Internal compiler error related to sizing of unboxes closures

[TethysSvensson]

$ apt-cache policy rust-nightly && rustc -v verbose
rust-nightly:
  Installed: 201408270406~e61ec99~utopic
  Candidate: 201408270406~e61ec99~utopic
  Version table:
 *** 201408270406~e61ec99~utopic 0
        500 http://ppa.launchpad.net/hansjorg/rust/ubuntu/ utopic/main amd64 Packages
        100 /var/lib/dpkg/status
rustc 0.12.0-pre
binary: rustc
commit-hash: unknown
commit-date: unknown
host: x86_64-unknown-linux-gnu
release: 0.12.0-pre
$ cat main.rs 
#![feature(unboxed_closures)]

pub fn foo<T>(val: &mut Box<FnOnce<(), T>>) {
  *val = (box |:| fail!()) as Box<FnOnce<(), T>>;
}

fn main() {
  foo::<uint>(fail!());
}
$ RUST_BACKTRACE=1 rustc main.rs 
error: internal compiler error: fictitious type T in sizing_type_of()
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 'Box<Any>', /build/buildd/rust-nightly-201408270406~e61ec99~utopic/src/libsyntax/ast_util.rs:776

stack backtrace:
   1:     0x7ffe660e1570 - rt::backtrace::imp::write::h7ecc632a9b3f8170c0q
   2:     0x7ffe660e4760 - <unknown>
   3:     0x7ffe668cb950 - unwind::begin_unwind_inner::he71f311595519d03Zie
   4:     0x7ffe648d48a0 - <unknown>
   5:     0x7ffe648d5210 - diagnostic::Handler::bug::h71a8332c712ab61fshF
   6:     0x7ffe66cb9480 - driver::session::Session::bug::h368ac7c552292ba9VWz
   7:     0x7ffe67082060 - middle::trans::type_of::sizing_type_of::h07776af08b7a3e8dna9
   8:     0x7ffe67093370 - middle::trans::common::type_is_immediate::h3c7174239cf11b44KK5
   9:     0x7ffe670f98c0 - middle::trans::type_of::type_of_rust_fn::hdd7ebcc9914412b5Y68
  10:     0x7ffe6710dfa0 - middle::trans::base::decl_rust_fn::h2c22481267fa98f9rwc
  11:     0x7ffe670a2f20 - middle::trans::closure::get_or_create_declaration_if_unboxed_closure::hf773d28cab905f70XQi
  12:     0x7ffe670cb090 - middle::trans::closure::trans_unboxed_closure::haa3242fe8e2e464boWi
  13:     0x7ffe670b2c60 - <unknown>
  14:     0x7ffe6706cdd0 - middle::trans::expr::trans_into::h63efa240a252a4b9js2
  15:     0x7ffe670beb30 - <unknown>
  16:     0x7ffe670bf750 - <unknown>
  17:     0x7ffe670b1d00 - <unknown>
  18:     0x7ffe6706e5a0 - middle::trans::expr::trans::h489987e1dd80e087fw2
  19:     0x7ffe670b1d00 - <unknown>
  20:     0x7ffe6706e5a0 - middle::trans::expr::trans::h489987e1dd80e087fw2
  21:     0x7ffe670b2c60 - <unknown>
  22:     0x7ffe670b1d00 - <unknown>
  23:     0x7ffe6706e5a0 - middle::trans::expr::trans::h489987e1dd80e087fw2
  24:     0x7ffe670b5510 - <unknown>
  25:     0x7ffe6706cdd0 - middle::trans::expr::trans_into::h63efa240a252a4b9js2
  26:     0x7ffe6706c280 - middle::trans::controlflow::trans_stmt_semi::hab7df555c62b5a36dlY
  27:     0x7ffe6706b950 - middle::trans::controlflow::trans_stmt::h2e9e6b84acdd95beWgY
  28:     0x7ffe6706d370 - middle::trans::controlflow::trans_block::hef69e6e8a650479d7lY
  29:     0x7ffe67122d00 - middle::trans::base::trans_closure::h7b69e84eff2769876xe
  30:     0x7ffe6705dda0 - middle::trans::base::trans_fn::h19628e9480b57bbaTJe
  31:     0x7ffe6705e3f0 - middle::trans::monomorphize::monomorphic_fn::h076aedfb221422245IX
  32:     0x7ffe67099040 - middle::trans::callee::trans_fn_ref_with_vtables::h39f7f4eaad71e3f2Wc1
  33:     0x7ffe67096710 - middle::trans::callee::trans_fn_ref::ha50314f0ad039cab4Y0
  34:     0x7ffe670a40a0 - <unknown>
  35:     0x7ffe670765c0 - middle::trans::callee::trans_call_inner::h10aebb5fe7685fdaLD1
  36:     0x7ffe670a3e30 - middle::trans::callee::trans_call::hc4f2c9ea0dad7130Qx1
  37:     0x7ffe670b2c60 - <unknown>
  38:     0x7ffe6706cdd0 - middle::trans::expr::trans_into::h63efa240a252a4b9js2
  39:     0x7ffe6706c280 - middle::trans::controlflow::trans_stmt_semi::hab7df555c62b5a36dlY
  40:     0x7ffe6706b950 - middle::trans::controlflow::trans_stmt::h2e9e6b84acdd95beWgY
  41:     0x7ffe6706d370 - middle::trans::controlflow::trans_block::hef69e6e8a650479d7lY
  42:     0x7ffe67122d00 - middle::trans::base::trans_closure::h7b69e84eff2769876xe
  43:     0x7ffe6705dda0 - middle::trans::base::trans_fn::h19628e9480b57bbaTJe
  44:     0x7ffe670590e0 - middle::trans::base::trans_item::h699a0ee17313c445T1e
  45:     0x7ffe6712d9c0 - middle::trans::base::trans_crate::hab4da120219fc0d5kWf
  46:     0x7ffe674ff480 - driver::driver::phase_4_translate_to_llvm::h070ebeccefe401090yy
  47:     0x7ffe674f6e30 - driver::driver::compile_input::hbae99ff27dbd49ferby
  48:     0x7ffe67588c50 - <unknown>
  49:     0x7ffe67588b60 - <unknown>
  50:     0x7ffe6759ade0 - <unknown>
  51:     0x7ffe6759abe0 - <unknown>
  52:     0x7ffe67fd75f0 - <unknown>
  53:     0x7ffe669241d0 - <unknown>
  54:     0x7ffe669241c0 - rust_try
  55:     0x7ffe668c8f80 - unwind::try::hcf3a6c26a049b912f7d
  56:     0x7ffe668c8d40 - task::Task::run::hb31a60d7e6df8450zdd
  57:     0x7ffe67fd7350 - <unknown>
  58:     0x7ffe668cab40 - <unknown>
  59:     0x7ffe65b780c0 - start_thread
  60:     0x7ffe66592359 - __clone
  61:                0x0 - <unknown>

[bkoropoff]

This seems to be due to the ty_unboxed_closure variant having no way to track substititions, resulting in monomorphization not working properly.

[bkoropoff]

I'm working on plumbing Substs throughout the compiler for ty_unboxed_closure. It seems promising so far.