[ICE]: `unexpected generic param: GenericParam`

[matthiaskrgr]

original:

#![feature(non_lifetime_binders)]
#![feature(impl_trait_in_bindings)]
fn main() {
  let i = 0;
  let j: impl for<T> Clone = i;
}

Version information

rustc 1.96.0-nightly (08cd08fbe 2026-03-31)
binary: rustc
commit-hash: 08cd08fbef8c6663b052d8d9e4930d5696cbb8a7
commit-date: 2026-03-31
host: x86_64-unknown-linux-gnu
release: 1.96.0-nightly
LLVM version: 22.1.2

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

Program output

warning: the feature `non_lifetime_binders` is incomplete and may not be safe to use and/or cause compiler crashes
 --> /tmp/icemaker_global_tempdir.qVJ0uwKvZ1dL/rustc_testrunner_tmpdir_reporting.Aj4Epcfg8Ht1/mvce.rs:1:12
  |
1 | #![feature(non_lifetime_binders)]
  |            ^^^^^^^^^^^^^^^^^^^^
  |
  = note: see issue #108185 <https://github.com/rust-lang/rust/issues/108185> for more information
  = note: `#[warn(incomplete_features)]` on by default

warning: unused variable: `j`
 --> /tmp/icemaker_global_tempdir.qVJ0uwKvZ1dL/rustc_testrunner_tmpdir_reporting.Aj4Epcfg8Ht1/mvce.rs:5:9
  |
5 |     let j: impl for<T> Clone = i;
  |         ^ help: if this is intentional, prefix it with an underscore: `_j`
  |
  = note: `#[warn(unused_variables)]` (part of `#[warn(unused)]`) on by default

warning: 2 warnings emitted

note: no errors encountered even though delayed bugs were created

note: those delayed bugs will now be shown as internal compiler errors

error: internal compiler error: unexpected generic param: GenericParam { hir_id: HirId(DefId(0:3 ~ mvce[7019]::main).7), def_id: DefId(0:4 ~ mvce[7019]::main::T), name: Plain(T#0), span: /tmp/icemaker_global_tempdir.qVJ0uwKvZ1dL/rustc_testrunner_tmpdir_reporting.Aj4Epcfg8Ht1/mvce.rs:5:21: 5:22 (#0), pure_wrt_drop: false, kind: Type { default: None, synthetic: false }, colon_span: None, source: Binder }
 --> /tmp/icemaker_global_tempdir.qVJ0uwKvZ1dL/rustc_testrunner_tmpdir_reporting.Aj4Epcfg8Ht1/mvce.rs:5:21
  |
5 |     let j: impl for<T> Clone = i;
  |                     ^
  |
note: delayed at /rustc-dev/08cd08fbef8c6663b052d8d9e4930d5696cbb8a7/compiler/rustc_hir_typeck/src/writeback.rs:303:22
         0: <rustc_errors::DiagCtxtInner>::emit_diagnostic
         1: <rustc_errors::DiagCtxtHandle>::emit_diagnostic
         2: <rustc_span::ErrorGuaranteed as rustc_errors::diagnostic::EmissionGuarantee>::emit_producing_guarantee
         3: <rustc_errors::DiagCtxtHandle>::span_delayed_bug::<rustc_span::span_encoding::Span, alloc::string::String>
         4: <rustc_hir_typeck::writeback::WritebackCx as rustc_hir::intravisit::Visitor>::visit_generic_param.cold
         5: <rustc_hir_typeck::writeback::WritebackCx as rustc_hir::intravisit::Visitor>::visit_poly_trait_ref
         6: rustc_hir::intravisit::walk_unambig_ty::<rustc_hir_typeck::writeback::WritebackCx>
         7: <rustc_hir_typeck::writeback::WritebackCx as rustc_hir::intravisit::Visitor>::visit_local
         8: <rustc_hir_typeck::writeback::WritebackCx as rustc_hir::intravisit::Visitor>::visit_expr
         9: <rustc_hir_typeck::fn_ctxt::FnCtxt>::resolve_type_vars_in_body
        10: rustc_hir_typeck::typeck_with_inspect::{closure#0}
        11: rustc_query_impl::query_impl::typeck_root::invoke_provider_fn::__rust_begin_short_backtrace
        12: rustc_query_impl::execution::try_execute_query::<rustc_data_structures::vec_cache::VecCache<rustc_span::def_id::LocalDefId, rustc_middle::query::erase::ErasedData<[u8; 8]>, rustc_middle::dep_graph::graph::DepNodeIndex>, false>
        13: rustc_query_impl::query_impl::typeck_root::execute_query_non_incr::__rust_end_short_backtrace
        14: <rustc_middle::ty::context::TyCtxt>::par_hir_body_owners::<rustc_hir_analysis::check_crate::{closure#1}>::{closure#0}
        15: rustc_hir_analysis::check_crate
        16: rustc_interface::passes::analysis
        17: rustc_query_impl::execution::try_execute_query::<rustc_middle::query::caches::SingleCache<rustc_middle::query::erase::ErasedData<[u8; 0]>>, false>
        18: rustc_query_impl::query_impl::analysis::execute_query_non_incr::__rust_end_short_backtrace
        19: rustc_interface::interface::run_compiler::<(), rustc_driver_impl::run_compiler::{closure#0}>::{closure#1}
        20: std::sys::backtrace::__rust_begin_short_backtrace::<rustc_interface::util::run_in_thread_with_globals<rustc_interface::util::run_in_thread_pool_with_globals<rustc_interface::interface::run_compiler<(), rustc_driver_impl::run_compiler::{closure#0}>::{closure#1}, ()>::{closure#0}, ()>::{closure#0}::{closure#0}, ()>
        21: <std::thread::lifecycle::spawn_unchecked<rustc_interface::util::run_in_thread_with_globals<rustc_interface::util::run_in_thread_pool_with_globals<rustc_interface::interface::run_compiler<(), rustc_driver_impl::run_compiler::{closure#0}>::{closure#1}, ()>::{closure#0}, ()>::{closure#0}::{closure#0}, ()>::{closure#1} as core::ops::function::FnOnce<()>>::call_once::{shim:vtable#0}
        22: <std::sys::thread::unix::Thread>::new::thread_start
        23: <unknown>
        24: <unknown>
      
 --> /tmp/icemaker_global_tempdir.qVJ0uwKvZ1dL/rustc_testrunner_tmpdir_reporting.Aj4Epcfg8Ht1/mvce.rs:5:21
  |
5 |    let j: impl for<T> Clone = i;
  |                     ^

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 1.96.0-nightly (08cd08fbe 2026-03-31) running on x86_64-unknown-linux-gnu

query stack during panic:
end of query stack

@rustbot label +F-non_lifetime_binders +F-impl_trait_in_bindings

[matthiaskrgr]

Regression in nightly-2024-12-15
my guess would be #134185