#[allow_internal_unstable] - backtrace

bug.rs

#![feature(allow_internal_unstable)]
// #![feature(wrapping_next_power_of_two, const_transmute)]

#[allow_internal_unstable(wrapping_next_power_of_two)]
fn g(a: u64) -> u64 {
    a.wrapping_next_power_of_two()
}

#[allow_internal_unstable(const_transmute)]
const fn h(a: u64) -> i64 {
    unsafe { std::mem::transmute(a) }
}

fn main() {
    println!("Hello, world!");
}

rustc.log

error[E0658]: use of unstable library feature 'wrapping_next_power_of_two': needs decision on wrapping behaviour
 --> bug.rs:6:7
  |
6 |     a.wrapping_next_power_of_two()
  |       ^^^^^^^^^^^^^^^^^^^^^^^^^^
  |
  = note: see issue #32463 <https://github.com/rust-lang/rust/issues/32463> for more information
  = help: add `#![feature(wrapping_next_power_of_two)]` to the crate attributes to enable

thread 'rustc' panicked at 'aborting due to `-Z treat-err-as-bug=1`', compiler/rustc_errors/src/lib.rs:977:27
stack backtrace:
   0:     0x7f7458d1aa21 - <std::sys_common::backtrace::_print::DisplayBacktrace as core::fmt::Display>::fmt::hba66826ca3f1d2aa
   1:     0x7f7458dc02e7 - core::fmt::write::hb2f2f22911c1678d
   2:     0x7f7458d1a5a4 - std::io::Write::write_fmt::hdb31fd9606fe8f69
   3:     0x7f7458d1a8af - std::sys_common::backtrace::print::h2e3ccd21a8052f35
   4:     0x7f7458d4e6d7 - std::panicking::default_hook::{{closure}}::hdfa5e1ebc5add0e3
   5:     0x7f7458d4e4e2 - std::panicking::default_hook::hd88c33b01312b0d3
   6:     0x7f74594ab18d - rustc_driver::report_ice::hed817cc78bed1513
   7:     0x7f7458d4eb39 - std::panicking::rust_panic_with_hook::h269c9b34303e7c0b
   8:     0x7f745bc63824 - std::panicking::begin_panic::{{closure}}::h1bf7ab491319027c
   9:     0x7f745bc637ec - std::sys_common::backtrace::__rust_end_short_backtrace::h13ab5760f7650afa
  10:     0x7f745bc836bc - std::panicking::begin_panic::hd825546a48eb1570
  11:     0x7f745bc8955f - rustc_errors::HandlerInner::emit_diagnostic::h7a994f77e42fbd31
  12:     0x7f745bc890db - rustc_errors::Handler::emit_diagnostic::h44f41f27619320c2
  13:     0x7f745bc792d4 - rustc_errors::diagnostic_builder::DiagnosticBuilder::emit::h7ba97a1036097b96
  14:     0x7f745b5d0b98 - rustc_middle::middle::stability::report_unstable::h6962b92fb0a0d725
  15:     0x7f745b82aa54 - rustc_middle::middle::stability::<impl rustc_middle::ty::context::TyCtxt>::check_optional_stability::hd028732b8dc3399e
  16:     0x7f745b686827 - rustc_middle::middle::stability::<impl rustc_middle::ty::context::TyCtxt>::check_stability::h2629b32865c3cb89
  17:     0x7f7459c39bd7 - rustc_typeck::check::method::<impl rustc_typeck::check::fn_ctxt::FnCtxt>::lookup_method::hbaf36a68ed66999f
  18:     0x7f7459c1625d - rustc_typeck::check::expr::<impl rustc_typeck::check::fn_ctxt::FnCtxt>::check_expr_kind::hf8b4fad8cffd50bf
  19:     0x7f7459c15707 - rustc_typeck::check::expr::<impl rustc_typeck::check::fn_ctxt::FnCtxt>::check_expr_with_expectation::h61410014431d3e2b
  20:     0x7f7459f41ebc - rustc_typeck::check::fn_ctxt::_impl::<impl rustc_typeck::check::fn_ctxt::FnCtxt>::with_breakable_ctxt::h8fc683799f065af9
  21:     0x7f7459c2cadf - rustc_typeck::check::fn_ctxt::checks::<impl rustc_typeck::check::fn_ctxt::FnCtxt>::check_block_with_expected::h866ae5263b8dab6f
  22:     0x7f7459c169a9 - rustc_typeck::check::expr::<impl rustc_typeck::check::fn_ctxt::FnCtxt>::check_expr_kind::hf8b4fad8cffd50bf
  23:     0x7f7459c15707 - rustc_typeck::check::expr::<impl rustc_typeck::check::fn_ctxt::FnCtxt>::check_expr_with_expectation::h61410014431d3e2b
  24:     0x7f7459c1bfe9 - rustc_typeck::check::expr::<impl rustc_typeck::check::fn_ctxt::FnCtxt>::check_return_expr::h28fca05cb83937a0
  25:     0x7f7459ea5142 - rustc_typeck::check::check::check_fn::h46cbb50f1093f95c
  26:     0x7f7459dc1271 - rustc_infer::infer::InferCtxtBuilder::enter::hcef4d7443a264753
  27:     0x7f7459d9dcbe - rustc_typeck::check::inherited::InheritedBuilder::enter::h71addbf1f499dda9
  28:     0x7f7459d42353 - rustc_typeck::check::typeck_with_fallback::hbebbdef18178b43b
  29:     0x7f7459d70a4c - rustc_typeck::check::typeck::h35b0e80973279aac
  30:     0x7f7459f1073e - rustc_middle::ty::query::<impl rustc_query_system::query::config::QueryAccessors<rustc_middle::ty::context::TyCtxt> for rustc_middle::ty::query::queries::typeck>::compute::hf35f16d5c9bfea01
  31:     0x7f7459e02cf3 - rustc_query_system::dep_graph::graph::DepGraph<K>::with_task_impl::h423efba5d4e181c1
  32:     0x7f7459d3eb13 - rustc_data_structures::stack::ensure_sufficient_stack::hc0e686376c242906
  33:     0x7f7459ca16d9 - rustc_query_system::query::plumbing::get_query_impl::h94f852ed14400fff
  34:     0x7f7459cbd75f - rustc_query_system::query::plumbing::ensure_query_impl::hc0f816870a2bfffa
  35:     0x7f7459f105c9 - rustc_middle::ty::<impl rustc_middle::ty::context::TyCtxt>::par_body_owners::h2ab78a7a23e58b9f
  36:     0x7f7459d744bd - rustc_typeck::check::typeck_item_bodies::h464ea73f3951b05e
  37:     0x7f7459f1a78e - rustc_middle::ty::query::<impl rustc_query_system::query::config::QueryAccessors<rustc_middle::ty::context::TyCtxt> for rustc_middle::ty::query::queries::typeck_item_bodies>::compute::hd034196c1f9eef28
  38:     0x7f7459e04e63 - rustc_query_system::dep_graph::graph::DepGraph<K>::with_task_impl::h6d3836a44537399e
  39:     0x7f7459d38813 - rustc_data_structures::stack::ensure_sufficient_stack::h22daf6ebcb24adfd
  40:     0x7f7459cae88e - rustc_query_system::query::plumbing::get_query_impl::hcb2cf243e4a9e127
  41:     0x7f7459f1ad70 - rustc_session::utils::<impl rustc_session::session::Session>::time::h1b2b21c9df5bdf78
  42:     0x7f7459c51a7e - rustc_typeck::check_crate::h95cf2851407b7182
  43:     0x7f745958029f - rustc_interface::passes::analysis::hcb2e4c480c3f4804
  44:     0x7f745946a4db - rustc_middle::ty::query::<impl rustc_query_system::query::config::QueryAccessors<rustc_middle::ty::context::TyCtxt> for rustc_middle::ty::query::queries::analysis>::compute::h431c18cf6447aaab
  45:     0x7f745940b243 - rustc_query_system::dep_graph::graph::DepGraph<K>::with_task_impl::h4dc2b65fdcc1076a
  46:     0x7f745940c620 - rustc_query_system::dep_graph::graph::DepGraph<K>::with_eval_always_task::hda6901b0c85d91e6
  47:     0x7f7459375d64 - rustc_data_structures::stack::ensure_sufficient_stack::h9178f3038dff360d
  48:     0x7f74594a1e36 - rustc_query_system::query::plumbing::get_query_impl::he2ce1312a09bf015
  49:     0x7f745946ac48 - rustc_interface::passes::QueryContext::enter::h4d880c0ab90b6b06
  50:     0x7f7459453d37 - rustc_interface::queries::<impl rustc_interface::interface::Compiler>::enter::h16b1a7b038030ec1
  51:     0x7f745937e590 - rustc_span::with_source_map::h81b1fac5897a16ea
  52:     0x7f7459454ee1 - rustc_interface::interface::create_compiler_and_run::h8cc6c2a06c54ddf0
  53:     0x7f7459462301 - scoped_tls::ScopedKey<T>::set::hd2dde7f0027ab524
  54:     0x7f745937edc7 - rustc_span::with_session_globals::hcadb1873e902fc8f
  55:     0x7f745937917f - std::sys_common::backtrace::__rust_begin_short_backtrace::h077d3e86d0a92fa5
  56:     0x7f74594b0006 - std::panicking::try::h952bc32cd4bc410a
  57:     0x7f745948865e - core::ops::function::FnOnce::call_once{{vtable.shim}}::he4f7f1821d9db07e
  58:     0x7f7458d22998 - <alloc::boxed::Box<F> as core::ops::function::FnOnce<A>>::call_once::h795da1c5ae07dbe4
  59:     0x7f7458d5e5aa - std::sys::unix::thread::Thread::new::thread_start::h35a86ce7f09bc6f1
  60:     0x7f7453dd7f27 - start_thread
                               at /builddir/glibc-2.30/nptl/pthread_create.c:479:8
  61:     0x7f7458bbde0f - clone
  62:                0x0 - <unknown>

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/issues/new?labels=C-bug%2C+I-ICE%2C+T-compiler&template=ice.md

note: rustc 1.49.0-dev running on x86_64-unknown-linux-gnu

note: compiler flags: -Z treat-err-as-bug=1

query stack during panic:
#0 [typeck] type-checking `g`
#1 [typeck_item_bodies] type-checking all item bodies
#2 [analysis] running analysis passes on this crate
end of query stack