&dyn* causes an ICE

[DutchGhost]

Code

#![feature(dyn_star)]
#![allow(incomplete_features)]

use core::fmt::Debug;

fn main() {
    let i = 42 as &dyn* Debug;
}

Meta

rustc --version --verbose:

rustc 1.66.0-nightly (e7119a030 2022-09-22)

Error output

[<output>](error: internal compiler error: compiler/rustc_trait_selection/src/traits/select/confirmation.rs:1147:18: impossible case reached)

Backtrace

error: internal compiler error: compiler/rustc_trait_selection/src/traits/select/confirmation.rs:1147:18: impossible case reached

thread 'rustc' panicked at 'Box<dyn Any>', /rustc/e7119a0300b87a3d670408ee8e847c6821b3ae80/compiler/rustc_errors/src/lib.rs:1496:9
stack backtrace:
   0:     0x7f6117c4bff0 - std::backtrace_rs::backtrace::libunwind::trace::hf4e04b2e4313927b
                               at /rustc/e7119a0300b87a3d670408ee8e847c6821b3ae80/library/std/src/../../backtrace/src/backtrace/mod.rs:66:5
   1:     0x7f6117c4bff0 - std::backtrace_rs::backtrace::trace_unsynchronized::h2771cf061d4680d1
                               at /rustc/e7119a0300b87a3d670408ee8e847c6821b3ae80/library/std/src/../../backtrace/src/backtrace/mod.rs:66:5
   2:     0x7f6117c4bff0 - std::sys_common::backtrace::_print_fmt::h2e413508900ead1c
                               at /rustc/e7119a0300b87a3d670408ee8e847c6821b3ae80/library/std/src/sys_common/backtrace.rs:66:5
   3:     0x7f6117c4bff0 - <std::sys_common::backtrace::_print::DisplayBacktrace as core::fmt::Display>::fmt::hb886319318f6b897
                               at /rustc/e7119a0300b87a3d670408ee8e847c6821b3ae80/library/std/src/sys_common/backtrace.rs:45:22
   4:     0x7f6117ca6e1e - core::fmt::write::hd7350cb51945e18c
                               at /rustc/e7119a0300b87a3d670408ee8e847c6821b3ae80/library/core/src/fmt/mod.rs:1202:17
   5:     0x7f6117c3caf5 - std::io::Write::write_fmt::ha7bc763f922fc662
                               at /rustc/e7119a0300b87a3d670408ee8e847c6821b3ae80/library/std/src/io/mod.rs:1679:15
   6:     0x7f6117c4ed73 - std::sys_common::backtrace::_print::h7ad0003e1b032609
                               at /rustc/e7119a0300b87a3d670408ee8e847c6821b3ae80/library/std/src/sys_common/backtrace.rs:48:5
   7:     0x7f6117c4ed73 - std::sys_common::backtrace::print::h6f247b59322d4826
                               at /rustc/e7119a0300b87a3d670408ee8e847c6821b3ae80/library/std/src/sys_common/backtrace.rs:35:9
   8:     0x7f6117c4ed73 - std::panicking::default_hook::{{closure}}::h71a394bfa368bc38
                               at /rustc/e7119a0300b87a3d670408ee8e847c6821b3ae80/library/std/src/panicking.rs:267:22
   9:     0x7f6117c4ea5f - std::panicking::default_hook::h353829743ca9a29f
                               at /rustc/e7119a0300b87a3d670408ee8e847c6821b3ae80/library/std/src/panicking.rs:286:9
  10:     0x7f611a464ef1 - <rustc_driver[7857f239df018eab]::DEFAULT_HOOK::{closure#0}::{closure#0} as core[cde1ce9e21f08391]::ops::function::FnOnce<(&core[cde1ce9e21f08391]::panic::panic_info::PanicInfo,)>>::call_once::{shim:vtable#0}
  11:     0x7f6117c4f5ab - <alloc::boxed::Box<F,A> as core::ops::function::Fn<Args>>::call::h5c7ac9f6a4be07e2
                               at /rustc/e7119a0300b87a3d670408ee8e847c6821b3ae80/library/alloc/src/boxed.rs:1954:9
  12:     0x7f6117c4f5ab - std::panicking::rust_panic_with_hook::h6ad4960c15699d95
                               at /rustc/e7119a0300b87a3d670408ee8e847c6821b3ae80/library/std/src/panicking.rs:673:13
  13:     0x7f611b3f3ec1 - std[35bb8192b5670ad2]::panicking::begin_panic::<rustc_errors[354c2d440e1385ac]::ExplicitBug>::{closure#0}
  14:     0x7f611b3f19b6 - std[35bb8192b5670ad2]::sys_common::backtrace::__rust_end_short_backtrace::<std[35bb8192b5670ad2]::panicking::begin_panic<rustc_errors[354c2d440e1385ac]::ExplicitBug>::{closure#0}, !>
  15:     0x7f611b44a376 - std[35bb8192b5670ad2]::panicking::begin_panic::<rustc_errors[354c2d440e1385ac]::ExplicitBug>
  16:     0x7f611b3ee5a6 - std[35bb8192b5670ad2]::panic::panic_any::<rustc_errors[354c2d440e1385ac]::ExplicitBug>
  17:     0x7f611b3eb13f - <rustc_errors[354c2d440e1385ac]::HandlerInner>::bug::<&alloc[70f1755a93720895]::string::String>
  18:     0x7f611b3eab70 - <rustc_errors[354c2d440e1385ac]::Handler>::bug::<&alloc[70f1755a93720895]::string::String>
  19:     0x7f611b4aa73d - rustc_middle[33a3dc3ec8228005]::ty::context::tls::with_context_opt::<rustc_middle[33a3dc3ec8228005]::ty::context::tls::with_opt<rustc_middle[33a3dc3ec8228005]::util::bug::opt_span_bug_fmt<rustc_span[4a0a9e8ceb64f0f4]::span_encoding::Span>::{closure#0}, ()>::{closure#0}, ()>
  20:     0x7f611b4ac2b6 - rustc_middle[33a3dc3ec8228005]::util::bug::opt_span_bug_fmt::<rustc_span[4a0a9e8ceb64f0f4]::span_encoding::Span>
  21:     0x7f6118ecf583 - rustc_middle[33a3dc3ec8228005]::util::bug::bug_fmt
  22:     0x7f6118ecc3e5 - <rustc_trait_selection[c58af949e91f9309]::traits::select::SelectionContext>::confirm_candidate
  23:     0x7f6118eb3a55 - <rustc_trait_selection[c58af949e91f9309]::traits::select::SelectionContext>::select
  24:     0x7f6118ea96b8 - <rustc_infer[ab48729dad9c09b9]::infer::InferCtxt>::commit_if_ok::<rustc_infer[ab48729dad9c09b9]::infer::InferOk<(alloc[70f1755a93720895]::vec::Vec<rustc_middle[33a3dc3ec8228005]::ty::adjustment::Adjustment>, rustc_middle[33a3dc3ec8228005]::ty::Ty)>, rustc_middle[33a3dc3ec8228005]::ty::error::TypeError, <rustc_typeck[3342d60c7785d15]::check::fn_ctxt::FnCtxt>::try_coerce::{closure#1}>
  25:     0x7f6118f11e10 - <rustc_typeck[3342d60c7785d15]::check::fn_ctxt::FnCtxt>::try_coerce
  26:     0x7f611a850712 - <rustc_typeck[3342d60c7785d15]::check::cast::CastCheck>::report_cast_error
  27:     0x7f6119f0a50b - <rustc_typeck[3342d60c7785d15]::check::cast::CastCheck>::check
  28:     0x7f6119a6b725 - <rustc_infer[ab48729dad9c09b9]::infer::InferCtxtBuilder>::enter::<&rustc_middle[33a3dc3ec8228005]::ty::context::TypeckResults, <rustc_typeck[3342d60c7785d15]::check::inherited::InheritedBuilder>::enter<rustc_typeck[3342d60c7785d15]::check::typeck_with_fallback<rustc_typeck[3342d60c7785d15]::check::typeck::{closure#0}>::{closure#1}, &rustc_middle[33a3dc3ec8228005]::ty::context::TypeckResults>::{closure#0}>
  29:     0x7f6119a68629 - rustc_typeck[3342d60c7785d15]::check::typeck
  30:     0x7f6119816f65 - rustc_query_system[d3b2657d85679091]::query::plumbing::try_execute_query::<rustc_query_impl[542bbd4b66bfb449]::plumbing::QueryCtxt, rustc_query_system[d3b2657d85679091]::query::caches::DefaultCache<rustc_span[4a0a9e8ceb64f0f4]::def_id::LocalDefId, &rustc_middle[33a3dc3ec8228005]::ty::context::TypeckResults>>
  31:     0x7f611a3a6c0e - <rustc_query_impl[542bbd4b66bfb449]::Queries as rustc_middle[33a3dc3ec8228005]::ty::query::QueryEngine>::typeck
  32:     0x7f611a1ef747 - rustc_data_structures[bf19c7e493ef6519]::sync::par_for_each_in::<&[rustc_span[4a0a9e8ceb64f0f4]::def_id::LocalDefId], <rustc_middle[33a3dc3ec8228005]::hir::map::Map>::par_body_owners<rustc_typeck[3342d60c7785d15]::check::typeck_item_bodies::{closure#0}>::{closure#0}>
  33:     0x7f611a1ef503 - rustc_typeck[3342d60c7785d15]::check::typeck_item_bodies
  34:     0x7f611a0f2e5a - rustc_query_system[d3b2657d85679091]::query::plumbing::try_execute_query::<rustc_query_impl[542bbd4b66bfb449]::plumbing::QueryCtxt, rustc_query_system[d3b2657d85679091]::query::caches::DefaultCache<(), ()>>
  35:     0x7f611a0f2b87 - rustc_query_system[d3b2657d85679091]::query::plumbing::get_query::<rustc_query_impl[542bbd4b66bfb449]::queries::typeck_item_bodies, rustc_query_impl[542bbd4b66bfb449]::plumbing::QueryCtxt>
  36:     0x7f6119842ebf - <rustc_session[fa757ff4c2b8954a]::session::Session>::time::<(), rustc_typeck[3342d60c7785d15]::check_crate::{closure#7}>
  37:     0x7f6119842a7f - rustc_typeck[3342d60c7785d15]::check_crate
  38:     0x7f6119842047 - rustc_interface[f2560d97934cc6f6]::passes::analysis
  39:     0x7f611a233e34 - rustc_query_system[d3b2657d85679091]::query::plumbing::try_execute_query::<rustc_query_impl[542bbd4b66bfb449]::plumbing::QueryCtxt, rustc_query_system[d3b2657d85679091]::query::caches::DefaultCache<(), core[cde1ce9e21f08391]::result::Result<(), rustc_errors[354c2d440e1385ac]::ErrorGuaranteed>>>
  40:     0x7f611a233b67 - rustc_query_system[d3b2657d85679091]::query::plumbing::get_query::<rustc_query_impl[542bbd4b66bfb449]::queries::analysis, rustc_query_impl[542bbd4b66bfb449]::plumbing::QueryCtxt>
  41:     0x7f61191fb0c3 - <rustc_interface[f2560d97934cc6f6]::passes::QueryContext>::enter::<rustc_driver[7857f239df018eab]::run_compiler::{closure#1}::{closure#2}::{closure#3}, core[cde1ce9e21f08391]::result::Result<(), rustc_errors[354c2d440e1385ac]::ErrorGuaranteed>>
  42:     0x7f61191f5a0c - rustc_interface[f2560d97934cc6f6]::interface::create_compiler_and_run::<core[cde1ce9e21f08391]::result::Result<(), rustc_errors[354c2d440e1385ac]::ErrorGuaranteed>, rustc_driver[7857f239df018eab]::run_compiler::{closure#1}>
  43:     0x7f61191f4342 - <scoped_tls[8ee1aa185b4607e2]::ScopedKey<rustc_span[4a0a9e8ceb64f0f4]::SessionGlobals>>::set::<rustc_interface[f2560d97934cc6f6]::interface::run_compiler<core[cde1ce9e21f08391]::result::Result<(), rustc_errors[354c2d440e1385ac]::ErrorGuaranteed>, rustc_driver[7857f239df018eab]::run_compiler::{closure#1}>::{closure#0}, core[cde1ce9e21f08391]::result::Result<(), rustc_errors[354c2d440e1385ac]::ErrorGuaranteed>>
  44:     0x7f61191f402f - std[35bb8192b5670ad2]::sys_common::backtrace::__rust_begin_short_backtrace::<rustc_interface[f2560d97934cc6f6]::util::run_in_thread_pool_with_globals<rustc_interface[f2560d97934cc6f6]::interface::run_compiler<core[cde1ce9e21f08391]::result::Result<(), rustc_errors[354c2d440e1385ac]::ErrorGuaranteed>, rustc_driver[7857f239df018eab]::run_compiler::{closure#1}>::{closure#0}, core[cde1ce9e21f08391]::result::Result<(), rustc_errors[354c2d440e1385ac]::ErrorGuaranteed>>::{closure#0}, core[cde1ce9e21f08391]::result::Result<(), rustc_errors[354c2d440e1385ac]::ErrorGuaranteed>>
  45:     0x7f611a2c9980 - <<std[35bb8192b5670ad2]::thread::Builder>::spawn_unchecked_<rustc_interface[f2560d97934cc6f6]::util::run_in_thread_pool_with_globals<rustc_interface[f2560d97934cc6f6]::interface::run_compiler<core[cde1ce9e21f08391]::result::Result<(), rustc_errors[354c2d440e1385ac]::ErrorGuaranteed>, rustc_driver[7857f239df018eab]::run_compiler::{closure#1}>::{closure#0}, core[cde1ce9e21f08391]::result::Result<(), rustc_errors[354c2d440e1385ac]::ErrorGuaranteed>>::{closure#0}, core[cde1ce9e21f08391]::result::Result<(), rustc_errors[354c2d440e1385ac]::ErrorGuaranteed>>::{closure#1} as core[cde1ce9e21f08391]::ops::function::FnOnce<()>>::call_once::{shim:vtable#0}
  46:     0x7f6117c59393 - <alloc::boxed::Box<F,A> as core::ops::function::FnOnce<Args>>::call_once::hbe492c93bea3125c
                               at /rustc/e7119a0300b87a3d670408ee8e847c6821b3ae80/library/alloc/src/boxed.rs:1940:9
  47:     0x7f6117c59393 - <alloc::boxed::Box<F,A> as core::ops::function::FnOnce<Args>>::call_once::h1c6cb812ee67c431
                               at /rustc/e7119a0300b87a3d670408ee8e847c6821b3ae80/library/alloc/src/boxed.rs:1940:9
  48:     0x7f6117c59393 - std::sys::unix::thread::Thread::new::thread_start::hcd53b5f11cecf106
                               at /rustc/e7119a0300b87a3d670408ee8e847c6821b3ae80/library/std/src/sys/unix/thread.rs:108:17
  49:     0x7f6117b2c609 - start_thread
  50:     0x7f6117a4f133 - clone
  51:                0x0 - <unknown>

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 1.66.0-nightly (e7119a030 2022-09-22) running on x86_64-unknown-linux-gnu

note: compiler flags: --crate-type bin -C embed-bitcode=no -C codegen-units=1 -C debuginfo=2

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

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

[eholk]

This looks like it should be a type error. The versions that should work are let i = 42 as dyn* Debug; and let i = &(42 as dyn* Debug);, and possibly let i = &42 as &dyn* Debug;. But, we definitely need a more helpful message than an ICE.

[dwrensha]

including the (unsurprising) output of cargo-bisect-rustc for completness...

---

searched nightlies: from nightly-2021-02-10 to nightly-2022-10-05
regressed nightly: nightly-2022-09-15
searched commit range: 17cbdfd...750bd1a
regressed commit: 6153d3c

bisected with cargo-bisect-rustc v0.6.4

Host triple: x86_64-unknown-linux-gnu
Reproduce with:

cargo bisect-rustc --end=2022-10-05 --regress ice 

[Rageking8]

Another example to produce the same ICE

trait Trait {}

fn main() {
    let i = Box::new(1) as Box<dyn* Trait>;
}