rustc failed at `Option::unwrap()` on `None` value

[bnavetta]

This looks like #17014, but I'm running rustc 0.13.0-nightly (adb44f53d 2014-10-12 00:07:15 +0000).

The error message was

task 'rustc' failed at 'called `Option::unwrap()` on a `None` value', /home/rustbuild/src/rust-buildbot/slave/nightly-linux/build/src/libcore/option.rs:347`

With this stacktrace:

stack backtrace:
   1: 0xb39abb20 - rt::backtrace::imp::write::h113591595974fd57gDq
   2: 0xb39aeab0 - failure::on_fail::h53bcbf0d6728b9a4DYq
   3: 0xb654f300 - unwind::begin_unwind_inner::h390adebca4b37a7cGxd
   4: 0xb654ef20 - unwind::begin_unwind_fmt::h2ab0cb3c7f32f2e08ud
   5: 0xb654eec0 - rust_begin_unwind
   6: 0xb65a0c70 - failure::fail_fmt::hcf1705a633b76faeiqk
   7: 0xb6599f10 - failure::fail::h21932e19d876c5a9mnk
   8: 0xb7060570 - metadata::loader::Context<'a>::find_commandline_library::closure.143127
   9: 0xb7052120 - metadata::loader::Context<'a>::find_library_crate::hb7d39ec83bb2f876uVv
  10: 0xb704b9a0 - metadata::loader::Context<'a>::load_library_crate::hfcf80cf8850dfd6fgLv
  11: 0xb7048080 - metadata::creader::resolve_crate::h618fc91e660b92cePCu
  12: 0xb7041fd0 - metadata::creader::Env<'a>.visit..Visitor<'v>::visit_view_item::h754710013e4ad0ddN4t
  13: 0xb7041370 - metadata::creader::read_crates::h5ce2f208ac611d5803t
  14: 0xb70c99a0 - driver::driver::phase_3_run_analysis_passes::closure.146356
  15: 0xb676ad60 - util::common::time::h7498289541688678291
  16: 0xb706c1d0 - driver::driver::phase_3_run_analysis_passes::h572bf37cf58d3b03eKx
  17: 0xb7066420 - driver::driver::compile_input::h0095013daad50e330qx
  18: 0xb70f4120 - driver::run_compiler::hcf637e3c8e3cc6b5jfB
  19: 0xb70f3fd0 - driver::run::closure.147672
  20: 0xb6783d10 - task::TaskBuilder<S>::try_future::closure.101749
  21: 0xb6783af0 - task::TaskBuilder<S>::spawn_internal::closure.101720
  22: 0xb6689830 - task::spawn_opts::closure.8446
  23: 0xb654ecc0 - unwind::try::try_fn::h437e1f25521f3085zod
  24: 0xb65b1ae0 - rust_try_inner
  25: 0xb65b1aa0 - rust_try
  26: 0xb654cca0 - unwind::try::h7e69991d1495f99bomd
  27: 0xb654cb10 - task::Task::run::hc2ee9a91acc1be872Bc
  28: 0xb66895b0 - task::spawn_opts::closure.8386
  29: 0xb654e3c0 - thread::thread_start::h90c05e75e06cfc47dWc
  30: 0xb3816ea0 - start_thread
  31: 0xb64424c2 - clone
  32:        0x0 - <unknown>

I'm on an i686 Ubuntu 14.04.1 LTS Vagrant VM (the official Ubuntu box) on OS X 10.9.5

[bnavetta]

Actually, I just took another look at the command line, and it had --extern core=. That's probably where the None value came from, but I don't know if it's the expected error message.

[sfackler]

Yep, this should definitely have a better error message.

[huonw]

Do you happen to have a code example that triggers this?

[bnavetta]

I don't have code, but specifying a value for --extern core= seemed to fix the problem, so I think that's it.

[sfackler]

@huonw fixing it now.