ICE when combining impl_trait and lifetime elision

[Pratyush]

Hi! The following code snippet utilizing impl Trait and lifetime elision fails to compile (resulting in a ICE) on the latest nightly, as well as nightlies stretching back to (at least) 2017/08/02. If I explicitly specify the lifetimes, I don't get the ICE.

// lib.rs
#![feature(conservative_impl_trait)]
use std::collections::BTreeMap;

pub struct Wrapper<T> {
    map: BTreeMap<T, T>
}

impl<T> Wrapper<T> {
    pub fn iter(&self) -> impl Iterator<Item = &T> {
        self.block.iter() // notice that there is no field named block. The same error happens even when using self.map
    }
}

I get the following error:

error: internal compiler error: /checkout/src/librustc_typeck/check/mod.rs:626: escaping regions in predicate Obligation(predicate=Binder(ProjectionPredicate(ProjectionTy { substs: Slice([_]), item_def_id: DefId { krate: CrateNum(2), node: DefIndex(1588) => core/ded319f::iter[0]::iterator[0]::Iterator[0]::Item[0] } }, &T)),depth=0)
 --> lib.rs:9:27
  |
9 |     pub fn iter(&self) -> impl Iterator<Item = &T> {
  |                           ^^^^^^^^^^^^^^^^^^^^^^^^

The backtrace is:

thread 'rustc' panicked at 'Box<Any>', /checkout/src/librustc_errors/lib.rs:436:8
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:71
   2: std::panicking::default_hook::{{closure}}
             at /checkout/src/libstd/sys_common/backtrace.rs:60
             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:611
   5: std::panicking::begin_panic
   6: rustc_errors::Handler::span_bug
   7: rustc::session::opt_span_bug_fmt::{{closure}}
   8: rustc::session::span_bug_fmt
   9: rustc_typeck::check::Inherited::register_predicate
  10: <rustc::ty::fold::BottomUpFolder<'a, 'gcx, 'tcx, F> as rustc::ty::fold::TypeFolder<'gcx, 'tcx>>::fold_ty
  11: rustc_typeck::check::check_fn
  12: rustc_typeck::check::typeck_tables_of::{{closure}}
  13: rustc_typeck::check::typeck_tables_of
  14: rustc::dep_graph::graph::DepGraph::with_task
  15: rustc::ty::maps::<impl rustc::ty::maps::queries::typeck_tables_of<'tcx>>::try_get
  16: rustc::ty::maps::TyCtxtAt::typeck_tables_of
  17: rustc::ty::maps::<impl rustc::ty::context::TyCtxt<'a, 'tcx, 'lcx>>::typeck_tables_of
  18: rustc_typeck::check::typeck_item_bodies
  19: rustc::dep_graph::graph::DepGraph::with_task
  20: rustc::ty::maps::<impl rustc::ty::maps::queries::typeck_item_bodies<'tcx>>::try_get
  21: rustc::ty::maps::TyCtxtAt::typeck_item_bodies
  22: rustc::ty::maps::<impl rustc::ty::context::TyCtxt<'a, 'tcx, 'lcx>>::typeck_item_bodies
  23: rustc_typeck::check_crate
  24: rustc::ty::context::TyCtxt::create_and_enter
  25: rustc_driver::driver::compile_input
  26: rustc_driver::run_compiler

[cramertj]

Duplicate of #43396.

[shepmaster]

Closing as duplicate.