internal compiler error: librustc_traits_structural_impls.rs:180: impossible case reached

[jray@jr-dl core]$ RUST_BACKTRACE=1 cargo doc --verbose
       Fresh semver-parser v0.7.0
       Fresh byteorder v1.2.7
       Fresh cfg-if v0.1.6
       Fresh byte-tools v0.3.0
       Fresh futures v0.1.25
       Fresh subtle v1.0.0
       Fresh void v1.0.2
       Fresh rand_core v0.3.0
       Fresh fake-simd v0.1.2
       Fresh stable_deref_trait v1.1.1
       Fresh opaque-debug v0.2.1
       Fresh scopeguard v0.3.3
       Fresh sha1 v0.6.0
       Fresh byteorder v0.4.2
       Fresh slab v0.4.1
       Fresh data-encoding v2.1.1
       Fresh arrayref v0.3.5
       Fresh bs58 v0.2.2
       Fresh quick-error v1.2.2
       Fresh fnv v1.0.6
       Fresh semver v0.9.0
       Fresh log v0.4.6
       Fresh crossbeam-utils v0.6.1
       Fresh block-padding v0.1.2
       Fresh tokio-executor v0.1.5
       Fresh unreachable v1.0.0
       Fresh rand_isaac v0.1.1
       Fresh rand_xorshift v0.1.0
       Fresh rand_hc v0.1.0
       Fresh owning_ref v0.4.0
       Fresh libc v0.2.44
       Fresh rustc_version v0.2.3
 Documenting typenum v1.10.0
       Fresh crunchy v0.1.6
     Running `rustdoc --crate-name typenum /home/jray/.cargo/registry/src/github.com-1ecc6299db9ec823/typenum-1.10.0/src/lib.rs --cap-lints allow --color always -o /home/jray/rlb/target/doc -L dependency=/home/jray/rlb/target/debug/deps`
       Fresh tokio-timer v0.2.8
       Fresh smallvec v0.6.7
       Fresh serde v1.0.80
       Fresh lock_api v0.1.5
       Fresh protobuf v2.2.0
       Fresh iovec v0.1.2
    Checking generic-array v0.12.0
 Documenting tiny-keccak v1.4.2
    Checking tiny-keccak v1.4.2
     Running `rustc --crate-name generic_array /home/jray/.cargo/registry/src/github.com-1ecc6299db9ec823/generic-array-0.12.0/src/lib.rs --color always --crate-type lib --emit=dep-info,metadata -C debuginfo=2 -C metadata=24ed887a9e667d4a -C extra-filename=-24ed887a9e667d4a --out-dir /home/jray/rlb/target/debug/deps -L dependency=/home/jray/rlb/target/debug/deps --extern typenum=/home/jray/rlb/target/debug/deps/libtypenum-ddb9066ccf3c3f69.rmeta --cap-lints allow`
     Running `rustdoc --crate-name tiny_keccak /home/jray/.cargo/registry/src/github.com-1ecc6299db9ec823/tiny-keccak-1.4.2/src/lib.rs --cap-lints allow --color always -o /home/jray/rlb/target/doc -L dependency=/home/jray/rlb/target/debug/deps --extern crunchy=/home/jray/rlb/target/debug/deps/libcrunchy-5c554dc4afb9da08.rmeta`
     Running `rustc --crate-name tiny_keccak /home/jray/.cargo/registry/src/github.com-1ecc6299db9ec823/tiny-keccak-1.4.2/src/lib.rs --color always --crate-type lib --emit=dep-info,metadata -C debuginfo=2 -C metadata=b95308e8734de802 -C extra-filename=-b95308e8734de802 --out-dir /home/jray/rlb/target/debug/deps -L dependency=/home/jray/rlb/target/debug/deps --extern crunchy=/home/jray/rlb/target/debug/deps/libcrunchy-5c554dc4afb9da08.rmeta --cap-lints allow`
    Checking bytes v0.4.11
     Running `rustc --crate-name bytes /home/jray/.cargo/registry/src/github.com-1ecc6299db9ec823/bytes-0.4.11/src/lib.rs --color always --crate-type lib --emit=dep-info,metadata -C debuginfo=2 -C metadata=771d10d185e6e82d -C extra-filename=-771d10d185e6e82d --out-dir /home/jray/rlb/target/debug/deps -L dependency=/home/jray/rlb/target/debug/deps --extern byteorder=/home/jray/rlb/target/debug/deps/libbyteorder-f1fb7d587533d29e.rmeta --extern iovec=/home/jray/rlb/target/debug/deps/libiovec-ece892a96b8088c7.rmeta --cap-lints allow`
 Documenting bytes v0.4.11
     Running `rustdoc --crate-name bytes /home/jray/.cargo/registry/src/github.com-1ecc6299db9ec823/bytes-0.4.11/src/lib.rs --cap-lints allow --color always -o /home/jray/rlb/target/doc -L dependency=/home/jray/rlb/target/debug/deps --extern byteorder=/home/jray/rlb/target/debug/deps/libbyteorder-f1fb7d587533d29e.rmeta --extern iovec=/home/jray/rlb/target/debug/deps/libiovec-ece892a96b8088c7.rmeta`
    Checking block-buffer v0.7.0
     Running `rustc --crate-name block_buffer /home/jray/.cargo/registry/src/github.com-1ecc6299db9ec823/block-buffer-0.7.0/src/lib.rs --color always --crate-type lib --emit=dep-info,metadata -C debuginfo=2 -C metadata=6a21d68d0cc61ab6 -C extra-filename=-6a21d68d0cc61ab6 --out-dir /home/jray/rlb/target/debug/deps -L dependency=/home/jray/rlb/target/debug/deps --extern block_padding=/home/jray/rlb/target/debug/deps/libblock_padding-d10106eb2bc85cbc.rmeta --extern byte_tools=/home/jray/rlb/target/debug/deps/libbyte_tools-27ac4e50ff5b609d.rmeta --extern byteorder=/home/jray/rlb/target/debug/deps/libbyteorder-f1fb7d587533d29e.rmeta --extern generic_array=/home/jray/rlb/target/debug/deps/libgeneric_array-24ed887a9e667d4a.rmeta --cap-lints allow`
    Checking digest v0.8.0
     Running `rustc --crate-name digest /home/jray/.cargo/registry/src/github.com-1ecc6299db9ec823/digest-0.8.0/src/lib.rs --color always --crate-type lib --emit=dep-info,metadata -C debuginfo=2 -C metadata=42db31434a234cec -C extra-filename=-42db31434a234cec --out-dir /home/jray/rlb/target/debug/deps -L dependency=/home/jray/rlb/target/debug/deps --extern generic_array=/home/jray/rlb/target/debug/deps/libgeneric_array-24ed887a9e667d4a.rmeta --cap-lints allow`
    Checking crypto-mac v0.7.0
     Running `rustc --crate-name crypto_mac /home/jray/.cargo/registry/src/github.com-1ecc6299db9ec823/crypto-mac-0.7.0/src/lib.rs --color always --crate-type lib --emit=dep-info,metadata -C debuginfo=2 -C metadata=71ec208809446ae4 -C extra-filename=-71ec208809446ae4 --out-dir /home/jray/rlb/target/debug/deps -L dependency=/home/jray/rlb/target/debug/deps --extern generic_array=/home/jray/rlb/target/debug/deps/libgeneric_array-24ed887a9e667d4a.rmeta --extern subtle=/home/jray/rlb/target/debug/deps/libsubtle-2abab7e52c45222d.rmeta --cap-lints allow`
    Checking rand_pcg v0.1.1
     Running `rustc --crate-name rand_pcg /home/jray/.cargo/registry/src/github.com-1ecc6299db9ec823/rand_pcg-0.1.1/src/lib.rs --color always --crate-type lib --emit=dep-info,metadata -C debuginfo=2 -C metadata=12bc9d30b37f09ef -C extra-filename=-12bc9d30b37f09ef --out-dir /home/jray/rlb/target/debug/deps -L dependency=/home/jray/rlb/target/debug/deps --extern rand_core=/home/jray/rlb/target/debug/deps/librand_core-1dd403da6fad2d1f.rmeta --cap-lints allow --cfg rust_1_26`
 Documenting rand_pcg v0.1.1
     Running `rustdoc --crate-name rand_pcg /home/jray/.cargo/registry/src/github.com-1ecc6299db9ec823/rand_pcg-0.1.1/src/lib.rs --cap-lints allow --color always -o /home/jray/rlb/target/doc -L dependency=/home/jray/rlb/target/debug/deps --extern rand_core=/home/jray/rlb/target/debug/deps/librand_core-1dd403da6fad2d1f.rmeta --cfg rust_1_26`
error: internal compiler error: librustc/traits/structural_impls.rs:178: impossible case reached

thread '<unnamed>' panicked at 'Box<Any>', librustc_errors/lib.rs:587:9
    Checking rand_chacha v0.1.0
     Running `rustc --crate-name rand_chacha /home/jray/.cargo/registry/src/github.com-1ecc6299db9ec823/rand_chacha-0.1.0/src/lib.rs --color always --crate-type lib --emit=dep-info,metadata -C debuginfo=2 -C metadata=1d5213033ce60fb8 -C extra-filename=-1d5213033ce60fb8 --out-dir /home/jray/rlb/target/debug/deps -L dependency=/home/jray/rlb/target/debug/deps --extern rand_core=/home/jray/rlb/target/debug/deps/librand_core-1dd403da6fad2d1f.rmeta --cap-lints allow --cfg rust_1_26`
 Documenting rand_chacha v0.1.0
     Running `rustdoc --crate-name rand_chacha /home/jray/.cargo/registry/src/github.com-1ecc6299db9ec823/rand_chacha-0.1.0/src/lib.rs --cap-lints allow --color always -o /home/jray/rlb/target/doc -L dependency=/home/jray/rlb/target/debug/deps --extern rand_core=/home/jray/rlb/target/debug/deps/librand_core-1dd403da6fad2d1f.rmeta --cfg rust_1_26`
    Checking sha2 v0.8.0
     Running `rustc --crate-name sha2 /home/jray/.cargo/registry/src/github.com-1ecc6299db9ec823/sha2-0.8.0/src/lib.rs --color always --crate-type lib --emit=dep-info,metadata -C debuginfo=2 -C metadata=dd179c29ac1c7dbd -C extra-filename=-dd179c29ac1c7dbd --out-dir /home/jray/rlb/target/debug/deps -L dependency=/home/jray/rlb/target/debug/deps --extern block_buffer=/home/jray/rlb/target/debug/deps/libblock_buffer-6a21d68d0cc61ab6.rmeta --extern digest=/home/jray/rlb/target/debug/deps/libdigest-42db31434a234cec.rmeta --extern fake_simd=/home/jray/rlb/target/debug/deps/libfake_simd-c14268679a54bd71.rmeta --extern opaque_debug=/home/jray/rlb/target/debug/deps/libopaque_debug-b41b536ffc0ea40a.rmeta --cap-lints allow`
    Checking blake2 v0.8.0
     Running `rustc --crate-name blake2 /home/jray/.cargo/registry/src/github.com-1ecc6299db9ec823/blake2-0.8.0/src/lib.rs --color always --crate-type lib --emit=dep-info,metadata -C debuginfo=2 -C metadata=b461b6261fa29a61 -C extra-filename=-b461b6261fa29a61 --out-dir /home/jray/rlb/target/debug/deps -L dependency=/home/jray/rlb/target/debug/deps --extern byte_tools=/home/jray/rlb/target/debug/deps/libbyte_tools-27ac4e50ff5b609d.rmeta --extern crypto_mac=/home/jray/rlb/target/debug/deps/libcrypto_mac-71ec208809446ae4.rmeta --extern digest=/home/jray/rlb/target/debug/deps/libdigest-42db31434a234cec.rmeta --extern opaque_debug=/home/jray/rlb/target/debug/deps/libopaque_debug-b41b536ffc0ea40a.rmeta --cap-lints allow`
    Checking tokio-io v0.1.10
     Running `rustc --crate-name tokio_io /home/jray/.cargo/registry/src/github.com-1ecc6299db9ec823/tokio-io-0.1.10/src/lib.rs --color always --crate-type lib --emit=dep-info,metadata -C debuginfo=2 -C metadata=e7d36a8ce8f7f51e -C extra-filename=-e7d36a8ce8f7f51e --out-dir /home/jray/rlb/target/debug/deps -L dependency=/home/jray/rlb/target/debug/deps --extern bytes=/home/jray/rlb/target/debug/deps/libbytes-771d10d185e6e82d.rmeta --extern futures=/home/jray/rlb/target/debug/deps/libfutures-1ab4072b41383b75.rmeta --extern log=/home/jray/rlb/target/debug/deps/liblog-b77987c657fff32d.rmeta --cap-lints allow`
    Checking rand v0.6.1
     Running `rustc --crate-name rand /home/jray/.cargo/registry/src/github.com-1ecc6299db9ec823/rand-0.6.1/src/lib.rs --color always --crate-type lib --emit=dep-info,metadata -C debuginfo=2 --cfg 'feature="alloc"' --cfg 'feature="cloudabi"' --cfg 'feature="default"' --cfg 'feature="fuchsia-zircon"' --cfg 'feature="libc"' --cfg 'feature="rand_core"' --cfg 'feature="std"' --cfg 'feature="winapi"' -C metadata=f819a935b20ada8d -C extra-filename=-f819a935b20ada8d --out-dir /home/jray/rlb/target/debug/deps -L dependency=/home/jray/rlb/target/debug/deps --extern libc=/home/jray/rlb/target/debug/deps/liblibc-05daab16be91154f.rmeta --extern rand_chacha=/home/jray/rlb/target/debug/deps/librand_chacha-1d5213033ce60fb8.rmeta --extern rand_core=/home/jray/rlb/target/debug/deps/librand_core-1dd403da6fad2d1f.rmeta --extern rand_hc=/home/jray/rlb/target/debug/deps/librand_hc-e464e43828a84162.rmeta --extern rand_isaac=/home/jray/rlb/target/debug/deps/librand_isaac-8249ef147f791068.rmeta --extern rand_pcg=/home/jray/rlb/target/debug/deps/librand_pcg-12bc9d30b37f09ef.rmeta --extern rand_xorshift=/home/jray/rlb/target/debug/deps/librand_xorshift-cc866e87704c9616.rmeta --cap-lints allow --cfg rust_1_25 --cfg rust_1_26 --cfg rust_1_27`
 Documenting rand v0.6.1
     Running `rustdoc --crate-name rand /home/jray/.cargo/registry/src/github.com-1ecc6299db9ec823/rand-0.6.1/src/lib.rs --cap-lints allow --color always -o /home/jray/rlb/target/doc --cfg 'feature="alloc"' --cfg 'feature="cloudabi"' --cfg 'feature="default"' --cfg 'feature="fuchsia-zircon"' --cfg 'feature="libc"' --cfg 'feature="rand_core"'--cfg 'feature="std"' --cfg 'feature="winapi"' -L dependency=/home/jray/rlb/target/debug/deps --extern libc=/home/jray/rlb/target/debug/deps/liblibc-05daab16be91154f.rmeta--extern rand_chacha=/home/jray/rlb/target/debug/deps/librand_chacha-1d5213033ce60fb8.rmeta --extern rand_core=/home/jray/rlb/target/debug/deps/librand_core-1dd403da6fad2d1f.rmeta --extern rand_hc=/home/jray/rlb/target/debug/deps/librand_hc-e464e43828a84162.rmeta --extern rand_isaac=/home/jray/rlb/target/debug/deps/librand_isaac-8249ef147f791068.rmeta --extern rand_pcg=/home/jray/rlb/target/debug/deps/librand_pcg-12bc9d30b37f09ef.rmeta --extern rand_xorshift=/home/jray/rlb/target/debug/deps/librand_xorshift-cc866e87704c9616.rmeta --cfg rust_1_25 --cfg rust_1_26 --cfg rust_1_27`
stack backtrace:
   0: std::sys::unix::backtrace::tracing::imp::unwind_backtrace
             at libstd/sys/unix/backtrace/tracing/gcc_s.rs:49
   1: std::sys_common::backtrace::print
             at libstd/sys_common/backtrace.rs:71
             at libstd/sys_common/backtrace.rs:59
   2: std::panicking::default_hook::{{closure}}
             at libstd/panicking.rs:211
   3: std::panicking::default_hook
             at libstd/panicking.rs:227
   4: std::panicking::rust_panic_with_hook
             at libstd/panicking.rs:477
   5: std::panicking::begin_panic
   6: rustc_errors::Handler::bug
   7: rustc::util::bug::opt_span_bug_fmt::{{closure}}
   8: rustc::ty::context::tls::with_opt::{{closure}}
   9: rustc::ty::context::tls::with_context_opt
  10: rustc::ty::context::tls::with_opt
  11: rustc::util::bug::opt_span_bug_fmt
  12: rustc::util::bug::bug_fmt
  13: rustc::traits::structural_impls::<impl rustc::ty::context::Lift<'tcx> for rustc::traits::SelectionError<'a>>::lift_to_tcx
  14: rustc::ty::context::TyCtxt::lift_to_global
  15: rustc::traits::select::SelectionContext::candidate_from_obligation
  16: rustc::traits::select::SelectionContext::evaluate_stack
  17: rustc::dep_graph::graph::DepGraph::with_anon_task
  18: rustc::traits::select::SelectionContext::evaluate_predicate_recursively
  19: rustc::infer::InferCtxt::probe
  20: <&'a mut I as core::iter::iterator::Iterator>::next
  21: <alloc::vec::Vec<T> as alloc::vec::SpecExtend<T, I>>::from_iter
  22: rustc::traits::select::SelectionContext::candidate_from_obligation_no_cache
  23: rustc::dep_graph::graph::DepGraph::with_anon_task
  24: rustc::traits::select::SelectionContext::candidate_from_obligation
  25: rustc::traits::select::SelectionContext::evaluate_stack
  26: rustc::dep_graph::graph::DepGraph::with_anon_task
  27: rustc::traits::select::SelectionContext::evaluate_predicate_recursively
  28: rustc::infer::InferCtxt::probe
  29: <&'a mut I as core::iter::iterator::Iterator>::next
  30: <alloc::vec::Vec<T> as alloc::vec::SpecExtend<T, I>>::from_iter
  31: rustc::traits::select::SelectionContext::candidate_from_obligation_no_cache
  32: rustc::dep_graph::graph::DepGraph::with_anon_task
  33: rustc::traits::select::SelectionContext::candidate_from_obligation
  34: rustc::traits::select::SelectionContext::evaluate_stack
  35: rustc::dep_graph::graph::DepGraph::with_anon_task
  36: rustc::traits::select::SelectionContext::evaluate_predicate_recursively
  37: rustc::infer::InferCtxt::probe
  38: <&'a mut I as core::iter::iterator::Iterator>::next
  39: <alloc::vec::Vec<T> as alloc::vec::SpecExtend<T, I>>::from_iter
  40: rustc::traits::select::SelectionContext::candidate_from_obligation_no_cache
  41: rustc::dep_graph::graph::DepGraph::with_anon_task
  42: rustc::traits::select::SelectionContext::candidate_from_obligation
  43: rustc::traits::select::SelectionContext::evaluate_stack
  44: rustc::dep_graph::graph::DepGraph::with_anon_task
  45: rustc::traits::select::SelectionContext::evaluate_predicate_recursively
  46: rustc::infer::InferCtxt::probe
  47: <&'a mut I as core::iter::iterator::Iterator>::next
  48: <alloc::vec::Vec<T> as alloc::vec::SpecExtend<T, I>>::from_iter
  49: rustc::traits::select::SelectionContext::candidate_from_obligation_no_cache
  50: rustc::dep_graph::graph::DepGraph::with_anon_task
  51: rustc::traits::select::SelectionContext::candidate_from_obligation
  52: rustc::traits::select::SelectionContext::evaluate_stack
  53: rustc::dep_graph::graph::DepGraph::with_anon_task
  54: rustc::traits::select::SelectionContext::evaluate_predicate_recursively
  55: rustc::infer::InferCtxt::probe
  56: <&'a mut I as core::iter::iterator::Iterator>::next
  57: <alloc::vec::Vec<T> as alloc::vec::SpecExtend<T, I>>::from_iter
  58: rustc::traits::select::SelectionContext::candidate_from_obligation_no_cache
  59: rustc::dep_graph::graph::DepGraph::with_anon_task
  60: rustc::traits::select::SelectionContext::candidate_from_obligation
  61: rustc::traits::select::SelectionContext::evaluate_stack
  62: rustc::dep_graph::graph::DepGraph::with_anon_task
  63: rustc::traits::select::SelectionContext::evaluate_predicate_recursively
  64: rustc::infer::InferCtxt::probe
  65: <&'a mut I as core::iter::iterator::Iterator>::next
  66: <alloc::vec::Vec<T> as alloc::vec::SpecExtend<T, I>>::from_iter
  67: rustc::traits::select::SelectionContext::candidate_from_obligation_no_cache
  68: rustc::dep_graph::graph::DepGraph::with_anon_task
  69: rustc::traits::select::SelectionContext::candidate_from_obligation
  70: rustc::traits::select::SelectionContext::evaluate_stack
  71: rustc::dep_graph::graph::DepGraph::with_anon_task
  72: rustc::traits::select::SelectionContext::evaluate_predicate_recursively
  73: rustc::infer::InferCtxt::probe
  74: <&'a mut I as core::iter::iterator::Iterator>::next
  75: <alloc::vec::Vec<T> as alloc::vec::SpecExtend<T, I>>::from_iter
  76: rustc::traits::select::SelectionContext::candidate_from_obligation_no_cache
  77: rustc::dep_graph::graph::DepGraph::with_anon_task
  78: rustc::traits::select::SelectionContext::candidate_from_obligation
  79: rustc::traits::select::SelectionContext::evaluate_stack
  80: rustc::dep_graph::graph::DepGraph::with_anon_task
  81: rustc::traits::select::SelectionContext::evaluate_predicate_recursively
  82: rustc::infer::InferCtxt::probe
  83: <&'a mut I as core::iter::iterator::Iterator>::next
  84: <alloc::vec::Vec<T> as alloc::vec::SpecExtend<T, I>>::from_iter
  85: rustc::traits::select::SelectionContext::candidate_from_obligation_no_cache
  86: rustc::dep_graph::graph::DepGraph::with_anon_task
  87: rustc::traits::select::SelectionContext::candidate_from_obligation
  88: rustc::traits::select::SelectionContext::evaluate_stack
  89: rustc::dep_graph::graph::DepGraph::with_anon_task
  90: rustc::traits::select::SelectionContext::evaluate_predicate_recursively
  91: rustc::infer::InferCtxt::probe
  92: <&'a mut I as core::iter::iterator::Iterator>::next
  93: <alloc::vec::Vec<T> as alloc::vec::SpecExtend<T, I>>::from_iter
  94: rustc::traits::select::SelectionContext::candidate_from_obligation_no_cache
  95: rustc::dep_graph::graph::DepGraph::with_anon_task
  96: rustc::traits::select::SelectionContext::candidate_from_obligation
  97: rustc::traits::select::SelectionContext::evaluate_stack
  98: rustc::dep_graph::graph::DepGraph::with_anon_task
  99: rustc::traits::select::SelectionContext::evaluate_predicate_recursively

note: the compiler unexpectedly panicked. this is a bug.

note: we would appreciate a bug report: https://github.com/rust-lang/rust/blob/master/CONTRIBUTING.md#bug-reports

note: rustc 1.30.0 (da5f414c2 2018-10-24) running on x86_64-unknown-linux-gnu

error: Could not document `typenum`.

Caused by:
  process didn't exit successfully: `rustdoc --crate-name typenum /home/jray/.cargo/registry/src/github.com-1ecc6299db9ec823/typenum-1.10.0/src/lib.rs --cap-lints allow --color always -o /home/jray/rlb/target/doc -L dependency=/home/jray/rlb/target/debug/deps` (exit code: 1)
warning: build failed, waiting for other jobs to finish...
error: build failed