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ICE index out of bounds: the len is 0 but the index is 0 #127804

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@gurry

Description

@gurry

Code

struct Thing;

pub trait Every {
    type Assoc;
}
impl<T: ?Sized> Every for Thing {
    type Assoc = T;
}

fn foo(_: <Thing as Every>::Assoc) {}

Meta

rustc --version --verbose:

rustc 1.81.0-dev
binary: rustc
commit-hash: unknown
commit-date: unknown
host: aarch64-apple-darwin
release: 1.81.0-dev
LLVM version: 18.1.7

Error output

Compiling playground v0.0.1 (/playground)
error[E0207]: the type parameter `T` is not constrained by the impl trait, self type, or predicates
 --> src/lib.rs:6:6
  |
6 | impl<T: ?Sized> Every for Thing {
  |      ^ unconstrained type parameter

error[E0282]: type annotations needed
  --> src/lib.rs:10:11
   |
10 | fn foo(_: <Thing as Every>::Assoc) {}
   |           ^^^^^^^^^^^^^^^^^^^^^^^ cannot infer type for type parameter `T`

error[E0282]: type annotations needed
  --> src/lib.rs:10:8
   |
10 | fn foo(_: <Thing as Every>::Assoc) {}
   |        ^ cannot infer type for type parameter `T`
Backtrace

thread 'rustc' panicked at /rust/deps/ena-0.14.2/src/snapshot_vec.rs:199:10:
index out of bounds: the len is 0 but the index is 0
stack backtrace:
   0:     0x7f0d4f6d5035 - std::backtrace_rs::backtrace::libunwind::trace::h1a07e5dba0da0cd2
                               at /rustc/129f3b9964af4d4a709d1383930ade12dfe7c081/library/std/src/../../backtrace/src/backtrace/libunwind.rs:105:5
   1:     0x7f0d4f6d5035 - std::backtrace_rs::backtrace::trace_unsynchronized::h61b9b8394328c0bc
                               at /rustc/129f3b9964af4d4a709d1383930ade12dfe7c081/library/std/src/../../backtrace/src/backtrace/mod.rs:66:5
   2:     0x7f0d4f6d5035 - std::sys_common::backtrace::_print_fmt::h1c5e18b460934cff
                               at /rustc/129f3b9964af4d4a709d1383930ade12dfe7c081/library/std/src/sys_common/backtrace.rs:68:5
   3:     0x7f0d4f6d5035 - <std::sys_common::backtrace::_print::DisplayBacktrace as core::fmt::Display>::fmt::h1e1a1972118942ad
                               at /rustc/129f3b9964af4d4a709d1383930ade12dfe7c081/library/std/src/sys_common/backtrace.rs:44:22
   4:     0x7f0d4f72429b - core::fmt::rt::Argument::fmt::h07af2b4071d536cd
                               at /rustc/129f3b9964af4d4a709d1383930ade12dfe7c081/library/core/src/fmt/rt.rs:165:63
   5:     0x7f0d4f72429b - core::fmt::write::hc090a2ffd6b28c4a
                               at /rustc/129f3b9964af4d4a709d1383930ade12dfe7c081/library/core/src/fmt/mod.rs:1157:21
   6:     0x7f0d4f6c9bdf - std::io::Write::write_fmt::h8898bac6ff039a23
                               at /rustc/129f3b9964af4d4a709d1383930ade12dfe7c081/library/std/src/io/mod.rs:1832:15
   7:     0x7f0d4f6d4e0e - std::sys_common::backtrace::_print::h4e80c5803d4ee35b
                               at /rustc/129f3b9964af4d4a709d1383930ade12dfe7c081/library/std/src/sys_common/backtrace.rs:47:5
   8:     0x7f0d4f6d4e0e - std::sys_common::backtrace::print::ha96650907276675e
                               at /rustc/129f3b9964af4d4a709d1383930ade12dfe7c081/library/std/src/sys_common/backtrace.rs:34:9
   9:     0x7f0d4f6d7779 - std::panicking::default_hook::{{closure}}::h215c2a0a8346e0e0
  10:     0x7f0d4f6d74bd - std::panicking::default_hook::h207342be97478370
                               at /rustc/129f3b9964af4d4a709d1383930ade12dfe7c081/library/std/src/panicking.rs:298:9
  11:     0x7f0d525d21b7 - std[3c8ba8ebcf555201]::panicking::update_hook::<alloc[bfbae7e348dce413]::boxed::Box<rustc_driver_impl[c88438ade88661f4]::install_ice_hook::{closure#0}>>::{closure#0}
  12:     0x7f0d4f6d7e76 - <alloc::boxed::Box<F,A> as core::ops::function::Fn<Args>>::call::ha9c3bc81d312fd83
                               at /rustc/129f3b9964af4d4a709d1383930ade12dfe7c081/library/alloc/src/boxed.rs:2036:9
  13:     0x7f0d4f6d7e76 - std::panicking::rust_panic_with_hook::hac8bdceee1e4fe2c
                               at /rustc/129f3b9964af4d4a709d1383930ade12dfe7c081/library/std/src/panicking.rs:799:13
  14:     0x7f0d4f6d7c24 - std::panicking::begin_panic_handler::{{closure}}::h00d785e82757ce3c
                               at /rustc/129f3b9964af4d4a709d1383930ade12dfe7c081/library/std/src/panicking.rs:664:13
  15:     0x7f0d4f6d54f9 - std::sys_common::backtrace::__rust_end_short_backtrace::h1628d957bcd06996
                               at /rustc/129f3b9964af4d4a709d1383930ade12dfe7c081/library/std/src/sys_common/backtrace.rs:171:18
  16:     0x7f0d4f6d7957 - rust_begin_unwind
                               at /rustc/129f3b9964af4d4a709d1383930ade12dfe7c081/library/std/src/panicking.rs:652:5
  17:     0x7f0d4f720763 - core::panicking::panic_fmt::hdc63834ffaaefae5
                               at /rustc/129f3b9964af4d4a709d1383930ade12dfe7c081/library/core/src/panicking.rs:72:14
  18:     0x7f0d4f720987 - core::panicking::panic_bounds_check::hd7e618b1b39cc1c3
                               at /rustc/129f3b9964af4d4a709d1383930ade12dfe7c081/library/core/src/panicking.rs:275:5
  19:     0x7f0d54a5f768 - <ena[7ba0c23a1613b29]::unify::UnificationTable<ena[7ba0c23a1613b29]::unify::backing_vec::InPlace<rustc_infer[abd41066181445be]::infer::type_variable::TyVidEqKey, &mut alloc[bfbae7e348dce413]::vec::Vec<ena[7ba0c23a1613b29]::unify::VarValue<rustc_infer[abd41066181445be]::infer::type_variable::TyVidEqKey>>, &mut rustc_infer[abd41066181445be]::infer::snapshot::undo_log::InferCtxtUndoLogs>>>::uninlined_get_root_key.llvm.6537034541696690420.cold
  20:     0x7f0d507a0045 - <rustc_infer[abd41066181445be]::infer::canonical::canonicalizer::Canonicalizer as rustc_type_ir[a145be3c51398263]::fold::TypeFolder<rustc_middle[3ff731b746e7b038]::ty::context::TyCtxt>>::fold_ty
  21:     0x7f0d53dd6b38 - <rustc_infer[abd41066181445be]::infer::canonical::canonicalizer::Canonicalizer as rustc_type_ir[a145be3c51398263]::fold::FallibleTypeFolder<rustc_middle[3ff731b746e7b038]::ty::context::TyCtxt>>::try_fold_predicate
  22:     0x7f0d5115701f - rustc_trait_selection[173dcaf5d960508e]::traits::type_known_to_meet_bound_modulo_regions
  23:     0x7f0d53ba840b - rustc_query_impl[a12402620de91e8]::plumbing::__rust_begin_short_backtrace::<rustc_query_impl[a12402620de91e8]::query_impl::is_copy_raw::dynamic_query::{closure#2}::{closure#0}, rustc_middle[3ff731b746e7b038]::query::erase::Erased<[u8; 1usize]>>
  24:     0x7f0d53ba93c6 - rustc_query_system[4e189ce2c77124d]::query::plumbing::try_execute_query::<rustc_query_impl[a12402620de91e8]::DynamicConfig<rustc_query_system[4e189ce2c77124d]::query::caches::DefaultCache<rustc_middle[3ff731b746e7b038]::ty::ParamEnvAnd<rustc_middle[3ff731b746e7b038]::ty::Ty>, rustc_middle[3ff731b746e7b038]::query::erase::Erased<[u8; 1usize]>>, false, false, false>, rustc_query_impl[a12402620de91e8]::plumbing::QueryCtxt, false>
  25:     0x7f0d53ba90ce - rustc_query_impl[a12402620de91e8]::query_impl::is_copy_raw::get_query_non_incr::__rust_end_short_backtrace
  26:     0x7f0d53baa0eb - rustc_ty_utils[b79b74a9f824867d]::needs_drop::needs_drop_raw
  27:     0x7f0d53ba9b59 - rustc_query_impl[a12402620de91e8]::plumbing::__rust_begin_short_backtrace::<rustc_query_impl[a12402620de91e8]::query_impl::needs_drop_raw::dynamic_query::{closure#2}::{closure#0}, rustc_middle[3ff731b746e7b038]::query::erase::Erased<[u8; 1usize]>>
  28:     0x7f0d53ba936a - rustc_query_system[4e189ce2c77124d]::query::plumbing::try_execute_query::<rustc_query_impl[a12402620de91e8]::DynamicConfig<rustc_query_system[4e189ce2c77124d]::query::caches::DefaultCache<rustc_middle[3ff731b746e7b038]::ty::ParamEnvAnd<rustc_middle[3ff731b746e7b038]::ty::Ty>, rustc_middle[3ff731b746e7b038]::query::erase::Erased<[u8; 1usize]>>, false, false, false>, rustc_query_impl[a12402620de91e8]::plumbing::QueryCtxt, false>
  29:     0x7f0d53ba900e - rustc_query_impl[a12402620de91e8]::query_impl::needs_drop_raw::get_query_non_incr::__rust_end_short_backtrace
  30:     0x7f0d50b12f93 - <rustc_mir_transform[2984d3182075647]::elaborate_drops::ElaborateDrops as rustc_middle[3ff731b746e7b038]::mir::MirPass>::run_pass
  31:     0x7f0d5394a4cd - rustc_mir_transform[2984d3182075647]::pass_manager::run_passes_inner
  32:     0x7f0d5141bff7 - rustc_mir_transform[2984d3182075647]::mir_drops_elaborated_and_const_checked
  33:     0x7f0d53a5ec31 - rustc_query_impl[a12402620de91e8]::plumbing::__rust_begin_short_backtrace::<rustc_query_impl[a12402620de91e8]::query_impl::mir_drops_elaborated_and_const_checked::dynamic_query::{closure#2}::{closure#0}, rustc_middle[3ff731b746e7b038]::query::erase::Erased<[u8; 8usize]>>
  34:     0x7f0d53a5ef2d - rustc_query_system[4e189ce2c77124d]::query::plumbing::try_execute_query::<rustc_query_impl[a12402620de91e8]::DynamicConfig<rustc_query_system[4e189ce2c77124d]::query::caches::VecCache<rustc_span[8c7415e9d33ddd75]::def_id::LocalDefId, rustc_middle[3ff731b746e7b038]::query::erase::Erased<[u8; 8usize]>>, false, false, false>, rustc_query_impl[a12402620de91e8]::plumbing::QueryCtxt, false>
  35:     0x7f0d53a5e78c - rustc_query_impl[a12402620de91e8]::query_impl::mir_drops_elaborated_and_const_checked::get_query_non_incr::__rust_end_short_backtrace
  36:     0x7f0d542d2432 - rustc_interface[640972162e3c086f]::passes::analysis
  37:     0x7f0d542d1aef - rustc_query_impl[a12402620de91e8]::plumbing::__rust_begin_short_backtrace::<rustc_query_impl[a12402620de91e8]::query_impl::analysis::dynamic_query::{closure#2}::{closure#0}, rustc_middle[3ff731b746e7b038]::query::erase::Erased<[u8; 1usize]>>
  38:     0x7f0d5462b022 - rustc_query_system[4e189ce2c77124d]::query::plumbing::try_execute_query::<rustc_query_impl[a12402620de91e8]::DynamicConfig<rustc_query_system[4e189ce2c77124d]::query::caches::SingleCache<rustc_middle[3ff731b746e7b038]::query::erase::Erased<[u8; 1usize]>>, false, false, false>, rustc_query_impl[a12402620de91e8]::plumbing::QueryCtxt, false>
  39:     0x7f0d5462adc9 - rustc_query_impl[a12402620de91e8]::query_impl::analysis::get_query_non_incr::__rust_end_short_backtrace
  40:     0x7f0d544cc149 - rustc_interface[640972162e3c086f]::interface::run_compiler::<core[868bc93c3f2beb33]::result::Result<(), rustc_span[8c7415e9d33ddd75]::ErrorGuaranteed>, rustc_driver_impl[c88438ade88661f4]::run_compiler::{closure#0}>::{closure#1}
  41:     0x7f0d54489f8b - std[3c8ba8ebcf555201]::sys_common::backtrace::__rust_begin_short_backtrace::<rustc_interface[640972162e3c086f]::util::run_in_thread_with_globals<rustc_interface[640972162e3c086f]::interface::run_compiler<core[868bc93c3f2beb33]::result::Result<(), rustc_span[8c7415e9d33ddd75]::ErrorGuaranteed>, rustc_driver_impl[c88438ade88661f4]::run_compiler::{closure#0}>::{closure#1}, core[868bc93c3f2beb33]::result::Result<(), rustc_span[8c7415e9d33ddd75]::ErrorGuaranteed>>::{closure#0}::{closure#0}, core[868bc93c3f2beb33]::result::Result<(), rustc_span[8c7415e9d33ddd75]::ErrorGuaranteed>>
  42:     0x7f0d54489d80 - <<std[3c8ba8ebcf555201]::thread::Builder>::spawn_unchecked_<rustc_interface[640972162e3c086f]::util::run_in_thread_with_globals<rustc_interface[640972162e3c086f]::interface::run_compiler<core[868bc93c3f2beb33]::result::Result<(), rustc_span[8c7415e9d33ddd75]::ErrorGuaranteed>, rustc_driver_impl[c88438ade88661f4]::run_compiler::{closure#0}>::{closure#1}, core[868bc93c3f2beb33]::result::Result<(), rustc_span[8c7415e9d33ddd75]::ErrorGuaranteed>>::{closure#0}::{closure#0}, core[868bc93c3f2beb33]::result::Result<(), rustc_span[8c7415e9d33ddd75]::ErrorGuaranteed>>::{closure#2} as core[868bc93c3f2beb33]::ops::function::FnOnce<()>>::call_once::{shim:vtable#0}
  43:     0x7f0d4f6e1cab - <alloc::boxed::Box<F,A> as core::ops::function::FnOnce<Args>>::call_once::h09e5a4c541afa800
                               at /rustc/129f3b9964af4d4a709d1383930ade12dfe7c081/library/alloc/src/boxed.rs:2022:9
  44:     0x7f0d4f6e1cab - <alloc::boxed::Box<F,A> as core::ops::function::FnOnce<Args>>::call_once::h9c8b03c22f4e7026
                               at /rustc/129f3b9964af4d4a709d1383930ade12dfe7c081/library/alloc/src/boxed.rs:2022:9
  45:     0x7f0d4f6e1cab - std::sys::pal::unix::thread::Thread::new::thread_start::h522bc89a54da820a
                               at /rustc/129f3b9964af4d4a709d1383930ade12dfe7c081/library/std/src/sys/pal/unix/thread.rs:108:17
  46:     0x7f0d4f5ef609 - start_thread
  47:     0x7f0d4f512353 - clone
  48:                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 1.79.0 (129f3b996 2024-06-10) running on x86_64-unknown-linux-gnu

note: compiler flags: --crate-type lib -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 [is_copy_raw] computing whether `_` is `Copy`
#1 [needs_drop_raw] computing whether `_` needs drop
#2 [mir_drops_elaborated_and_const_checked] elaborating drops for `foo`
#3 [analysis] running analysis passes on this crate
end of query stack
Some errors have detailed explanations: E0207, E0282.
For more information about an error, try `rustc --explain E0207`.
error: could not compile `playground` (lib) due to 3 previous errors

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    C-bugCategory: This is a bug.I-ICEIssue: The compiler panicked, giving an Internal Compilation Error (ICE) ❄️S-bug-has-testStatus: This bug is tracked inside the repo by a `known-bug` test.T-compilerRelevant to the compiler team, which will review and decide on the PR/issue.

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