Associated types: ICE "get_unique_type_id_of_type() - unexpected type"

[kinghajj]

I thought that my example in #20368 was sufficient to cover one of my desired uses of associated types, but, while that example does now successfully compile, the module I really wanted to improve still fails with yet another ICE. Here's the module in full:

    use std::default::Default;
    use std::io::IoResult;
    use std::io::fs;
    use std::io::fs::PathExtensions;

    /// A strategy for acquiring more subpaths to walk.
    pub trait Strategy {
      type P: PathExtensions;
      /// Get additional subpaths from a given path.
      fn get_more(&self, item: &Self::P) -> IoResult<Vec<Self::P>>;
      /// Determine whether a path should be walked further.
      /// This is run against each item from `get_more()`.
      fn prune(&self, p: &Self::P) -> bool;
    }

    /// The basic fully-recursive strategy. Nothing is pruned.
    #[derive(Copy, Default)]
    pub struct Recursive;

    impl Strategy for Recursive {
      type P = Path;
      fn get_more(&self, p: &Path) -> IoResult<Vec<Path>> { fs::readdir(p) }

      fn prune(&self, _: &Path) -> bool { false }
    }

    /// A directory walker of `P` using strategy `S`.
    pub struct Subpaths<S: Strategy> {
        stack: Vec<S::P>,
        strategy: S,
    }

    impl<S: Strategy> Subpaths<S> {
      /// Create a directory walker with a root path and strategy.
      pub fn new(p: &S::P, strategy: S) -> IoResult<Subpaths<S>> {
        let stack = try!(strategy.get_more(p));
        Ok(Subpaths { stack: stack, strategy: strategy })
      }
    }

    impl<S: Default + Strategy> Subpaths<S> {
      /// Create a directory walker with a root path and a default strategy.
      pub fn walk(p: &S::P) -> IoResult<Subpaths<S>> {
          Subpaths::new(p, Default::default())
      }
    }

    impl<S: Default + Strategy> Default for Subpaths<S> {
      fn default() -> Subpaths<S> {
        Subpaths { stack: Vec::new(), strategy: Default::default() }
      }
    }

    impl<S: Strategy> Iterator for Subpaths<S> {
      type Item = S::P;
      fn next (&mut self) -> Option<S::P> {
        let mut opt_path = self.stack.pop();
        while opt_path.is_some() && self.strategy.prune(opt_path.as_ref().unwrap()) {
          opt_path = self.stack.pop();
        }
        match opt_path {
          Some(path) => {
            if PathExtensions::is_dir(&path) {
              let result = self.strategy.get_more(&path);
              match result {
                Ok(dirs) => { self.stack.extend(dirs.into_iter()); },
                Err(..) => { }
              }
            }
            Some(path)
          }
          None => None,
        }
      }
    }

    #[test]
    fn woot() {
      let mut walker: Subpaths<Recursive> = Subpaths::walk(&Path::new("/home")).unwrap();
    }

Here's the error and backtrace:

error: internal compiler error: get_unique_type_id_of_type() - unexpected type: <Recursive as Strategy>::P, ty_projection(ProjectionTy { trait_ref: Rc(TraitRef { def_id: DefId { krate: 0u32, node: 8u32 }, substs: Substs { types: VecPerParamSpace {TypeSpace: [], SelfSpace: [TyS { sty: ty_struct(DefId { krate: 0u32, node: 40u32 }, Substs { types: VecPerParamSpace {TypeSpace: [], SelfSpace: [], FnSpace: [], }, regions: ErasedRegions }), flags: 0, region_depth: 0u32 }], FnSpace: [], }, regions: NonerasedRegions(VecPerParamSpace {TypeSpace: [], SelfSpace: [], FnSpace: [], }) } }), item_name: "P"(73) })
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
thread 'rustc' panicked at 'Box<Any>', /home/samuel/rust/src/libsyntax/diagnostic.rs:182

stack backtrace:
   1:     0x7f4a265a0570 - sys::backtrace::write::h3452feb04e320bcfCzt
   2:     0x7f4a265c2780 - failure::on_fail::hd0efae8686875716aPz
   3:     0x7f4a26530300 - rt::unwind::begin_unwind_inner::h229232f5734654792tz
   4:     0x7f4a214ada20 - rt::unwind::begin_unwind::h9438643137198476843
   5:     0x7f4a214ae2d0 - diagnostic::Handler::bug::he657a4296d705a33tWF
   6:     0x7f4a2488f180 - session::Session::bug::ha8836431c543757ciRq
   7:     0x7f4a25673ba0 - trans::debuginfo::TypeMap<'tcx>::get_unique_type_id_of_type::h606c89215412cd5brGD
   8:     0x7f4a256778d0 - trans::debuginfo::TypeMap<'tcx>::get_unique_type_id_of_type::from_def_id_and_substs::h9fa1f90635ed12d03PD
   9:     0x7f4a25673ba0 - trans::debuginfo::TypeMap<'tcx>::get_unique_type_id_of_type::h606c89215412cd5brGD
  10:     0x7f4a25679e30 - trans::debuginfo::type_metadata::h7557684678d0dd25RSF
  11:     0x7f4a25682220 - trans::debuginfo::StructMemberDescriptionFactory<'tcx>::create_member_descriptions::unboxed_closure.45598
  12:     0x7f4a25681e00 - vec::Vec<T>.FromIterator<T>::from_iter::h9648212210143919248
  13:     0x7f4a2567dda0 - trans::debuginfo::StructMemberDescriptionFactory<'tcx>::create_member_descriptions::hf79fdc4d3167c5d0j9E
  14:     0x7f4a25680980 - trans::debuginfo::RecursiveTypeDescription<'tcx>::finalize::h0ff9cf1ab1bdbcef26E
  15:     0x7f4a25679e30 - trans::debuginfo::type_metadata::h7557684678d0dd25RSF
  16:     0x7f4a25684fd0 - trans::debuginfo::VariantMemberDescriptionFactory<'tcx>::create_member_descriptions::unboxed_closure.45632
  17:     0x7f4a25684be0 - vec::Vec<T>.FromIterator<T>::from_iter::h5453357870208096995
  18:     0x7f4a25683270 - trans::debuginfo::EnumMemberDescriptionFactory<'tcx>::create_member_descriptions::unboxed_closure.45606
  19:     0x7f4a25682e50 - vec::Vec<T>.FromIterator<T>::from_iter::h13188062602912948975
  20:     0x7f4a2567de90 - trans::debuginfo::EnumMemberDescriptionFactory<'tcx>::create_member_descriptions::h1355d0387a727939hgF
  21:     0x7f4a25680980 - trans::debuginfo::RecursiveTypeDescription<'tcx>::finalize::h0ff9cf1ab1bdbcef26E
  22:     0x7f4a25679e30 - trans::debuginfo::type_metadata::h7557684678d0dd25RSF
  23:     0x7f4a25688070 - trans::debuginfo::subroutine_type_metadata::haec4c13f9a5d7a59vOF
  24:     0x7f4a25679e30 - trans::debuginfo::type_metadata::h7557684678d0dd25RSF
  25:     0x7f4a25620ae0 - trans::debuginfo::create_function_debug_context::h985b11ad61da52fdwsE
  26:     0x7f4a25580890 - trans::base::new_fn_ctxt::hbe79965b1049ecf2Zxt
  27:     0x7f4a25626410 - trans::base::trans_closure::h5c0a7253f08a6c1bEYt
  28:     0x7f4a255452b0 - trans::base::trans_fn::h84cc11dd50b05f50j9t
  29:     0x7f4a25545710 - trans::monomorphize::monomorphic_fn::h44708ba9400c75dbFpd
  30:     0x7f4a25597ff0 - trans::callee::trans_fn_ref_with_substs::h1741ea29b53c270fGxg
  31:     0x7f4a25596590 - trans::callee::trans_fn_ref::h611f01f0cbdf2e42Rlg
  32:     0x7f4a25593870 - trans::callee::trans::h2d6fbfb713fd152ayag
  33:     0x7f4a2559da90 - trans::callee::trans_call_inner::h893956557312987459
  34:     0x7f4a255a34b0 - trans::expr::trans_rvalue_dps_unadjusted::h4ab35d4af002299e1Si
  35:     0x7f4a255a2790 - trans::expr::trans_unadjusted::h15f19eba475549d3Oji
  36:     0x7f4a2555b000 - trans::expr::trans::ha962b869e642f0b8eCh
  37:     0x7f4a2556c0b0 - trans::callee::trans_args::h2dbfd3d1c7128174xch
  38:     0x7f4a2559f460 - trans::callee::trans_call_inner::h11730372111330536098
  39:     0x7f4a255a34b0 - trans::expr::trans_rvalue_dps_unadjusted::h4ab35d4af002299e1Si
  40:     0x7f4a25559d90 - trans::expr::trans_into::h70023b40e1df277dKyh
  41:     0x7f4a2565e030 - trans::_match::mk_binding_alloca::h14708251032129145358
  42:     0x7f4a25559390 - trans::base::init_local::h17113ff3a822f41bC7s
  43:     0x7f4a2555a3e0 - trans::controlflow::trans_block::hd4046f45161d1f00B3d
  44:     0x7f4a25626410 - trans::base::trans_closure::h5c0a7253f08a6c1bEYt
  45:     0x7f4a255452b0 - trans::base::trans_fn::h84cc11dd50b05f50j9t
  46:     0x7f4a25540840 - trans::base::trans_item::h560b1558a6cec5e6Ewu
  47:     0x7f4a2562dc30 - trans::base::trans_crate::heb94c899d24982b8lsv
  48:     0x7f4a26b09fa0 - driver::phase_4_translate_to_llvm::h4be77ff61772864dPFa
  49:     0x7f4a26ae3f30 - driver::compile_input::hefa96b3bea08e00bxba
  50:     0x7f4a26bb3bc0 - monitor::unboxed_closure.22498
  51:     0x7f4a26bb3a20 - thunk::F.Invoke<A, R>::invoke::h2604081160332846052
  52:     0x7f4a26bb27a0 - rt::unwind::try::try_fn::h10712615664574212328
  53:     0x7f4a26630f00 - rust_try_inner
  54:     0x7f4a26630ef0 - rust_try
  55:     0x7f4a26bb2a90 - thunk::F.Invoke<A, R>::invoke::h6088602545528080049
  56:     0x7f4a265b0630 - sys::thread::thread_start::h803dac673dcdb1abqrw
  57:     0x7f4a20cc7250 - start_thread
  58:     0x7f4a261e0219 - clone
  59:                0x0 - <unknown>

Could not compile `subpaths`.

[erickt]

I just ran into this as well with a smaller example:

struct Peekable<I> where I: Iterator {
    _iter: I,
    _next: Option<<I as Iterator>::Item>,
}

fn main() {
    let mut iter = Vec::<i32>::new().into_iter();
    let next = iter.next();
    let _v = Peekable {
        _iter: iter,
        _next : next,
    };
}

With this error:

error: internal compiler error: get_unique_type_id_of_type() - unexpected type: <collections::vec::IntoIter<i32> as core::iter::Iterator>::Item, ty_projection(ProjectionTy { trait_ref: Rc(TraitRef { def_id: DefId { krate: 2u32, node: 42866u32 }, substs: Substs { types: VecPerParamSpace {TypeSpace: [], SelfSpace: [TyS { sty: ty_struct(DefId { krate: 3u32, node: 36733u32 }, Substs { types: VecPerParamSpace {TypeSpace: [TyS { sty: ty_int(i32), flags: 0, region_depth: 0u32 }], SelfSpace: [], FnSpace: [], }, regions: ErasedRegions }), flags: 0, region_depth: 0u32 }], FnSpace: [], }, regions: NonerasedRegions(VecPerParamSpace {TypeSpace: [], SelfSpace: [], FnSpace: [], }) } }), item_name: "Item"(67) })
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
thread 'rustc' panicked at 'Box<Any>', /Users/rustbuild/src/rust-buildbot/slave/nightly-dist-rustc-mac/build/src/libsyntax/diagnostic.rs:182

stack backtrace:
   1:        0x1113f24b5 - sys::backtrace::write::h64ca2fb259c4ae97lCt
   2:        0x11141494f - failure::on_fail::h64ff5ae6887860cc0Hz
   3:        0x1113805ca - rt::unwind::begin_unwind_inner::h1d4bc098fd350446Qpz
   4:        0x10f0880b7 - rt::unwind::begin_unwind::h1123425023578864118
   5:        0x10f088a28 - diagnostic::Handler::bug::h6d2bfe842975d6e0tWF
   6:        0x10e68c788 - session::Session::bug::h5da8d79b0a6f5276iRq
   7:        0x10deb5805 - trans::debuginfo::TypeMap<'tcx>::get_unique_type_id_of_type::hf00d365d13fe5f42rGD
   8:        0x10deb9557 - trans::debuginfo::TypeMap<'tcx>::get_unique_type_id_of_type::from_def_id_and_substs::h891ec143e99916f43PD
   9:        0x10deb5705 - trans::debuginfo::TypeMap<'tcx>::get_unique_type_id_of_type::hf00d365d13fe5f42rGD
  10:        0x10debb7cb - trans::debuginfo::type_metadata::h9edd372a193ff094RSF
  11:        0x10dec3cf5 - trans::debuginfo::StructMemberDescriptionFactory<'tcx>::create_member_descriptions::unboxed_closure.45659
  12:        0x10dec37b2 - vec::Vec<T>.FromIterator<T>::from_iter::h4078323428656498456
  13:        0x10debf54d - trans::debuginfo::StructMemberDescriptionFactory<'tcx>::create_member_descriptions::he532502aebbbff41j9E
  14:        0x10dec23e2 - trans::debuginfo::RecursiveTypeDescription<'tcx>::finalize::h4e94b4649bcaa46e26E
  15:        0x10debc539 - trans::debuginfo::type_metadata::h9edd372a193ff094RSF
  16:        0x10debdad2 - trans::debuginfo::declare_local::h82cfc8c7fa3e6298CPE
  17:        0x10debd32d - ast_util::walk_pat::walk_pat_::h14410195268450947789
  18:        0x10dda22a7 - trans::controlflow::trans_block::h1b3762e019b88de7B3d
  19:        0x10de6ba39 - trans::base::trans_closure::h83147acece2ec0c6EYt
  20:        0x10dd8d5f5 - trans::base::trans_fn::h99bd3c17ad60972dj9t
  21:        0x10dd88d4e - trans::base::trans_item::hdbddd5abd5742b0cEwu
  22:        0x10de7202c - trans::base::trans_crate::h6077c32a4f7ba4e9lsv
  23:        0x10dc2eb3e - driver::phase_4_translate_to_llvm::ha92297f2357a645fPFa
  24:        0x10dc0af4b - driver::compile_input::h31580cbd7ea87613xba
  25:        0x10dcd5fda - monitor::unboxed_closure.22557
  26:        0x10dcd4735 - thunk::F.Invoke<A, R>::invoke::h6367419564961841226
  27:        0x10dcd3510 - rt::unwind::try::try_fn::h7763956589852599824
  28:        0x11147b2a9 - rust_try_inner
  29:        0x11147b296 - rust_try
  30:        0x10dcd3c0c - thunk::F.Invoke<A, R>::invoke::h16724184168577887652
  31:        0x111402154 - sys::thread::thread_start::hbd8f2f8bdd3a3baadrw
  32:     0x7fff9358c2fc - _pthread_body
  33:     0x7fff9358c279 - _pthread_body

[kinghajj]

bors should not have closed this issue, as I mentioned in #20960, my original example still causes an ICE even after that pull request was merged.

[nikomatsakis]

@kinghajj can you retest on the latest master? It seems to work for me, I suspect because of #20955

[kinghajj]

No luck yet.

bash-3.2$ rustc -V
rustc 1.0.0-dev (170c4399e 2015-01-14 00:41:55 +0000)
bash-3.2$ RUST_BACKTRACE=1 cargo test
   Compiling subpaths v0.0.1 (file:///Users/samuel/Documents/Programming/filehash/src/subpaths)
error: internal compiler error: type_of with ty_projection
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
thread 'rustc' panicked at 'Box<Any>', /Users/samuel/Documents/rust/src/libsyntax/diagnostic.rs:182

stack backtrace:
   1:        0x110640dec - sys::backtrace::write::h724c84ec96e82337RUt
   2:        0x110662a8f - failure::on_fail::h6f2a6126417d36beIYz
   3:        0x1105cf74e - rt::unwind::begin_unwind_inner::hb2d99935a1d8bde1yGz
   4:        0x10e30ac4f - rt::unwind::begin_unwind::h6101901676675217320
   5:        0x10e30b5bb - diagnostic::Handler::bug::ha27a4766170cb062A1F
   6:        0x10d8e1670 - metadata::tydecode::parse_existential_bounds_::h10742984024508526701
   7:        0x10d022c88 - trans::type_of::type_of::h6ebeadb230102bb3Y1o
   8:        0x10d023225 - trans::type_of::type_of::h6ebeadb230102bb3Y1o
   9:        0x10d022190 - trans::type_of::type_of::h6ebeadb230102bb3Y1o
  10:        0x10d13929c - trans::debuginfo::StructMemberDescriptionFactory<'tcx>::create_member_descriptions::unboxed_closure.45482
  11:        0x10d138e82 - vec::Vec<T>.FromIterator<T>::from_iter::h1395047669026947608
  12:        0x10d1358bd - trans::debuginfo::StructMemberDescriptionFactory<'tcx>::create_member_descriptions::h153e84111a2448b60fF
  13:        0x10d137b0d - trans::debuginfo::RecursiveTypeDescription<'tcx>::finalize::h0a20b015282159ecJdF
  14:        0x10d1327a3 - trans::debuginfo::type_metadata::h594d4c508338d95dyZF
  15:        0x10d1392d4 - trans::debuginfo::StructMemberDescriptionFactory<'tcx>::create_member_descriptions::unboxed_closure.45482
  16:        0x10d138e82 - vec::Vec<T>.FromIterator<T>::from_iter::h1395047669026947608
  17:        0x10d1358bd - trans::debuginfo::StructMemberDescriptionFactory<'tcx>::create_member_descriptions::h153e84111a2448b60fF
  18:        0x10d137b0d - trans::debuginfo::RecursiveTypeDescription<'tcx>::finalize::h0a20b015282159ecJdF
  19:        0x10d1327a3 - trans::debuginfo::type_metadata::h594d4c508338d95dyZF
  20:        0x10d1392d4 - trans::debuginfo::StructMemberDescriptionFactory<'tcx>::create_member_descriptions::unboxed_closure.45482
  21:        0x10d138e82 - vec::Vec<T>.FromIterator<T>::from_iter::h1395047669026947608
  22:        0x10d1358bd - trans::debuginfo::StructMemberDescriptionFactory<'tcx>::create_member_descriptions::h153e84111a2448b60fF
  23:        0x10d137b0d - trans::debuginfo::RecursiveTypeDescription<'tcx>::finalize::h0a20b015282159ecJdF
  24:        0x10d1327a3 - trans::debuginfo::type_metadata::h594d4c508338d95dyZF
  25:        0x10d13bc32 - trans::debuginfo::VariantMemberDescriptionFactory<'tcx>::create_member_descriptions::unboxed_closure.45516
  26:        0x10d13b7f2 - vec::Vec<T>.FromIterator<T>::from_iter::h5500603777858505790
  27:        0x10d13a28b - trans::debuginfo::EnumMemberDescriptionFactory<'tcx>::create_member_descriptions::unboxed_closure.45490
  28:        0x10d139da2 - vec::Vec<T>.FromIterator<T>::from_iter::h14361925877225366780
  29:        0x10d135b83 - trans::debuginfo::EnumMemberDescriptionFactory<'tcx>::create_member_descriptions::hdd1b6f55c4c7b16eYmF
  30:        0x10d137b2b - trans::debuginfo::RecursiveTypeDescription<'tcx>::finalize::h0a20b015282159ecJdF
  31:        0x10d131bf9 - trans::debuginfo::type_metadata::h594d4c508338d95dyZF
  32:        0x10d13eca8 - trans::debuginfo::subroutine_type_metadata::h9bff0740736a5de7cVF
  33:        0x10d13262f - trans::debuginfo::type_metadata::h594d4c508338d95dyZF
  34:        0x10d0dba0b - trans::debuginfo::create_function_debug_context::h447bd3a847c41d0adzE
  35:        0x10d03fb3e - trans::base::new_fn_ctxt::h80d01085022bea25Tzt
  36:        0x10d0e04cd - trans::base::trans_closure::h32d8ee0946ac5386y0t
  37:        0x10d006197 - trans::base::trans_fn::ha19d856a27ef8fdadbu
  38:        0x10d007d13 - trans::monomorphize::monomorphic_fn::he3114699339f1503Fpd
  39:        0x10d0578e9 - trans::callee::trans_fn_ref_with_substs::h8ab7a417361225b5Ixg
  40:        0x10d0553e3 - trans::callee::trans_fn_ref::haab38ef68aad01e0Tlg
  41:        0x10d052edc - trans::callee::trans::h30cee5a1ce99c1e8Aag
  42:        0x10d05bbee - trans::callee::trans_call_inner::h17375577365636780878
  43:        0x10d062823 - trans::expr::trans_rvalue_dps_unadjusted::h698caf6d437867f53Si
  44:        0x10d06026a - trans::expr::trans_unadjusted::h527db00c397125ebQji
  45:        0x10d01af76 - trans::expr::trans::he91bdea9edc285d3gCh
  46:        0x10d02bda1 - trans::callee::trans_args::h5d1792d9a12db34czch
  47:        0x10d05e00e - trans::callee::trans_call_inner::h15873392703759300422
  48:        0x10d061296 - trans::expr::trans_rvalue_dps_unadjusted::h698caf6d437867f53Si
  49:        0x10d019f6b - trans::expr::trans_into::hd03a9a170d995fabMyh
  50:        0x10d115669 - trans::_match::mk_binding_alloca::h5771621100645690575
  51:        0x10d019564 - trans::base::init_local::ha40ddf9a1cd925e6w9s
  52:        0x10d01a826 - trans::controlflow::trans_block::h382e5b424a79fcedC3d
  53:        0x10d0e290c - trans::base::trans_closure::h32d8ee0946ac5386y0t
  54:        0x10d006197 - trans::base::trans_fn::ha19d856a27ef8fdadbu
  55:        0x10d00183b - trans::base::trans_item::h5af943f055925df9yyu
  56:        0x10d0e8a8c - trans::base::trans_crate::h1ae727bd77425dc1fuv
  57:        0x10ceb5d74 - driver::phase_4_translate_to_llvm::h5abdfc397f265750YMa
  58:        0x10ce97a36 - driver::compile_input::hb8b4e569f22b04afAba
  59:        0x10cf54c40 - run_compiler::hfcb743c274cb2b48e5b
  60:        0x10cf51fe3 - thunk::F.Invoke<A, R>::invoke::h5297055281723610762
  61:        0x10cf50e48 - rt::unwind::try::try_fn::h6169901515804371881
  62:        0x1106cf149 - rust_try_inner
  63:        0x1106cf136 - rust_try
  64:        0x10cf51486 - thunk::F.Invoke<A, R>::invoke::h14156849340732247684
  65:        0x110650162 - sys::thread::thread_start::hd3418b70b5ddcf22IJw
  66:     0x7fff8d7932fc - _pthread_body
  67:     0x7fff8d793279 - _pthread_body

Could not compile `subpaths`.

[michaelwoerister]

I'll take a closer look at this asap.

[erickt]

@nikomatsakis / @michaelwoerister: I just ran into this other error as well. Here's my reduced test case:

trait DeclaredTrait {
    type Type;
}
impl DeclaredTrait for i32 {
    type Type = i32;
}
struct Struct<B: DeclaredTrait> {
    b: B,
    b1: B::Type,
}
fn main() {
    let e = Struct {
        b: 0,
        b1: 0,
    };
}

Errors with:

% rustc --version
rustc 1.0.0-nightly (3d0d9bb6f 2015-01-12 22:56:20 +0000)
% rustc -g bad.rs
bad.rs:8:5: 8:10 warning: struct field is never used: `b`, #[warn(dead_code)] on by default
bad.rs:8     b : B,
             ^~~~~
bad.rs:9:5: 9:17 warning: struct field is never used: `b1`, #[warn(dead_code)] on by default
bad.rs:9     b1 : B::Type,
             ^~~~~~~~~~~~
bad.rs:12:9: 12:10 warning: unused variable: `e`, #[warn(unused_variables)] on by default
bad.rs:12     let e = Struct {
                  ^
error: internal compiler error: type_of with ty_projection
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
thread 'rustc' panicked at 'Box<Any>', /Users/rustbuild/src/rust-buildbot/slave/nightly-dist-rustc-mac/build/src/libsyntax/diagnostic.rs:182

stack backtrace:
   1:        0x105ca1a2c - sys::backtrace::write::h27c3ddb426dd9587RUt
   2:        0x105cc3a4f - failure::on_fail::h63fb027d8b3cc19ca1z
   3:        0x105c302de - rt::unwind::begin_unwind_inner::hafe5720113b93d950Iz
   4:        0x10394cdcf - rt::unwind::begin_unwind::h11195957873796278085
   5:        0x10394d73b - diagnostic::Handler::bug::h8c0937a4743d025ctWF
   6:        0x102f4bce0 - metadata::tydecode::parse_existential_bounds_::h1282082665815765083
   7:        0x10268be98 - trans::type_of::type_of::h77cc5a392ec4c7efX1o
   8:        0x10268b3a0 - trans::type_of::type_of::h77cc5a392ec4c7efX1o
   9:        0x1027a391c - trans::debuginfo::StructMemberDescriptionFactory<'tcx>::create_member_descriptions::unboxed_closure.45662
  10:        0x1027a3502 - vec::Vec<T>.FromIterator<T>::from_iter::h6250772183958048706
  11:        0x10279f68d - trans::debuginfo::StructMemberDescriptionFactory<'tcx>::create_member_descriptions::hf67e5668f84ac65cZeF
  12:        0x1027a218d - trans::debuginfo::RecursiveTypeDescription<'tcx>::finalize::h0585555c78b3f769IcF
  13:        0x10279c5b3 - trans::debuginfo::type_metadata::h08ada392314e61a8xYF
  14:        0x10279dc77 - trans::debuginfo::declare_local::hcf0a2c0d72819844iVE
  15:        0x10279d4d3 - ast_util::walk_pat::walk_pat_::h4796394502832644510
  16:        0x102683aef - trans::controlflow::trans_block::h9179bd0e311bbf71B3d
  17:        0x10274d0ac - trans::base::trans_closure::h0a187eeead3ee5f9E0t
  18:        0x10266f387 - trans::base::trans_fn::h5f00e8761486c618jbu
  19:        0x10266a9cb - trans::base::trans_item::hb876c423cf52a967Eyu
  20:        0x10275322c - trans::base::trans_crate::hd8e597ceb97fa3f8luv
  21:        0x102516c44 - driver::phase_4_translate_to_llvm::hf1a267085ea57e05YMa
  22:        0x1024f3a91 - driver::compile_input::ha4f10a5f4de94c11Aba
  23:        0x1025bb380 - run_compiler::h0e39ba09c41b0c3de5b
  24:        0x1025b8723 - thunk::F.Invoke<A, R>::invoke::h7667196022708996715
  25:        0x1025b7588 - rt::unwind::try::try_fn::h602527677678223085
  26:        0x105d2d8e9 - rust_try_inner
  27:        0x105d2d8d6 - rust_try
  28:        0x1025b7bc6 - thunk::F.Invoke<A, R>::invoke::h5116215899158159820
  29:        0x105cb1232 - sys::thread::thread_start::hd67e9dc06fcd0bebIJw
  30:     0x7fff9358c2fc - _pthread_body
  31:     0x7fff9358c279 - _pthread_body