'rustc' failed at 'called `Result::unwrap()` on an `Err` value'

[blastrock]

When you run

rustc a.rs --dep-info b/c/d

with "b/c/d" a non existent path, rustc fails with:

error: internal compiler error: unexpected failure
note: the compiler hit an unexpected failure path. this is a bug.
note: we would appreciate a bug report: http://static.rust-lang.org/doc/master/complement-bugreport.html
note: run with `RUST_BACKTRACE=1` for a backtrace
task 'rustc' failed at 'called `Result::unwrap()` on an `Err` value', /home/blastrock/packages/rust/src/libstd/result.rs:187
stack backtrace:
   1:     0x7f26140d9a20 - rt::backtrace::imp::write::h987c266f24b5dc06gZb::v0.10
   2:     0x7f261403ad50 - rt::unwind::begin_unwind_inner::hb9f03d7eac5ad766Jzb::v0.10
   3:     0x7f2614c98fb0 - rt::unwind::begin_unwind::h4d23f723c663afb4nfr::v0.10
   4:     0x7f26154946f0 - driver::driver::compile_input::h114b1222f6ba70aesWf::v0.10
   5:     0x7f26154b8be0 - run_compiler::hc8f4096777353458Yzn::v0.10
   6:     0x7f26154d0320 - main_args::closure.92072
   7:     0x7f26154cec50 - monitor::closure.91957
   8:     0x7f26154ca630 - task::TaskBuilder::try::closure.91732
   9:     0x7f261477cf80 - task::spawn_opts::closure.7828
  10:     0x7f26140d4b00 - rt::task::Task::run::closure.41627
  11:     0x7f26140e0470 - rust_try
  12:     0x7f26140d4a50 - rt::task::Task::run::hf5faab7a4b27dcc1fs9::v0.10
  13:     0x7f261477cd50 - task::spawn_opts::closure.7801
  14:     0x7f26140d8570 - rt::thread::thread_start::hed02916383a2b92bW69::v0.10
  15:     0x7f26119a6f40 - start_thread
  16:     0x7f2613d06179 - clone
  17:                0x0 - <unknown>

[flaper87]

cc #12865 not exactly the same bug but still related. I'm willing to mentor on this fix.