% RUST_BACKTRACE=1 cargo run
   Compiling intfn6 v0.1.0 (/home/bjc/src/MyStuff/intfn6)
error: internal compiler error: src/librustc_mir/monomorphize/collector.rs:776: Cannot create local mono-item for DefId(11/0:10 ~ intfn6[c1a9]::{{impl}}[0]::default_handler[0])

thread 'rustc' panicked at 'Box<Any>', src/librustc_errors/lib.rs:636:9
note: Some details are omitted, run with `RUST_BACKTRACE=full` for a verbose backtrace.
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:71
   2: std::panicking::default_hook::{{closure}}
             at src/libstd/sys_common/backtrace.rs:59
             at src/libstd/panicking.rs:197
   3: std::panicking::default_hook
             at src/libstd/panicking.rs:211
   4: rustc::util::common::panic_hook
   5: std::panicking::rust_panic_with_hook
             at src/libstd/panicking.rs:478
   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 as rustc::mir::visit::Visitor>::visit_terminator_kind
  17: rustc_mir::monomorphize::collector::collect_items_rec
  18: rustc_mir::monomorphize::collector::collect_items_rec
  19: rustc_mir::monomorphize::collector::collect_crate_mono_items::{{closure}}
  20: rustc::util::common::time
  21: rustc_mir::monomorphize::collector::collect_crate_mono_items
  22: rustc::util::common::time
  23: rustc_mir::monomorphize::partitioning::collect_and_partition_mono_items
  24: rustc::ty::query::__query_compute::collect_and_partition_mono_items
  25: rustc::ty::query::<impl rustc::ty::query::config::QueryAccessors for rustc::ty::query::queries::collect_and_partition_mono_items>::compute
  26: rustc::dep_graph::graph::DepGraph::with_task_impl
  27: rustc::ty::query::plumbing::<impl rustc::ty::context::TyCtxt>::get_query
  28: rustc_codegen_ssa::base::codegen_crate
  29: <rustc_codegen_llvm::LlvmCodegenBackend as rustc_codegen_utils::codegen_backend::CodegenBackend>::codegen_crate
  30: rustc::util::common::time
  31: rustc_interface::passes::start_codegen
  32: rustc::ty::context::tls::enter_global
  33: rustc_interface::passes::BoxedGlobalCtxt::access::{{closure}}
  34: rustc_interface::passes::create_global_ctxt::{{closure}}
  35: rustc_interface::passes::BoxedGlobalCtxt::enter
  36: rustc_interface::queries::Query<T>::compute
  37: rustc_interface::queries::<impl rustc_interface::interface::Compiler>::ongoing_codegen
  38: rustc_interface::interface::run_compiler_in_existing_thread_pool
  39: std::thread::local::LocalKey<T>::with
  40: scoped_tls::ScopedKey<T>::set
  41: syntax::with_globals
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 1.36.0-nightly (6d599337f 2019-04-22) 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 `intfn6`.

To learn more, run the command again with --verbose.
[1]    9047 exit 101   RUST_BACKTRACE=1 cargo run