rust-lang / rust-lang/rust

[ICE]: did not expect duplicate `ConstParamHasTy` for `!BoundConst .. in param-env

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@biscuitrescue is already working on this.

Since Sep 14, 2026.

C-bug F-fn_delegation I-ICE needs-triage T-compiler
Dominant language
Rust
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Description

auto-reduced (treereduce-rust):

struct S<A, const C: usize>;

impl<'b, 'c, C, const C: usize> S<C, C> {
    fn foo_self<T>() {}
}

reuse S::<(), 123>::foo_self ;

original:

#![feature(fn_delegation)]

struct S<A, const C: usize>;

impl<'b, 'c, C, const C: usize> S<C, C> {
    fn foo_self<T, const B: bool>() {}
}

reuse S::<(), 123>::foo_self ;

fn main() {}

Version information

rustc 1.100.0-nightly (a8a1e6fd9 2026-09-14)
binary: rustc
commit-hash: a8a1e6fd9df2e094d6f09c0d57991508680acc1c
commit-date: 2026-09-14
host: x86_64-unknown-linux-gnu
release: 1.100.0-nightly
LLVM version: 23.1.1

Possibly related line of code:
https://github.com/rust-lang/rust/blob/a8a1e6fd9df2e094d6f09c0d57991508680acc1c/compiler/rustc_type_ir/src/binder.rs#L826-L838

Command:
/home/matthias/.rustup/toolchains/master/bin/rustc

Program output 

error[E0403]: the name `C` is already used for a generic parameter in this item's generic parameters
 --> /tmp/icemaker_global_tempdir.kd6F3Ltfxebv/rustc_testrunner_tmpdir_reporting.Fb803AuC7DnC/mvce.rs:3:23
  |
3 | impl<'b, 'c, C, const C: usize> S<C, C> {
  |              -        ^ already used
  |              |
  |              first use of `C`

error[E0658]: functions delegation is not yet fully implemented
 --> /tmp/icemaker_global_tempdir.kd6F3Ltfxebv/rustc_testrunner_tmpdir_reporting.Fb803AuC7DnC/mvce.rs:7:1
  |
7 | reuse S::<(), 123>::foo_self ;
  | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  |
  = note: see issue #118212 <https://github.com/rust-lang/rust/issues/118212> for more information
  = help: add `#![feature(fn_delegation)]` to the crate attributes to enable
  = note: this compiler was built on 2026-09-14; consider upgrading it if it is out of date

error[E0747]: type provided when a constant was expected
 --> /tmp/icemaker_global_tempdir.kd6F3Ltfxebv/rustc_testrunner_tmpdir_reporting.Fb803AuC7DnC/mvce.rs:3:38
  |
3 | impl<'b, 'c, C, const C: usize> S<C, C> {
  |                                      ^
  |
help: consider changing this type parameter to a const parameter
  |
3 - impl<'b, 'c, C, const C: usize> S<C, C> {
3 + impl<'b, 'c, const C: usize, const C: usize> S<C, C> {
  |

error[E0601]: `main` function not found in crate `mvce`
 --> /tmp/icemaker_global_tempdir.kd6F3Ltfxebv/rustc_testrunner_tmpdir_reporting.Fb803AuC7DnC/mvce.rs:7:31
  |
7 | reuse S::<(), 123>::foo_self ;
  |                               ^ consider adding a `main` function to `/tmp/icemaker_global_tempdir.kd6F3Ltfxebv/rustc_testrunner_tmpdir_reporting.Fb803AuC7DnC/mvce.rs`

error[E0392]: type parameter `A` is never used
 --> /tmp/icemaker_global_tempdir.kd6F3Ltfxebv/rustc_testrunner_tmpdir_reporting.Fb803AuC7DnC/mvce.rs:1:10
  |
1 | struct S<A, const C: usize>;
  |          ^ unused type parameter
  |
  = help: consider removing `A`, referring to it in a field, or using a marker such as `PhantomData`
  = help: if you intended `A` to be a const parameter, use `const A: /* Type */` instead


thread 'rustc' (398858) panicked at /rustc-dev/a8a1e6fd9df2e094d6f09c0d57991508680acc1c/compiler/rustc_type_ir/src/binder.rs:832:9:
const parameter `C/#3` (C/#3/3) out of range when instantiating args=[(), 123_usize, T/#0]
stack backtrace:
   0:     0x7f8a2ee3f2d6 - <<std[a7b27443cb86e72e]::sys::backtrace::BacktraceLock>::print::DisplayBacktrace as core[79c33294d41ca149]::fmt::Display>::fmt
   1:     0x7f8a2f40984f - core[79c33294d41ca149]::fmt::write
   2:     0x7f8a2ee542ac - <std[a7b27443cb86e72e]::sys::stdio::unix::Stderr as core[79c33294d41ca149]::io::write::Write>::write_fmt
   3:     0x7f8a2ee11dda - std[a7b27443cb86e72e]::panicking::default_hook::{closure#0}
   4:     0x7f8a2ee33883 - std[a7b27443cb86e72e]::panicking::default_hook
   5:     0x7f8a2db60c1f - std[a7b27443cb86e72e]::panicking::update_hook::<alloc[3f0bce58745c44b0]::boxed::Box<rustc_driver_impl[d9671ccd84038dcc]::install_ice_hook::{closure#1}>>::{closure#0}
   6:     0x7f8a2ee33d22 - std[a7b27443cb86e72e]::panicking::panic_with_hook
   7:     0x7f8a2ee11e92 - std[a7b27443cb86e72e]::panicking::panic_handler::{closure#0}
   8:     0x7f8a2ee0aca9 - std[a7b27443cb86e72e]::sys::backtrace::__rust_end_short_backtrace::<std[a7b27443cb86e72e]::panicking::panic_handler::{closure#0}, !>
   9:     0x7f8a2ee13a6d - __rustc[bcd6120e59dddf0]::rust_begin_unwind
  10:     0x7f8a2b877c2c - core[79c33294d41ca149]::panicking::panic_fmt
  11:     0x7f8a2e247b05 - <rustc_type_ir[b90822c65e3927f6]::binder::ArgFolder<rustc_middle[d55d5a36bb0d2487]::ty::context::TyCtxt>>::const_param_out_of_range
  12:     0x7f8a2f4c7701 - <rustc_type_ir[b90822c65e3927f6]::binder::ArgFolder<rustc_middle[d55d5a36bb0d2487]::ty::context::TyCtxt> as rustc_type_ir[b90822c65e3927f6]::fold::TypeFolder<rustc_middle[d55d5a36bb0d2487]::ty::context::TyCtxt>>::fold_const
  13:     0x7f8a2dc822ff - <rustc_type_ir[b90822c65e3927f6]::binder::EarlyBinder<rustc_middle[d55d5a36bb0d2487]::ty::context::TyCtxt, rustc_middle[d55d5a36bb0d2487]::ty::consts::Const>>::instantiate::<&[rustc_middle[d55d5a36bb0d2487]::ty::generic_args::GenericArg]>
  14:     0x7f8a2dc43994 - <rustc_hir_analysis[c48a938ba26deb33]::delegation::inherit_clauses_for_delegation_item::ClausesCollector>::with_own_clauses::<rustc_hir_analysis[c48a938ba26deb33]::delegation::inherit_clauses_for_delegation_item::{closure#0}>
  15:     0x7f8a2dd3bb28 - rustc_hir_analysis[c48a938ba26deb33]::delegation::inherit_clauses_for_delegation_item
  16:     0x7f8a305d8aa7 - rustc_hir_analysis[c48a938ba26deb33]::collect::clauses_of::gather_explicit_clauses_of
  17:     0x7f8a2f84616e - rustc_query_impl[efa7ca13a3339b39]::query_vtables::explicit_clauses_of::invoke_provider_fn::__rust_begin_short_backtrace
  18:     0x7f8a2f847707 - rustc_query_impl[efa7ca13a3339b39]::execution::try_execute_query::<rustc_middle[d55d5a36bb0d2487]::query::caches::DefIdCache<rustc_middle[d55d5a36bb0d2487]::query::erase::ErasedData<[u8; 24usize]>>, false>
  19:     0x7f8a2f84727d - rustc_query_impl[efa7ca13a3339b39]::query_vtables::explicit_clauses_of::execute_query_non_incr::__rust_end_short_backtrace
  20:     0x7f8a2f848545 - rustc_query_impl[efa7ca13a3339b39]::query_vtables::clauses_of::invoke_provider_fn::__rust_begin_short_backtrace
  21:     0x7f8a2f8475ad - rustc_query_impl[efa7ca13a3339b39]::execution::try_execute_query::<rustc_middle[d55d5a36bb0d2487]::query::caches::DefIdCache<rustc_middle[d55d5a36bb0d2487]::query::erase::ErasedData<[u8; 24usize]>>, false>
  22:     0x7f8a2f847239 - rustc_query_impl[efa7ca13a3339b39]::query_vtables::clauses_of::execute_query_non_incr::__rust_end_short_backtrace
  23:     0x7f8a30213eb8 - rustc_hir_analysis[c48a938ba26deb33]::check::check::check_item_type
  24:     0x7f8a3020efb8 - rustc_hir_analysis[c48a938ba26deb33]::check::wfcheck::check_well_formed
  25:     0x7f8a3020ef99 - rustc_query_impl[efa7ca13a3339b39]::query_vtables::check_well_formed::invoke_provider_fn::__rust_begin_short_backtrace
  26:     0x7f8a3020e5fd - rustc_query_impl[efa7ca13a3339b39]::execution::try_execute_query::<rustc_data_structures[f8e48b9204458190]::vec_cache::VecCache<rustc_span[ed161bac8b76d3dd]::def_id::LocalDefId, rustc_middle[d55d5a36bb0d2487]::query::erase::ErasedData<[u8; 1usize]>, rustc_middle[d55d5a36bb0d2487]::dep_graph::graph::DepNodeIndex>, false>
  27:     0x7f8a3020e395 - rustc_query_impl[efa7ca13a3339b39]::query_vtables::check_well_formed::execute_query_non_incr::__rust_end_short_backtrace
  28:     0x7f8a3020b942 - rustc_hir_analysis[c48a938ba26deb33]::check::wfcheck::check_type_wf
  29:     0x7f8a3020b827 - rustc_query_impl[efa7ca13a3339b39]::query_vtables::check_type_wf::invoke_provider_fn::__rust_begin_short_backtrace
  30:     0x7f8a304ec509 - rustc_query_impl[efa7ca13a3339b39]::execution::try_execute_query::<rustc_middle[d55d5a36bb0d2487]::query::caches::SingleCache<rustc_middle[d55d5a36bb0d2487]::query::erase::ErasedData<[u8; 1usize]>>, false>
  31:     0x7f8a304ec2ed - rustc_query_impl[efa7ca13a3339b39]::query_vtables::check_type_wf::execute_query_non_incr::__rust_end_short_backtrace
  32:     0x7f8a2fbf2f5a - rustc_hir_analysis[c48a938ba26deb33]::check_crate
  33:     0x7f8a2f9af7b3 - rustc_interface[e79ce05d4d9d9ef5]::passes::analysis
  34:     0x7f8a304ebc4a - rustc_query_impl[efa7ca13a3339b39]::execution::try_execute_query::<rustc_middle[d55d5a36bb0d2487]::query::caches::SingleCache<rustc_middle[d55d5a36bb0d2487]::query::erase::ErasedData<[u8; 0usize]>>, false>
  35:     0x7f8a304eb9d3 - rustc_query_impl[efa7ca13a3339b39]::query_vtables::analysis::execute_query_non_incr::__rust_end_short_backtrace
  36:     0x7f8a306d476c - rustc_interface[e79ce05d4d9d9ef5]::interface::run_compiler::<(), rustc_driver_impl[d9671ccd84038dcc]::run_compiler::{closure#0}>::{closure#2}
  37:     0x7f8a3072c324 - std[a7b27443cb86e72e]::sys::backtrace::__rust_begin_short_backtrace::<rustc_interface[e79ce05d4d9d9ef5]::util::run_in_thread_with_globals<rustc_interface[e79ce05d4d9d9ef5]::util::run_in_thread_pool_with_globals<rustc_interface[e79ce05d4d9d9ef5]::interface::run_compiler<(), rustc_driver_impl[d9671ccd84038dcc]::run_compiler::{closure#0}>::{closure#2}, ()>::{closure#0}, ()>::{closure#0}::{closure#0}, ()>
  38:     0x7f8a3072c0cb - <std[a7b27443cb86e72e]::thread::lifecycle::spawn_unchecked<rustc_interface[e79ce05d4d9d9ef5]::util::run_in_thread_with_globals<rustc_interface[e79ce05d4d9d9ef5]::util::run_in_thread_pool_with_globals<rustc_interface[e79ce05d4d9d9ef5]::interface::run_compiler<(), rustc_driver_impl[d9671ccd84038dcc]::run_compiler::{closure#0}>::{closure#2}, ()>::{closure#0}, ()>::{closure#0}::{closure#0}, ()>::{closure#1} as core[79c33294d41ca149]::ops::function::FnOnce<()>>::call_once::{shim:vtable#0}
  39:     0x7f8a30734fdb - <std[a7b27443cb86e72e]::sys::thread::unix::Thread>::new::thread_start
  40:     0x7f8a296980a2 - <unknown>
  41:     0x7f8a2972080c - <unknown>
  42:                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 1.100.0-nightly (a8a1e6fd9 2026-09-14) running on x86_64-unknown-linux-gnu

query stack during panic:
#0 [explicit_clauses_of] computing explicit predicates of `foo_self`
#1 [clauses_of] computing clauses of `foo_self`
#2 [check_well_formed] checking that `foo_self` is well-formed
#3 [check_type_wf] checking that types are well-formed
#4 [analysis] running analysis passes on crate `mvce`
end of query stack
error: aborting due to 5 previous errors

Some errors have detailed explanations: E0392, E0403, E0601, E0658, E0747.
For more information about an error, try `rustc --explain E0392`.

@rustbot label +F-fn_delegation

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