rustdoc panic on nul in docstring

[kw217]

In certain circumstances, a nul in a docstring causes rustdoc to panic with a NulError.

I tried this code:

#[macro_use]
extern crate error_chain;

error_chain! {
    foreign_links {
        StringContainsNul(::std::ffi::NulError)
            #[doc = "Attempted to pass a string containing `\0`"];
    }
}

(See https://gist.github.com/kw217/4687d8c42b890f8f7c75533f64cb00c8)

Notice the probably-wrong literal nul char in the docstring - the author intended to use a double-backslash.

When I ran cargo doc, I expected this to either work (emitting HTML output containing the literal nul or somehow eliding it) or give me an appropriate error message (e.g., "Docstring contains NUL at lib.rs:7").

Instead, I got the following panic:

$ RUST_BACKTRACE=1 cargo doc
 Documenting repro v0.1.0 (file:///data/ksw/repro)
error: internal compiler error: unexpected panic

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: run with `RUST_BACKTRACE=1` for a backtrace

thread 'rustc' panicked at 'called `Result::unwrap()` on an `Err` value: NulError(6, [60, 99, 111, 100, 101, 62, 0, 60, 47, 99, 111, 100, 101, 62])', /checkout/src/libcore/result.rs:860
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:69
   9: core::result::unwrap_failed
  10: rustdoc::html::markdown::render::codespan
  11: char_codespan
  12: parse_inline
  13: parse_block.part.19
  14: hoedown_document_render
  15: rustdoc::html::markdown::render
  16: core::fmt::write
             at /checkout/src/libcore/fmt/mod.rs:954
  17: core::fmt::Formatter::write_fmt
             at /checkout/src/libcore/fmt/mod.rs:1262
  18: rustdoc::html::render::document_full
  19: <rustdoc::html::render::Item<'a> as core::fmt::Display>::fmt
  20: core::fmt::write
             at /checkout/src/libcore/fmt/mod.rs:994
             at /checkout/src/libcore/fmt/mod.rs:962
  21: std::io::Write::write_fmt
  22: rustdoc::html::render::Context::render_item
  23: rustdoc::html::render::run

error: Could not document `repro`.

Caused by:
  process didn't exit successfully: `rustdoc --crate-name repro src/lib.rs -o /data/ksw/repro/target/doc -L dependency=/data/ksw/repro/target/debug/deps --extern error_chain=/data/ksw/repro/target/debug/deps/liberror_chain-4a7bcc9cb68d5e79.rlib` (exit code: 101)

Meta

rustc --version --verbose:

rustc 1.19.0 (0ade33941 2017-07-17)
binary: rustc
commit-hash: 0ade339411587887bf01bcfa2e9ae4414c8900d4
commit-date: 2017-07-17
host: x86_64-unknown-linux-gnu
release: 1.19.0
LLVM version: 4.0

[kw217]

Awesome, thanks!