ICE: generics: index out of bounds

[matthiaskrgr]

auto-reduced (treereduce-rust):

trait Foo {
    type Assoc<const N: Self>;
    fn foo(&Assoc) -> Self::Assoc<3>;
}

original:

// run-pass

// This test unsures that with_opt_const_param returns the
// def_id of the N param in the Foo::Assoc GAT.

trait Foo {
    type Assoc<const N: N>;
    fn foo(&self) -> Self::Assoc<3>;
}

impl Foo for () {
    fn foo(&Assoc) -> Self::Assoc<3>;
    fn foo(&Assoc) -> Self::Assoc<3>;
}

trait Foo {
    type Assoc<const N: Self>;
    fn foo(&Assoc) -> Self::Assoc<3>;
}

Version information

rustc 1.87.0-nightly (8c392966a 2025-03-01)
binary: rustc
commit-hash: 8c392966a013fd8a09e6b78b3c8d6e442bc278e1
commit-date: 2025-03-01
host: x86_64-unknown-linux-gnu
release: 1.87.0-nightly
LLVM version: 20.1.0

Possibly related line of code:

rust/compiler/rustc_middle/src/ty/generics.rs

Lines 217 to 229 in 8c39296

	false
	}
	/// Returns the `GenericParamDef` with the given index.
	pub fn param_at(&'tcx self, param_index: usize, tcx: TyCtxt<'tcx>) -> &'tcx GenericParamDef {
	if let Some(index) = param_index.checked_sub(self.parent_count) {
	&self.own_params[index]
	} else {
	tcx.generics_of(self.parent.expect("parent_count > 0 but no parent?"))
	.param_at(param_index, tcx)
	}
	}

Command:
/home/matthias/.rustup/toolchains/master/bin/rustc -Zincremental-verify-ich=yes -Cincremental=<dir> -Cdebuginfo=2 -Clink-dead-code=true -Zvalidate-mir --edition=2024

Program output

error: expected one of `:`, `@`, or `|`, found `)`
  --> /tmp/icemaker_global_tempdir.lSkQubIYoEeM/rustc_testrunner_tmpdir_reporting.42tnKAQbDl1C/mvce.rs:12:18
   |
12 |     fn foo(&Assoc) -> Self::Assoc<3>;
   |                  ^ expected one of `:`, `@`, or `|`
   |
   = note: anonymous parameters are removed in the 2018 edition (see RFC 1685)
help: if this is a `self` type, give it a parameter name
   |
12 |     fn foo(self: &Assoc) -> Self::Assoc<3>;
   |            +++++
help: if this is a parameter name, give it a type
   |
12 -     fn foo(&Assoc) -> Self::Assoc<3>;
12 +     fn foo(Assoc: &TypeName) -> Self::Assoc<3>;
   |
help: if this is a type, explicitly ignore the parameter name
   |
12 |     fn foo(_: &Assoc) -> Self::Assoc<3>;
   |            ++

error[E0601]: `main` function not found in crate `mvce`
  --> /tmp/icemaker_global_tempdir.lSkQubIYoEeM/rustc_testrunner_tmpdir_reporting.42tnKAQbDl1C/mvce.rs:13:2
   |
13 | }
   |  ^ consider adding a `main` function to `/tmp/icemaker_global_tempdir.lSkQubIYoEeM/rustc_testrunner_tmpdir_reporting.42tnKAQbDl1C/mvce.rs`

error: `Self` is forbidden as the type of a const generic parameter
  --> /tmp/icemaker_global_tempdir.lSkQubIYoEeM/rustc_testrunner_tmpdir_reporting.42tnKAQbDl1C/mvce.rs:11:25
   |
11 |     type Assoc<const N: Self>;
   |                         ^^^^
   |
   = note: the only supported types are integers, `bool`, and `char`


thread 'rustc' panicked at compiler/rustc_middle/src/ty/generics.rs:223:29:
index out of bounds: the len is 0 but the index is 0
stack backtrace:
   0:     0x7295de3bedf4 - <std::sys::backtrace::BacktraceLock::print::DisplayBacktrace as core::fmt::Display>::fmt::hdbd106d724e72c20
   1:     0x7295dec057e2 - core::fmt::write::h861eecc74abebf7a
   2:     0x7295dfc4dd51 - std::io::Write::write_fmt::h493b3152b071fba0
   3:     0x7295de3bec52 - std::sys::backtrace::BacktraceLock::print::h71f315c25fc266cb
   4:     0x7295de3c1532 - std::panicking::default_hook::{{closure}}::h8019dc6a2c6c0fe7
   5:     0x7295de3c1124 - std::panicking::default_hook::h497f769686a88dd6
   6:     0x7295dd518417 - std[e7ccd300aecc5933]::panicking::update_hook::<alloc[8cc49891b291256f]::boxed::Box<rustc_driver_impl[b622dd38a520489a]::install_ice_hook::{closure#1}>>::{closure#0}
   7:     0x7295de3c1da3 - std::panicking::rust_panic_with_hook::h98fc165e90ef379e
   8:     0x7295de3c1a9a - std::panicking::begin_panic_handler::{{closure}}::h2c1a60d0a908eaec
   9:     0x7295de3bf2c9 - std::sys::backtrace::__rust_end_short_backtrace::he8aba8f9b7ddf304
  10:     0x7295de3c175d - rust_begin_unwind
  11:     0x7295db05a680 - core::panicking::panic_fmt::hcbf39f8c1e585f84
  12:     0x7295dc33968c - core::panicking::panic_bounds_check::h56f1c876f8f7fa1a
  13:     0x7295e063a055 - <rustc_middle[464f7c4b782fc90]::ty::generics::Generics>::type_param.cold
  14:     0x7295de1c2278 - <rustc_trait_selection[4edfcc70fd15c568]::error_reporting::TypeErrCtxt>::note_and_explain_type_err
  15:     0x7295de272c77 - <rustc_trait_selection[4edfcc70fd15c568]::error_reporting::TypeErrCtxt>::note_type_err
  16:     0x7295de1ea498 - <rustc_trait_selection[4edfcc70fd15c568]::error_reporting::TypeErrCtxt>::report_and_explain_type_error
  17:     0x7295db9da079 - <rustc_trait_selection[4edfcc70fd15c568]::error_reporting::TypeErrCtxt>::report_mismatched_types
  18:     0x7295dee76923 - <rustc_hir_typeck[2e27b1bdaf23c662]::fn_ctxt::FnCtxt>::check_expr_coercible_to_type
  19:     0x7295df16f7a1 - rustc_hir_typeck[2e27b1bdaf23c662]::typeck_with_inspect::{closure#0}
  20:     0x7295df16c5f0 - rustc_query_impl[f11a5069a0fc322c]::plumbing::__rust_begin_short_backtrace::<rustc_query_impl[f11a5069a0fc322c]::query_impl::typeck::dynamic_query::{closure#2}::{closure#0}, rustc_middle[464f7c4b782fc90]::query::erase::Erased<[u8; 8usize]>>
  21:     0x7295df163005 - rustc_query_system[18aefac76bbd956a]::query::plumbing::try_execute_query::<rustc_query_impl[f11a5069a0fc322c]::DynamicConfig<rustc_data_structures[fa39f8fcd9225f43]::vec_cache::VecCache<rustc_span[eeaf0b3b2812840a]::def_id::LocalDefId, rustc_middle[464f7c4b782fc90]::query::erase::Erased<[u8; 8usize]>, rustc_query_system[18aefac76bbd956a]::dep_graph::graph::DepNodeIndex>, false, false, false>, rustc_query_impl[f11a5069a0fc322c]::plumbing::QueryCtxt, true>
  22:     0x7295df15f787 - rustc_query_impl[f11a5069a0fc322c]::query_impl::typeck::get_query_incr::__rust_end_short_backtrace
  23:     0x7295df1614c1 - rustc_query_impl[f11a5069a0fc322c]::plumbing::__rust_begin_short_backtrace::<rustc_query_impl[f11a5069a0fc322c]::query_impl::used_trait_imports::dynamic_query::{closure#2}::{closure#0}, rustc_middle[464f7c4b782fc90]::query::erase::Erased<[u8; 8usize]>>
  24:     0x7295df163005 - rustc_query_system[18aefac76bbd956a]::query::plumbing::try_execute_query::<rustc_query_impl[f11a5069a0fc322c]::DynamicConfig<rustc_data_structures[fa39f8fcd9225f43]::vec_cache::VecCache<rustc_span[eeaf0b3b2812840a]::def_id::LocalDefId, rustc_middle[464f7c4b782fc90]::query::erase::Erased<[u8; 8usize]>, rustc_query_system[18aefac76bbd956a]::dep_graph::graph::DepNodeIndex>, false, false, false>, rustc_query_impl[f11a5069a0fc322c]::plumbing::QueryCtxt, true>
  25:     0x7295dee21838 - rustc_query_impl[f11a5069a0fc322c]::query_impl::used_trait_imports::get_query_incr::__rust_end_short_backtrace
  26:     0x7295df45cb94 - rustc_middle[464f7c4b782fc90]::query::plumbing::query_get_at::<rustc_data_structures[fa39f8fcd9225f43]::vec_cache::VecCache<rustc_span[eeaf0b3b2812840a]::def_id::LocalDefId, rustc_middle[464f7c4b782fc90]::query::erase::Erased<[u8; 8usize]>, rustc_query_system[18aefac76bbd956a]::dep_graph::graph::DepNodeIndex>>
  27:     0x7295df45c2ad - rustc_hir_analysis[6dcb172f42838441]::check_unused::check_unused_traits
  28:     0x7295df45c007 - rustc_query_impl[f11a5069a0fc322c]::plumbing::__rust_begin_short_backtrace::<rustc_query_impl[f11a5069a0fc322c]::query_impl::check_unused_traits::dynamic_query::{closure#2}::{closure#0}, rustc_middle[464f7c4b782fc90]::query::erase::Erased<[u8; 0usize]>>
  29:     0x7295dfc4571f - rustc_query_system[18aefac76bbd956a]::query::plumbing::try_execute_query::<rustc_query_impl[f11a5069a0fc322c]::DynamicConfig<rustc_query_system[18aefac76bbd956a]::query::caches::SingleCache<rustc_middle[464f7c4b782fc90]::query::erase::Erased<[u8; 0usize]>>, false, false, false>, rustc_query_impl[f11a5069a0fc322c]::plumbing::QueryCtxt, true>
  30:     0x7295dfc44c4e - rustc_query_impl[f11a5069a0fc322c]::query_impl::check_unused_traits::get_query_incr::__rust_end_short_backtrace
  31:     0x7295df15e937 - rustc_hir_analysis[6dcb172f42838441]::check_crate
  32:     0x7295df15831c - rustc_interface[f15b12210e2206a6]::passes::run_required_analyses
  33:     0x7295dfc49cfa - rustc_interface[f15b12210e2206a6]::passes::analysis
  34:     0x7295dfc49cd9 - rustc_query_impl[f11a5069a0fc322c]::plumbing::__rust_begin_short_backtrace::<rustc_query_impl[f11a5069a0fc322c]::query_impl::analysis::dynamic_query::{closure#2}::{closure#0}, rustc_middle[464f7c4b782fc90]::query::erase::Erased<[u8; 0usize]>>
  35:     0x7295dfc455aa - rustc_query_system[18aefac76bbd956a]::query::plumbing::try_execute_query::<rustc_query_impl[f11a5069a0fc322c]::DynamicConfig<rustc_query_system[18aefac76bbd956a]::query::caches::SingleCache<rustc_middle[464f7c4b782fc90]::query::erase::Erased<[u8; 0usize]>>, false, false, false>, rustc_query_impl[f11a5069a0fc322c]::plumbing::QueryCtxt, true>
  36:     0x7295dfc44fa2 - rustc_query_impl[f11a5069a0fc322c]::query_impl::analysis::get_query_incr::__rust_end_short_backtrace
  37:     0x7295dfd38b3d - rustc_interface[f15b12210e2206a6]::passes::create_and_enter_global_ctxt::<core[9e5e7b8b77114b88]::option::Option<rustc_interface[f15b12210e2206a6]::queries::Linker>, rustc_driver_impl[b622dd38a520489a]::run_compiler::{closure#0}::{closure#2}>::{closure#2}::{closure#0}
  38:     0x7295dfd03a20 - rustc_interface[f15b12210e2206a6]::interface::run_compiler::<(), rustc_driver_impl[b622dd38a520489a]::run_compiler::{closure#0}>::{closure#1}
  39:     0x7295dfb59bc8 - std[e7ccd300aecc5933]::sys::backtrace::__rust_begin_short_backtrace::<rustc_interface[f15b12210e2206a6]::util::run_in_thread_with_globals<rustc_interface[f15b12210e2206a6]::util::run_in_thread_pool_with_globals<rustc_interface[f15b12210e2206a6]::interface::run_compiler<(), rustc_driver_impl[b622dd38a520489a]::run_compiler::{closure#0}>::{closure#1}, ()>::{closure#0}, ()>::{closure#0}::{closure#0}, ()>
  40:     0x7295dfb5a4b4 - <<std[e7ccd300aecc5933]::thread::Builder>::spawn_unchecked_<rustc_interface[f15b12210e2206a6]::util::run_in_thread_with_globals<rustc_interface[f15b12210e2206a6]::util::run_in_thread_pool_with_globals<rustc_interface[f15b12210e2206a6]::interface::run_compiler<(), rustc_driver_impl[b622dd38a520489a]::run_compiler::{closure#0}>::{closure#1}, ()>::{closure#0}, ()>::{closure#0}::{closure#0}, ()>::{closure#1} as core[9e5e7b8b77114b88]::ops::function::FnOnce<()>>::call_once::{shim:vtable#0}
  41:     0x7295dfb5b8ab - std::sys::pal::unix::thread::Thread::new::thread_start::h20288ab9ea215a81
  42:     0x7295d9c5e70a - <unknown>
  43:     0x7295d9ce2aac - <unknown>
  44:                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: rustc 1.87.0-nightly (8c392966a 2025-03-01) running on x86_64-unknown-linux-gnu

note: compiler flags: -Z incremental-verify-ich=yes -C incremental=[REDACTED] -C debuginfo=2 -C link-dead-code=true -Z validate-mir

query stack during panic:
#0 [typeck] type-checking `Foo::foo::{constant#0}`
#1 [used_trait_imports] finding used_trait_imports `Foo::foo::{constant#0}`
#2 [check_unused_traits] checking unused trait imports in crate
#3 [analysis] running analysis passes on this crate
end of query stack
error: aborting due to 3 previous errors

For more information about this error, try `rustc --explain E0601`.

[matthiaskrgr]

bisects to #137617

[cyrgani]

trait Foo {
    type Assoc<const N: Self>;
    fn foo() -> Self::Assoc<3>;
}

without any extra flags ICEs

[xizheyin]

@rustbot claim
I might try it.