rust-lang / rust-lang/rust

[ICE]: `unimplemented` in `is_trivially_not_async_drop` (w. feature unsafe_binders)

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C-bug F-unsafe_binders I-ICE needs-triage T-compiler
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Rust
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Description

Code
#![feature(unsafe_binders)]
#![feature(coroutines, coroutine_trait, stmt_expr_attributes)]

#[derive(Copy, Clone)]
struct Adt<'a>(&'a ());

use std::{cell::RefCell, ops::Coroutine, sync::Arc};

pub fn make_gen2<T>(t: T) -> impl Coroutine<Return = T> {
    #[coroutine]
    || {
        yield;
        t
    }
}
fn make_non_send_coroutine2() -> (unsafe<'a> Adt<'a>, Box<dyn Send>) {
    make_gen2(Arc::new(RefCell::new(0)))
}

fn test2() {
    let send_gen = #[coroutine]
    || {
        let _non_send_gen = make_non_send_coroutine2();
        yield;
    };
}

fn main() {}

A mutant of tests/ui/coroutine/issue-68112.rs, manually reduced.

Meta

rustc --version --verbose:

rustc 1.99.0-nightly (8ab9fdff5 2026-07-30)
binary: rustc
commit-hash: 8ab9fdff5a91b9f2b5ed57fb0275452d9a0d0280
commit-date: 2026-07-30
host: x86_64-apple-darwin
release: 1.99.0-nightly
LLVM version: 22.1.8
Error output
warning: the feature `unsafe_binders` is incomplete and may not be safe to use and/or cause compiler crashes
 --> asdf1234.rs:1:12
  |
1 | #![feature(unsafe_binders)]
  |            ^^^^^^^^^^^^^^
  |
  = note: see issue #130516 <https://github.com/rust-lang/rust/issues/130516> for more information
  = note: `#[warn(incomplete_features)]` on by default

error[E0308]: mismatched types
  --> asdf1234.rs:17:5
   |
 9 | pub fn make_gen2<T>(t: T) -> impl Coroutine<Return = T> {
   |                              -------------------------- the found opaque type
...
16 | fn make_non_send_coroutine2() -> (unsafe<'a> Adt<'a>, Box<dyn Send>) {
   |                                  ----------------------------------- expected `(unsafe<'a> Adt<'a>, Box<(dyn Send + 'static)>)` because of return type
17 |     make_gen2(Arc::new(RefCell::new(0)))
   |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ expected `(unsafe<'a> Adt<'a>, Box<dyn Send>)`, found opaque type
   |
   = note:    expected tuple `(unsafe<'a> Adt<'a>, Box<(dyn Send + 'static)>)`
           found opaque type `impl Coroutine<Return = Arc<RefCell<{integer}>>>`


thread 'rustc' (9809511) panicked at /rustc-dev/8ab9fdff5a91b9f2b5ed57fb0275452d9a0d0280/compiler/rustc_middle/src/ty/util.rs:1306:36:
not implemented
Backtrace 

thread 'rustc' (9809511) panicked at /rustc-dev/8ab9fdff5a91b9f2b5ed57fb0275452d9a0d0280/compiler/rustc_middle/src/ty/util.rs:1306:36:
not implemented
stack backtrace:
   0:        0x11842ebe4 - <<std[f2c2cedbd8f6b153]::sys::backtrace::BacktraceLock>::print::DisplayBacktrace as core[784a811b45041e7]::fmt::Display>::fmt
   1:        0x114e978a7 - core[784a811b45041e7]::fmt::write
   2:        0x118445a5b - <std[f2c2cedbd8f6b153]::sys::stdio::unix::Stderr as core[784a811b45041e7]::io::write::Write>::write_fmt
   3:        0x1183fa960 - std[f2c2cedbd8f6b153]::panicking::default_hook::{closure#0}
   4:        0x11841f267 - std[f2c2cedbd8f6b153]::panicking::default_hook
   5:        0x115ca51e1 - std[f2c2cedbd8f6b153]::panicking::update_hook::<alloc[7e0cdee874db494e]::boxed::Box<rustc_driver_impl[24407bf9feb5cca2]::install_ice_hook::{closure#1}>>::{closure#0}
   6:        0x11841f877 - std[f2c2cedbd8f6b153]::panicking::panic_with_hook
   7:        0x1183faa42 - std[f2c2cedbd8f6b153]::panicking::panic_handler::{closure#0}
   8:        0x1183f1489 - std[f2c2cedbd8f6b153]::sys::backtrace::__rust_end_short_backtrace::<std[f2c2cedbd8f6b153]::panicking::panic_handler::{closure#0}, !>
   9:        0x1183fbfc4 - __rustc[6d8fcb733e91df4b]::rust_begin_unwind
  10:        0x118509a9b - core[784a811b45041e7]::panicking::panic_fmt
  11:        0x118509a6e - core[784a811b45041e7]::panicking::panic
  12:        0x116b41b74 - <rustc_middle[af96f57ab0f7186f]::ty::Ty>::is_trivially_not_async_drop
  13:        0x116b41b52 - <rustc_middle[af96f57ab0f7186f]::ty::Ty>::is_trivially_not_async_drop
  14:        0x116b4122b - <rustc_middle[af96f57ab0f7186f]::ty::Ty>::is_async_drop
  15:        0x116d06209 - <rustc_mir_build[9bce8ebed9edaeb6]::builder::Builder>::is_async_drop_impl
  16:        0x116d070b1 - <rustc_mir_build[9bce8ebed9edaeb6]::builder::Builder>::pop_scope
  17:        0x116ce06d4 - <rustc_mir_build[9bce8ebed9edaeb6]::builder::Builder>::ast_block_stmts
  18:        0x116ce0dcf - <rustc_mir_build[9bce8ebed9edaeb6]::builder::Builder>::ast_block
  19:        0x116ced757 - <rustc_mir_build[9bce8ebed9edaeb6]::builder::Builder>::expr_into_dest
  20:        0x116cc664c - <rustc_mir_build[9bce8ebed9edaeb6]::builder::Builder>::expr_into_dest::{closure#0}
  21:        0x116ced13a - <rustc_mir_build[9bce8ebed9edaeb6]::builder::Builder>::expr_into_dest
  22:        0x116d3965c - rustc_mir_build[9bce8ebed9edaeb6]::builder::build_mir_inner_impl
  23:        0x116f0155d - rustc_mir_transform[8b8727d42f95eaa2]::mir_built
  24:        0x117550a25 - rustc_query_impl[2186e76c44399dcc]::execution::try_execute_query::<rustc_data_structures[865c5849d7a29d1f]::vec_cache::VecCache<rustc_span[16b4ad8c2c3c9fc3]::def_id::LocalDefId, rustc_middle[af96f57ab0f7186f]::query::erase::ErasedData<[u8; 8usize]>, rustc_middle[af96f57ab0f7186f]::dep_graph::graph::DepNodeIndex>, false>
  25:        0x1177ee6e9 - rustc_query_impl[2186e76c44399dcc]::query_impl::mir_built::execute_query_non_incr::__rust_end_short_backtrace
  26:        0x116cd43e0 - <rustc_mir_build[9bce8ebed9edaeb6]::check_unsafety::UnsafetyVisitor>::visit_inner_body
  27:        0x116dba8eb - <rustc_mir_build[9bce8ebed9edaeb6]::check_unsafety::UnsafetyVisitor as rustc_middle[af96f57ab0f7186f]::thir::visit::Visitor>::visit_expr
  28:        0x116dbb001 - <rustc_mir_build[9bce8ebed9edaeb6]::check_unsafety::UnsafetyVisitor as rustc_middle[af96f57ab0f7186f]::thir::visit::Visitor>::visit_expr
  29:        0x116c98383 - rustc_middle[af96f57ab0f7186f]::thir::visit::walk_block::<rustc_mir_build[9bce8ebed9edaeb6]::check_unsafety::UnsafetyVisitor>
  30:        0x116dba8f6 - <rustc_mir_build[9bce8ebed9edaeb6]::check_unsafety::UnsafetyVisitor as rustc_middle[af96f57ab0f7186f]::thir::visit::Visitor>::visit_expr
  31:        0x116dbb001 - <rustc_mir_build[9bce8ebed9edaeb6]::check_unsafety::UnsafetyVisitor as rustc_middle[af96f57ab0f7186f]::thir::visit::Visitor>::visit_expr
  32:        0x116d34337 - rustc_mir_build[9bce8ebed9edaeb6]::check_unsafety::check_unsafety
  33:        0x11753ebe0 - rustc_query_impl[2186e76c44399dcc]::execution::try_execute_query::<rustc_data_structures[865c5849d7a29d1f]::vec_cache::VecCache<rustc_span[16b4ad8c2c3c9fc3]::def_id::LocalDefId, rustc_middle[af96f57ab0f7186f]::query::erase::ErasedData<[u8; 0usize]>, rustc_middle[af96f57ab0f7186f]::dep_graph::graph::DepNodeIndex>, false>
  34:        0x1177b65cb - rustc_query_impl[2186e76c44399dcc]::query_impl::check_unsafety::execute_query_non_incr::__rust_end_short_backtrace
  35:        0x1166c1972 - <rustc_middle[af96f57ab0f7186f]::ty::context::TyCtxt>::par_hir_body_owners::<rustc_interface[425151dc7a4e057d]::passes::run_required_analyses::{closure#2}::{closure#0}>::{closure#0}
  36:        0x1166ed950 - rustc_interface[425151dc7a4e057d]::passes::analysis
  37:        0x11757eef7 - rustc_query_impl[2186e76c44399dcc]::execution::try_execute_query::<rustc_middle[af96f57ab0f7186f]::query::caches::SingleCache<rustc_middle[af96f57ab0f7186f]::query::erase::ErasedData<[u8; 0usize]>>, false>
  38:        0x1177ec3d2 - rustc_query_impl[2186e76c44399dcc]::query_impl::analysis::execute_query_non_incr::__rust_end_short_backtrace
  39:        0x115c50180 - rustc_interface[425151dc7a4e057d]::passes::create_and_enter_global_ctxt::<core[784a811b45041e7]::option::Option<rustc_interface[425151dc7a4e057d]::queries::Linker>, rustc_driver_impl[24407bf9feb5cca2]::run_compiler::{closure#0}::{closure#1}>
  40:        0x115ca3b6f - rustc_interface[425151dc7a4e057d]::interface::run_compiler::<(), rustc_driver_impl[24407bf9feb5cca2]::run_compiler::{closure#0}>::{closure#2}
  41:        0x115c9889c - std[f2c2cedbd8f6b153]::sys::backtrace::__rust_begin_short_backtrace::<rustc_interface[425151dc7a4e057d]::util::run_in_thread_with_globals<rustc_interface[425151dc7a4e057d]::util::run_in_thread_pool_with_globals<rustc_interface[425151dc7a4e057d]::interface::run_compiler<(), rustc_driver_impl[24407bf9feb5cca2]::run_compiler::{closure#0}>::{closure#2}, ()>::{closure#0}, ()>::{closure#0}::{closure#0}, ()>
  42:        0x115caa42b - <std[f2c2cedbd8f6b153]::thread::lifecycle::spawn_unchecked<rustc_interface[425151dc7a4e057d]::util::run_in_thread_with_globals<rustc_interface[425151dc7a4e057d]::util::run_in_thread_pool_with_globals<rustc_interface[425151dc7a4e057d]::interface::run_compiler<(), rustc_driver_impl[24407bf9feb5cca2]::run_compiler::{closure#0}>::{closure#2}, ()>::{closure#0}, ()>::{closure#0}::{closure#0}, ()>::{closure#1} as core[784a811b45041e7]::ops::function::FnOnce<()>>::call_once::{shim:vtable#0}
  43:        0x11842b79d - <std[f2c2cedbd8f6b153]::sys::thread::unix::Thread>::new::thread_start
  44:     0x7ff81b77ee05 - __pthread_start

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: please attach the file at `/Volumes/T7/workspace/tmp/rustc-ice-2026-07-31T09_35_18-13878.txt` to your bug report

note: rustc 1.99.0-nightly (8ab9fdff5 2026-07-30) running on x86_64-apple-darwin

query stack during panic:
#0 [mir_built] building MIR for `test2::{closure#0}`
#1 [check_unsafety] unsafety-checking `test2`
... and 1 other queries... use `env RUST_BACKTRACE=1` to see the full query stack
error: aborting due to 1 previous error; 1 warning emitted

For more information about this error, try `rustc --explain E0308`.

Notes

@rustbot label +F-unsafe_binders

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 compiler/rustc_middle/src/ty/util.rs around line 1306 and the MIR/unsafety query stack shown in the report; run the minimized example on the reported nightly to reproduce the ICE. Done means the example produces a normal compiler diagnostic without panicking, with a regression test based on tests/ui/coroutine/issue-68112.rs.

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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