-Znext-solver errors with impl for projected Self type

[fee1-dead]

cc tracking issue #107374

godbolt

The code below compiles on nightly but errors with -Znext-solver:

pub trait Index {
    type Output;
}

impl Index for () { type Output = (); }

pub trait IndexMut where Self: Index {
    fn foo(&mut self);
}

impl IndexMut for <() as Index>::Output {
    fn foo(&mut self) {}
}

Error message:

error[E0271]: type mismatch resolving `<() as Index>::Output == &mut <() as Index>::Output`
  --> <source>:12:12
   |
12 |     fn foo(&mut self) {}
   |            ^^^^^^^^^ types differ

error: aborting due to 1 previous error

For more information about this error, try `rustc --explain E0271`.
Compiler returned: 1

Backtrace

thread 'rustc' panicked at compiler/rustc_errors/src/lib.rs:1767:17:
aborting due to `-Z treat-err-as-bug=1`
stack backtrace:
   0:     0x7fdd27b382b5 - std::backtrace_rs::backtrace::libunwind::trace::hfcb0e6e919fe8b02
                               at /rustc/e9e6e2e444c30c23a9c878a88fbc3978c2acad95/library/std/src/../../backtrace/src/backtrace/libunwind.rs:116:5
   1:     0x7fdd27b382b5 - std::backtrace_rs::backtrace::trace_unsynchronized::h2d7390b1768cc057
                               at /rustc/e9e6e2e444c30c23a9c878a88fbc3978c2acad95/library/std/src/../../backtrace/src/backtrace/mod.rs:66:5
   2:     0x7fdd27b382b5 - std::sys::backtrace::_print_fmt::h0a1fe72c74c3c92f
                               at /rustc/e9e6e2e444c30c23a9c878a88fbc3978c2acad95/library/std/src/sys/backtrace.rs:68:5
   3:     0x7fdd27b382b5 - <std::sys::backtrace::_print::DisplayBacktrace as core::fmt::Display>::fmt::h0efe09574522ab48
                               at /rustc/e9e6e2e444c30c23a9c878a88fbc3978c2acad95/library/std/src/sys/backtrace.rs:44:22
   4:     0x7fdd27b87d9b - core::fmt::rt::Argument::fmt::h86493f731d852471
                               at /rustc/e9e6e2e444c30c23a9c878a88fbc3978c2acad95/library/core/src/fmt/rt.rs:173:76
   5:     0x7fdd27b87d9b - core::fmt::write::hf027121cd79920f8
                               at /rustc/e9e6e2e444c30c23a9c878a88fbc3978c2acad95/library/core/src/fmt/mod.rs:1174:21
   6:     0x7fdd27b2ce9f - std::io::Write::write_fmt::h50f231aebdd6b44e
                               at /rustc/e9e6e2e444c30c23a9c878a88fbc3978c2acad95/library/std/src/io/mod.rs:1835:15
   7:     0x7fdd27b3808e - std::sys::backtrace::_print::ha583d08861e89abe
                               at /rustc/e9e6e2e444c30c23a9c878a88fbc3978c2acad95/library/std/src/sys/backtrace.rs:47:5
   8:     0x7fdd27b3808e - std::sys::backtrace::print::h326dfb2de669d6a9
                               at /rustc/e9e6e2e444c30c23a9c878a88fbc3978c2acad95/library/std/src/sys/backtrace.rs:34:9
   9:     0x7fdd27b3a9d9 - std::panicking::default_hook::{{closure}}::h338582459520bc95
  10:     0x7fdd27b3a77c - std::panicking::default_hook::ha253d2f95ed1a278
                               at /rustc/e9e6e2e444c30c23a9c878a88fbc3978c2acad95/library/std/src/panicking.rs:292:9
  11:     0x7fdd243bbe7f - std[a9a046d33cddffde]::panicking::update_hook::<alloc[acf10b35c0018119]::boxed::Box<rustc_driver_impl[f6a9d0df02f1d1bf]::install_ice_hook::{closure#0}>>::{closure#0}
  12:     0x7fdd27b3b2af - <alloc::boxed::Box<F,A> as core::ops::function::Fn<Args>>::call::h59cfa4ec21be1b23
                               at /rustc/e9e6e2e444c30c23a9c878a88fbc3978c2acad95/library/alloc/src/boxed.rs:2078:9
  13:     0x7fdd27b3b2af - std::panicking::rust_panic_with_hook::he6d3da0d6872d7e9
                               at /rustc/e9e6e2e444c30c23a9c878a88fbc3978c2acad95/library/std/src/panicking.rs:804:13
  14:     0x7fdd27b3aea3 - std::panicking::begin_panic_handler::{{closure}}::h562044d4931308b4
                               at /rustc/e9e6e2e444c30c23a9c878a88fbc3978c2acad95/library/std/src/panicking.rs:663:13
  15:     0x7fdd27b38779 - std::sys::backtrace::__rust_end_short_backtrace::h8d43a914ad44f7b8
                               at /rustc/e9e6e2e444c30c23a9c878a88fbc3978c2acad95/library/std/src/sys/backtrace.rs:171:18
  16:     0x7fdd27b3abb4 - rust_begin_unwind
                               at /rustc/e9e6e2e444c30c23a9c878a88fbc3978c2acad95/library/std/src/panicking.rs:661:5
  17:     0x7fdd27b84353 - core::panicking::panic_fmt::h72d84f0a9e5170e6
                               at /rustc/e9e6e2e444c30c23a9c878a88fbc3978c2acad95/library/core/src/panicking.rs:74:14
  18:     0x7fdd271d3096 - <rustc_errors[e779a9bbb6c56598]::DiagCtxtInner>::panic_if_treat_err_as_bug.cold
  19:     0x7fdd263f6022 - <rustc_errors[e779a9bbb6c56598]::DiagCtxtInner>::emit_diagnostic::{closure#3}
  20:     0x7fdd263e4246 - rustc_interface[2a6dcbe82196fb3f]::callbacks::track_diagnostic::<core[563965cbb8764b56]::option::Option<rustc_span[6197d43b7fdbf68b]::ErrorGuaranteed>>
  21:     0x7fdd263e237f - <rustc_errors[e779a9bbb6c56598]::DiagCtxtInner>::emit_diagnostic
  22:     0x7fdd263e2255 - <rustc_errors[e779a9bbb6c56598]::DiagCtxtHandle>::emit_diagnostic
  23:     0x7fdd268f929c - <rustc_span[6197d43b7fdbf68b]::ErrorGuaranteed as rustc_errors[e779a9bbb6c56598]::diagnostic::EmissionGuarantee>::emit_producing_guarantee
  24:     0x7fdd2509513d - <rustc_infer[3fbee8995ea8e832]::infer::error_reporting::TypeErrCtxt as rustc_trait_selection[5bf7e99b6c60346]::traits::error_reporting::type_err_ctxt_ext::InferCtxtPrivExt>::report_projection_error
  25:     0x7fdd25094926 - <rustc_infer[3fbee8995ea8e832]::infer::error_reporting::TypeErrCtxt as rustc_trait_selection[5bf7e99b6c60346]::traits::error_reporting::type_err_ctxt_ext::InferCtxtPrivExt>::report_fulfillment_error
  26:     0x7fdd2507f92e - <rustc_infer[3fbee8995ea8e832]::infer::error_reporting::TypeErrCtxt as rustc_trait_selection[5bf7e99b6c60346]::traits::error_reporting::type_err_ctxt_ext::TypeErrCtxtExt>::report_fulfillment_errors
  27:     0x7fdd25e782a6 - rustc_hir_analysis[e4ed5cdf7069fdab]::check::wfcheck::check_associated_item
  28:     0x7fdd23507eae - rustc_hir_analysis[e4ed5cdf7069fdab]::check::wfcheck::check_well_formed
  29:     0x7fdd25bdfcbd - rustc_query_impl[bd968423f59ba745]::plumbing::__rust_begin_short_backtrace::<rustc_query_impl[bd968423f59ba745]::query_impl::check_well_formed::dynamic_query::{closure#2}::{closure#0}, rustc_middle[1a9a6fb822666db]::query::erase::Erased<[u8; 1usize]>>
  30:     0x7fdd25bdff35 - rustc_query_system[411a21868c0145ef]::query::plumbing::try_execute_query::<rustc_query_impl[bd968423f59ba745]::DynamicConfig<rustc_query_system[411a21868c0145ef]::query::caches::VecCache<rustc_hir[4b11660a3be69043]::hir_id::OwnerId, rustc_middle[1a9a6fb822666db]::query::erase::Erased<[u8; 1usize]>>, false, false, false>, rustc_query_impl[bd968423f59ba745]::plumbing::QueryCtxt, false>
  31:     0x7fdd25bdfc9a - rustc_query_impl[bd968423f59ba745]::query_impl::check_well_formed::get_query_non_incr::__rust_end_short_backtrace
  32:     0x7fdd25be0af4 - rustc_hir_analysis[e4ed5cdf7069fdab]::check::wfcheck::check_mod_type_wf
  33:     0x7fdd25be0799 - rustc_query_impl[bd968423f59ba745]::plumbing::__rust_begin_short_backtrace::<rustc_query_impl[bd968423f59ba745]::query_impl::check_mod_type_wf::dynamic_query::{closure#2}::{closure#0}, rustc_middle[1a9a6fb822666db]::query::erase::Erased<[u8; 1usize]>>
  34:     0x7fdd2635eeb8 - rustc_query_system[411a21868c0145ef]::query::plumbing::try_execute_query::<rustc_query_impl[bd968423f59ba745]::DynamicConfig<rustc_query_system[411a21868c0145ef]::query::caches::DefaultCache<rustc_span[6197d43b7fdbf68b]::def_id::LocalModDefId, rustc_middle[1a9a6fb822666db]::query::erase::Erased<[u8; 1usize]>>, false, false, false>, rustc_query_impl[bd968423f59ba745]::plumbing::QueryCtxt, false>
  35:     0x7fdd2635ec59 - rustc_query_impl[bd968423f59ba745]::query_impl::check_mod_type_wf::get_query_non_incr::__rust_end_short_backtrace
  36:     0x7fdd25bf27a3 - rustc_hir_analysis[e4ed5cdf7069fdab]::check_crate
  37:     0x7fdd260c7255 - rustc_interface[2a6dcbe82196fb3f]::passes::analysis
  38:     0x7fdd260c6e15 - rustc_query_impl[bd968423f59ba745]::plumbing::__rust_begin_short_backtrace::<rustc_query_impl[bd968423f59ba745]::query_impl::analysis::dynamic_query::{closure#2}::{closure#0}, rustc_middle[1a9a6fb822666db]::query::erase::Erased<[u8; 1usize]>>
  39:     0x7fdd2665a1a5 - rustc_query_system[411a21868c0145ef]::query::plumbing::try_execute_query::<rustc_query_impl[bd968423f59ba745]::DynamicConfig<rustc_query_system[411a21868c0145ef]::query::caches::SingleCache<rustc_middle[1a9a6fb822666db]::query::erase::Erased<[u8; 1usize]>>, false, false, false>, rustc_query_impl[bd968423f59ba745]::plumbing::QueryCtxt, false>
  40:     0x7fdd26659f0f - rustc_query_impl[bd968423f59ba745]::query_impl::analysis::get_query_non_incr::__rust_end_short_backtrace
  41:     0x7fdd2656a9bf - rustc_interface[2a6dcbe82196fb3f]::interface::run_compiler::<core[563965cbb8764b56]::result::Result<(), rustc_span[6197d43b7fdbf68b]::ErrorGuaranteed>, rustc_driver_impl[f6a9d0df02f1d1bf]::run_compiler::{closure#0}>::{closure#1}
  42:     0x7fdd263cfd89 - std[a9a046d33cddffde]::sys::backtrace::__rust_begin_short_backtrace::<rustc_interface[2a6dcbe82196fb3f]::util::run_in_thread_with_globals<rustc_interface[2a6dcbe82196fb3f]::util::run_in_thread_pool_with_globals<rustc_interface[2a6dcbe82196fb3f]::interface::run_compiler<core[563965cbb8764b56]::result::Result<(), rustc_span[6197d43b7fdbf68b]::ErrorGuaranteed>, rustc_driver_impl[f6a9d0df02f1d1bf]::run_compiler::{closure#0}>::{closure#1}, core[563965cbb8764b56]::result::Result<(), rustc_span[6197d43b7fdbf68b]::ErrorGuaranteed>>::{closure#0}, core[563965cbb8764b56]::result::Result<(), rustc_span[6197d43b7fdbf68b]::ErrorGuaranteed>>::{closure#0}::{closure#0}, core[563965cbb8764b56]::result::Result<(), rustc_span[6197d43b7fdbf68b]::ErrorGuaranteed>>
  43:     0x7fdd263cfb3a - <<std[a9a046d33cddffde]::thread::Builder>::spawn_unchecked_<rustc_interface[2a6dcbe82196fb3f]::util::run_in_thread_with_globals<rustc_interface[2a6dcbe82196fb3f]::util::run_in_thread_pool_with_globals<rustc_interface[2a6dcbe82196fb3f]::interface::run_compiler<core[563965cbb8764b56]::result::Result<(), rustc_span[6197d43b7fdbf68b]::ErrorGuaranteed>, rustc_driver_impl[f6a9d0df02f1d1bf]::run_compiler::{closure#0}>::{closure#1}, core[563965cbb8764b56]::result::Result<(), rustc_span[6197d43b7fdbf68b]::ErrorGuaranteed>>::{closure#0}, core[563965cbb8764b56]::result::Result<(), rustc_span[6197d43b7fdbf68b]::ErrorGuaranteed>>::{closure#0}::{closure#0}, core[563965cbb8764b56]::result::Result<(), rustc_span[6197d43b7fdbf68b]::ErrorGuaranteed>>::{closure#2} as core[563965cbb8764b56]::ops::function::FnOnce<()>>::call_once::{shim:vtable#0}
  44:     0x7fdd27b4510b - <alloc::boxed::Box<F,A> as core::ops::function::FnOnce<Args>>::call_once::h7cabb6ffc85af816
                               at /rustc/e9e6e2e444c30c23a9c878a88fbc3978c2acad95/library/alloc/src/boxed.rs:2064:9
  45:     0x7fdd27b4510b - <alloc::boxed::Box<F,A> as core::ops::function::FnOnce<Args>>::call_once::h074441c25350c542
                               at /rustc/e9e6e2e444c30c23a9c878a88fbc3978c2acad95/library/alloc/src/boxed.rs:2064:9
  46:     0x7fdd27b4510b - std::sys::pal::unix::thread::Thread::new::thread_start::h8b982c8d97422db7
                               at /rustc/e9e6e2e444c30c23a9c878a88fbc3978c2acad95/library/std/src/sys/pal/unix/thread.rs:108:17
  47:     0x7fdd20c94ac3 - <unknown>
  48:     0x7fdd20d26850 - <unknown>
  49:                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: please make sure that you have updated to the latest nightly

note: please attach the file at `/app/rustc-ice-2024-06-30T07_05_54-1.txt` to your bug report

note: compiler flags: -C debuginfo=1 -C llvm-args=--x86-asm-syntax=intel --crate-type rlib -Z next-solver -Z treat-err-as-bug

query stack during panic:
#0 [check_well_formed] checking that `<impl at <source>:11:1: 11:40>::foo` is well-formed
#1 [check_mod_type_wf] checking that types are well-formed in top-level module
end of query stack
Compiler returned: 101