[ICE]: Wrust-2021-incompatible-closure-captures

[matthiaskrgr]

original:

//@compile-flags: -Wrust-2021-incompatible-closure-captures
struct Foo((u32, i128));

fn main() {
    type T = impl async FnOnce() -> T;
    let foo: T = Foo();
    let x = move || {
        let x = move || {
            let Foo((a, b)) = foo;
        };
    };
}

Version information

rustc 1.97.0-nightly (8da2d28cb 2026-04-18)
binary: rustc
commit-hash: 8da2d28cbd5a4e2b93e028e709afe09541671663
commit-date: 2026-04-18
host: x86_64-unknown-linux-gnu
release: 1.97.0-nightly
LLVM version: 22.1.2

Possibly related line of code:

rust/compiler/rustc_hir_typeck/src/upvar.rs

Lines 1770 to 1782 in 8da2d28

	paths_using_field,
	)
	})
	}
	// Anything else would be completely captured and therefore handled already.
	_ => unreachable!(),
	}
	}
	fn init_capture_kind_for_place(
	&self,
	place: &Place<'tcx>,

Command:
/home/matthias/.rustup/toolchains/master/bin/rustc -Wrust-2021-incompatible-closure-captures

Program output

error: `async` trait bounds are only allowed in Rust 2018 or later
 --> /tmp/icemaker_global_tempdir.ZoarixqjDRq1/rustc_testrunner_tmpdir_reporting.C70SpvInghNQ/mvce.rs:4:19
  |
4 |     type T = impl async FnOnce() -> T;
  |                   ^^^^^
  |
  = help: pass `--edition 2024` to `rustc`
  = note: for more on editions, read https://doc.rust-lang.org/edition-guide

error[E0658]: `async` trait bounds are unstable
 --> /tmp/icemaker_global_tempdir.ZoarixqjDRq1/rustc_testrunner_tmpdir_reporting.C70SpvInghNQ/mvce.rs:4:19
  |
4 |     type T = impl async FnOnce() -> T;
  |                   ^^^^^
  |
  = note: see issue #62290 <https://github.com/rust-lang/rust/issues/62290> for more information
  = help: add `#![feature(async_trait_bounds)]` to the crate attributes to enable
  = note: this compiler was built on 2026-04-18; consider upgrading it if it is out of date
  = help: use the desugared name of the async trait, such as `AsyncFn`

error[E0658]: `impl Trait` in type aliases is unstable
 --> /tmp/icemaker_global_tempdir.ZoarixqjDRq1/rustc_testrunner_tmpdir_reporting.C70SpvInghNQ/mvce.rs:4:14
  |
4 |     type T = impl async FnOnce() -> T;
  |              ^^^^^^^^^^^^^^^^^^^^^^^^
  |
  = note: see issue #63063 <https://github.com/rust-lang/rust/issues/63063> for more information
  = help: add `#![feature(type_alias_impl_trait)]` to the crate attributes to enable
  = note: this compiler was built on 2026-04-18; consider upgrading it if it is out of date

error[E0061]: this struct takes 1 argument but 0 arguments were supplied
 --> /tmp/icemaker_global_tempdir.ZoarixqjDRq1/rustc_testrunner_tmpdir_reporting.C70SpvInghNQ/mvce.rs:5:18
  |
5 |     let foo: T = Foo();
  |                  ^^^-- argument #1 of type `(u32, i128)` is missing
  |
note: tuple struct defined here
 --> /tmp/icemaker_global_tempdir.ZoarixqjDRq1/rustc_testrunner_tmpdir_reporting.C70SpvInghNQ/mvce.rs:1:8
  |
1 | struct Foo((u32, i128));
  |        ^^^
help: provide the argument
  |
5 |     let foo: T = Foo(/* (u32, i128) */);
  |                      +++++++++++++++++

error[E0277]: the trait bound `Foo: AsyncFnOnce()` is not satisfied
 --> /tmp/icemaker_global_tempdir.ZoarixqjDRq1/rustc_testrunner_tmpdir_reporting.C70SpvInghNQ/mvce.rs:5:18
  |
5 |     let foo: T = Foo();
  |                  ^^^^^ unsatisfied trait bound
  |
help: the trait `AsyncFnOnce()` is not implemented for `Foo`
 --> /tmp/icemaker_global_tempdir.ZoarixqjDRq1/rustc_testrunner_tmpdir_reporting.C70SpvInghNQ/mvce.rs:1:1
  |
1 | struct Foo((u32, i128));
  | ^^^^^^^^^^

error[E0277]: the trait bound `Foo: AsyncFnOnce()` is not satisfied
 --> /tmp/icemaker_global_tempdir.ZoarixqjDRq1/rustc_testrunner_tmpdir_reporting.C70SpvInghNQ/mvce.rs:8:17
  |
8 |             let Foo((a, b)) = foo;
  |                 ^^^^^^^^^^^ unsatisfied trait bound
  |
help: the trait `AsyncFnOnce()` is not implemented for `Foo`
 --> /tmp/icemaker_global_tempdir.ZoarixqjDRq1/rustc_testrunner_tmpdir_reporting.C70SpvInghNQ/mvce.rs:1:1
  |
1 | struct Foo((u32, i128));
  | ^^^^^^^^^^


thread 'rustc' (2435430) panicked at /rustc-dev/8da2d28cbd5a4e2b93e028e709afe09541671663/compiler/rustc_hir_typeck/src/upvar.rs:1776:18:
internal error: entered unreachable code
stack backtrace:
   0:     0x7f14ce422ceb - <<std[d6a62db279dbae46]::sys::backtrace::BacktraceLock>::print::DisplayBacktrace as core[e86e8f32962a9819]::fmt::Display>::fmt
   1:     0x7f14cea2e808 - core[e86e8f32962a9819]::fmt::write
   2:     0x7f14ce439ce6 - <std[d6a62db279dbae46]::sys::stdio::unix::Stderr as std[d6a62db279dbae46]::io::Write>::write_fmt
   3:     0x7f14ce3f8f68 - std[d6a62db279dbae46]::panicking::default_hook::{closure#0}
   4:     0x7f14ce416353 - std[d6a62db279dbae46]::panicking::default_hook
   5:     0x7f14cd3db02c - std[d6a62db279dbae46]::panicking::update_hook::<alloc[26814c36517be32d]::boxed::Box<rustc_driver_impl[945e7c8a3fc176fa]::install_ice_hook::{closure#1}>>::{closure#0}
   6:     0x7f14ce416632 - std[d6a62db279dbae46]::panicking::panic_with_hook
   7:     0x7f14ce3f905a - std[d6a62db279dbae46]::panicking::panic_handler::{closure#0}
   8:     0x7f14ce3efd69 - std[d6a62db279dbae46]::sys::backtrace::__rust_end_short_backtrace::<std[d6a62db279dbae46]::panicking::panic_handler::{closure#0}, !>
   9:     0x7f14ce3faa8d - __rustc[3f76c9a779ba9221]::rust_begin_unwind
  10:     0x7f14caf8aa3c - core[e86e8f32962a9819]::panicking::panic_fmt
  11:     0x7f14cc2d3d52 - core[e86e8f32962a9819]::panicking::panic
  12:     0x7f14cd6f1d08 - <rustc_hir_typeck[1ebf63e3d4a70057]::fn_ctxt::FnCtxt>::has_significant_drop_outside_of_captures
  13:     0x7f14cd6ee7f1 - <rustc_hir_typeck[1ebf63e3d4a70057]::fn_ctxt::FnCtxt>::perform_2229_migration_analysis
  14:     0x7f14cf5fbf03 - <rustc_hir_typeck[1ebf63e3d4a70057]::fn_ctxt::FnCtxt>::analyze_closure
  15:     0x7f14ced0fe92 - <rustc_hir_typeck[1ebf63e3d4a70057]::upvar::InferBorrowKindVisitor as rustc_hir[364cc9694d698482]::intravisit::Visitor>::visit_expr
  16:     0x7f14ced0fd11 - <rustc_hir_typeck[1ebf63e3d4a70057]::upvar::InferBorrowKindVisitor as rustc_hir[364cc9694d698482]::intravisit::Visitor>::visit_block
  17:     0x7f14ced0fe6b - <rustc_hir_typeck[1ebf63e3d4a70057]::upvar::InferBorrowKindVisitor as rustc_hir[364cc9694d698482]::intravisit::Visitor>::visit_expr
  18:     0x7f14ced0fd11 - <rustc_hir_typeck[1ebf63e3d4a70057]::upvar::InferBorrowKindVisitor as rustc_hir[364cc9694d698482]::intravisit::Visitor>::visit_block
  19:     0x7f14cfc1418a - rustc_hir_typeck[1ebf63e3d4a70057]::typeck_with_inspect::{closure#0}
  20:     0x7f14cfc12570 - rustc_query_impl[a6166eb9fe0387cf]::query_impl::typeck_root::invoke_provider_fn::__rust_begin_short_backtrace
  21:     0x7f14ceb2be26 - rustc_query_impl[a6166eb9fe0387cf]::execution::try_execute_query::<rustc_data_structures[7b9148a745519926]::vec_cache::VecCache<rustc_span[63e5a877534af3f7]::def_id::LocalDefId, rustc_middle[253f0d05195ba05e]::query::erase::ErasedData<[u8; 8usize]>, rustc_middle[253f0d05195ba05e]::dep_graph::graph::DepNodeIndex>, false>
  22:     0x7f14ceb2b643 - rustc_query_impl[a6166eb9fe0387cf]::query_impl::typeck_root::execute_query_non_incr::__rust_end_short_backtrace
  23:     0x7f14cf03f7d8 - rustc_mir_build[d8e4297702baa306]::thir::pattern::check_match::check_match
  24:     0x7f14cf03ec1b - rustc_query_impl[a6166eb9fe0387cf]::query_impl::check_match::invoke_provider_fn::__rust_begin_short_backtrace
  25:     0x7f14cf33f4e6 - rustc_query_impl[a6166eb9fe0387cf]::execution::try_execute_query::<rustc_data_structures[7b9148a745519926]::vec_cache::VecCache<rustc_span[63e5a877534af3f7]::def_id::LocalDefId, rustc_middle[253f0d05195ba05e]::query::erase::ErasedData<[u8; 1usize]>, rustc_middle[253f0d05195ba05e]::dep_graph::graph::DepNodeIndex>, false>
  26:     0x7f14cf33f142 - rustc_query_impl[a6166eb9fe0387cf]::query_impl::check_match::execute_query_non_incr::__rust_end_short_backtrace
  27:     0x7f14cf046c49 - rustc_mir_build[d8e4297702baa306]::builder::build_mir_inner_impl
  28:     0x7f14cea0b7ea - rustc_mir_transform[5e6f23ecb9c29fca]::mir_built
  29:     0x7f14ceb2be26 - rustc_query_impl[a6166eb9fe0387cf]::execution::try_execute_query::<rustc_data_structures[7b9148a745519926]::vec_cache::VecCache<rustc_span[63e5a877534af3f7]::def_id::LocalDefId, rustc_middle[253f0d05195ba05e]::query::erase::ErasedData<[u8; 8usize]>, rustc_middle[253f0d05195ba05e]::dep_graph::graph::DepNodeIndex>, false>
  30:     0x7f14ceb2b943 - rustc_query_impl[a6166eb9fe0387cf]::query_impl::mir_built::execute_query_non_incr::__rust_end_short_backtrace
  31:     0x7f14cea3856e - rustc_mir_transform[5e6f23ecb9c29fca]::ffi_unwind_calls::has_ffi_unwind_calls
  32:     0x7f14cea37fd9 - rustc_query_impl[a6166eb9fe0387cf]::query_impl::has_ffi_unwind_calls::invoke_provider_fn::__rust_begin_short_backtrace
  33:     0x7f14cf33f4e6 - rustc_query_impl[a6166eb9fe0387cf]::execution::try_execute_query::<rustc_data_structures[7b9148a745519926]::vec_cache::VecCache<rustc_span[63e5a877534af3f7]::def_id::LocalDefId, rustc_middle[253f0d05195ba05e]::query::erase::ErasedData<[u8; 1usize]>, rustc_middle[253f0d05195ba05e]::dep_graph::graph::DepNodeIndex>, false>
  34:     0x7f14cf33f0b6 - rustc_query_impl[a6166eb9fe0387cf]::query_impl::has_ffi_unwind_calls::execute_query_non_incr::__rust_end_short_backtrace
  35:     0x7f14cf4d6d1c - rustc_mir_transform[5e6f23ecb9c29fca]::mir_promoted
  36:     0x7f14cf4d6ba0 - rustc_query_impl[a6166eb9fe0387cf]::query_impl::mir_promoted::invoke_provider_fn::__rust_begin_short_backtrace
  37:     0x7f14cf3cebb7 - rustc_query_impl[a6166eb9fe0387cf]::execution::try_execute_query::<rustc_data_structures[7b9148a745519926]::vec_cache::VecCache<rustc_span[63e5a877534af3f7]::def_id::LocalDefId, rustc_middle[253f0d05195ba05e]::query::erase::ErasedData<[u8; 16usize]>, rustc_middle[253f0d05195ba05e]::dep_graph::graph::DepNodeIndex>, false>
  38:     0x7f14cf3ce743 - rustc_query_impl[a6166eb9fe0387cf]::query_impl::mir_promoted::execute_query_non_incr::__rust_end_short_backtrace
  39:     0x7f14cfb1f6b3 - rustc_borrowck[6886b9bd56e1eb31]::mir_borrowck
  40:     0x7f14cfb1f62d - rustc_query_impl[a6166eb9fe0387cf]::query_impl::mir_borrowck::invoke_provider_fn::__rust_begin_short_backtrace
  41:     0x7f14ceb2be26 - rustc_query_impl[a6166eb9fe0387cf]::execution::try_execute_query::<rustc_data_structures[7b9148a745519926]::vec_cache::VecCache<rustc_span[63e5a877534af3f7]::def_id::LocalDefId, rustc_middle[253f0d05195ba05e]::query::erase::ErasedData<[u8; 8usize]>, rustc_middle[253f0d05195ba05e]::dep_graph::graph::DepNodeIndex>, false>
  42:     0x7f14ceb2b4c3 - rustc_query_impl[a6166eb9fe0387cf]::query_impl::mir_borrowck::execute_query_non_incr::__rust_end_short_backtrace
  43:     0x7f14cd563987 - <rustc_hir_analysis[1a46041d384d7932]::collect::type_of::opaque::TaitConstraintLocator>::check
  44:     0x7f14cd5a7361 - rustc_hir_analysis[1a46041d384d7932]::collect::type_of::opaque::find_opaque_ty_constraints_for_tait
  45:     0x7f14d0806822 - rustc_hir_analysis[1a46041d384d7932]::collect::type_of::type_of_opaque.cold
  46:     0x7f14cea143cd - rustc_query_impl[a6166eb9fe0387cf]::execution::try_execute_query::<rustc_middle[253f0d05195ba05e]::query::caches::DefIdCache<rustc_middle[253f0d05195ba05e]::query::erase::ErasedData<[u8; 8usize]>>, false>
  47:     0x7f14cfbbed98 - rustc_query_impl[a6166eb9fe0387cf]::query_impl::type_of_opaque::execute_query_non_incr::__rust_end_short_backtrace
  48:     0x7f14ceedda6c - rustc_hir_analysis[1a46041d384d7932]::collect::type_of::type_of
  49:     0x7f14cece1726 - rustc_query_impl[a6166eb9fe0387cf]::query_impl::type_of::invoke_provider_fn::__rust_begin_short_backtrace
  50:     0x7f14cea143cd - rustc_query_impl[a6166eb9fe0387cf]::execution::try_execute_query::<rustc_middle[253f0d05195ba05e]::query::caches::DefIdCache<rustc_middle[253f0d05195ba05e]::query::erase::ErasedData<[u8; 8usize]>>, false>
  51:     0x7f14cea13f50 - rustc_query_impl[a6166eb9fe0387cf]::query_impl::type_of::execute_query_non_incr::__rust_end_short_backtrace
  52:     0x7f14cf9e7c50 - rustc_hir_analysis[1a46041d384d7932]::check::check::check_opaque
  53:     0x7f14cf348e44 - rustc_hir_analysis[1a46041d384d7932]::check::check::check_item_type
  54:     0x7f14cf33ff1c - rustc_hir_analysis[1a46041d384d7932]::check::wfcheck::check_well_formed
  55:     0x7f14cf33fef9 - rustc_query_impl[a6166eb9fe0387cf]::query_impl::check_well_formed::invoke_provider_fn::__rust_begin_short_backtrace
  56:     0x7f14cf33f4e6 - rustc_query_impl[a6166eb9fe0387cf]::execution::try_execute_query::<rustc_data_structures[7b9148a745519926]::vec_cache::VecCache<rustc_span[63e5a877534af3f7]::def_id::LocalDefId, rustc_middle[253f0d05195ba05e]::query::erase::ErasedData<[u8; 1usize]>, rustc_middle[253f0d05195ba05e]::dep_graph::graph::DepNodeIndex>, false>
  57:     0x7f14cf33f27b - rustc_query_impl[a6166eb9fe0387cf]::query_impl::check_well_formed::execute_query_non_incr::__rust_end_short_backtrace
  58:     0x7f14cf33b4c6 - rustc_hir_analysis[1a46041d384d7932]::check::wfcheck::check_type_wf
  59:     0x7f14cf33b353 - rustc_query_impl[a6166eb9fe0387cf]::query_impl::check_type_wf::invoke_provider_fn::__rust_begin_short_backtrace
  60:     0x7f14cfbb7bd0 - rustc_query_impl[a6166eb9fe0387cf]::execution::try_execute_query::<rustc_middle[253f0d05195ba05e]::query::caches::SingleCache<rustc_middle[253f0d05195ba05e]::query::erase::ErasedData<[u8; 1usize]>>, false>
  61:     0x7f14cfbb79a9 - rustc_query_impl[a6166eb9fe0387cf]::query_impl::check_type_wf::execute_query_non_incr::__rust_end_short_backtrace
  62:     0x7f14cf03c05b - rustc_hir_analysis[1a46041d384d7932]::check_crate
  63:     0x7f14cf8f2567 - rustc_interface[1d873664835f04c7]::passes::analysis
  64:     0x7f14cfbb5449 - rustc_query_impl[a6166eb9fe0387cf]::execution::try_execute_query::<rustc_middle[253f0d05195ba05e]::query::caches::SingleCache<rustc_middle[253f0d05195ba05e]::query::erase::ErasedData<[u8; 0usize]>>, false>
  65:     0x7f14cfbb50a9 - rustc_query_impl[a6166eb9fe0387cf]::query_impl::analysis::execute_query_non_incr::__rust_end_short_backtrace
  66:     0x7f14cfb9386d - rustc_interface[1d873664835f04c7]::interface::run_compiler::<(), rustc_driver_impl[945e7c8a3fc176fa]::run_compiler::{closure#0}>::{closure#1}
  67:     0x7f14cfb6b28a - std[d6a62db279dbae46]::sys::backtrace::__rust_begin_short_backtrace::<rustc_interface[1d873664835f04c7]::util::run_in_thread_with_globals<rustc_interface[1d873664835f04c7]::util::run_in_thread_pool_with_globals<rustc_interface[1d873664835f04c7]::interface::run_compiler<(), rustc_driver_impl[945e7c8a3fc176fa]::run_compiler::{closure#0}>::{closure#1}, ()>::{closure#0}, ()>::{closure#0}::{closure#0}, ()>
  68:     0x7f14cfb6b96d - <std[d6a62db279dbae46]::thread::lifecycle::spawn_unchecked<rustc_interface[1d873664835f04c7]::util::run_in_thread_with_globals<rustc_interface[1d873664835f04c7]::util::run_in_thread_pool_with_globals<rustc_interface[1d873664835f04c7]::interface::run_compiler<(), rustc_driver_impl[945e7c8a3fc176fa]::run_compiler::{closure#0}>::{closure#1}, ()>::{closure#0}, ()>::{closure#0}::{closure#0}, ()>::{closure#1} as core[e86e8f32962a9819]::ops::function::FnOnce<()>>::call_once::{shim:vtable#0}
  69:     0x7f14cfb6c7ec - <std[d6a62db279dbae46]::sys::thread::unix::Thread>::new::thread_start
  70:     0x7f14c96a597a - <unknown>
  71:     0x7f14c97292bc - <unknown>
  72:                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 1.97.0-nightly (8da2d28cb 2026-04-18) running on x86_64-unknown-linux-gnu

note: compiler flags: -Z dump-mir-dir=dir

query stack during panic:
#0 [typeck_root] type-checking `main`
#1 [check_match] match-checking `main`
#2 [mir_built] building MIR for `main`
#3 [has_ffi_unwind_calls] checking if `main` contains FFI-unwind calls
#4 [mir_promoted] promoting constants in MIR for `main`
#5 [mir_borrowck] borrow-checking `main`
#6 [type_of_opaque] computing type of opaque `main::T::{opaque#0}`
#7 [type_of] computing type of `main::T::{opaque#0}`
#8 [check_well_formed] checking that `main::T::{opaque#0}` is well-formed
#9 [check_type_wf] checking that types are well-formed
#10 [analysis] running analysis passes on crate `mvce`
end of query stack
error: aborting due to 6 previous errors

Some errors have detailed explanations: E0061, E0277, E0658.
For more information about an error, try `rustc --explain E0061`.

[matthiaskrgr]

without errors:

#![feature(type_alias_impl_trait)]
#![warn(rust_2021_incompatible_closure_captures)]
struct Foo(());
fn main() {
    type T = impl Sized;
    let foo: T = todo!();
    let x = ();
    (move || Foo(x) = foo)()
}

ICEs with edition 2015, 2018 but not 2021 or later
bisects to nightly-2021-07-08
EDIT: the lint was renamed in this nightly 😒

with #![warn(disjoint_capture_migration)]
this bisects to nightly-2021-05-13