rustdoc internal compiler error

[ArcaneNibble]

When I run cargo rustdoc --lib -- --no-defaults --passes "collapse-docs" --passes "unindent-comments" on this commit of the xc2bit crate: https://github.com/azonenberg/openfpga/tree/d91cc0e9927a5c106b8b50c76111a33970a81def/src/xc2bit, the compiler encounters an unexpected panic. The backtrace is:

thread 'rustc' panicked at 'index 18446744073709551615 out of range for slice of length 0', /checkout/src/libcore/slice/mod.rs:672
stack backtrace:
   0: std::sys::imp::backtrace::tracing::imp::unwind_backtrace
             at /checkout/src/libstd/sys/unix/backtrace/tracing/gcc_s.rs:49
   1: std::sys_common::backtrace::_print
             at /checkout/src/libstd/sys_common/backtrace.rs:71
   2: std::panicking::default_hook::{{closure}}
             at /checkout/src/libstd/sys_common/backtrace.rs:60
             at /checkout/src/libstd/panicking.rs:355
   3: std::panicking::default_hook
             at /checkout/src/libstd/panicking.rs:365
   4: std::panicking::rust_panic_with_hook
             at /checkout/src/libstd/panicking.rs:549
   5: std::panicking::begin_panic
             at /checkout/src/libstd/panicking.rs:511
   6: std::panicking::begin_panic_fmt
             at /checkout/src/libstd/panicking.rs:495
   7: rust_begin_unwind
             at /checkout/src/libstd/panicking.rs:471
   8: core::panicking::panic_fmt
             at /checkout/src/libcore/panicking.rs:69
   9: core::slice::slice_index_len_fail
             at /checkout/src/libcore/slice/mod.rs:672
  10: rustdoc::html::format::resolved_path
  11: core::fmt::write
             at /checkout/src/libcore/fmt/mod.rs:954
  12: core::fmt::Formatter::write_fmt
             at /checkout/src/libcore/fmt/mod.rs:1262
  13: rustdoc::html::format::<impl core::fmt::Display for rustdoc::clean::Import>::fmt
  14: core::fmt::write
             at /checkout/src/libcore/fmt/mod.rs:954
  15: core::fmt::Formatter::write_fmt
             at /checkout/src/libcore/fmt/mod.rs:1262
  16: <rustdoc::html::render::Item<'a> as core::fmt::Display>::fmt
  17: core::fmt::write
             at /checkout/src/libcore/fmt/mod.rs:994
             at /checkout/src/libcore/fmt/mod.rs:962
  18: std::io::Write::write_fmt
  19: rustdoc::html::render::Context::render_item
  20: rustdoc::html::render::Context::item::{{closure}}
  21: rustdoc::html::render::run
  22: rustdoc::rust_input::{{closure}}
  23: std::panicking::try::do_call
  24: __rust_maybe_catch_panic
             at /checkout/src/libpanic_unwind/lib.rs:98
  25: <F as alloc::boxed::FnBox<A>>::call_box
  26: std::sys::imp::thread::Thread::new::thread_start
             at /checkout/src/liballoc/boxed.rs:650
             at /checkout/src/libstd/sys_common/thread.rs:21
             at /checkout/src/libstd/sys/unix/thread.rs:84
  27: start_thread
  28: __clone

$ rustc --version --verbose
rustc 1.18.0 (03fc9d622 2017-06-06)
binary: rustc
commit-hash: 03fc9d622e0ea26a3d37f5ab030737fcca6928b9
commit-date: 2017-06-06
host: x86_64-unknown-linux-gnu
release: 1.18.0
LLVM version: 3.9
$ rustdoc --version --verbose
rustdoc 1.18.0 (03fc9d622 2017-06-06)
binary: rustdoc
commit-hash: 03fc9d622e0ea26a3d37f5ab030737fcca6928b9
commit-date: 2017-06-06
host: x86_64-unknown-linux-gnu
release: 1.18.0
LLVM version: 3.9

[ArcaneNibble]

I just tested nighty and it's broken there too:

thread 'rustc' panicked at 'called `Option::unwrap()` on a `None` value', /checkout/src/libcore/option.rs:335
note: Some details are omitted, run with `RUST_BACKTRACE=full` for a verbose backtrace.
stack backtrace:
   0: std::sys::imp::backtrace::tracing::imp::unwind_backtrace
             at /checkout/src/libstd/sys/unix/backtrace/tracing/gcc_s.rs:49
   1: std::sys_common::backtrace::_print
             at /checkout/src/libstd/sys_common/backtrace.rs:71
   2: std::panicking::default_hook::{{closure}}
             at /checkout/src/libstd/sys_common/backtrace.rs:60
             at /checkout/src/libstd/panicking.rs:355
   3: std::panicking::default_hook
             at /checkout/src/libstd/panicking.rs:365
   4: std::panicking::rust_panic_with_hook
             at /checkout/src/libstd/panicking.rs:549
   5: std::panicking::begin_panic
             at /checkout/src/libstd/panicking.rs:511
   6: std::panicking::begin_panic_fmt
             at /checkout/src/libstd/panicking.rs:495
   7: rust_begin_unwind
             at /checkout/src/libstd/panicking.rs:471
   8: core::panicking::panic_fmt
             at /checkout/src/libcore/panicking.rs:71
   9: core::panicking::panic
             at /checkout/src/libcore/panicking.rs:51
  10: rustdoc::html::format::resolved_path
  11: core::fmt::write
             at /checkout/src/libcore/fmt/mod.rs:954
  12: core::fmt::Formatter::write_fmt
             at /checkout/src/libcore/fmt/mod.rs:1262
  13: rustdoc::html::format::<impl core::fmt::Display for rustdoc::clean::Import>::fmt
  14: core::fmt::write
             at /checkout/src/libcore/fmt/mod.rs:954
  15: core::fmt::Formatter::write_fmt
             at /checkout/src/libcore/fmt/mod.rs:1262
  16: <rustdoc::html::render::Item<'a> as core::fmt::Display>::fmt
  17: core::fmt::write
             at /checkout/src/libcore/fmt/mod.rs:994
             at /checkout/src/libcore/fmt/mod.rs:962
  18: std::io::Write::write_fmt
  19: rustdoc::html::render::Context::render_item
  20: rustdoc::html::render::Context::item::{{closure}}
  21: rustdoc::html::render::run

$ rustc --verbose --version
rustc 1.20.0-nightly (229d0d326 2017-06-23)
binary: rustc
commit-hash: 229d0d3266002d343cdd2f4a3bf7f2fe9da15f38
commit-date: 2017-06-23
host: x86_64-unknown-linux-gnu
release: 1.20.0-nightly
LLVM version: 4.0
$ rustdoc --verbose --version
rustdoc 1.20.0-nightly (229d0d326 2017-06-23)
binary: rustdoc
commit-hash: 229d0d3266002d343cdd2f4a3bf7f2fe9da15f38
commit-date: 2017-06-23
host: x86_64-unknown-linux-gnu
release: 1.20.0-nightly
LLVM version: 4.0

[Mark-Simulacrum]

Unwrap is here: https://github.com/rust-lang/rust/blob/b0081b36b457b697d4b87670ca66b6d082c8ebfd/src/librustdoc/html/format.rs#L462. With the command rustdoc --no-defaults --passes "collapse-docs" --passes "unindent-comments" lib.rs this reproduces given this file:

mod a {
    use *;
}

[ollie27]

I'm working on a fix.

EDIT: #42885