Design needed for interaction between pin ergonomics and match ergonomics 2024 (RFC 3627)
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A-patterns
C-discussion
F-pin_ergonomics
I-ICE
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Description
snippet:
#![feature(ref_pat_eat_one_layer_2024)]
#![feature(pin_ergonomics)]
struct Foo;
fn tuple_tuple_ref_pin_mut_pat_and_pin_mut_of_tuple_mut_of_tuple_pin_mut_ty<'a, T>(
((&pin mut x,),): &'a pin mut (&'a mut (&'a Foo,),),
) {
}
Version information
rustc 1.95.0-nightly (1e5065a4d 2026-01-28)
binary: rustc
commit-hash: 1e5065a4d99e0e3ccf1a1719055308e7a20e8f36
commit-date: 2026-01-28
host: x86_64-unknown-linux-gnu
release: 1.95.0-nightly
LLVM version: 22.1.0
Possibly related line of code:
https://github.com/rust-lang/rust/blob/1e5065a4d99e0e3ccf1a1719055308e7a20e8f36/compiler/rustc_pattern_analysis/src/rustc.rs#L474-L486
Command:
/home/matthias/.rustup/toolchains/master/bin/rustc
Program output
warning: the feature `ref_pat_eat_one_layer_2024` is incomplete and may not be safe to use and/or cause compiler crashes
--> /tmp/icemaker_global_tempdir.fPH37lBeHLY7/rustc_testrunner_tmpdir_reporting.dQ5J2SqxBQ1S/mvce.rs:1:12
|
1 | #![feature(ref_pat_eat_one_layer_2024)]
| ^^^^^^^^^^^^^^^^^^^^^^^^^^
|
= note: see issue #123076 <https://github.com/rust-lang/rust/issues/123076> 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
--> /tmp/icemaker_global_tempdir.fPH37lBeHLY7/rustc_testrunner_tmpdir_reporting.dQ5J2SqxBQ1S/mvce.rs:2:12
|
2 | #![feature(pin_ergonomics)]
| ^^^^^^^^^^^^^^
|
= note: see issue #130494 <https://github.com/rust-lang/rust/issues/130494> for more information
error[E0601]: `main` function not found in crate `mvce`
--> /tmp/icemaker_global_tempdir.fPH37lBeHLY7/rustc_testrunner_tmpdir_reporting.dQ5J2SqxBQ1S/mvce.rs:8:2
|
8 | }
| ^ consider adding a `main` function to `/tmp/icemaker_global_tempdir.fPH37lBeHLY7/rustc_testrunner_tmpdir_reporting.dQ5J2SqxBQ1S/mvce.rs`
error: internal compiler error: /rustc-dev/1e5065a4d99e0e3ccf1a1719055308e7a20e8f36/compiler/rustc_pattern_analysis/src/rustc.rs:480:26: pattern has unexpected type: pat: Deref { pin: Pinned, subpattern: Pat { ty: Foo, span: /tmp/icemaker_global_tempdir.fPH37lBeHLY7/rustc_testrunner_tmpdir_reporting.dQ5J2SqxBQ1S/mvce.rs:6:16: 6:17 (#0), extra: None, kind: Binding { name: "x", mode: BindingMode(No, Not), var: LocalVarId(HirId(DefId(0:5 ~ mvce[d603]::tuple_tuple_ref_pin_mut_pat_and_pin_mut_of_tuple_mut_of_tuple_pin_mut_ty).5)), ty: Foo, subpattern: None, is_primary: true, is_shorthand: false } } }, ty: &'{erased} Foo
--> /tmp/icemaker_global_tempdir.fPH37lBeHLY7/rustc_testrunner_tmpdir_reporting.dQ5J2SqxBQ1S/mvce.rs:6:7
|
6 | ((&pin mut x,),): &'a pin mut (&'a mut (&'a Foo,),),
| ^^^^^^^^^^
thread 'rustc' (2683406) panicked at /rustc-dev/1e5065a4d99e0e3ccf1a1719055308e7a20e8f36/compiler/rustc_pattern_analysis/src/rustc.rs:480:26:
Box<dyn Any>
stack backtrace:
0: 0x7f823a64826b - <<std[d7a9ad9d2397029e]::sys::backtrace::BacktraceLock>::print::DisplayBacktrace as core[5cc72673e270ff3e]::fmt::Display>::fmt
1: 0x7f823ac0f108 - core[5cc72673e270ff3e]::fmt::write
2: 0x7f823a65f146 - <std[d7a9ad9d2397029e]::sys::stdio::unix::Stderr as std[d7a9ad9d2397029e]::io::Write>::write_fmt
3: 0x7f823a61e318 - std[d7a9ad9d2397029e]::panicking::default_hook::{closure#0}
4: 0x7f823a63b633 - std[d7a9ad9d2397029e]::panicking::default_hook
5: 0x7f823961ac6d - std[d7a9ad9d2397029e]::panicking::update_hook::<alloc[207d8e8634fd4110]::boxed::Box<rustc_driver_impl[f932d213bb3ade3d]::install_ice_hook::{closure#1}>>::{closure#0}
6: 0x7f823a63b912 - std[d7a9ad9d2397029e]::panicking::panic_with_hook
7: 0x7f823964f3e1 - std[d7a9ad9d2397029e]::panicking::begin_panic::<rustc_errors[3e39d25ea04ed4bf]::ExplicitBug>::{closure#0}
8: 0x7f8239648186 - std[d7a9ad9d2397029e]::sys::backtrace::__rust_end_short_backtrace::<std[d7a9ad9d2397029e]::panicking::begin_panic<rustc_errors[3e39d25ea04ed4bf]::ExplicitBug>::{closure#0}, !>
9: 0x7f8239647efa - std[d7a9ad9d2397029e]::panicking::begin_panic::<rustc_errors[3e39d25ea04ed4bf]::ExplicitBug>
10: 0x7f823965aa01 - <rustc_errors[3e39d25ea04ed4bf]::diagnostic::BugAbort as rustc_errors[3e39d25ea04ed4bf]::diagnostic::EmissionGuarantee>::emit_producing_guarantee
11: 0x7f8239bdfc0c - <rustc_errors[3e39d25ea04ed4bf]::DiagCtxtHandle>::span_bug::<rustc_span[101d8a10560d0148]::span_encoding::Span, alloc[207d8e8634fd4110]::string::String>
12: 0x7f8239c08436 - rustc_middle[ae72f8db201c45fb]::util::bug::opt_span_bug_fmt::<rustc_span[101d8a10560d0148]::span_encoding::Span>::{closure#0}
13: 0x7f8239c085e2 - rustc_middle[ae72f8db201c45fb]::ty::context::tls::with_opt::<rustc_middle[ae72f8db201c45fb]::util::bug::opt_span_bug_fmt<rustc_span[101d8a10560d0148]::span_encoding::Span>::{closure#0}, !>::{closure#0}
14: 0x7f8239bf9c4b - rustc_middle[ae72f8db201c45fb]::ty::context::tls::with_context_opt::<rustc_middle[ae72f8db201c45fb]::ty::context::tls::with_opt<rustc_middle[ae72f8db201c45fb]::util::bug::opt_span_bug_fmt<rustc_span[101d8a10560d0148]::span_encoding::Span>::{closure#0}, !>::{closure#0}, !>
15: 0x7f82374a1a88 - rustc_middle[ae72f8db201c45fb]::util::bug::span_bug_fmt::<rustc_span[101d8a10560d0148]::span_encoding::Span>
16: 0x7f8237b13d86 - <rustc_pattern_analysis[7dd64aeb450fd0d2]::rustc::RustcPatCtxt>::lower_pat
17: 0x7f8237b132c0 - <rustc_pattern_analysis[7dd64aeb450fd0d2]::rustc::RustcPatCtxt>::lower_pat
18: 0x7f8237b13140 - <rustc_pattern_analysis[7dd64aeb450fd0d2]::rustc::RustcPatCtxt>::lower_pat
19: 0x7f8237b132c0 - <rustc_pattern_analysis[7dd64aeb450fd0d2]::rustc::RustcPatCtxt>::lower_pat
20: 0x7f8237b13140 - <rustc_pattern_analysis[7dd64aeb450fd0d2]::rustc::RustcPatCtxt>::lower_pat
21: 0x7f823b31d7c0 - rustc_mir_build[caaca64e226810d2]::thir::pattern::check_match::check_match
22: 0x7f823b31d1db - rustc_query_impl[13bcb7b07dc4d660]::plumbing::__rust_begin_short_backtrace::<rustc_query_impl[13bcb7b07dc4d660]::query_impl::check_match::make_query_vtable::{closure#2}::{closure#0}, rustc_middle[ae72f8db201c45fb]::query::erase::Erased<[u8; 1usize]>>
23: 0x7f823b3d7a52 - rustc_query_system[fda0dd1a18d51465]::query::plumbing::try_execute_query::<rustc_query_impl[13bcb7b07dc4d660]::SemiDynamicQueryDispatcher<rustc_data_structures[c9669210c0b9186b]::vec_cache::VecCache<rustc_span[101d8a10560d0148]::def_id::LocalDefId, rustc_middle[ae72f8db201c45fb]::query::erase::Erased<[u8; 1usize]>, rustc_query_system[fda0dd1a18d51465]::dep_graph::graph::DepNodeIndex>, false, false, false>, rustc_query_impl[13bcb7b07dc4d660]::plumbing::QueryCtxt, false>
24: 0x7f823b3d7711 - rustc_query_impl[13bcb7b07dc4d660]::query_impl::check_match::get_query_non_incr::__rust_end_short_backtrace
25: 0x7f823b19ea1e - rustc_mir_build[caaca64e226810d2]::builder::build_mir_inner_impl
26: 0x7f823ac08e6a - rustc_mir_transform[917e19d7d4dd96cc]::mir_built
27: 0x7f823ac08e25 - rustc_query_impl[13bcb7b07dc4d660]::plumbing::__rust_begin_short_backtrace::<rustc_query_impl[13bcb7b07dc4d660]::query_impl::mir_built::make_query_vtable::{closure#2}::{closure#0}, rustc_middle[ae72f8db201c45fb]::query::erase::Erased<[u8; 8usize]>>
28: 0x7f823ad30ff5 - rustc_query_system[fda0dd1a18d51465]::query::plumbing::try_execute_query::<rustc_query_impl[13bcb7b07dc4d660]::SemiDynamicQueryDispatcher<rustc_data_structures[c9669210c0b9186b]::vec_cache::VecCache<rustc_hir_id[b437bd80822f8ed3]::OwnerId, rustc_middle[ae72f8db201c45fb]::query::erase::Erased<[u8; 8usize]>, rustc_query_system[fda0dd1a18d51465]::dep_graph::graph::DepNodeIndex>, false, false, false>, rustc_query_impl[13bcb7b07dc4d660]::plumbing::QueryCtxt, false>
29: 0x7f823ad308c9 - rustc_query_impl[13bcb7b07dc4d660]::query_impl::mir_built::get_query_non_incr::__rust_end_short_backtrace
30: 0x7f823ad29b2a - rustc_mir_build[caaca64e226810d2]::check_unsafety::check_unsafety
31: 0x7f823ad29899 - rustc_query_impl[13bcb7b07dc4d660]::plumbing::__rust_begin_short_backtrace::<rustc_query_impl[13bcb7b07dc4d660]::query_impl::check_unsafety::make_query_vtable::{closure#2}::{closure#0}, rustc_middle[ae72f8db201c45fb]::query::erase::Erased<[u8; 0usize]>>
32: 0x7f823ad27302 - rustc_query_system[fda0dd1a18d51465]::query::plumbing::try_execute_query::<rustc_query_impl[13bcb7b07dc4d660]::SemiDynamicQueryDispatcher<rustc_data_structures[c9669210c0b9186b]::vec_cache::VecCache<rustc_span[101d8a10560d0148]::def_id::LocalDefId, rustc_middle[ae72f8db201c45fb]::query::erase::Erased<[u8; 0usize]>, rustc_query_system[fda0dd1a18d51465]::dep_graph::graph::DepNodeIndex>, false, false, false>, rustc_query_impl[13bcb7b07dc4d660]::plumbing::QueryCtxt, false>
33: 0x7f823ad2707d - rustc_query_impl[13bcb7b07dc4d660]::query_impl::check_unsafety::get_query_non_incr::__rust_end_short_backtrace
34: 0x7f823ad260e6 - <rustc_middle[ae72f8db201c45fb]::ty::context::TyCtxt>::par_hir_body_owners::<rustc_interface[909c88ca5ae84a20]::passes::run_required_analyses::{closure#1}::{closure#0}>::{closure#0}
35: 0x7f823ad23c0a - rustc_interface[909c88ca5ae84a20]::passes::analysis
36: 0x7f823ad2302b - rustc_query_impl[13bcb7b07dc4d660]::plumbing::__rust_begin_short_backtrace::<rustc_query_impl[13bcb7b07dc4d660]::query_impl::analysis::make_query_vtable::{closure#2}::{closure#0}, rustc_middle[ae72f8db201c45fb]::query::erase::Erased<[u8; 0usize]>>
37: 0x7f823bdea1e6 - rustc_query_system[fda0dd1a18d51465]::query::plumbing::try_execute_query::<rustc_query_impl[13bcb7b07dc4d660]::SemiDynamicQueryDispatcher<rustc_query_system[fda0dd1a18d51465]::query::caches::SingleCache<rustc_middle[ae72f8db201c45fb]::query::erase::Erased<[u8; 0usize]>>, false, false, false>, rustc_query_impl[13bcb7b07dc4d660]::plumbing::QueryCtxt, false>
38: 0x7f823bde9ec2 - rustc_query_impl[13bcb7b07dc4d660]::query_impl::analysis::get_query_non_incr::__rust_end_short_backtrace
39: 0x7f823bf28a6c - <rustc_interface[909c88ca5ae84a20]::passes::create_and_enter_global_ctxt<core[5cc72673e270ff3e]::option::Option<rustc_interface[909c88ca5ae84a20]::queries::Linker>, rustc_driver_impl[f932d213bb3ade3d]::run_compiler::{closure#0}::{closure#2}>::{closure#2} as core[5cc72673e270ff3e]::ops::function::FnOnce<(&rustc_session[76fc6592b209b26]::session::Session, rustc_middle[ae72f8db201c45fb]::ty::context::CurrentGcx, alloc[207d8e8634fd4110]::sync::Arc<rustc_data_structures[c9669210c0b9186b]::jobserver::Proxy>, &std[d7a9ad9d2397029e]::sync::once_lock::OnceLock<rustc_middle[ae72f8db201c45fb]::ty::context::GlobalCtxt>, &rustc_data_structures[c9669210c0b9186b]::sync::worker_local::WorkerLocal<rustc_middle[ae72f8db201c45fb]::arena::Arena>, &rustc_data_structures[c9669210c0b9186b]::sync::worker_local::WorkerLocal<rustc_hir[6fb796084409818f]::Arena>, rustc_driver_impl[f932d213bb3ade3d]::run_compiler::{closure#0}::{closure#2})>>::call_once::{shim:vtable#0}
40: 0x7f823bdaf488 - rustc_interface[909c88ca5ae84a20]::interface::run_compiler::<(), rustc_driver_impl[f932d213bb3ade3d]::run_compiler::{closure#0}>::{closure#1}
41: 0x7f823bdd0d3e - std[d7a9ad9d2397029e]::sys::backtrace::__rust_begin_short_backtrace::<rustc_interface[909c88ca5ae84a20]::util::run_in_thread_with_globals<rustc_interface[909c88ca5ae84a20]::util::run_in_thread_pool_with_globals<rustc_interface[909c88ca5ae84a20]::interface::run_compiler<(), rustc_driver_impl[f932d213bb3ade3d]::run_compiler::{closure#0}>::{closure#1}, ()>::{closure#0}, ()>::{closure#0}::{closure#0}, ()>
42: 0x7f823bdd1260 - <std[d7a9ad9d2397029e]::thread::lifecycle::spawn_unchecked<rustc_interface[909c88ca5ae84a20]::util::run_in_thread_with_globals<rustc_interface[909c88ca5ae84a20]::util::run_in_thread_pool_with_globals<rustc_interface[909c88ca5ae84a20]::interface::run_compiler<(), rustc_driver_impl[f932d213bb3ade3d]::run_compiler::{closure#0}>::{closure#1}, ()>::{closure#0}, ()>::{closure#0}::{closure#0}, ()>::{closure#1} as core[5cc72673e270ff3e]::ops::function::FnOnce<()>>::call_once::{shim:vtable#0}
43: 0x7f823bdd20ec - <std[d7a9ad9d2397029e]::sys::thread::unix::Thread>::new::thread_start
44: 0x7f823569698b - <unknown>
45: 0x7f823571a9cc - <unknown>
46: 0x0 - <unknown>
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 1.95.0-nightly (1e5065a4d 2026-01-28) running on x86_64-unknown-linux-gnu
query stack during panic:
#0 [check_match] match-checking `tuple_tuple_ref_pin_mut_pat_and_pin_mut_of_tuple_mut_of_tuple_pin_mut_ty`
#1 [mir_built] building MIR for `tuple_tuple_ref_pin_mut_pat_and_pin_mut_of_tuple_mut_of_tuple_pin_mut_ty`
#2 [check_unsafety] unsafety-checking `tuple_tuple_ref_pin_mut_pat_and_pin_mut_of_tuple_mut_of_tuple_pin_mut_ty`
#3 [analysis] running analysis passes on crate `mvce`
end of query stack
error: aborting due to 2 previous errors; 2 warnings emitted
For more information about this error, try `rustc --explain E0601`.
@rustbot label +F-ref_pat_eat_one_layer_2024 +F-pin_ergonomics
Contributor guide
First steps
- Read the whole issue, then the project's contributing guide.
- Comment on the issue to say you are picking it up — it saves two people doing the same work.
- Fork the repository and make your change on a branch.
- Open a pull request that references the issue number.
Research direction
Start by reproducing the supplied snippet with the referenced nightly toolchain, then read compiler/rustc_pattern_analysis/src/rustc.rs around lines 474-486 and the ICE backtrace through RustcPatCtxt::lower_pat. The design must establish how pin ergonomics interacts with match ergonomics and RFC 3627 before determining the expected behavior and how the panic is resolved.
Written by the indexing model from the issue text.
Assessment
- Tech stack
- rust
- Domain
- compilers
- Issue type
- Bug
- Difficulty
- 5/5
- Estimated time
- Over a week
- Activity status
- Stale
- Clarity
- Needs clarification
- Newbie friendliness
- 25/100