ICE: `Unexpected type Binder for Field projection`

[cushionbadak]

Code

#![feature(unsafe_binders)]
#![allow(incomplete_features)]

use std::unsafe_binder::unwrap_binder;

#[derive(Copy, Clone)]
pub struct S([usize; 8]);

pub fn outer_function(x: unsafe<'a> S) -> usize {
    (|| unwrap_binder!(x).0[0])()
}

fn main() {}

A mutant from tests/ui/attributes/no-mangle-closure.rs

Meta

rustc --version --verbose:

rustc 1.89.0-nightly (2eef47813 2025-05-22)
binary: rustc
commit-hash: 2eef47813f25df637026ce3288880e5c587abd92
commit-date: 2025-05-22
host: x86_64-apple-darwin
release: 1.89.0-nightly
LLVM version: 20.1.5

Error output

command: rustc --edition=2021

error: internal compiler error: compiler/rustc_middle/src/ty/closure.rs:116:25: Unexpected type Binder { value: S, bound_vars: [Region(BrNamed(DefId(0:5 ~ clos_r[2488]::outer_function::'a), 'a))] } for `Field` projection


thread 'rustc' panicked at compiler/rustc_middle/src/ty/closure.rs:116:25:
Box<dyn Any>

Backtrace

stack backtrace:
   0: std::panicking::begin_panic::<rustc_errors::ExplicitBug>
   1: <rustc_errors::diagnostic::BugAbort as rustc_errors::diagnostic::EmissionGuarantee>::emit_producing_guarantee
   2: rustc_middle::util::bug::opt_span_bug_fmt::<rustc_span::span_encoding::Span>::{closure#0}
   3: rustc_middle::ty::context::tls::with_opt::<rustc_middle::util::bug::opt_span_bug_fmt<rustc_span::span_encoding::Span>::{closure#0}, !>::{closure#0}
   4: rustc_middle::ty::context::tls::with_context_opt::<rustc_middle::ty::context::tls::with_opt<rustc_middle::util::bug::opt_span_bug_fmt<rustc_span::span_encoding::Span>::{closure#0}, !>::{closure#0}, !>
   5: rustc_middle::util::bug::bug_fmt
   6: <rustc_middle::ty::closure::CapturedPlace>::to_symbol
   7: <core::iter::adapters::map::Map<core::iter::adapters::enumerate::Enumerate<itertools::zip_eq_impl::ZipEq<core::slice::iter::Iter<&rustc_middle::ty::closure::CapturedPlace>, core::iter::adapters::copied::Copied<core::slice::iter::Iter<rustc_middle::ty::Ty>>>>, <rustc_mir_build::builder::Builder>::insert_upvar_arg::{closure#0}> as core::iter::traits::iterator::Iterator>::next
   8: rustc_mir_build::builder::construct_fn
   9: rustc_mir_build::builder::build_mir
  10: rustc_mir_transform::mir_built
      [... omitted 1 frame ...]
  11: <rustc_mir_build::check_unsafety::UnsafetyVisitor>::visit_inner_body
  12: <rustc_mir_build::check_unsafety::UnsafetyVisitor as rustc_middle::thir::visit::Visitor>::visit_expr
  13: <rustc_mir_build::check_unsafety::UnsafetyVisitor as rustc_middle::thir::visit::Visitor>::visit_expr
  14: <rustc_mir_build::check_unsafety::UnsafetyVisitor as rustc_middle::thir::visit::Visitor>::visit_expr
  15: rustc_middle::thir::visit::walk_expr::<rustc_mir_build::check_unsafety::UnsafetyVisitor>
  16: <rustc_mir_build::check_unsafety::UnsafetyVisitor as rustc_middle::thir::visit::Visitor>::visit_expr
  17: <rustc_mir_build::check_unsafety::UnsafetyVisitor as rustc_middle::thir::visit::Visitor>::visit_expr
  18: <rustc_mir_build::check_unsafety::UnsafetyVisitor as rustc_middle::thir::visit::Visitor>::visit_expr
  19: <rustc_mir_build::check_unsafety::UnsafetyVisitor as rustc_middle::thir::visit::Visitor>::visit_expr
  20: rustc_mir_build::check_unsafety::check_unsafety
      [... omitted 1 frame ...]
  21: <rustc_middle::ty::context::TyCtxt>::par_hir_body_owners::<rustc_interface::passes::run_required_analyses::{closure#2}::{closure#0}>::{closure#0}
  22: rustc_interface::passes::run_required_analyses
  23: rustc_interface::passes::analysis
      [... omitted 1 frame ...]
  24: rustc_interface::passes::create_and_enter_global_ctxt::<core::option::Option<rustc_interface::queries::Linker>, rustc_driver_impl::run_compiler::{closure#0}::{closure#2}>
  25: rustc_interface::interface::run_compiler::<(), rustc_driver_impl::run_compiler::{closure#0}>::{closure#1}
note: Some details are omitted, run with `RUST_BACKTRACE=full` for a verbose backtrace.

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/scratch_250523/run_250522_250505_feat_unsafe_binder/scratch/rustc-ice-2025-05-23T04_29_20-9154.txt` to your bug report

query stack during panic:
#0 [mir_built] building MIR for `outer_function::{closure#0}`
#1 [check_unsafety] unsafety-checking `outer_function`
#2 [analysis] running analysis passes on this crate
end of query stack
error: aborting due to 1 previous error

Bisects to

searched nightlies: from nightly-2024-05-01 to nightly-2025-05-22
regressed nightly: nightly-2025-02-02
searched commit range: 854f225...8239a37
regressed commit: 8239a37

bisected with cargo-bisect-rustc v0.6.9

Host triple: x86_64-unknown-linux-gnu
Reproduce with:

cargo bisect-rustc --end=2025-05-22 --regress ice --preserve --script rustc -- clos_r.rs --edition=2021

********************************************************************************
Regression in 8239a37f9c0951a037cfc51763ea52a20e71e6bd
********************************************************************************

Attempting to search unrolled perf builds
Found commits ["be995312", "150da37e", "20325765", "9264389d", "d38d22f1", "590d9bf4"]
installing be995312299b441ca428237a2b2ba69b769d517e
testing...
RESULT: be995312299b441ca428237a2b2ba69b769d517e, ===> Script found ICE

Regression in https://github.com/rust-lang-ci/rust/commit/be995312299b441ca428237a2b2ba69b769d517e
The PR introducing the regression in this rollup is #130514: Implement MIR lowering for unsafe binders

Notes

• ICE location: compiler/rustc_middle/src/ty/closure.rs Line-116
  

  rust/compiler/rustc_middle/src/ty/closure.rs

  Lines 99 to 118 in 2eef478

  	pub fn to_symbol(&self) -> Symbol {
  	let mut symbol = self.var_ident.to_string();
  	let mut ty = self.place.base_ty;
  	for proj in self.place.projections.iter() {
  	match proj.kind {
  	HirProjectionKind::Field(idx, variant) => match ty.kind() {
  	ty::Tuple(_) => write!(&mut symbol, "__{}", idx.index()).unwrap(),
  	ty::Adt(def, ..) => {
  	write!(
  	&mut symbol,
  	"__{}",
  	def.variant(variant).fields[idx].name.as_str(),
  	)
  	.unwrap();
  	}
  	ty => {
  	bug!("Unexpected type {:?} for `Field` projection", ty)
  	}
  	},

• Issue-117707 has identical ICE location

• The code in this report is nearly identical to that in ICE: could not resolve upvar: LocalVarId(HirId(DefId)) #141417, except that it uses x: unsafe<'a> S as a parameter, whereas issue-141417 uses x: unsafe<'a> &'a S.

@rustbot label +F-unsafe_binders