ICE when trait alias with projection predicate is used in trait object types

[lowr]

Code

#![feature(trait_alias)]

trait C {
    type Assoc;
}
trait D {}
trait Alias<T> = D where usize: C<Assoc = i32>;

fn foo(_: &dyn Alias<()>) {}

Meta

rustc --version --verbose:

rustc 1.69.0-nightly (5243ea5c2 2023-02-20)                                                                                                                                          
binary: rustc                                                                                                                                                                        
commit-hash: 5243ea5c29b136137c36bd773e5baa663790e097                                                                                                                                
commit-date: 2023-02-20                                                                                                                                                              
host: x86_64-unknown-linux-gnu                                                                                                                                                       
release: 1.69.0-nightly                                                                                                                                                              
LLVM version: 15.0.7

Error output

thread 'rustc' panicked at 'assertion failed: `(left == right)`
  left: `usize`,
 right: `FreshTy(0)`', compiler/rustc_hir_analysis/src/astconv/mod.rs:1571:17

Backtrace

   0:     0x7f9a25a92b3a - std::backtrace_rs::backtrace::libunwind::trace::h12b28b68eb26bd66
                               at /rustc/5243ea5c29b136137c36bd773e5baa663790e097/library/std/src/../../backtrace/src/backtrace/libunwind.rs:93:5
   1:     0x7f9a25a92b3a - std::backtrace_rs::backtrace::trace_unsynchronized::h200511c4f08d08ef
                               at /rustc/5243ea5c29b136137c36bd773e5baa663790e097/library/std/src/../../backtrace/src/backtrace/mod.rs:66:5
   2:     0x7f9a25a92b3a - std::sys_common::backtrace::_print_fmt::h73434ecb073097d4
                               at /rustc/5243ea5c29b136137c36bd773e5baa663790e097/library/std/src/sys_common/backtrace.rs:65:5
   3:     0x7f9a25a92b3a - <std::sys_common::backtrace::_print::DisplayBacktrace as core::fmt::Display>::fmt::h7808d0be79b5d1ec
                               at /rustc/5243ea5c29b136137c36bd773e5baa663790e097/library/std/src/sys_common/backtrace.rs:44:22
   4:     0x7f9a25af2b0e - core::fmt::write::hafefc351fbfaa415
                               at /rustc/5243ea5c29b136137c36bd773e5baa663790e097/library/core/src/fmt/mod.rs:1232:17
   5:     0x7f9a25a82fe5 - std::io::Write::write_fmt::hc1d6b1569406505e
                               at /rustc/5243ea5c29b136137c36bd773e5baa663790e097/library/std/src/io/mod.rs:1684:15
   6:     0x7f9a25a92905 - std::sys_common::backtrace::_print::hd45cfc7e9c4b34ea
                               at /rustc/5243ea5c29b136137c36bd773e5baa663790e097/library/std/src/sys_common/backtrace.rs:47:5
   7:     0x7f9a25a92905 - std::sys_common::backtrace::print::h5e03fe95d9240812
                               at /rustc/5243ea5c29b136137c36bd773e5baa663790e097/library/std/src/sys_common/backtrace.rs:34:9
   8:     0x7f9a25a9567f - std::panicking::default_hook::{{closure}}::hf95a102fbb1a711a
                               at /rustc/5243ea5c29b136137c36bd773e5baa663790e097/library/std/src/panicking.rs:267:22
   9:     0x7f9a25a953bb - std::panicking::default_hook::h0e224ad71e4cf3c6
                               at /rustc/5243ea5c29b136137c36bd773e5baa663790e097/library/std/src/panicking.rs:286:9
  10:     0x7f9a28d47cb5 - <rustc_driver_impl[6598fd657388da4]::DEFAULT_HOOK::{closure#0}::{closure#0} as core[e6e25e2e3d2ed08b]::ops::function::FnOnce<(&core[e6e25e2e3d2ed08b]::panic::panic_info::PanicInfo,)>>::call_once::{shim:vtable#0}
  11:     0x7f9a25a95ebd - <alloc::boxed::Box<F,A> as core::ops::function::Fn<Args>>::call::ha8273e13c0202daf
                               at /rustc/5243ea5c29b136137c36bd773e5baa663790e097/library/alloc/src/boxed.rs:2002:9
  12:     0x7f9a25a95ebd - std::panicking::rust_panic_with_hook::hfa97f871b11d16ea
                               at /rustc/5243ea5c29b136137c36bd773e5baa663790e097/library/std/src/panicking.rs:692:13
  13:     0x7f9a25a95c39 - std::panicking::begin_panic_handler::{{closure}}::hd45660eb8177c8ba
                               at /rustc/5243ea5c29b136137c36bd773e5baa663790e097/library/std/src/panicking.rs:579:13
  14:     0x7f9a25a92fa6 - std::sys_common::backtrace::__rust_end_short_backtrace::h24cc9aac7fd6776a
                               at /rustc/5243ea5c29b136137c36bd773e5baa663790e097/library/std/src/sys_common/backtrace.rs:137:18
  15:     0x7f9a25a95942 - rust_begin_unwind
                               at /rustc/5243ea5c29b136137c36bd773e5baa663790e097/library/std/src/panicking.rs:575:5
  16:     0x7f9a25aef4b3 - core::panicking::panic_fmt::he7b2d47a249dbf70
                               at /rustc/5243ea5c29b136137c36bd773e5baa663790e097/library/core/src/panicking.rs:64:14
  17:     0x7f9a25aef8cf - core::panicking::assert_failed_inner::he10230044ecb69e8
  18:     0x7f9a28e8d6bc - core[e6e25e2e3d2ed08b]::panicking::assert_failed::<rustc_middle[6454e605f0b552d3]::ty::Ty, rustc_middle[6454e605f0b552d3]::ty::Ty>
  19:     0x7f9a2837aafc - <rustc_middle[6454e605f0b552d3]::ty::sty::Binder<rustc_middle[6454e605f0b552d3]::ty::ProjectionPredicate>>::map_bound::<<dyn rustc_hir_analysis[63c8f16ce92b0e6a]::astconv::AstConv>::conv_object_ty_poly_trait_ref::{closure#13}::{closure#0}, rustc_middle[6454e605f0b552d3]::ty::sty::ExistentialProjection>
  20:     0x7f9a27ab6ff4 - <core[e6e25e2e3d2ed08b]::iter::adapters::chain::Chain<core[e6e25e2e3d2ed08b]::iter::adapters::chain::Chain<core[e6e25e2e3d2ed08b]::iter::adapters::map::Map<core[e6e25e2e3d2ed08b]::iter::adapters::map::Map<core[e6e25e2e3d2ed08b]::slice::iter::Iter<rustc_trait_selection[e5de21e4b6b03324]::traits::util::TraitAliasExpansionInfo>, <dyn rustc_hir_analysis[63c8f16ce92b0e6a]::astconv::AstConv>::conv_object_ty_poly_trait_ref::{closure#12}>, <dyn rustc_hir_analysis[63c8f16ce92b0e6a]::astconv::AstConv>::conv_object_ty_poly_trait_ref::{closure#14}>, core[e6e25e2e3d2ed08b]::iter::adapters::map::Map<core[e6e25e2e3d2ed08b]::iter::adapters::map::Map<core[e6e25e2e3d2ed08b]::slice::iter::Iter<(rustc_middle[6454e605f0b552d3]::ty::sty::Binder<rustc_middle[6454e605f0b552d3]::ty::ProjectionPredicate>, rustc_span[5f03c33a4a98a2db]::span_encoding::Span)>, <dyn rustc_hir_analysis[63c8f16ce92b0e6a]::astconv::AstConv>::conv_object_ty_poly_trait_ref::{closure#13}>, <dyn rustc_hir_analysis[63c8f16ce92b0e6a]::astconv::AstConv>::conv_object_ty_poly_trait_ref::{closure#16}>>, core[e6e25e2e3d2ed08b]::iter::adapters::map::Map<alloc[3f8e9f68cf11003c]::vec::into_iter::IntoIter<rustc_trait_selection[e5de21e4b6b03324]::traits::util::TraitAliasExpansionInfo>, <dyn rustc_hir_analysis[63c8f16ce92b0e6a]::astconv::AstConv>::conv_object_ty_poly_trait_ref::{closure#15}>> as core[e6e25e2e3d2ed08b]::iter::traits::iterator::Iterator>::next
  21:     0x7f9a27ab696b - <smallvec[777b36135c6d6da2]::SmallVec<[rustc_middle[6454e605f0b552d3]::ty::sty::Binder<rustc_middle[6454e605f0b552d3]::ty::sty::ExistentialPredicate>; 8usize]> as core[e6e25e2e3d2ed08b]::iter::traits::collect::Extend<<[rustc_middle[6454e605f0b552d3]::ty::sty::Binder<rustc_middle[6454e605f0b552d3]::ty::sty::ExistentialPredicate>; 8usize] as smallvec[777b36135c6d6da2]::Array>::Item>>::extend::<core[e6e25e2e3d2ed08b]::iter::adapters::chain::Chain<core[e6e25e2e3d2ed08b]::iter::adapters::chain::Chain<core[e6e25e2e3d2ed08b]::iter::adapters::map::Map<core[e6e25e2e3d2ed08b]::iter::adapters::map::Map<core[e6e25e2e3d2ed08b]::slice::iter::Iter<rustc_trait_selection[e5de21e4b6b03324]::traits::util::TraitAliasExpansionInfo>, <dyn rustc_hir_analysis[63c8f16ce92b0e6a]::astconv::AstConv>::conv_object_ty_poly_trait_ref::{closure#12}>, <dyn rustc_hir_analysis[63c8f16ce92b0e6a]::astconv::AstConv>::conv_object_ty_poly_trait_ref::{closure#14}>, core[e6e25e2e3d2ed08b]::iter::adapters::map::Map<core[e6e25e2e3d2ed08b]::iter::adapters::map::Map<core[e6e25e2e3d2ed08b]::slice::iter::Iter<(rustc_middle[6454e605f0b552d3]::ty::sty::Binder<rustc_middle[6454e605f0b552d3]::ty::ProjectionPredicate>, rustc_span[5f03c33a4a98a2db]::span_encoding::Span)>, <dyn rustc_hir_analysis[63c8f16ce92b0e6a]::astconv::AstConv>::conv_object_ty_poly_trait_ref::{closure#13}>, <dyn rustc_hir_analysis[63c8f16ce92b0e6a]::astconv::AstConv>::conv_object_ty_poly_trait_ref::{closure#16}>>, core[e6e25e2e3d2ed08b]::iter::adapters::map::Map<alloc[3f8e9f68cf11003c]::vec::into_iter::IntoIter<rustc_trait_selection[e5de21e4b6b03324]::traits::util::TraitAliasExpansionInfo>, <dyn rustc_hir_analysis[63c8f16ce92b0e6a]::astconv::AstConv>::conv_object_ty_poly_trait_ref::{closure#15}>>>
  22:     0x7f9a27ab0762 - <dyn rustc_hir_analysis[63c8f16ce92b0e6a]::astconv::AstConv>::conv_object_ty_poly_trait_ref
  23:     0x7f9a27a8dd39 - <dyn rustc_hir_analysis[63c8f16ce92b0e6a]::astconv::AstConv>::ast_ty_to_ty_inner::{closure#0}
  24:     0x7f9a27a8d710 - <dyn rustc_hir_analysis[63c8f16ce92b0e6a]::astconv::AstConv>::ast_ty_to_ty_inner::{closure#0}
  25:     0x7f9a27c890ca - <dyn rustc_hir_analysis[63c8f16ce92b0e6a]::astconv::AstConv>::ty_of_fn::{closure#0}
  26:     0x7f9a27f1dd1d - rustc_hir_analysis[63c8f16ce92b0e6a]::collect::infer_return_ty_for_fn_sig
  27:     0x7f9a27f1bddb - rustc_hir_analysis[63c8f16ce92b0e6a]::collect::fn_sig
  28:     0x7f9a27f1a2d9 - rustc_query_system[e1d6d01a6f4eeda5]::query::plumbing::get_query::<rustc_query_impl[2383e868c5804bd1]::queries::fn_sig, rustc_query_impl[2383e868c5804bd1]::plumbing::QueryCtxt, rustc_middle[6454e605f0b552d3]::dep_graph::dep_node::DepKind>
  29:     0x7f9a27f19f48 - <rustc_query_impl[2383e868c5804bd1]::Queries as rustc_middle[6454e605f0b552d3]::ty::query::QueryEngine>::fn_sig
  30:     0x7f9a2741c8ee - <rustc_hir_analysis[63c8f16ce92b0e6a]::collect::CollectItemTypesVisitor as rustc_hir[bfe16e97a69c80df]::intravisit::Visitor>::visit_item
  31:     0x7f9a2741b665 - <rustc_middle[6454e605f0b552d3]::hir::map::Map>::visit_item_likes_in_module::<rustc_hir_analysis[63c8f16ce92b0e6a]::collect::CollectItemTypesVisitor>
  32:     0x7f9a2741b57c - rustc_hir_analysis[63c8f16ce92b0e6a]::collect::collect_mod_item_types
  33:     0x7f9a2834accf - rustc_query_system[e1d6d01a6f4eeda5]::query::plumbing::try_execute_query::<rustc_query_impl[2383e868c5804bd1]::queries::collect_mod_item_types, rustc_query_impl[2383e868c5804bd1]::plumbing::QueryCtxt>
  34:     0x7f9a2874640d - <rustc_query_impl[2383e868c5804bd1]::Queries as rustc_middle[6454e605f0b552d3]::ty::query::QueryEngine>::collect_mod_item_types
  35:     0x7f9a27158fff - <rustc_middle[6454e605f0b552d3]::hir::map::Map>::for_each_module::<rustc_hir_analysis[63c8f16ce92b0e6a]::check_crate::{closure#0}::{closure#0}::{closure#0}>
  36:     0x7f9a27156aec - rustc_hir_analysis[63c8f16ce92b0e6a]::check_crate
  37:     0x7f9a2714e222 - rustc_interface[a4c456754224e9c7]::passes::analysis
  38:     0x7f9a28574ef2 - rustc_query_system[e1d6d01a6f4eeda5]::query::plumbing::try_execute_query::<rustc_query_impl[2383e868c5804bd1]::queries::analysis, rustc_query_impl[2383e868c5804bd1]::plumbing::QueryCtxt>
  39:     0x7f9a2873fd4a - <rustc_query_impl[2383e868c5804bd1]::Queries as rustc_middle[6454e605f0b552d3]::ty::query::QueryEngine>::analysis
  40:     0x7f9a27ff3bf6 - <rustc_middle[6454e605f0b552d3]::ty::context::GlobalCtxt>::enter::<rustc_driver_impl[6598fd657388da4]::run_compiler::{closure#1}::{closure#2}::{closure#3}, core[e6e25e2e3d2ed08b]::result::Result<(), rustc_errors[e1f9be18bff28896]::ErrorGuaranteed>>
  41:     0x7f9a27ff2f07 - <rustc_interface[a4c456754224e9c7]::interface::Compiler>::enter::<rustc_driver_impl[6598fd657388da4]::run_compiler::{closure#1}::{closure#2}, core[e6e25e2e3d2ed08b]::result::Result<core[e6e25e2e3d2ed08b]::option::Option<rustc_interface[a4c456754224e9c7]::queries::Linker>, rustc_errors[e1f9be18bff28896]::ErrorGuaranteed>>
  42:     0x7f9a27ff0fe4 - rustc_span[5f03c33a4a98a2db]::with_source_map::<core[e6e25e2e3d2ed08b]::result::Result<(), rustc_errors[e1f9be18bff28896]::ErrorGuaranteed>, rustc_interface[a4c456754224e9c7]::interface::run_compiler<core[e6e25e2e3d2ed08b]::result::Result<(), rustc_errors[e1f9be18bff28896]::ErrorGuaranteed>, rustc_driver_impl[6598fd657388da4]::run_compiler::{closure#1}>::{closure#0}::{closure#0}>
  43:     0x7f9a27ff054d - std[33065b4dbfe75df]::sys_common::backtrace::__rust_begin_short_backtrace::<rustc_interface[a4c456754224e9c7]::util::run_in_thread_pool_with_globals<rustc_interface[a4c456754224e9c7]::interface::run_compiler<core[e6e25e2e3d2ed08b]::result::Result<(), rustc_errors[e1f9be18bff28896]::ErrorGuaranteed>, rustc_driver_impl[6598fd657388da4]::run_compiler::{closure#1}>::{closure#0}, core[e6e25e2e3d2ed08b]::result::Result<(), rustc_errors[e1f9be18bff28896]::ErrorGuaranteed>>::{closure#0}::{closure#0}, core[e6e25e2e3d2ed08b]::result::Result<(), rustc_errors[e1f9be18bff28896]::ErrorGuaranteed>>
  44:     0x7f9a27feff9c - <<std[33065b4dbfe75df]::thread::Builder>::spawn_unchecked_<rustc_interface[a4c456754224e9c7]::util::run_in_thread_pool_with_globals<rustc_interface[a4c456754224e9c7]::interface::run_compiler<core[e6e25e2e3d2ed08b]::result::Result<(), rustc_errors[e1f9be18bff28896]::ErrorGuaranteed>, rustc_driver_impl[6598fd657388da4]::run_compiler::{closure#1}>::{closure#0}, core[e6e25e2e3d2ed08b]::result::Result<(), rustc_errors[e1f9be18bff28896]::ErrorGuaranteed>>::{closure#0}::{closure#0}, core[e6e25e2e3d2ed08b]::result::Result<(), rustc_errors[e1f9be18bff28896]::ErrorGuaranteed>>::{closure#1} as core[e6e25e2e3d2ed08b]::ops::function::FnOnce<()>>::call_once::{shim:vtable#0}
  45:     0x7f9a25a9fd93 - <alloc::boxed::Box<F,A> as core::ops::function::FnOnce<Args>>::call_once::hfdd75e8d431ebcab
                               at /rustc/5243ea5c29b136137c36bd773e5baa663790e097/library/alloc/src/boxed.rs:1988:9
  46:     0x7f9a25a9fd93 - <alloc::boxed::Box<F,A> as core::ops::function::FnOnce<Args>>::call_once::hac9c6d75eef1e452
                               at /rustc/5243ea5c29b136137c36bd773e5baa663790e097/library/alloc/src/boxed.rs:1988:9
  47:     0x7f9a25a9fd93 - std::sys::unix::thread::Thread::new::thread_start::h1e79a6f313450114
                               at /rustc/5243ea5c29b136137c36bd773e5baa663790e097/library/std/src/sys/unix/thread.rs:108:17
  48:     0x7f9a25962609 - start_thread
  49:     0x7f9a25885133 - clone
  50:                0x0 - <unknown>

[lowr]

It seems we return every predicate from where clause as superpredicates for trait aliases, but apparently conv_object_ty_poly_trait_ref() expects every predicate to be a bound on Self.

cc #41517
@rustbot label +F-trait_alias

[compiler-errors]

Thanks for the error report -- this is a duplicate of #106238, and should be fixed by #107614.