Compiler panic on self-referencing trait with associated types

[jmitchell]

The compiler unexpectedly panicked due to a trait with associated types referencing itself. Likely related to #23073, but this trace goes one frame deeper before unwinding.

I tried this code:

use std::ops::{Index};

trait Hierarchy {
    type Value;
    type ChildKey;
    type Children = Index<Self::ChildKey, Output=Hierarchy>;

    fn data(&self) -> Option<(Self::Value, Self::Children)>;
}

I was expecting this to compile, and hoped Output=Hierarchy part would automatically reuse the associated types. Explicitly setting them using Hierarchy<Value=Self::Value,ChildKey=Self::ChildKey> doesn't seem to change anything.

Clearly there's a compiler bug somewhere, but I wouldn't mind feedback about the validity of my expectations. I'm fairly new to Rust. For now I've worked around the issue by moving the associated types into the trait signature.

Meta

rustc --version --verbose:

rustc 1.0.0-dev (e2fa53e59 2015-03-20) (built 2015-03-20)
binary: rustc
commit-hash: e2fa53e593a854a609ae9efe5a1bbe15265f0a6f
commit-date: 2015-03-20
build-date: 2015-03-20
host: x86_64-apple-darwin
release: 1.0.0-dev

Backtrace:

thread 'rustc' panicked at 'path not fully resolved: PathResolution { base_def: DefSelfTy(6), last_private: LastMod(AllPublic), depth: 1 }', /Users/jake/src/rust/src/librustc/middle/def.rs:79

stack backtrace:
   1:        0x1106312cb - sys::backtrace::write::hbea0685a50659608A7C
   2:        0x11065cfa8 - panicking::on_panic::hc1f3ff62cc45fceafXI
   3:        0x110578eb9 - rt::unwind::begin_unwind_inner::h189021cc7e69d195ZFI
   4:        0x11057935e - rt::unwind::begin_unwind_fmt::h93fcd46877260e86AEI
   5:        0x10d53b6af - middle::def::PathResolution::full_def::h38fd56f2ad8d940182k
   6:        0x10d44b2ba - PrivacyVisitor<'a, 'tcx>::check_path::h05c78fb3c2c4592fM4a
   7:        0x10d44c4d1 - PrivacyVisitor<'a, 'tcx>.Visitor<'v>::visit_path::hdbc4bac3ff8b01f6Tsb
   8:        0x10d44c5fe - visit::walk_path::h3479848768788528522
   9:        0x10d44c35e - PrivacyVisitor<'a, 'tcx>.Visitor<'v>::visit_item::h5358ad00fed0ec7ajdb
  10:        0x10d45386a - check_crate::hb1c6527f25d590b7lVb
  11:        0x10cb5f0a2 - driver::phase_3_run_analysis_passes::hf44129b9377f1b66sGa
  12:        0x10cb45556 - driver::compile_input::h363b4befa2afe902Rba
  13:        0x10cc05c53 - run_compiler::he317b7c6af5d4656v2b
  14:        0x10cc03775 - thunk::F.Invoke<A, R>::invoke::h4452396910537927981
  15:        0x10cc02b37 - rt::unwind::try::try_fn::h13708605604948619026
  16:        0x1106e4308 - rust_try_inner
  17:        0x1106e42f5 - rust_try
  18:        0x10cc02ed5 - thunk::F.Invoke<A, R>::invoke::h1733875596228645594
  19:        0x110647a5d - sys::thread::create::thread_start::hc225c8ea020565ecNDH
  20:     0x7fff9692c267 - _pthread_body
  21:     0x7fff9692c1e4 - _pthread_start

[jmitchell]

By the way, does "ICE" stand for Internal Compiler Error? I've seen it on other compiler panic issues, but didn't want to label it as such without knowing.

@jmitchell It does indeed. :)

[soltanmm]

I believe this is a reduced form of the problem (playground):

pub struct C<AType: A> {a:AType}

pub trait A {
    type B = C<Self::anything_here_kills_it>;
}

fn main(){}

Note that anything_here_kills_it can be anything whatsoever.

EDIT: I... take that back. I'm not sure if it's the same as this one or the bug @jmitchell referenced.

[pmarcelll]

On rustc 1.2.0-nightly (0250ff9a5 2015-06-17), both cases produce regular build errors.

1,

test.rs:6:50: 6:59 error: the value of the associated type `ChildKey` (from the trait `Hierarchy`) must be specified [E0191]
test.rs:6     type Children = Index<Self::ChildKey, Output=Hierarchy>;
                                                           ^~~~~~~~~
test.rs:6:50: 6:59 error: the value of the associated type `Children` (from the trait `Hierarchy`) must be specified [E0191]
test.rs:6     type Children = Index<Self::ChildKey, Output=Hierarchy>;
                                                           ^~~~~~~~~
test.rs:6:50: 6:59 error: the value of the associated type `Value` (from the trait `Hierarchy`) must be specified [E0191]
test.rs:6     type Children = Index<Self::ChildKey, Output=Hierarchy>;
                                                           ^~~~~~~~~
error: aborting due to 3 previous errors

2,

test.rs:4:16: 4:44 error: associated type `anything_here_kills_it` not found for `Self` [E0220]
test.rs:4     type B = C<Self::anything_here_kills_it>;
                         ^~~~~~~~~~~~~~~~~~~~~~~~~~~~
error: aborting due to previous error