ICE using associated type in trait bound

[pythonesque]

It actually happens even if you take out the type T but I figured that would be too confusing of a testcase.

#![feature(associated_types)]

pub trait Foo {
    type T;
    type S: Bar<Self::T>;
}

pub trait Bar<T> {}

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
thread 'rustc' panicked at 'no entry found for key', /Users/rustbuild/src/rust-buildbot/slave/nightly-mac/build/src/libcore/option.rs:329

stack backtrace:
   1:        0x1078c7c38 - sys::backtrace::write::h329291c3ffa2342c0Jt
   2:        0x1078e8a03 - failure::on_fail::h17e4ace9633d727be0z
   3:        0x107854c3a - rt::unwind::begin_unwind_inner::h190be063817ae06eFHz
   4:        0x10785915d - rt::unwind::begin_unwind_fmt::hc68ebd2b3de4118e2Ez
   5:        0x1078e8302 - rust_begin_unwind
   6:        0x107935d0c - panicking::panic_fmt::h6d9a452b0d084e9dLkl
   7:        0x1046960b9 - collections::hash::map::HashMap<K,$u{20}V$C$$u{20}H$GT$.Index$LT$Q$C$$u{20}V$GT$::index::h4548773097338651390
   8:        0x104756a96 - astconv::ast_ty_to_ty::unboxed_closure.36753
   9:        0x104755323 - astconv::ast_ty_to_ty::h3464216238889989760
  10:        0x10475497c - iter::IteratorExt::collect::h1178474147849539242
  11:        0x104862cf1 - astconv::ast_path_to_trait_ref::h12290017992957141453
  12:        0x1048625e6 - astconv::instantiate_poly_trait_ref::h3434886886043991751
  13:        0x104862350 - vec::Vec<T>.FromIterator<T>::from_iter::h6759705047736047902
  14:        0x1048c987d - collect::compute_bounds::h9074989142750734463
  15:        0x104860e9b - collect::ty_generics_for_trait::ha23d00f7844cb7b4quv
  16:        0x1047321ee - collect::trait_def_of_item::h2e00c54b47ce1f2cgdv
  17:        0x10472ed30 - collect::CollectTraitDefVisitor<$u{27}a$C$$u{20}$u{27}tcx$GT$.visit..Visitor$LT$$u{27}v$GT$::visit_item::h913166666a1bcfc7dSt
  18:        0x10492237f - check_crate::unboxed_closure.43401
  19:        0x10492048a - check_crate::hcab218417b8f1f7f51y
  20:        0x103ff9113 - driver::phase_3_run_analysis_passes::hb0ac12e829cd00e7Jta
  21:        0x103fdaffe - driver::compile_input::hdcb29128a43ec322wba
  22:        0x10417aff8 - thunk::Thunk<(*,$u{20}R$GT$::new::unboxed_closure.30336
  23:        0x104179038 - thunk::F.Invoke<A,$u{20}R$GT$::invoke::h12480167585331118411
  24:        0x1041777d9 - rt::unwind::try::try_fn::h9666833473335668351
  25:        0x107950669 - rust_try_inner
  26:        0x107950656 - rust_try
  27:        0x104177ed7 - thunk::F.Invoke<A,$u{20}R$GT$::invoke::h4838524648863172491
  28:        0x1078d7c24 - sys::thread::thread_start::h7394d69fbc5b85e9vFw
  29:     0x7fff8115e899 - _pthread_body
  30:     0x7fff8115e72a - _pthread_struct_init

[pythonesque]

Note: this still ICEs, but now gives a different backtrace:

---

thread 'rustc' panicked at 'assertion failed: did.krate != ast::LOCAL_CRATE', /Users/rustbuild/src/rust-buildbot/slave/nightly-dist-rustc-mac/build/src/librustc/middle/ty.rs:5429

stack backtrace:
   1:        0x112a5ea85 - sys::backtrace::write::h99bbbbef588b9184Klt
   2:        0x112a83f1f - failure::on_fail::h8b1c6fd57e4213d95nz
   3:        0x1129e895a - rt::unwind::begin_unwind_inner::hfd8d974c1cdeb74f35y
   4:        0x10fb41dfc - rt::unwind::begin_unwind::h9670423602147760625
   5:        0x10fec0a48 - middle::ty::lookup_trait_def::h0d278c058dac7da0bJ8
   6:        0x10f71a8bf - astconv::trait_defines_associated_type_named::h6e1f2adb924a7a3ed8r
   7:        0x10f729f14 - astconv::associated_path_def_to_ty::he58c9dd43523b1ady3r
   8:        0x10f7f5b58 - astconv::ast_ty_to_ty::unboxed_closure.36572
   9:        0x10f7f4217 - astconv::ast_ty_to_ty::h9692175568744562300
  10:        0x10f7f3889 - vec::Vec<T>.FromIterator<T>::from_iter::h2513327853763018693
  11:        0x10f81ca4b - astconv::instantiate_poly_trait_ref::h13560246163170871033
  12:        0x10f81c340 - vec::Vec<T>.FromIterator<T>::from_iter::h14680717809933419516
  13:        0x10f86855e - collect::conv_param_bounds::h18412785619248994413
  14:        0x10f897bbb - collect::ty_generics_for_trait::predicates_for_associated_types::unboxed_closure.38347
  15:        0x10f8975f1 - vec::Vec<T>.FromIterator<T>::from_iter::h5667342797167702362
  16:        0x10f86764e - collect::ty_generics_for_trait::h86232192f12b9d3cL6t
  17:        0x10f7d313a - collect::trait_def_of_item::h38b7e2843be79580FSt
  18:        0x10f7d0441 - collect::CollectTraitDefVisitor<'a, 'tcx>.visit..Visitor<'v>::visit_item::he1dd377f8daa9f9cm6s
  19:        0x10f8d00ff - check_crate::unboxed_closure.40064
  20:        0x10f8ce0eb - check_crate::h8fb6181edbba0f5bjsx
  21:        0x10f12d592 - driver::phase_3_run_analysis_passes::h80f5730bb84ad4dbTva
  22:        0x10f119f1c - driver::compile_input::h3940b6305f304e80wba
  23:        0x10f1e1853 - thunk::F.Invoke<A, R>::invoke::h10598202800189765697
  24:        0x10f1de9b0 - rt::unwind::try::try_fn::h2354011666368721707
  25:        0x112aec409 - rust_try_inner
  26:        0x112aec3f6 - rust_try
  27:        0x10f1df0f6 - thunk::F.Invoke<A, R>::invoke::h10531483554991743553
  28:        0x112a6fed4 - sys::thread::thread_start::h156b750c645e6d54M8v
  29:     0x7fff8115e899 - _pthread_body
  30:     0x7fff8115e72a - _pthread_struct_init

[japaric]

cc @nikomatsakis

[Gankra]

Just ran into this in collect-rs, trying to migrate some of our iterator traits/adaptors to associate types. :(

[alexcrichton]

Another example:

#![crate_type = "lib"]
trait IntoIterator {
    type Item;
    type IntoIter: Iterator<Item=Self::Item>;

    fn into_iter(self) -> Self::IntoIter;
}

$ rustc foo.rs
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
thread 'rustc' panicked at 'assertion failed: did.krate != ast::LOCAL_CRATE', /home/rustbuild/src/rust-buildbot/slave/nightly-dist-rustc-linux/build/src/librustc/middle/ty.rs:5341

[nikomatsakis]

I suspect you can workaround this with Iterator<Item=<Self as IntoIterator>::Item>

[alexcrichton]

It got rid of the ICE at least!

$ rustc foo.rs
foo.rs:4:34: 4:62 error: illegal recursive type; insert an enum or struct in the cycle, if this is desired [E0246]
foo.rs:4     type IntoIter: Iterator<Item=<Self as IntoIterator>::Item>;
                                          ^~~~~~~~~~~~~~~~~~~~~~~~~~~~

[nikomatsakis]

@alexcrichton d'oh. I'll look into resolving this, I think it's blocking @pnkfelix too. It's a bit non-trivial I fear.