ty::each_bound_trait_and_supertraits::h1394aaa7b3715888YlJ
   8:        0x104ad65ec - middle::typeck::check::vtable::lookup_vtables_for_param::hda7e4f654a5b55a101L
   9:        0x104ad445b - middle::typeck::check::vtable::lookup_vtables::h215a3cc54c6aa8822VL
  10:        0x104ae3a24 - middle::typeck::check::vtable::early_resolve_expr::closure.122212
  11:        0x104ae3442 - middle::typeck::check::FnCtxt<'a>::opt_node_ty_substs::h322d50051e130cb7twV
  12:        0x104ae1474 - middle::typeck::check::vtable::early_resolve_expr::hc1a86dd775e028b5PUM
  13:        0x104ae6bdb - visit::walk_expr::h2228446824831897429
  14:        0x104ae7d3b - visit::walk_local::h15217184139303618153
  15:        0x104ae848a - middle::typeck::check::vtable::resolve_in_block::h512c693e91bd056eZEN
  16:        0x104b42774 - middle::typeck::check::check_bare_fn::hea96be15969fc08bWBT
  17:        0x104b3badb - middle::typeck::check::check_item::h03dd381d5ee24cf84aU
  18:        0x104b424fd - middle::typeck::check::check_item_types::h66154ed2b2471f75dBT
  19:        0x10456afe6 - util::common::time::h8593819081890839475
  20:        0x104d3faac - middle::typeck::check_crate::h01f2334d92065f26Fel
  21:        0x104e0be60 - driver::driver::phase_3_run_analysis_passes::h875833fb36cd3ebdMPz
  22:        0x104e06e53 - driver::driver::compile_input::h6f91988ab025da07SBz
  23:        0x104eaeb82 - driver::run_compiler::h7fbb31eb141b1300M9C
  24:        0x104ead266 - driver::main_args::closure.137573
  25:        0x104ebf3bb - task::TaskBuilder<S>::try_future::closure.138734
  26:        0x104ebf2c5 - task::TaskBuilder<S>::spawn_internal::closure.138711
  27:        0x1059ae86c - task::spawn_opts::closure.8427
  28:        0x107df45cc - rust_try_inner
  29:        0x107df45b6 - rust_try
  30:        0x107d8aa6b - unwind::try::hb02e6a03665b7aa7K3d
  31:        0x107d8a80b - task::Task::run::hbb7219e7e81ccdc1Bad
  32:        0x1059ae6ca - task::spawn_opts::closure.8372
  33:        0x107d8c626 - thread::thread_start::h41227a904179836dnzd
  34:     0x7fff82db2899 - _pthread_body
  35:     0x7fff82db272a - _pthread_struct_init

cc @nikomatsakis

[ghost]

Closing as a dupe of #16562.