Nightly: trait_alias compiler panic

[redpandamonium]

Code

#![feature(trait_alias)]
trait ReturnsVoidFn<T: Fn() -> ()> = Fn() -> T;

type A<'a, T: Fn() -> ()> = Vec<&'a dyn ReturnsVoidFn<T>>;

Found while playing around in compiler explorer: https://rust.godbolt.org/z/sb31Teqsa. Looks pretty minimal to me already. I'm pretty sure this is the same bug, but I'm linking it just in case: https://rust.godbolt.org/z/89s8hcf85

Meta

rustc --version --verbose:

rustc 1.70.0-nightly (700938c07 2023-04-04) running on x86_64-unknown-linux-gnu

Error output + Backtrace

thread 'rustc' panicked at 'assertion failed: `(left == right)`
  left: `T`,
 right: `FreshTy(0)`', compiler/rustc_hir_analysis/src/astconv/mod.rs:1668:17
stack backtrace:
   0:     0x7f27be027f8a - std::backtrace_rs::backtrace::libunwind::trace::h08bd4b4334e680d9
                               at /rustc/700938c0781c9f135244bb1ec846fe1a5e03ae7d/library/std/src/../../backtrace/src/backtrace/libunwind.rs:93:5
   1:     0x7f27be027f8a - std::backtrace_rs::backtrace::trace_unsynchronized::hf594b03fffc7c3a4
                               at /rustc/700938c0781c9f135244bb1ec846fe1a5e03ae7d/library/std/src/../../backtrace/src/backtrace/mod.rs:66:5
   2:     0x7f27be027f8a - std::sys_common::backtrace::_print_fmt::h1134a35071387263
                               at /rustc/700938c0781c9f135244bb1ec846fe1a5e03ae7d/library/std/src/sys_common/backtrace.rs:65:5
   3:     0x7f27be027f8a - <std::sys_common::backtrace::_print::DisplayBacktrace as core::fmt::Display>::fmt::h69f04f53733d3891
                               at /rustc/700938c0781c9f135244bb1ec846fe1a5e03ae7d/library/std/src/sys_common/backtrace.rs:44:22
   4:     0x7f27be08c05f - core::fmt::write::heb1c797211b5fb3d
                               at /rustc/700938c0781c9f135244bb1ec846fe1a5e03ae7d/library/core/src/fmt/mod.rs:1254:17
   5:     0x7f27be01aac5 - std::io::Write::write_fmt::h0753f8e473762982
                               at /rustc/700938c0781c9f135244bb1ec846fe1a5e03ae7d/library/std/src/io/mod.rs:1698:15
   6:     0x7f27be027d55 - std::sys_common::backtrace::_print::h91ef833f3b8da05b
                               at /rustc/700938c0781c9f135244bb1ec846fe1a5e03ae7d/library/std/src/sys_common/backtrace.rs:47:5
   7:     0x7f27be027d55 - std::sys_common::backtrace::print::h95ac49619fd683a6
                               at /rustc/700938c0781c9f135244bb1ec846fe1a5e03ae7d/library/std/src/sys_common/backtrace.rs:34:9
   8:     0x7f27be02a9fe - std::panicking::default_hook::{{closure}}::hd0ccf67e3d41bed4
                               at /rustc/700938c0781c9f135244bb1ec846fe1a5e03ae7d/library/std/src/panicking.rs:269:22
   9:     0x7f27be02a7a5 - std::panicking::default_hook::he9eeede79fcc44f5
                               at /rustc/700938c0781c9f135244bb1ec846fe1a5e03ae7d/library/std/src/panicking.rs:288:9
  10:     0x7f27c134f1c5 - <rustc_driver_impl[ed94cf31389203e0]::DEFAULT_HOOK::{closure#0}::{closure#0} as core[be46bbda2f522b03]::ops::function::FnOnce<(&core[be46bbda2f522b03]::panic::panic_info::PanicInfo,)>>::call_once::{shim:vtable#0}
  11:     0x7f27be02b1f4 - <alloc::boxed::Box<F,A> as core::ops::function::Fn<Args>>::call::hd73ef4fa9fa0cd04
                               at /rustc/700938c0781c9f135244bb1ec846fe1a5e03ae7d/library/alloc/src/boxed.rs:1990:9
  12:     0x7f27be02b1f4 - std::panicking::rust_panic_with_hook::hfee790920b2b90a3
                               at /rustc/700938c0781c9f135244bb1ec846fe1a5e03ae7d/library/std/src/panicking.rs:694:13
  13:     0x7f27be02af69 - std::panicking::begin_panic_handler::{{closure}}::h3bfe84e5bbd52252
                               at /rustc/700938c0781c9f135244bb1ec846fe1a5e03ae7d/library/std/src/panicking.rs:581:13
  14:     0x7f27be0283f6 - std::sys_common::backtrace::__rust_end_short_backtrace::hd97ff4e01dc5cc20
                               at /rustc/700938c0781c9f135244bb1ec846fe1a5e03ae7d/library/std/src/sys_common/backtrace.rs:150:18
  15:     0x7f27be02acc2 - rust_begin_unwind
                               at /rustc/700938c0781c9f135244bb1ec846fe1a5e03ae7d/library/std/src/panicking.rs:577:5
  16:     0x7f27be088373 - core::panicking::panic_fmt::h6a7ef2d25e2f2c88
                               at /rustc/700938c0781c9f135244bb1ec846fe1a5e03ae7d/library/core/src/panicking.rs:67:14
  17:     0x7f27be08882f - core::panicking::assert_failed_inner::hcc738cf093fdf2e1
  18:     0x7f27c1433fdc - core[be46bbda2f522b03]::panicking::assert_failed::<rustc_middle[64ae24b83add495e]::ty::Ty, rustc_middle[64ae24b83add495e]::ty::Ty>
  19:     0x7f27c01d420e - <rustc_middle[64ae24b83add495e]::ty::sty::Binder<rustc_middle[64ae24b83add495e]::ty::ProjectionPredicate>>::map_bound::<<dyn rustc_hir_analysis[13f29dc14ec113f8]::astconv::AstConv>::conv_object_ty_poly_trait_ref::{closure#14}::{closure#0}, rustc_middle[64ae24b83add495e]::ty::sty::ExistentialProjection>
  20:     0x7f27c01d30b1 - <core[be46bbda2f522b03]::iter::adapters::chain::Chain<core[be46bbda2f522b03]::iter::adapters::chain::Chain<core[be46bbda2f522b03]::iter::adapters::map::Map<core[be46bbda2f522b03]::iter::adapters::map::Map<core[be46bbda2f522b03]::slice::iter::Iter<rustc_trait_selection[5ed0f756c2c0cb57]::traits::util::TraitAliasExpansionInfo>, <dyn rustc_hir_analysis[13f29dc14ec113f8]::astconv::AstConv>::conv_object_ty_poly_trait_ref::{closure#13}>, <dyn rustc_hir_analysis[13f29dc14ec113f8]::astconv::AstConv>::conv_object_ty_poly_trait_ref::{closure#15}>, core[be46bbda2f522b03]::iter::adapters::map::Map<core[be46bbda2f522b03]::iter::adapters::map::Map<core[be46bbda2f522b03]::slice::iter::Iter<(rustc_middle[64ae24b83add495e]::ty::sty::Binder<rustc_middle[64ae24b83add495e]::ty::ProjectionPredicate>, rustc_span[e6b7ef559b56b356]::span_encoding::Span)>, <dyn rustc_hir_analysis[13f29dc14ec113f8]::astconv::AstConv>::conv_object_ty_poly_trait_ref::{closure#14}>, <dyn rustc_hir_analysis[13f29dc14ec113f8]::astconv::AstConv>::conv_object_ty_poly_trait_ref::{closure#17}>>, core[be46bbda2f522b03]::iter::adapters::map::Map<alloc[1f106ccfb1b21e78]::vec::into_iter::IntoIter<rustc_trait_selection[5ed0f756c2c0cb57]::traits::util::TraitAliasExpansionInfo>, <dyn rustc_hir_analysis[13f29dc14ec113f8]::astconv::AstConv>::conv_object_ty_poly_trait_ref::{closure#16}>> as core[be46bbda2f522b03]::iter::traits::iterator::Iterator>::next
  21:     0x7f27c01d2a5d - <smallvec[93594887a929d590]::SmallVec<[rustc_middle[64ae24b83add495e]::ty::sty::Binder<rustc_middle[64ae24b83add495e]::ty::sty::ExistentialPredicate>; 8usize]> as core[be46bbda2f522b03]::iter::traits::collect::Extend<<[rustc_middle[64ae24b83add495e]::ty::sty::Binder<rustc_middle[64ae24b83add495e]::ty::sty::ExistentialPredicate>; 8usize] as smallvec[93594887a929d590]::Array>::Item>>::extend::<core[be46bbda2f522b03]::iter::adapters::chain::Chain<core[be46bbda2f522b03]::iter::adapters::chain::Chain<core[be46bbda2f522b03]::iter::adapters::map::Map<core[be46bbda2f522b03]::iter::adapters::map::Map<core[be46bbda2f522b03]::slice::iter::Iter<rustc_trait_selection[5ed0f756c2c0cb57]::traits::util::TraitAliasExpansionInfo>, <dyn rustc_hir_analysis[13f29dc14ec113f8]::astconv::AstConv>::conv_object_ty_poly_trait_ref::{closure#13}>, <dyn rustc_hir_analysis[13f29dc14ec113f8]::astconv::AstConv>::conv_object_ty_poly_trait_ref::{closure#15}>, core[be46bbda2f522b03]::iter::adapters::map::Map<core[be46bbda2f522b03]::iter::adapters::map::Map<core[be46bbda2f522b03]::slice::iter::Iter<(rustc_middle[64ae24b83add495e]::ty::sty::Binder<rustc_middle[64ae24b83add495e]::ty::ProjectionPredicate>, rustc_span[e6b7ef559b56b356]::span_encoding::Span)>, <dyn rustc_hir_analysis[13f29dc14ec113f8]::astconv::AstConv>::conv_object_ty_poly_trait_ref::{closure#14}>, <dyn rustc_hir_analysis[13f29dc14ec113f8]::astconv::AstConv>::conv_object_ty_poly_trait_ref::{closure#17}>>, core[be46bbda2f522b03]::iter::adapters::map::Map<alloc[1f106ccfb1b21e78]::vec::into_iter::IntoIter<rustc_trait_selection[5ed0f756c2c0cb57]::traits::util::TraitAliasExpansionInfo>, <dyn rustc_hir_analysis[13f29dc14ec113f8]::astconv::AstConv>::conv_object_ty_poly_trait_ref::{closure#16}>>>
  22:     0x7f27c01ccdd0 - <dyn rustc_hir_analysis[13f29dc14ec113f8]::astconv::AstConv>::conv_object_ty_poly_trait_ref
  23:     0x7f27c01a846d - <dyn rustc_hir_analysis[13f29dc14ec113f8]::astconv::AstConv>::ast_ty_to_ty_inner::{closure#0}
  24:     0x7f27c01a79a3 - <dyn rustc_hir_analysis[13f29dc14ec113f8]::astconv::AstConv>::ast_ty_to_ty_inner::{closure#0}
  25:     0x7f27c01ac65f - <dyn rustc_hir_analysis[13f29dc14ec113f8]::astconv::AstConv>::res_to_ty
  26:     0x7f27c01a7770 - <dyn rustc_hir_analysis[13f29dc14ec113f8]::astconv::AstConv>::ast_ty_to_ty_inner::{closure#0}
  27:     0x7f27c06644a0 - rustc_hir_analysis[13f29dc14ec113f8]::collect::type_of::type_of
  28:     0x7f27bf989165 - rustc_query_system[dd711949c7ae4759]::query::plumbing::try_execute_query::<rustc_query_impl[17fce45f5d0458f2]::queries::type_of, rustc_query_impl[17fce45f5d0458f2]::plumbing::QueryCtxt>
  29:     0x7f27bf987ddd - <rustc_query_impl[17fce45f5d0458f2]::Queries as rustc_middle[64ae24b83add495e]::ty::query::QueryEngine>::type_of
  30:     0x7f27bf8e2208 - <rustc_hir_analysis[13f29dc14ec113f8]::collect::CollectItemTypesVisitor as rustc_hir[997ce0002422a023]::intravisit::Visitor>::visit_item
  31:     0x7f27bf8e0a44 - <rustc_middle[64ae24b83add495e]::hir::map::Map>::visit_item_likes_in_module::<rustc_hir_analysis[13f29dc14ec113f8]::collect::CollectItemTypesVisitor>
  32:     0x7f27bf8e096c - rustc_hir_analysis[13f29dc14ec113f8]::collect::collect_mod_item_types
  33:     0x7f27c0916071 - rustc_query_system[dd711949c7ae4759]::query::plumbing::try_execute_query::<rustc_query_impl[17fce45f5d0458f2]::queries::collect_mod_item_types, rustc_query_impl[17fce45f5d0458f2]::plumbing::QueryCtxt>
  34:     0x7f27c0915c99 - <rustc_query_impl[17fce45f5d0458f2]::Queries as rustc_middle[64ae24b83add495e]::ty::query::QueryEngine>::collect_mod_item_types
  35:     0x7f27c0757dff - <rustc_session[6c8e5f9a4f3dfafb]::session::Session>::track_errors::<rustc_hir_analysis[13f29dc14ec113f8]::check_crate::{closure#0}, ()>
  36:     0x7f27c07556b1 - rustc_hir_analysis[13f29dc14ec113f8]::check_crate
  37:     0x7f27c074f851 - rustc_interface[f9e4f758c3dbe73a]::passes::analysis
  38:     0x7f27c0ae0dd2 - rustc_query_system[dd711949c7ae4759]::query::plumbing::try_execute_query::<rustc_query_impl[17fce45f5d0458f2]::queries::analysis, rustc_query_impl[17fce45f5d0458f2]::plumbing::QueryCtxt>
  39:     0x7f27c0ae0ad0 - <rustc_query_impl[17fce45f5d0458f2]::Queries as rustc_middle[64ae24b83add495e]::ty::query::QueryEngine>::analysis
  40:     0x7f27c055e9de - <rustc_interface[f9e4f758c3dbe73a]::queries::QueryResult<&rustc_middle[64ae24b83add495e]::ty::context::GlobalCtxt>>::enter::<core[be46bbda2f522b03]::result::Result<(), rustc_span[e6b7ef559b56b356]::ErrorGuaranteed>, rustc_driver_impl[ed94cf31389203e0]::run_compiler::{closure#1}::{closure#2}::{closure#4}>
  41:     0x7f27c055d4be - <rustc_interface[f9e4f758c3dbe73a]::interface::Compiler>::enter::<rustc_driver_impl[ed94cf31389203e0]::run_compiler::{closure#1}::{closure#2}, core[be46bbda2f522b03]::result::Result<core[be46bbda2f522b03]::option::Option<rustc_interface[f9e4f758c3dbe73a]::queries::Linker>, rustc_span[e6b7ef559b56b356]::ErrorGuaranteed>>
  42:     0x7f27c055b671 - rustc_span[e6b7ef559b56b356]::set_source_map::<core[be46bbda2f522b03]::result::Result<(), rustc_span[e6b7ef559b56b356]::ErrorGuaranteed>, rustc_interface[f9e4f758c3dbe73a]::interface::run_compiler<core[be46bbda2f522b03]::result::Result<(), rustc_span[e6b7ef559b56b356]::ErrorGuaranteed>, rustc_driver_impl[ed94cf31389203e0]::run_compiler::{closure#1}>::{closure#0}::{closure#0}>
  43:     0x7f27c055ac1f - std[e75d324dc4549f18]::sys_common::backtrace::__rust_begin_short_backtrace::<rustc_interface[f9e4f758c3dbe73a]::util::run_in_thread_pool_with_globals<rustc_interface[f9e4f758c3dbe73a]::interface::run_compiler<core[be46bbda2f522b03]::result::Result<(), rustc_span[e6b7ef559b56b356]::ErrorGuaranteed>, rustc_driver_impl[ed94cf31389203e0]::run_compiler::{closure#1}>::{closure#0}, core[be46bbda2f522b03]::result::Result<(), rustc_span[e6b7ef559b56b356]::ErrorGuaranteed>>::{closure#0}::{closure#0}, core[be46bbda2f522b03]::result::Result<(), rustc_span[e6b7ef559b56b356]::ErrorGuaranteed>>
  44:     0x7f27c055a601 - <<std[e75d324dc4549f18]::thread::Builder>::spawn_unchecked_<rustc_interface[f9e4f758c3dbe73a]::util::run_in_thread_pool_with_globals<rustc_interface[f9e4f758c3dbe73a]::interface::run_compiler<core[be46bbda2f522b03]::result::Result<(), rustc_span[e6b7ef559b56b356]::ErrorGuaranteed>, rustc_driver_impl[ed94cf31389203e0]::run_compiler::{closure#1}>::{closure#0}, core[be46bbda2f522b03]::result::Result<(), rustc_span[e6b7ef559b56b356]::ErrorGuaranteed>>::{closure#0}::{closure#0}, core[be46bbda2f522b03]::result::Result<(), rustc_span[e6b7ef559b56b356]::ErrorGuaranteed>>::{closure#1} as core[be46bbda2f522b03]::ops::function::FnOnce<()>>::call_once::{shim:vtable#0}
  45:     0x7f27be0352d5 - <alloc::boxed::Box<F,A> as core::ops::function::FnOnce<Args>>::call_once::ha3e40da2642ee301
                               at /rustc/700938c0781c9f135244bb1ec846fe1a5e03ae7d/library/alloc/src/boxed.rs:1976:9
  46:     0x7f27be0352d5 - <alloc::boxed::Box<F,A> as core::ops::function::FnOnce<Args>>::call_once::h527cd1887e2c4efe
                               at /rustc/700938c0781c9f135244bb1ec846fe1a5e03ae7d/library/alloc/src/boxed.rs:1976:9
  47:     0x7f27be0352d5 - std::sys::unix::thread::Thread::new::thread_start::hc9f197c710586f02
                               at /rustc/700938c0781c9f135244bb1ec846fe1a5e03ae7d/library/std/src/sys/unix/thread.rs:108:17
  48:     0x7f27bdf06609 - start_thread
  49:     0x7f27bde29133 - clone
  50:                0x0 - <unknown>

error: 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 1.70.0-nightly (700938c07 2023-04-04) running on x86_64-unknown-linux-gnu

note: compiler flags: -C debuginfo=1 -C llvm-args=--x86-asm-syntax=intel --crate-type rlib

query stack during panic:
#0 [type_of] expanding type alias `A`
#1 [collect_mod_item_types] collecting item types in top-level module
#2 [analysis] running analysis passes on this crate
end of query stack
Compiler returned: 101

[compiler-errors]

This is fixed by #107614