Compiler panic when using impl Iterator<Item = &PathBuf>

[linclelinkpart5]

In my impl for a struct I'm working on, I have this:

    pub fn get_contains_dir<P: AsRef<Path>>(&self, rel_item_path: P) -> Option<PathBuf> {
        if let Ok((rel, abs)) = self.co_norm(rel_item_path) {
            if abs.is_dir() {
                return Some(rel)
            }
        }

        None
    }

    pub fn iter_contains_dir<P: AsRef<Path>>(&self, rel_item_path: P) -> impl Iterator<Item = &PathBuf> {
        self.get_contains_dir(rel_item_path).iter()
    }

When attempting to compile, I get this error (backtrace also included):

error: internal compiler error: /checkout/src/librustc_typeck/check/mod.rs:634: escaping regions in predicate Obligation(predicate=Binder(ProjectionPredicate(ProjectionTy { substs: Slice([_]), item_def_id: DefId { krate: CrateNum(2), index: DefIndex(0:1693) => core[373c]::iter[0]::iterator[0]::Iterator[0]::Item[0] } }, &std::path::PathBuf)),depth=0)
   --> src/library.rs:191:74
    |
191 |     pub fn iter_contains_dir<P: AsRef<Path>>(&self, rel_item_path: P) -> impl Iterator<Item = &PathBuf> {
    |                                                                          ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^

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-nightly (33374fa9d 2017-11-20) running on x86_64-unknown-linux-gnu

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

thread 'rustc' panicked at 'Box<Any>', /checkout/src/librustc_errors/lib.rs:418:8
note: Some details are omitted, run with `RUST_BACKTRACE=full` for a verbose backtrace.
stack backtrace:
   0: std::sys::imp::backtrace::tracing::imp::unwind_backtrace
             at /checkout/src/libstd/sys/unix/backtrace/tracing/gcc_s.rs:49
   1: std::sys_common::backtrace::_print
             at /checkout/src/libstd/sys_common/backtrace.rs:68
   2: std::panicking::default_hook::{{closure}}
             at /checkout/src/libstd/sys_common/backtrace.rs:57
             at /checkout/src/libstd/panicking.rs:381
   3: std::panicking::default_hook
             at /checkout/src/libstd/panicking.rs:391
   4: std::panicking::rust_panic_with_hook
             at /checkout/src/libstd/panicking.rs:577
   5: std::panicking::begin_panic
   6: rustc_errors::Handler::span_bug
   7: <std::thread::local::LocalKey<T>>::with
   8: rustc::ty::context::tls::with_opt
   9: rustc::session::span_bug_fmt
  10: rustc_typeck::check::Inherited::register_predicate
  11: <rustc::ty::fold::BottomUpFolder<'a, 'gcx, 'tcx, F> as rustc::ty::fold::TypeFolder<'gcx, 'tcx>>::fold_ty
  12: rustc_typeck::check::check_fn
  13: <std::thread::local::LocalKey<T>>::with
  14: rustc::ty::context::GlobalCtxt::enter_local
  15: _ZN12rustc_typeck5check16typeck_tables_of17h25d2aec5684f9308E.llvm.7E26391B
  16: rustc::ty::maps::<impl rustc::ty::maps::queries::typeck_tables_of<'tcx>>::compute_result
  17: _ZN5rustc9dep_graph5graph8DepGraph14with_task_impl17h47839a3014380fe2E.llvm.9C4F6362
  18: rustc_errors::Handler::track_diagnostics
  19: rustc::ty::maps::plumbing::<impl rustc::ty::context::TyCtxt<'a, 'gcx, 'tcx>>::cycle_check
  20: rustc::ty::maps::<impl rustc::ty::maps::queries::typeck_tables_of<'tcx>>::force
  21: rustc::ty::maps::<impl rustc::ty::maps::queries::typeck_tables_of<'tcx>>::try_get
  22: rustc::ty::maps::TyCtxtAt::typeck_tables_of
  23: rustc::ty::maps::<impl rustc::ty::maps::queries::typeck_tables_of<'tcx>>::ensure
  24: rustc::session::Session::track_errors
  25: _ZN12rustc_typeck5check18typeck_item_bodies17hd21b7190cdf37897E.llvm.7E26391B
  26: _ZN5rustc9dep_graph5graph8DepGraph14with_task_impl17hbd23d0600cb4f79bE.llvm.9C4F6362
  27: rustc_errors::Handler::track_diagnostics
  28: rustc::ty::maps::plumbing::<impl rustc::ty::context::TyCtxt<'a, 'gcx, 'tcx>>::cycle_check
  29: rustc::ty::maps::<impl rustc::ty::maps::queries::typeck_item_bodies<'tcx>>::force
  30: rustc::ty::maps::<impl rustc::ty::maps::queries::typeck_item_bodies<'tcx>>::try_get
  31: rustc::ty::maps::TyCtxtAt::typeck_item_bodies
  32: rustc::ty::maps::<impl rustc::ty::context::TyCtxt<'a, 'tcx, 'lcx>>::typeck_item_bodies
  33: rustc_typeck::check_crate
  34: <std::thread::local::LocalKey<T>>::with
  35: <std::thread::local::LocalKey<T>>::with
  36: rustc::ty::context::TyCtxt::create_and_enter
  37: rustc_driver::driver::compile_input
  38: rustc_driver::run_compiler

Output of rustc --version --verbose:

rustc 1.23.0-nightly (33374fa9d 2017-11-20)
binary: rustc
commit-hash: 33374fa9d09e2a790979b31e61100dfed4b44139
commit-date: 2017-11-20
host: x86_64-unknown-linux-gnu
release: 1.23.0-nightly
LLVM version: 4.0

[cramertj]

Lifetime elision isn't handled properly for impl Trait types right now. It's sort of an open question how this should behave (see #43396), however it definitely shouldn't ICE 😄.

[kennytm]

Closing as duplicate of #42479 and #43396.