Unexpected definition for an identifier in pattern Err

[Thinkofname]

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 '../src/librustc_resolve/lib.rs:2356: unexpected definition for an identifier in pattern Err', ../src/librustc/session/mod.rs:645
stack backtrace:
   1:     0x7f76eb31c12f - std::sys::backtrace::tracing::imp::write::h29f5fdb9fc0a7395
   2:     0x7f76eb3337fb - std::panicking::default_hook::_{{closure}}::h2cc84f0378700526
   3:     0x7f76eb32c377 - std::panicking::default_hook::hbbe7fa36a995aca0
   4:     0x7f76eb32ca9c - std::panicking::rust_panic_with_hook::h105c3d42fcd2fb5e
   5:     0x7f76ea8551f1 - std::panicking::begin_panic::hbf62ea4a5ff3f9de
   6:     0x7f76ea8ba624 - rustc::session::opt_span_bug_fmt::_{{closure}}::h62b0957667555cfe
   7:     0x7f76e82459cf - rustc::session::span_bug_fmt::hcdfbe9cf944f6fc3
   8:     0x7f76e82acdf3 - rustc_resolve::Resolver::resolve_pattern::_{{closure}}::_{{closure}}::hb7b740e316c3c0d0
   9:     0x7f76e82b1146 - rustc_resolve::Resolver::resolve_pattern::_{{closure}}::h07300d27c945a906
  10:     0x7f76e8256448 - syntax::ast::Pat::walk::h1484712129603134
  11:     0x7f76e8296cb2 - rustc_resolve::Resolver::resolve_function::h2a7b902c2b6958af
  12:     0x7f76e8269a58 - syntax::visit::walk_impl_item::h8bc6dcab3e98d366
  13:     0x7f76e82bd0a9 - rustc_resolve::Resolver::resolve_implementation::_{{closure}}::_{{closure}}::_{{closure}}::_{{closure}}::h484fc0970900fda7
  14:     0x7f76e8297281 - rustc_resolve::Resolver::with_current_self_type::hf92c74c5ea1895c1
  15:     0x7f76e8297dfe - rustc_resolve::Resolver::with_self_rib::h43557df3fff66562
  16:     0x7f76e8297962 - rustc_resolve::Resolver::with_optional_trait_ref::h8d15622d53ad887a
  17:     0x7f76e82951ae - rustc_resolve::Resolver::resolve_item::hf44c6991ef672266
  18:     0x7f76e826c6cf - syntax::visit::walk_item::h2160a748780131f2
  19:     0x7f76e8294d80 - rustc_resolve::Resolver::resolve_item::hf44c6991ef672266
  20:     0x7f76e826c6cf - syntax::visit::walk_item::h2160a748780131f2
  21:     0x7f76e8294d80 - rustc_resolve::Resolver::resolve_item::hf44c6991ef672266
  22:     0x7f76e829075e - rustc_resolve::Resolver::resolve_crate::h4fdbe2c5a29bae4d
  23:     0x7f76eb933577 - rustc_driver::driver::phase_2_configure_and_expand::_{{closure}}::h7f9235d9e9fe0dc9
  24:     0x7f76eb8e5b52 - rustc_driver::driver::phase_2_configure_and_expand::h23617908add5ca02
  25:     0x7f76eb8d89b7 - rustc_driver::driver::compile_input::hb4cc34cf85dc1edf
  26:     0x7f76eb90344c - rustc_driver::run_compiler::h50f95674bd902ab5
  27:     0x7f76eb96eb28 - rustc_driver::run::_{{closure}}::h578f58fb80a79b9c
  28:     0x7f76eb9699cb - rustc_driver::monitor::_{{closure}}::he296944eac047e81
  29:     0x7f76eb86d9fd - std::panicking::try::call::h4577500a5284c6ff
  30:     0x7f76eb34187b - __rust_try
  31:     0x7f76eb34175e - __rust_maybe_catch_panic
  32:     0x7f76eb918e4d - std::thread::Builder::spawn::_{{closure}}::haaf8628155e4305c
  33:     0x7f76eb88784e - _<F as alloc..boxed..FnBox<A>>::call_box::h24f3eb0b42327962
  34:     0x7f76eb32a2c4 - std::sys::thread::Thread::new::thread_start::h8f3bd45211e9f5ea
  35:     0x7f76e2712183 - start_thread
  36:     0x7f76eaf5337c - clone
  37:                0x0 - <unknown>

Happened on a private project so I can't release the source and I haven't been able to reduce it down to a small test case yet. It happened when I removed a large number of modules to move into a crate without updating the uses.

rustc 1.12.0-nightly (34f35ed29 2016-07-17)
binary: rustc
commit-hash: 34f35ed29c8acdbe1e3c172786fc41d6f4fb6090
commit-date: 2016-07-17
host: x86_64-unknown-linux-gnu
release: 1.12.0-nightly

[Thinkofname]

This actually triggers #34929 on beta so chances are they are the same issue or at least related?

[Thinkofname]

And a test case: https://is.gd/tDdrzI

use missing;

impl Test {
    pub fn test(&self, missing: &A) -> Option<Vec<missing::B>> {
        match *missing {
            A::Missing{keycode, ..} => {
                unimplemented!()
            },
            _ => {}
        }
        None
    }
}

The reduced case doesn't trigger #34929 so it was most likely me running into two bugs at once.

Beta and stable don't show the issue only nightly

[petrochenkov]

And a test case: https://is.gd/tDdrzI

Interesting, thanks.
I didn't expect resolve_identifier to return Def::Err, but it can happen with import error recovery, as your example shows. I'll fix this.