String-related panic when processing valid line of Markdown

[ebkalderon]

Note: Not sure whether the bug is in cobalt or in markdown.rs library, so reposting on the Cobalt issue tracker as well: cobalt-org/cobalt.rs#58.

The error message reported by the panic, when looked up on Google, led me to this Rust book page on string slicing. Could you please look into this? This is a pretty major bug. Thanks!

Update: I'm using cobalt 0.2.0 with rustc 1.9.0-nightly (eabfc160f) on 64-bit Arch Linux.

Output

[info]   Building from blog into web
[info]   Created web/index.html
[info]   Created web/_posts/week0.html
thread '<unnamed>' panicked at 'index 42 and/or 43 in `strictly read-only operations, so they don’t fit into either *views* or` do not lie on character boundary', ../src/libcore/str/mod.rs:1670
note: Run with `RUST_BACKTRACE=1` for a backtrace.
thread '<main>' panicked at 'called `Result::unwrap()` on an `Err` value: Any', ../src/libcore/result.rs:746
[info]   Created web/_posts/week6.html

Backtrace

stack backtrace:
   1:     0x55b8389646c0 - sys::backtrace::tracing::imp::write::h3e252ef592ef6f37cHv
   2:     0x55b83896757b - panicking::default_handler::_$u7b$$u7b$closure$u7d$$u7d$::closure.44999
   3:     0x55b8389671e8 - panicking::default_handler::h5a98c984225a759d1nA
   4:     0x55b838958bbc - sys_common::unwind::begin_unwind_inner::ha2071187f9cf0076vvu
   5:     0x55b838959008 - sys_common::unwind::begin_unwind_fmt::h65e28ed738ec1ab9Buu
   6:     0x55b838963b31 - rust_begin_unwind
   7:     0x55b83899e48f - panicking::panic_fmt::h98dcb863ad76e04b7mM
   8:     0x55b8389a5584 - str::slice_error_fail::h98e1db52ab0be957SIT
   9:     0x55b83890bbed - parser::span::parse_spans::hd76b1aa268612ed8qja
  10:     0x55b838907404 - parser::block::parse_blocks::h40207e955dc8e399kza
  11:     0x55b838902e54 - to_html::h178a80c20d1918a2kcb
  12:     0x55b8388ac73a - F.FnBox::call_box::h9582497645605739343
  13:     0x55b8388ae384 - sys_common::unwind::try::try_fn::h11935924224408508601
  14:     0x55b838963abb - __rust_try
  15:     0x55b8389616fd - sys_common::unwind::inner_try::h4a24c2847e3d9a74xsu
  16:     0x55b8388ae52a - boxed::F.FnBox<A>::call_box::h9605662001311154786
  17:     0x55b8389660f9 - sys::thread::Thread::new::thread_start::h486bc7814d54d94ellz
  18:     0x7fc45768f423 - start_thread
  19:     0x7fc4571b8cbc - clone
  20:                0x0 - <unknown>
thread '<main>' panicked at 'called `Result::unwrap()` on an `Err` value: Any', ../src/libcore/result.rs:746
stack backtrace:
   1:     0x55b8389646c0 - sys::backtrace::tracing::imp::write::h3e252ef592ef6f37cHv
   2:     0x55b83896757b - panicking::default_handler::_$u7b$$u7b$closure$u7d$$u7d$::closure.44999
   3:     0x55b8389671e8 - panicking::default_handler::h5a98c984225a759d1nA
   4:     0x55b838958bbc - sys_common::unwind::begin_unwind_inner::ha2071187f9cf0076vvu
   5:     0x55b838959008 - sys_common::unwind::begin_unwind_fmt::h65e28ed738ec1ab9Buu
   6:     0x55b838963b31 - rust_begin_unwind
   7:     0x55b83899e48f - panicking::panic_fmt::h98dcb863ad76e04b7mM
   8:     0x55b8388fd08a - result::unwrap_failed::h15670906751293521885
   9:     0x55b8388fce35 - scoped::JoinState::join::h13c7fea341a406c773a
  10:     0x55b8388ae938 - F.FnBox::call_box::h14351671975044799388
  11:     0x55b8388fd30b - scoped::Scope<'a>::drop_all::h06cdcd63e6265a66u5a
  12:     0x55b8388a3a82 - cobalt::build::he1a9e9c26970c869Uaa
  13:     0x55b838894e40 - main::h2e962ad0501d7c94Raa
  14:     0x55b838966e44 - sys_common::unwind::try::try_fn::h5354436054083437191
  15:     0x55b838963abb - __rust_try
  16:     0x55b8389668db - rt::lang_start::h673f33b817ea5ba77fA
  17:     0x7fc4570f170f - __libc_start_main
  18:     0x55b838891da8 - _start
  19:                0x0 - <unknown>