Unboxed closure ICE due to conflicting use of self param space

[bkoropoff]

Found while debugging #18661

#![feature(unboxed_closures, overloaded_calls)]

trait Tr {
    fn foo(&self);

    fn bar(&self) {
        (|:| { self.foo() })()
    }
}

impl Tr for () {
    fn foo(&self) {}
}

fn main() {
    ().bar();
}

Output:

error: internal compiler error: unexpected panic
note: the compiler unexpectedly panicked. 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' panicked at 'assertion failed: self.self_ty().is_none()', /home/bkoropoff/Projects/rust/src/librustc/middle/subst.rs:161

stack backtrace:
   1:     0x7f248d8634d0 - rt::backtrace::imp::write::hd5cf03b086df3c8bciq
   2:     0x7f248d866550 - failure::on_fail::h1883f65e4859f99aODq
   3:     0x7f248e014550 - unwind::begin_unwind_inner::h4724b673057aa7b2ZSd
   4:     0x7f248e3ee820 - unwind::begin_unwind::h14014107635648236996
   5:     0x7f248e73efe0 - middle::subst::Substs::with_self_ty::h2bc29c972ac1c03fKHV
   6:     0x7f248e787cb0 - middle::trans::meth::trans_method_callee::h577047eddd14a758DZm
   7:     0x7f248e787c30 - middle::trans::controlflow::trans_for::closure.122893
   8:     0x7f248ed45840 - middle::trans::expr::trans_overloaded_call::closure.123736
   9:     0x7f248e7862f0 - middle::trans::callee::trans_call_inner::h63140c053eb498d4Tr4
  10:     0x7f248e7b8c30 - middle::trans::expr::trans_rvalue_dps_unadjusted::hcfd8c05e4d3c050aOA6
  11:     0x7f248e77e510 - middle::trans::expr::trans_into::h513a5ff934428ca7Nb5
  12:     0x7f248e77e930 - middle::trans::controlflow::trans_block::h1f8437f97d982780ys1
  13:     0x7f248e81fa20 - middle::trans::base::trans_closure::hee28be544b5f82b7eAh
  14:     0x7f248e771b70 - middle::trans::base::trans_fn::h4c36ddee4bfba9759Lh
  15:     0x7f248e772280 - middle::trans::monomorphize::monomorphic_fn::h9b8dc1f03343f037YS0
  16:     0x7f248e7a4330 - middle::trans::callee::trans_fn_ref_with_substs::h0704b46911f5f6dd953
  17:     0x7f248e787cb0 - middle::trans::meth::trans_method_callee::h577047eddd14a758DZm
  18:     0x7f248e7aafd0 - middle::trans::callee::trans_method_call::closure.123334
  19:     0x7f248e7862f0 - middle::trans::callee::trans_call_inner::h63140c053eb498d4Tr4
  20:     0x7f248e7aaad0 - middle::trans::callee::trans_method_call::h983e88dde8c4f64fln4
  21:     0x7f248e7b8c30 - middle::trans::expr::trans_rvalue_dps_unadjusted::hcfd8c05e4d3c050aOA6
  22:     0x7f248e77e510 - middle::trans::expr::trans_into::h513a5ff934428ca7Nb5
  23:     0x7f248e77d970 - middle::trans::controlflow::trans_stmt_semi::hc8263f70f5ea8146Fr1
  24:     0x7f248e77cf20 - middle::trans::controlflow::trans_stmt::h4ab602fde4741168sn1
  25:     0x7f248e77e930 - middle::trans::controlflow::trans_block::h1f8437f97d982780ys1
  26:     0x7f248e81fa20 - middle::trans::base::trans_closure::hee28be544b5f82b7eAh
  27:     0x7f248e771b70 - middle::trans::base::trans_fn::h4c36ddee4bfba9759Lh
  28:     0x7f248e76f290 - middle::trans::base::trans_item::h671a84973f340984n5h
  29:     0x7f248e82a420 - middle::trans::base::trans_crate::hbe1167d59e4442a8s3i
  30:     0x7f248ec6ab70 - driver::driver::phase_4_translate_to_llvm::hd4dc6d8be6267a8b5sB
  31:     0x7f248ec61360 - driver::driver::compile_input::h8b6b9b7f64eba9a5ZZA
  32:     0x7f248ece5c20 - driver::run_compiler::hf2410821f04b1325cQE
  33:     0x7f248ece5b10 - driver::run::closure.145823
  34:     0x7f248e4266e0 - task::TaskBuilder<S>::try_future::closure.104097
  35:     0x7f248e4264d0 - task::TaskBuilder<S>::spawn_internal::closure.104068
  36:     0x7f248f55e370 - task::NativeSpawner.Spawner::spawn::closure.8434
  37:     0x7f248e06a4d0 - rust_try_inner
  38:     0x7f248e06a4c0 - rust_try
  39:     0x7f248e011ea0 - unwind::try::h2a8363f131a2efbejHd
  40:     0x7f248e011d30 - task::Task::run::ha950d1ffc07a77f09Mc
  41:     0x7f248f55e0b0 - task::NativeSpawner.Spawner::spawn::closure.8372
  42:     0x7f248e013540 - thread::thread_start::hc29987e17333695ao8c
  43:     0x7f248d32fe20 - start_thread
  44:     0x7f248dcdeb59 - clone
  45:                0x0 - <unknown>

This is due to the self param space being used both for the unboxed closure itself within the implicit FnOnce impl, and for the self type of the enclosing trait.

I don't think the first use is ever necessary since the self of the unboxed closure cannot actually be mentioned within it. The unboxed closure type may need to be plumbed through some other way, though.