ICE when merge join two btreemap

[WiSaGaN]

ICE on 1.23 stable

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: rustc 1.23.0 (766bd11c8 2018-01-01) running on x86_64-unknown-linux-gnu

note: run with `RUST_BACKTRACE=1` for a backtrace

thread 'rustc' panicked at 'region_obligations not empty: [
    (
        NodeId(
            0
        ),
        RegionObligation(sub_region='_#15r, sup_type=bool)
    ),
    (
        NodeId(
            0
        ),
        RegionObligation(sub_region='_#15r, sup_type=())
    ),
    (
        NodeId(
            0
        ),
        RegionObligation(sub_region='_#16r, sup_type=bool)
    ),
    (
        NodeId(
            0
        ),
        RegionObligation(sub_region='_#16r, sup_type=())
    )
]', /checkout/src/librustc/infer/mod.rs:1161:8
stack backtrace:
   0:     0x7f979832ed93 - std::sys::imp::backtrace::tracing::imp::unwind_backtrace::hd278582b7bf125b4
                               at /checkout/src/libstd/sys/unix/backtrace/tracing/gcc_s.rs:49
   1:     0x7f979832a46c - std::sys_common::backtrace::_print::h585aeaf99da81bd9
                               at /checkout/src/libstd/sys_common/backtrace.rs:68
   2:     0x7f979833c2e1 - std::panicking::default_hook::{{closure}}::h2cf5ae2c765258ee
                               at /checkout/src/libstd/sys_common/backtrace.rs:57
                               at /checkout/src/libstd/panicking.rs:381
   3:     0x7f979833bfee - std::panicking::default_hook::h4df9c6962fc8f370
                               at /checkout/src/libstd/panicking.rs:391
   4:     0x7f979833c7ea - std::panicking::rust_panic_with_hook::hec57cb9076b0053e
                               at /checkout/src/libstd/panicking.rs:577
   5:     0x7f979833c66e - std::panicking::begin_panic::hf1e5e0b8a9c20d4e
                               at /checkout/src/libstd/panicking.rs:538
   6:     0x7f979833c569 - std::panicking::begin_panic_fmt::hae9efc5efbaf8262
                               at /checkout/src/libstd/panicking.rs:522
   7:     0x7f979455d316 - rustc::infer::InferCtxt::resolve_regions_and_report_errors::h2489ea2ac57c357e
   8:     0x7f9794b8c7b7 - rustc_typeck::check::regionck::<impl rustc_typeck::check::FnCtxt<'a, 'gcx, 'tcx>>::regionck_fn::hc14e4293e3b679a8
   9:     0x7f9794c163ba - <std::thread::local::LocalKey<T>>::with::h01f73e03a15e8426
  10:     0x7f9794c8e67a - rustc::ty::context::GlobalCtxt::enter_local::h69d9e38a43681cbd
  11:     0x7f9794ba2e77 - _ZN12rustc_typeck5check16typeck_tables_of17hda1df5d1a781f516E.llvm.6CA2F5D0
  12:     0x7f979423d56f - rustc::ty::maps::<impl rustc::ty::maps::queries::typeck_tables_of<'tcx>>::compute_result::ha75df1fb9b8d3d18
  13:     0x7f97944915f7 - _ZN5rustc9dep_graph5graph8DepGraph14with_task_impl17hfeaf2a9e09dd54d2E.llvm.F50A461C
  14:     0x7f97940e612d - rustc_errors::Handler::track_diagnostics::h164606659a2ac147
  15:     0x7f9794631c8d - rustc::ty::maps::plumbing::<impl rustc::ty::context::TyCtxt<'a, 'gcx, 'tcx>>::cycle_check::h62e23c272a55a3c9
  16:     0x7f979423d605 - rustc::ty::maps::<impl rustc::ty::maps::queries::typeck_tables_of<'tcx>>::force::hd19c6c4a34fec988
  17:     0x7f979423dd74 - rustc::ty::maps::<impl rustc::ty::maps::queries::typeck_tables_of<'tcx>>::try_get::h68926bb8acb77cbb
  18:     0x7f97943f1caf - rustc::ty::maps::TyCtxtAt::typeck_tables_of::h7b9335e88bc1b0ba
  19:     0x7f979423d4e5 - rustc::ty::maps::<impl rustc::ty::maps::queries::typeck_tables_of<'tcx>>::ensure::h439a01508b470686
  20:     0x7f9794c2ee75 - rustc::session::Session::track_errors::h4dcf1131057a0881
  21:     0x7f9794ba273a - _ZN12rustc_typeck5check18typeck_item_bodies17hab9b46dbfd42ae52E.llvm.6CA2F5D0
  22:     0x7f979423c2ef - rustc::ty::maps::<impl rustc::ty::maps::queries::typeck_item_bodies<'tcx>>::compute_result::h1dbc736fd065c6cf
  23:     0x7f979448435b - _ZN5rustc9dep_graph5graph8DepGraph14with_task_impl17hc108b7b2e4ed98c4E.llvm.F50A461C
  24:     0x7f9794106c1f - rustc_errors::Handler::track_diagnostics::hc2b6cdaae0cd4c7a
  25:     0x7f9794637c8d - rustc::ty::maps::plumbing::<impl rustc::ty::context::TyCtxt<'a, 'gcx, 'tcx>>::cycle_check::h7c1717b072245c43
  26:     0x7f979423c379 - rustc::ty::maps::<impl rustc::ty::maps::queries::typeck_item_bodies<'tcx>>::force::h8f71571c8a351326
  27:     0x7f979423c991 - rustc::ty::maps::<impl rustc::ty::maps::queries::typeck_item_bodies<'tcx>>::try_get::h465200f11ebb0a04
  28:     0x7f97943f1bbd - rustc::ty::maps::TyCtxtAt::typeck_item_bodies::hf490bb31c6267e76
  29:     0x7f9794678673 - rustc::ty::maps::<impl rustc::ty::context::TyCtxt<'a, 'tcx, 'lcx>>::typeck_item_bodies::hee5e0ed807fbd890
  30:     0x7f9794c4c6f5 - rustc::util::common::time::h3d96e1b50037fb39
  31:     0x7f9794c807bb - rustc_typeck::check_crate::hc40e9fd329108497
  32:     0x7f97987757e8 - <std::thread::local::LocalKey<T>>::with::hab712da7b05f1721
  33:     0x7f9798774d2c - <std::thread::local::LocalKey<T>>::with::h860f3147313caedd
  34:     0x7f97986c0a0e - rustc::ty::context::TyCtxt::create_and_enter::h1e9eab2229a6f71b
  35:     0x7f9798708d31 - rustc_driver::driver::compile_input::h3ac66d54d480a26d
  36:     0x7f979876494a - rustc_driver::run_compiler::h189ce0baff261139
  37:     0x7f97986e4a02 - _ZN3std10sys_common9backtrace28__rust_begin_short_backtrace17h832a69c7866f656aE.llvm.E45E81C6
  38:     0x7f97983479de - __rust_maybe_catch_panic
                               at /checkout/src/libpanic_unwind/lib.rs:101
  39:     0x7f97987558c2 - _ZN50_$LT$F$u20$as$u20$alloc..boxed..FnBox$LT$A$GT$$GT$8call_box17h89fc984700f7576bE.llvm.5C5B5F27
  40:     0x7f979833b16b - std::sys::imp::thread::Thread::new::thread_start::h379d0fc65e150416
                               at /checkout/src/liballoc/boxed.rs:772
                               at /checkout/src/libstd/sys_common/thread.rs:24
                               at /checkout/src/libstd/sys/unix/thread.rs:90
  41:     0x7f979226d6b9 - start_thread
  42:     0x7f97980003dc - clone
  43:                0x0 - <unknown>

Minimal example I managed to reduce to:

extern crate itertools; 
use itertools::Itertools;
use std::collections::btree_map::BTreeMap;

pub fn foo() {
    let bar1 = BTreeMap::<(), ()>::new();
    let bar2 = BTreeMap::<(), ()>::new();
    let _ = bar1.iter().merge_join_by(bar2.iter(), |_, _| ::std::cmp::Ordering::Equal);
}

fn main() {}

Playground link: https://play.rust-lang.org/?gist=044e2ff3efea878618257649546c8753&version=stable

Works fine on 1.22.1, current beta, current nightly. ICE on 1.23.0.

[WiSaGaN]

Since this is fixed in nightly, I think we may only need to add a regression test if there isn't one already.

[bluss]

The ICE message is the same as #46069

[WiSaGaN]

Closing this because we already have a test added in #46069 fix: #46226.