rust-lang / rust-lang/rust

[ICE]: `explicit deref of non-derefable type`

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A-async-await C-bug F-pin_ergonomics I-ICE needs-triage T-compiler
Dominant language
Rust
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Description

auto-reduced (treereduce-rust):

//@compile-flags: --edition=2024 --cap-lints=warn
#![feature(min_generic_const_args)]
#![feature(adt_const_params)]
#![feature(pin_ergonomics)]
async fn other() {}

pub async fn uhoh() {
    other().await;
}

fn main() {}

original:

//@ edition:2018
#![feature(must_not_suspend)]
#![deny(must_not_suspend)]

#[must_not_suspend]
trait Wow {}

impl Wow for i32 {}

fn r#impl() -> impl Wow {
    1
}

fn r#dyn() -> Box<dyn Wow> {
    Box::new(1)
}

async fn other() {}

pub async fn uhoh() {
    let _guard1 = r#impl(); //~ ERROR implementer of `Wow` held across
    let _guard2 = r#dyn(); // Trying to access the data in a vtable does not work, either.

    other().await;
}

fn main() {
}

Version information

rustc 1.96.0-nightly (d1c79458b 2026-03-11)
binary: rustc
commit-hash: d1c79458b5d13bd0179d7dbafd5ca4ea9ae3e6aa
commit-date: 2026-03-11
host: x86_64-unknown-linux-gnu
release: 1.96.0-nightly
LLVM version: 22.1.0

Command:
/home/matthias/.rustup/toolchains/master/bin/rustc --edition=2024 --cap-lints=warn -Zcrate-attr=feature(min_generic_const_args) -Zcrate-attr=feature(adt_const_params) -Zcrate-attr=feature(pin_ergonomics)

Program output 

warning: the feature `min_generic_const_args` is incomplete and may not be safe to use and/or cause compiler crashes
 --> <crate attribute>:1:12
  |
1 | #![feature(min_generic_const_args)]
  |            ^^^^^^^^^^^^^^^^^^^^^^
  |
  = note: see issue #132980 <https://github.com/rust-lang/rust/issues/132980> for more information
  = note: `#[warn(incomplete_features)]` on by default

warning: the feature `pin_ergonomics` is incomplete and may not be safe to use and/or cause compiler crashes
 --> <crate attribute>:1:12
  |
1 | #![feature(pin_ergonomics)]
  |            ^^^^^^^^^^^^^^
  |
  = note: see issue #130494 <https://github.com/rust-lang/rust/issues/130494> for more information

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: explicit deref of non-derefable type
 --> /tmp/icemaker_global_tempdir.zSJT70QNghmg/rustc_testrunner_tmpdir_reporting.nyD9Mf6Fn4JA/mvce.rs:4:13
  |
4 |     other().await;
  |             ^^^^^
  |
note: delayed at /rustc-dev/d1c79458b5d13bd0179d7dbafd5ca4ea9ae3e6aa/compiler/rustc_hir_typeck/src/expr_use_visitor.rs:200:20
         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::fn_ctxt::FnCtxt as rustc_hir_typeck::expr_use_visitor::TypeInformationCtxt>::report_bug::<&str>
         5: <rustc_hir_typeck::expr_use_visitor::ExprUseVisitor<&rustc_hir_typeck::fn_ctxt::FnCtxt, &mut rustc_hir_typeck::upvar::InferBorrowKind>>::cat_deref
         6: <rustc_hir_typeck::expr_use_visitor::ExprUseVisitor<&rustc_hir_typeck::fn_ctxt::FnCtxt, &mut rustc_hir_typeck::upvar::InferBorrowKind>>::walk_expr
         7: <rustc_hir_typeck::expr_use_visitor::ExprUseVisitor<&rustc_hir_typeck::fn_ctxt::FnCtxt, &mut rustc_hir_typeck::upvar::InferBorrowKind>>::consume_expr
         8: <rustc_hir_typeck::expr_use_visitor::ExprUseVisitor<&rustc_hir_typeck::fn_ctxt::FnCtxt, &mut rustc_hir_typeck::upvar::InferBorrowKind>>::walk_expr
         9: <rustc_hir_typeck::expr_use_visitor::ExprUseVisitor<&rustc_hir_typeck::fn_ctxt::FnCtxt, &mut rustc_hir_typeck::upvar::InferBorrowKind>>::consume_expr
        10: <rustc_hir_typeck::expr_use_visitor::ExprUseVisitor<&rustc_hir_typeck::fn_ctxt::FnCtxt, &mut rustc_hir_typeck::upvar::InferBorrowKind>>::walk_block
        11: <rustc_hir_typeck::expr_use_visitor::ExprUseVisitor<&rustc_hir_typeck::fn_ctxt::FnCtxt, &mut rustc_hir_typeck::upvar::InferBorrowKind>>::walk_expr
        12: <rustc_hir_typeck::expr_use_visitor::ExprUseVisitor<&rustc_hir_typeck::fn_ctxt::FnCtxt, &mut rustc_hir_typeck::upvar::InferBorrowKind>>::walk_expr
        13: <rustc_hir_typeck::expr_use_visitor::ExprUseVisitor<&rustc_hir_typeck::fn_ctxt::FnCtxt, &mut rustc_hir_typeck::upvar::InferBorrowKind>>::consume_expr
        14: <rustc_hir_typeck::expr_use_visitor::ExprUseVisitor<&rustc_hir_typeck::fn_ctxt::FnCtxt, &mut rustc_hir_typeck::upvar::InferBorrowKind>>::walk_block
        15: <rustc_hir_typeck::expr_use_visitor::ExprUseVisitor<&rustc_hir_typeck::fn_ctxt::FnCtxt, &mut rustc_hir_typeck::upvar::InferBorrowKind>>::walk_expr
        16: <rustc_hir_typeck::expr_use_visitor::ExprUseVisitor<&rustc_hir_typeck::fn_ctxt::FnCtxt, &mut rustc_hir_typeck::upvar::InferBorrowKind>>::consume_expr
        17: <rustc_hir_typeck::expr_use_visitor::ExprUseVisitor<&rustc_hir_typeck::fn_ctxt::FnCtxt, &mut rustc_hir_typeck::upvar::InferBorrowKind>>::walk_expr
        18: <rustc_hir_typeck::expr_use_visitor::ExprUseVisitor<&rustc_hir_typeck::fn_ctxt::FnCtxt, &mut rustc_hir_typeck::upvar::InferBorrowKind>>::consume_expr
        19: <rustc_hir_typeck::expr_use_visitor::ExprUseVisitor<&rustc_hir_typeck::fn_ctxt::FnCtxt, &mut rustc_hir_typeck::upvar::InferBorrowKind>>::walk_block
        20: <rustc_hir_typeck::expr_use_visitor::ExprUseVisitor<&rustc_hir_typeck::fn_ctxt::FnCtxt, &mut rustc_hir_typeck::upvar::InferBorrowKind>>::walk_expr
        21: <rustc_hir_typeck::expr_use_visitor::ExprUseVisitor<&rustc_hir_typeck::fn_ctxt::FnCtxt, &mut rustc_hir_typeck::upvar::InferBorrowKind>>::consume_expr
        22: <rustc_hir_typeck::expr_use_visitor::ExprUseVisitor<&rustc_hir_typeck::fn_ctxt::FnCtxt, &mut rustc_hir_typeck::upvar::InferBorrowKind>>::walk_expr
        23: <rustc_hir_typeck::expr_use_visitor::ExprUseVisitor<&rustc_hir_typeck::fn_ctxt::FnCtxt, &mut rustc_hir_typeck::upvar::InferBorrowKind>>::consume_expr
        24: <rustc_hir_typeck::expr_use_visitor::ExprUseVisitor<&rustc_hir_typeck::fn_ctxt::FnCtxt, &mut rustc_hir_typeck::upvar::InferBorrowKind>>::walk_block
        25: <rustc_hir_typeck::expr_use_visitor::ExprUseVisitor<&rustc_hir_typeck::fn_ctxt::FnCtxt, &mut rustc_hir_typeck::upvar::InferBorrowKind>>::walk_expr
        26: <rustc_hir_typeck::expr_use_visitor::ExprUseVisitor<&rustc_hir_typeck::fn_ctxt::FnCtxt, &mut rustc_hir_typeck::upvar::InferBorrowKind>>::consume_expr
        27: <rustc_hir_typeck::fn_ctxt::FnCtxt>::analyze_closure
        28: <rustc_hir_typeck::upvar::InferBorrowKindVisitor as rustc_hir::intravisit::Visitor>::visit_expr
        29: rustc_hir_typeck::typeck_with_inspect::{closure#0}
        30: rustc_query_impl::query_impl::typeck::invoke_provider_fn::__rust_begin_short_backtrace
        31: 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>
        32: rustc_query_impl::query_impl::typeck::execute_query_non_incr::__rust_end_short_backtrace
        33: rustc_mir_build::thir::pattern::check_match::check_match
        34: rustc_query_impl::query_impl::check_match::invoke_provider_fn::__rust_begin_short_backtrace
        35: rustc_query_impl::execution::try_execute_query::<rustc_data_structures::vec_cache::VecCache<rustc_span::def_id::LocalDefId, rustc_middle::query::erase::ErasedData<[u8; 1]>, rustc_middle::dep_graph::graph::DepNodeIndex>, false>
        36: rustc_query_impl::query_impl::check_match::execute_query_non_incr::__rust_end_short_backtrace
        37: rustc_mir_build::builder::build_mir_inner_impl
        38: rustc_mir_transform::mir_built
        39: 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>
        40: rustc_query_impl::query_impl::mir_built::execute_query_non_incr::__rust_end_short_backtrace
        41: rustc_mir_transform::ffi_unwind_calls::has_ffi_unwind_calls
        42: rustc_query_impl::query_impl::has_ffi_unwind_calls::invoke_provider_fn::__rust_begin_short_backtrace
        43: rustc_query_impl::execution::try_execute_query::<rustc_data_structures::vec_cache::VecCache<rustc_span::def_id::LocalDefId, rustc_middle::query::erase::ErasedData<[u8; 1]>, rustc_middle::dep_graph::graph::DepNodeIndex>, false>
        44: rustc_query_impl::query_impl::has_ffi_unwind_calls::execute_query_non_incr::__rust_end_short_backtrace
        45: rustc_mir_transform::mir_promoted
        46: rustc_query_impl::query_impl::mir_promoted::invoke_provider_fn::__rust_begin_short_backtrace
        47: rustc_query_impl::execution::try_execute_query::<rustc_data_structures::vec_cache::VecCache<rustc_span::def_id::LocalDefId, rustc_middle::query::erase::ErasedData<[u8; 16]>, rustc_middle::dep_graph::graph::DepNodeIndex>, false>
        48: rustc_query_impl::query_impl::mir_promoted::execute_query_non_incr::__rust_end_short_backtrace
        49: rustc_borrowck::mir_borrowck
        50: rustc_query_impl::query_impl::mir_borrowck::invoke_provider_fn::__rust_begin_short_backtrace
        51: 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>
        52: rustc_query_impl::query_impl::mir_borrowck::execute_query_non_incr::__rust_end_short_backtrace
        53: rustc_hir_analysis::collect::type_of::opaque::find_opaque_ty_constraints_for_rpit
        54: rustc_hir_analysis::collect::type_of::type_of_opaque
        55: rustc_query_impl::execution::try_execute_query::<rustc_middle::query::caches::DefIdCache<rustc_middle::query::erase::ErasedData<[u8; 8]>>, false>
        56: rustc_query_impl::query_impl::type_of_opaque::execute_query_non_incr::__rust_end_short_backtrace
        57: rustc_hir_analysis::collect::type_of::type_of
        58: rustc_query_impl::query_impl::type_of::invoke_provider_fn::__rust_begin_short_backtrace
        59: rustc_query_impl::execution::try_execute_query::<rustc_middle::query::caches::DefIdCache<rustc_middle::query::erase::ErasedData<[u8; 8]>>, false>
        60: rustc_query_impl::query_impl::type_of::execute_query_non_incr::__rust_end_short_backtrace
        61: rustc_hir_analysis::check::check::check_opaque
        62: rustc_hir_analysis::check::check::check_item_type
        63: rustc_hir_analysis::check::wfcheck::check_well_formed
        64: rustc_query_impl::query_impl::check_well_formed::invoke_provider_fn::__rust_begin_short_backtrace
        65: rustc_query_impl::execution::try_execute_query::<rustc_data_structures::vec_cache::VecCache<rustc_span::def_id::LocalDefId, rustc_middle::query::erase::ErasedData<[u8; 1]>, rustc_middle::dep_graph::graph::DepNodeIndex>, false>
        66: rustc_query_impl::query_impl::check_well_formed::execute_query_non_incr::__rust_end_short_backtrace
        67: rustc_hir_analysis::check::wfcheck::check_type_wf
        68: rustc_query_impl::query_impl::check_type_wf::invoke_provider_fn::__rust_begin_short_backtrace
        69: rustc_query_impl::execution::try_execute_query::<rustc_middle::query::caches::SingleCache<rustc_middle::query::erase::ErasedData<[u8; 1]>>, false>
        70: rustc_query_impl::query_impl::check_type_wf::execute_query_non_incr::__rust_end_short_backtrace
        71: rustc_hir_analysis::check_crate
        72: rustc_interface::passes::analysis
        73: rustc_query_impl::execution::try_execute_query::<rustc_middle::query::caches::SingleCache<rustc_middle::query::erase::ErasedData<[u8; 0]>>, false>
        74: rustc_query_impl::query_impl::analysis::execute_query_non_incr::__rust_end_short_backtrace
        75: rustc_interface::interface::run_compiler::<(), rustc_driver_impl::run_compiler::{closure#0}>::{closure#1}
        76: 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}, ()>
        77: <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}
        78: <std::sys::thread::unix::Thread>::new::thread_start
        79: <unknown>
        80: <unknown>
      
 --> /tmp/icemaker_global_tempdir.zSJT70QNghmg/rustc_testrunner_tmpdir_reporting.nyD9Mf6Fn4JA/mvce.rs:4:13
  |
4 |     other().await;
  |             ^^^^^

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 (d1c79458b 2026-03-11) running on x86_64-unknown-linux-gnu

note: compiler flags: -Z crate-attr=feature(min_generic_const_args) -Z crate-attr=feature(adt_const_params) -Z crate-attr=feature(pin_ergonomics) -Z dump-mir-dir=dir

query stack during panic:
end of query stack

@rustbot label +F-min_generic_const_args +F-adt_const_params +F-pin_ergonomics

Contributor guide

Open the contributing guide

First steps

  1. Read the whole issue, then the project's contributing guide.
  2. Comment on the issue to say you are picking it up — it saves two people doing the same work.
  3. Fork the repository and make your change on a branch.
  4. Open a pull request that references the issue number.

Research direction

Start with the reduced a.rs reproducer and the delayed-bug location in compiler/rustc_hir_typeck/src/expr_use_visitor.rs:200, then run the reported rustc command to confirm the ICE. Trace the await expression through ExprUseVisitor::cat_deref and add a regression test; done means the reproducer no longer emits “explicit deref of non-derefable type” while preserving the intended diagnostics.

Written by the indexing model from the issue text.

Assessment

Tech stack
rust
Domain
compilers
Issue type
Bug
Difficulty
4/5
Estimated time
3-5 days
Activity status
Quiet
Clarity
Mostly clear
Newbie friendliness
45/100

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