rustdoc ICE while compiling im-rs

[mark-i-m]

$ rustc --version
rustc 1.30.0-nightly (33b923fd4 2018-08-18)

I ran cargo doc on https://github.com/bodil/im-rs at git commit d748deffadb2c2eafc62bf5add9fb31394ea9abe

$ cargo doc --open
 Documenting typenum v1.10.0                                                                                                                        
error: internal compiler error: librustc/traits/structural_impls.rs:178: impossible case reached

thread '<unnamed>' panicked at 'Box<Any>', librustc_errors/lib.rs:579:9
note: Run with `RUST_BACKTRACE=1` for a backtrace.

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-nightly (33b923fd4 2018-08-18) running on x86_64-unknown-linux-gnu

error: Could not document `typenum`.

Caused by:
  process didn't exit successfully: `rustdoc --crate-name typenum /nobackup/.cargo/registry/src/github.com-1ecc6299db9ec823/typenum-1.10.0/src/lib.rs --cap-lints allow -o /nobackup/im-rs/target/doc -L dependency=/nobackup/im-rs/target/debug/deps` (exit code: 1)

[GuillaumeGomez]

Same as #52873. Closing in favor for the other one (but thanks for reporting!).