Small program causes internal compiler error on rustc 1.45.0

[jesperdj]

Code

(I know this is probably incorrect code, but this is what triggered the internal compiler error).

struct ChunkingIterator<T, S: 'static + Iterator<Item = T>> {
    source: S,
}

impl<T, S: Iterator<Item = T>> Iterator for ChunkingIterator<T, S> {
    type Item = IteratorChunk<T, S>;

    fn next(&mut self) -> Option<IteratorChunk<T, S>> {
        todo!()
    }
}

struct IteratorChunk<'a, T, S: Iterator<Item = T>> {
    source: &'a mut S,
}

impl<T, S: Iterator<Item = T>> Iterator for IteratorChunk<'_, T, S> {
    type Item = T;

    fn next(&mut self) -> Option<T> {
        todo!()
    }
}

fn main() {}

Meta

rustc --version --verbose:

rustc 1.45.0 (5c1f21c3b 2020-07-13)
binary: rustc
commit-hash: 5c1f21c3b82297671ad3ae1e8c942d2ca92e84f2
commit-date: 2020-07-13
host: x86_64-unknown-linux-gnu
release: 1.45.0
LLVM version: 10.0

Error output

error[E0106]: missing lifetime specifier
 --> src/main.rs:6:31
  |
6 |     type Item = IteratorChunk<T, S>;
  |                               ^ expected named lifetime parameter
  |
help: consider introducing a named lifetime parameter
  |
6 |     type Item<'a> = IteratorChunk<<'a>T, S>;
  |              ^^^^                 ^^^^

thread 'rustc' panicked at 'index out of bounds: the len is 0 but the index is 0', /cargo/registry/src/github.com-1ecc6299db9ec823/ena-0.14.0/src/snapshot_vec.rs:199:10
note: run with `RUST_BACKTRACE=1` environment variable to display a backtrace

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 1.45.0 (5c1f21c3b 2020-07-13) running on x86_64-unknown-linux-gnu

note: compiler flags: -C embed-bitcode=no -C debuginfo=2 -C incremental --crate-type bin

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

error: aborting due to previous error

For more information about this error, try `rustc --explain E0106`.
error: could not compile `sandbox`.

To learn more, run the command again with --verbose.

Backtrace

thread 'rustc' panicked at 'index out of bounds: the len is 0 but the index is 0', /cargo/registry/src/github.com-1ecc6299db9ec823/ena-0.14.0/src/snapshot_vec.rs:199:10
stack backtrace:
   0: backtrace::backtrace::libunwind::trace
             at /cargo/registry/src/github.com-1ecc6299db9ec823/backtrace-0.3.46/src/backtrace/libunwind.rs:86
   1: backtrace::backtrace::trace_unsynchronized
             at /cargo/registry/src/github.com-1ecc6299db9ec823/backtrace-0.3.46/src/backtrace/mod.rs:66
   2: std::sys_common::backtrace::_print_fmt
             at src/libstd/sys_common/backtrace.rs:78
   3: <std::sys_common::backtrace::_print::DisplayBacktrace as core::fmt::Display>::fmt
             at src/libstd/sys_common/backtrace.rs:59
   4: core::fmt::write
             at src/libcore/fmt/mod.rs:1076
   5: std::io::Write::write_fmt
             at src/libstd/io/mod.rs:1537
   6: std::sys_common::backtrace::_print
             at src/libstd/sys_common/backtrace.rs:62
   7: std::sys_common::backtrace::print
             at src/libstd/sys_common/backtrace.rs:49
   8: std::panicking::default_hook::{{closure}}
             at src/libstd/panicking.rs:198
   9: std::panicking::default_hook
             at src/libstd/panicking.rs:218
  10: rustc_driver::report_ice
  11: std::panicking::rust_panic_with_hook
             at src/libstd/panicking.rs:490
  12: rust_begin_unwind
             at src/libstd/panicking.rs:388
  13: core::panicking::panic_fmt
             at src/libcore/panicking.rs:101
  14: core::panicking::panic_bounds_check
             at src/libcore/panicking.rs:73
  15: rustc_infer::infer::InferCtxt::shallow_resolve_ty
  16: core::ops::function::impls::<impl core::ops::function::FnOnce<A> for &mut F>::call_once
  17: <smallvec::SmallVec<A> as core::iter::traits::collect::Extend<<A as smallvec::Array>::Item>>::extend
  18: rustc_middle::ty::fold::TypeFoldable::fold_with
  19: rustc_middle::ty::structural_impls::<impl rustc_middle::ty::fold::TypeFoldable for &rustc_middle::ty::TyS>::super_fold_with
  20: rustc_middle::ty::fold::TypeFoldable::fold_with
  21: rustc_middle::ty::fold::TypeFoldable::fold_with
  22: rustc_middle::ty::structural_impls::<impl rustc_middle::ty::fold::TypeFoldable for &rustc_middle::ty::TyS>::super_fold_with
  23: rustc_middle::ty::structural_impls::fold_list
  24: rustc_middle::ty::structural_impls::<impl rustc_middle::ty::fold::TypeFoldable for &rustc_middle::ty::TyS>::super_fold_with
  25: rustc_middle::ty::fold::TypeFoldable::fold_with
  26: rustc_infer::infer::error_reporting::<impl rustc_infer::infer::InferCtxt>::expected_found_str_ty
  27: rustc_middle::ty::context::GlobalCtxt::enter_local
  28: rustc_infer::infer::error_reporting::nice_region_error::NiceRegionError::try_report
  29: rustc_infer::infer::error_reporting::<impl rustc_infer::infer::InferCtxt>::report_region_errors
  30: rustc_infer::infer::InferCtxt::resolve_regions_and_report_errors
  31: rustc_typeck::check::regionck::<impl rustc_typeck::check::FnCtxt>::regionck_item
  32: rustc_middle::ty::context::tls::with_context::{{closure}}
  33: rustc_infer::infer::InferCtxtBuilder::enter
  34: rustc_typeck::check::compare_method::compare_impl_method
  35: rustc_typeck::check::check_impl_items_against_trait
  36: rustc_typeck::check::check_item_type
  37: rustc_middle::hir::map::Map::visit_item_likes_in_module
  38: rustc_typeck::check::check_mod_item_types
  39: rustc_middle::ty::query::<impl rustc_query_system::query::config::QueryAccessors<rustc_middle::ty::context::TyCtxt> for rustc_middle::ty::query::queries::check_mod_item_types>::compute
  40: rustc_middle::dep_graph::<impl rustc_query_system::dep_graph::DepKind for rustc_middle::dep_graph::dep_node::DepKind>::with_deps
  41: rustc_query_system::dep_graph::graph::DepGraph<K>::with_task_impl
  42: rustc_query_system::query::plumbing::get_query_impl
  43: rustc_query_system::query::plumbing::ensure_query_impl
  44: rustc_typeck::check_crate
  45: rustc_interface::passes::analysis
  46: rustc_middle::ty::query::<impl rustc_query_system::query::config::QueryAccessors<rustc_middle::ty::context::TyCtxt> for rustc_middle::ty::query::queries::analysis>::compute
  47: rustc_middle::dep_graph::<impl rustc_query_system::dep_graph::DepKind for rustc_middle::dep_graph::dep_node::DepKind>::with_deps
  48: rustc_query_system::dep_graph::graph::DepGraph<K>::with_task_impl
  49: rustc_query_system::query::plumbing::get_query_impl
  50: rustc_middle::ty::context::tls::enter_global
  51: rustc_interface::interface::run_compiler_in_existing_thread_pool
  52: rustc_ast::attr::with_globals

[spastorino]

Assigning P-medium as discussed as part of the Prioritization Working Group procedure and removing I-prioritize.

[estebank]

1.44 doesn't have the ICE.

[jonas-schievink]

#75361 shows that this can result in no user-facing error message. I suggest increasing priority to P-high.