rustc 1.33.0-nightly (b2b7a063a 2019-01-01) compiler unexpectedly panics

[jonimake]

2019-01-01 nightly toolchain fails to compile the following: https://github.com/jonimake/rust-settings-test
The problem is the let _ = config::File::with_name("Settings"); line in main.rs. Below is the command line output.

RUST_BACKTRACE=1 cargo build --verbose
       Fresh version_check v0.1.5
       Fresh cfg-if v0.1.6
       Fresh ucd-util v0.1.3
       Fresh lazy_static v1.2.0
       Fresh serde v0.8.23
       Fresh utf8-ranges v1.0.2
       Fresh lazy_static v0.2.11
       Fresh linked-hash-map v0.5.1
       Fresh itoa v0.4.3
       Fresh rust-ini v0.12.2
       Fresh regex-syntax v0.6.4
       Fresh thread_local v0.3.6
       Fresh serde_test v0.8.23
       Fresh yaml-rust v0.4.2
       Fresh libc v0.2.45
       Fresh num-traits v0.2.6
       Fresh serde v1.0.84
       Fresh ryu v0.2.7
       Fresh linked-hash-map v0.3.0
       Fresh memchr v2.1.2
       Fresh num-traits v0.1.43
       Fresh toml v0.4.10
       Fresh serde_json v1.0.34
       Fresh aho-corasick v0.6.9
       Fresh nom v4.1.1
       Fresh regex v1.1.0
       Fresh serde-hjson v0.8.2
       Fresh config v0.9.1
   Compiling rust-setting-test v0.1.0 (/home/joni/repos/personal/rust-settings-test)
     Running `rustc --edition=2018 --crate-name rust_setting_test src/main.rs --color always --crate-type bin --emit=dep-info,link -C debuginfo=2 -C metadata=7a08d1f1dbdfe01a -C extra-filename=-7a08d1f1dbdfe01a --out-dir /home/joni/repos/personal/rust-settings-test/target/debug/deps -C incremental=/home/joni/repos/personal/rust-settings-test/target/debug/incremental -L dependency=/home/joni/repos/personal/rust-settings-test/target/debug/deps --extern config=/home/joni/repos/personal/rust-settings-test/target/debug/deps/libconfig-566e0d7013e1820e.rlib`
error: internal compiler error: src/librustc_mir/monomorphize/collector.rs:747: Cannot create local mono-item for DefId(11/0:303 ~ config[bb47]::file[0]::{{impl}}[1]::with_name[0])

thread 'rustc' panicked at 'Box<Any>', src/librustc_errors/lib.rs:590:9
stack backtrace:
   0: std::sys::unix::backtrace::tracing::imp::unwind_backtrace
             at src/libstd/sys/unix/backtrace/tracing/gcc_s.rs:39
   1: std::sys_common::backtrace::_print
             at src/libstd/sys_common/backtrace.rs:70
   2: std::panicking::default_hook::{{closure}}
             at src/libstd/sys_common/backtrace.rs:58
             at src/libstd/panicking.rs:200
   3: std::panicking::default_hook
             at src/libstd/panicking.rs:215
   4: rustc::util::common::panic_hook
   5: std::panicking::rust_panic_with_hook
             at src/libstd/panicking.rs:482
   6: std::panicking::begin_panic
   7: rustc_errors::Handler::bug
   8: rustc::util::bug::opt_span_bug_fmt::{{closure}}
   9: rustc::ty::context::tls::with_opt::{{closure}}
  10: rustc::ty::context::tls::with_context_opt
  11: rustc::ty::context::tls::with_opt
  12: rustc::util::bug::opt_span_bug_fmt
  13: rustc::util::bug::bug_fmt
  14: rustc_mir::monomorphize::collector::should_monomorphize_locally
  15: rustc_mir::monomorphize::collector::visit_instance_use
  16: <rustc_mir::monomorphize::collector::MirNeighborCollector<'a, 'tcx> as rustc::mir::visit::Visitor<'tcx>>::visit_terminator_kind
  17: rustc_mir::monomorphize::collector::collect_items_rec
  18: rustc_mir::monomorphize::collector::collect_crate_mono_items::{{closure}}
  19: rustc::util::common::time
  20: rustc_mir::monomorphize::collector::collect_crate_mono_items
  21: rustc::util::common::time
  22: rustc_mir::monomorphize::partitioning::collect_and_partition_mono_items
  23: rustc::ty::query::__query_compute::collect_and_partition_mono_items
  24: rustc::ty::query::<impl rustc::ty::query::config::QueryAccessors<'tcx> for rustc::ty::query::queries::collect_and_partition_mono_items<'tcx>>::compute
  25: rustc::dep_graph::graph::DepGraph::with_task_impl
  26: <rustc::ty::query::plumbing::JobOwner<'a, 'tcx, Q>>::start
  27: rustc::ty::query::plumbing::<impl rustc::ty::context::TyCtxt<'a, 'gcx, 'tcx>>::force_query_with_job
  28: rustc::ty::query::plumbing::<impl rustc::ty::context::TyCtxt<'a, 'gcx, 'tcx>>::try_get_with
  29: rustc_codegen_ssa::base::codegen_crate
  30: <rustc_codegen_llvm::LlvmCodegenBackend as rustc_codegen_utils::codegen_backend::CodegenBackend>::codegen_crate
  31: rustc_driver::driver::phase_4_codegen
  32: rustc_driver::driver::compile_input::{{closure}}
  33: <std::thread::local::LocalKey<T>>::with
  34: rustc::ty::context::TyCtxt::create_and_enter
  35: rustc_driver::driver::compile_input
  36: rustc_driver::run_compiler_with_pool
  37: <scoped_tls::ScopedKey<T>>::set
  38: rustc_driver::run_compiler
  39: <scoped_tls::ScopedKey<T>>::set
  40: syntax::with_globals
  41: __rust_maybe_catch_panic
             at src/libpanic_unwind/lib.rs:92
  42: <F as alloc::boxed::FnBox<A>>::call_box
  43: std::sys::unix::thread::Thread::new::thread_start
             at /rustc/b2b7a063af39455d7362524da3123c34c3f4842e/src/liballoc/boxed.rs:734
             at src/libstd/sys_common/thread.rs:14
             at src/libstd/sys/unix/thread.rs:81
  44: start_thread
  45: __clone
query stack during panic:
#0 [collect_and_partition_mono_items] collect_and_partition_mono_items
end of query stack
error: aborting due to previous error


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: rustc 1.33.0-nightly (b2b7a063a 2019-01-01) running on x86_64-unknown-linux-gnu

note: compiler flags: -C debuginfo=2 -C incremental --crate-type bin

note: some of the compiler flags provided by cargo are hidden

error: Could not compile `rust-setting-test`.

Caused by:
  process didn't exit successfully: `rustc --edition=2018 --crate-name rust_setting_test src/main.rs --color always --crate-type bin --emit=dep-info,link -C debuginfo=2 -C metadata=7a08d1f1dbdfe01a -C extra-filename=-7a08d1f1dbdfe01a --out-dir /home/joni/repos/personal/rust-settings-test/target/debug/deps -C incremental=/home/joni/repos/personal/rust-settings-test/target/debug/incremental -L dependency=/home/joni/repos/personal/rust-settings-test/target/debug/deps --extern config=/home/joni/repos/personal/rust-settings-test/target/debug/deps/libconfig-566e0d7013e1820e.rlib` (exit code: 101)

[cramertj]

I think this was caused by #56878, which seems to be causing some actually-reachable public functions to be identified as private (cc @petrochenkov). Specifically, the following code results in a warning "method is never used: new", but new is actually available to external crates, albeit causing an ICE when used:

pub mod pub_mod {
    use crate:;priv_mod::PubButUndexposedType;
    use std::marker::PhantomData;

    pub struct PubStruct<T>(PhantomData<T>);

    impl PubStruct<PubButUnexposedType> {
        pub fn new() -> Self { PubStruct(PhantomData) }
    }
}
mod priv_mod {
    pub struct PubButUnexposedType;
}

In a separate crate, it's possible to call PubStruct::new without naming PubButUnexposedType, making it visible. However, this results in an ICE, and the compiler thinks that new is unreachable and warns on its definition.

Adding a visible top-level re-export of PubButUnexposedType causes the warning and the ICE to go away.

[nagisa]

Discussed at the T-compiler meeting. Proactively assigning @petrochenkov although bisecting would make sense to be sure as to what exact cause really is.

[petrochenkov]

I'll look what happens.

[nikomatsakis]

Bisecting just because it's easy to do. Will post the results.

[nikomatsakis]

regression in nightly-2019-01-02

[nikomatsakis]

regression in fe6a54d, which is #56878, as @cramertj predicted

[petrochenkov]

Fixed in #57344