ICE: `encountered unexpected unsized field in layout of`

[matthiaskrgr]

Code

This is a more reduced & modified version of one of the snippets of #131342 but none of those seem to bisect to same nightly for me ( nightly-2024-04-05 )

fn problem_thingy(items: &mut impl Iterator<Item = str>) {
    let mut peeker = items.peekable();
    match peeker.peek() {
        Some(_) => (),
        None => return (),
    }
}

Meta

rustc --version --verbose:

rustc 1.85.0-nightly (45d11e51b 2025-01-01)
binary: rustc
commit-hash: 45d11e51bb66c2deb63a006fe3953c4b6fbc50c2
commit-date: 2025-01-01
host: x86_64-unknown-linux-gnu
release: 1.85.0-nightly
LLVM version: 19.1.6

Error output

<output>

Backtrace

warning: function `problem_thingy` is never used
 --> /tmp/crash.rs:1:4
  |
1 | fn problem_thingy(items: &mut impl Iterator<Item = str>) {
  |    ^^^^^^^^^^^^^^
  |
  = note: `#[warn(dead_code)]` on by default

warning: 1 warning 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: encountered unexpected unsized field in layout of std::option::Option<str>: TyAndLayout {
                                    ty: str,
                                    layout: Layout {
                                        size: Size(0 bytes),
                                        align: AbiAndPrefAlign {
                                            abi: Align(1 bytes),
                                            pref: Align(1 bytes),
                                        },
                                        abi: Memory {
                                            sized: false,
                                        },
                                        fields: Array {
                                            stride: Size(1 bytes),
                                            count: 0,
                                        },
                                        largest_niche: None,
                                        variants: Single {
                                            index: 0,
                                        },
                                        max_repr_align: None,
                                        unadjusted_abi_align: Align(1 bytes),
                                    },
                                }
  |
  = note: delayed at compiler/rustc_ty_utils/src/layout.rs:108:32
             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>::delayed_bug::<alloc::string::String>
             4: rustc_ty_utils::layout::map_error
             5: rustc_ty_utils::layout::layout_of_uncached
             6: rustc_ty_utils::layout::layout_of
             7: rustc_query_impl::plumbing::__rust_begin_short_backtrace::<rustc_query_impl::query_impl::layout_of::dynamic_query::{closure#2}::{closure#0}, rustc_middle::query::erase::Erased<[u8; 16]>>
             8: rustc_query_system::query::plumbing::try_execute_query::<rustc_query_impl::DynamicConfig<rustc_query_system::query::caches::DefaultCache<rustc_middle::ty::PseudoCanonicalInput<rustc_middle::ty::Ty>, rustc_middle::query::erase::Erased<[u8; 16]>>, false, true, false>, rustc_query_impl::plumbing::QueryCtxt, false>
             9: rustc_query_impl::query_impl::layout_of::get_query_non_incr::__rust_end_short_backtrace
            10: <core::iter::adapters::GenericShunt<core::iter::adapters::by_ref_sized::ByRefSized<core::iter::adapters::map::Map<core::slice::iter::Iter<rustc_middle::ty::VariantDef>, rustc_ty_utils::layout::layout_of_uncached::{closure#13}>>, core::result::Result<core::convert::Infallible, &rustc_middle::ty::layout::LayoutError>> as core::iter::traits::iterator::Iterator>::next
            11: rustc_ty_utils::layout::layout_of_uncached
            12: rustc_ty_utils::layout::layout_of
            13: rustc_query_impl::plumbing::__rust_begin_short_backtrace::<rustc_query_impl::query_impl::layout_of::dynamic_query::{closure#2}::{closure#0}, rustc_middle::query::erase::Erased<[u8; 16]>>
            14: rustc_query_system::query::plumbing::try_execute_query::<rustc_query_impl::DynamicConfig<rustc_query_system::query::caches::DefaultCache<rustc_middle::ty::PseudoCanonicalInput<rustc_middle::ty::Ty>, rustc_middle::query::erase::Erased<[u8; 16]>>, false, true, false>, rustc_query_impl::plumbing::QueryCtxt, false>
            15: rustc_query_impl::query_impl::layout_of::get_query_non_incr::__rust_end_short_backtrace
            16: rustc_middle::query::plumbing::query_get_at::<rustc_query_system::query::caches::DefaultCache<rustc_middle::ty::PseudoCanonicalInput<rustc_middle::ty::Ty>, rustc_middle::query::erase::Erased<[u8; 16]>>>
            17: rustc_ty_utils::layout::layout_of
            18: rustc_query_impl::plumbing::__rust_begin_short_backtrace::<rustc_query_impl::query_impl::layout_of::dynamic_query::{closure#2}::{closure#0}, rustc_middle::query::erase::Erased<[u8; 16]>>
            19: rustc_query_system::query::plumbing::try_execute_query::<rustc_query_impl::DynamicConfig<rustc_query_system::query::caches::DefaultCache<rustc_middle::ty::PseudoCanonicalInput<rustc_middle::ty::Ty>, rustc_middle::query::erase::Erased<[u8; 16]>>, false, true, false>, rustc_query_impl::plumbing::QueryCtxt, false>
            20: rustc_query_impl::query_impl::layout_of::get_query_non_incr::__rust_end_short_backtrace
            21: <core::iter::adapters::GenericShunt<core::iter::adapters::by_ref_sized::ByRefSized<core::iter::adapters::map::Map<core::slice::iter::Iter<rustc_middle::ty::VariantDef>, rustc_ty_utils::layout::layout_of_uncached::{closure#13}>>, core::result::Result<core::convert::Infallible, &rustc_middle::ty::layout::LayoutError>> as core::iter::traits::iterator::Iterator>::next
            22: rustc_ty_utils::layout::layout_of_uncached
            23: rustc_ty_utils::layout::layout_of
            24: rustc_query_impl::plumbing::__rust_begin_short_backtrace::<rustc_query_impl::query_impl::layout_of::dynamic_query::{closure#2}::{closure#0}, rustc_middle::query::erase::Erased<[u8; 16]>>
            25: rustc_query_system::query::plumbing::try_execute_query::<rustc_query_impl::DynamicConfig<rustc_query_system::query::caches::DefaultCache<rustc_middle::ty::PseudoCanonicalInput<rustc_middle::ty::Ty>, rustc_middle::query::erase::Erased<[u8; 16]>>, false, true, false>, rustc_query_impl::plumbing::QueryCtxt, false>
            26: rustc_query_impl::query_impl::layout_of::get_query_non_incr::__rust_end_short_backtrace
            27: <rustc_mir_transform::known_panics_lint::KnownPanicsLint as rustc_mir_transform::pass_manager::MirLint>::run_lint
            28: rustc_mir_transform::run_analysis_to_runtime_passes
            29: rustc_mir_transform::mir_drops_elaborated_and_const_checked
            30: rustc_query_impl::plumbing::__rust_begin_short_backtrace::<rustc_query_impl::query_impl::mir_drops_elaborated_and_const_checked::dynamic_query::{closure#2}::{closure#0}, rustc_middle::query::erase::Erased<[u8; 8]>>
            31: rustc_query_system::query::plumbing::try_execute_query::<rustc_query_impl::DynamicConfig<rustc_data_structures::vec_cache::VecCache<rustc_span::def_id::LocalDefId, rustc_middle::query::erase::Erased<[u8; 8]>, rustc_query_system::dep_graph::graph::DepNodeIndex>, false, false, false>, rustc_query_impl::plumbing::QueryCtxt, false>
            32: rustc_query_impl::query_impl::mir_drops_elaborated_and_const_checked::get_query_non_incr::__rust_end_short_backtrace
            33: rustc_interface::passes::run_required_analyses
            34: rustc_interface::passes::analysis
            35: rustc_query_impl::plumbing::__rust_begin_short_backtrace::<rustc_query_impl::query_impl::analysis::dynamic_query::{closure#2}::{closure#0}, rustc_middle::query::erase::Erased<[u8; 0]>>
            36: rustc_query_system::query::plumbing::try_execute_query::<rustc_query_impl::DynamicConfig<rustc_query_system::query::caches::SingleCache<rustc_middle::query::erase::Erased<[u8; 0]>>, false, false, false>, rustc_query_impl::plumbing::QueryCtxt, false>
            37: rustc_query_impl::query_impl::analysis::get_query_non_incr::__rust_end_short_backtrace
            38: rustc_interface::passes::create_and_enter_global_ctxt::<core::option::Option<rustc_interface::queries::Linker>, rustc_driver_impl::run_compiler::{closure#0}::{closure#2}>::{closure#2}::{closure#0}
            39: rustc_interface::interface::run_compiler::<(), rustc_driver_impl::run_compiler::{closure#0}>::{closure#1}
            40: 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}, ()>
            41: <<std::thread::Builder>::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}
            42: std::sys::pal::unix::thread::Thread::new::thread_start
            43: <unknown>
            44: <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: please attach the file at `/home/matthias/vcs/github/rust_bisect/rustc-ice-2025-01-02T11_37_14-1305953.txt` to your bug report

note: compiler flags: --crate-type lib

query stack during panic:
end of query stack

[matthiaskrgr]

This compiled without error with previous nightly rustc 1.79.0-nightly (4fd4797c2 2024-04-03) but 2024-04-04 issues ICE.

[matthiaskrgr]

This caught my eye because with --crate-type lib -Zmir-opt-level=3 -Zvalidate-mir
this issues a backtrace which I didn't remember seeing yet

error: internal compiler error: /rustc/45d11e51bb66c2deb63a006fe3953c4b6fbc50c2/compiler/rustc_const_eval/src/interpret/operand.rs:157:17: invalid field type in Immediate::offset: value Scalar(0x0000000000000000) does not match ABI ScalarPair(Initialized { value: Pointer(AddressSpace(0)), valid_range: 1..=18446744073709551615 }, Initialized { value: Int(I64, false), valid_range: 0..=18446744073709551615 }))

thread 'rustc' panicked at /rustc/45d11e51bb66c2deb63a006fe3953c4b6fbc50c2/compiler/rustc_const_eval/src/interpret/operand.rs:157:17:
Box<dyn Any>
stack backtrace:
   0:     0x7bcb786d196a - <std::sys::backtrace::BacktraceLock::print::DisplayBacktrace as core::fmt::Display>::fmt::h4f6a4ee866651707
   1:     0x7bcb78e13426 - core::fmt::write::h9e6f8d90343a57f6
   2:     0x7bcb79d30991 - std::io::Write::write_fmt::h66c66b1419a58ace
   3:     0x7bcb786d17c2 - std::sys::backtrace::BacktraceLock::print::h498d080cb25470cd
   4:     0x7bcb786d3cc9 - std::panicking::default_hook::{{closure}}::hbbfe0167a7d38133
   5:     0x7bcb786d3b12 - std::panicking::default_hook::h9a3de122a21c6cbb
   6:     0x7bcb77842398 - std[8bfb91823dd31ae1]::panicking::update_hook::<alloc[6d3b84562c9c9b42]::boxed::Box<rustc_driver_impl[a4f26dc2be1bc8fc]::install_ice_hook::{closure#1}>>::{closure#0}
   7:     0x7bcb786d4483 - std::panicking::rust_panic_with_hook::hce10802d9af4ae90
   8:     0x7bcb7787a6b1 - std[8bfb91823dd31ae1]::panicking::begin_panic::<rustc_errors[bdbedb9356ccbc6e]::ExplicitBug>::{closure#0}
   9:     0x7bcb7786f896 - std[8bfb91823dd31ae1]::sys::backtrace::__rust_end_short_backtrace::<std[8bfb91823dd31ae1]::panicking::begin_panic<rustc_errors[bdbedb9356ccbc6e]::ExplicitBug>::{closure#0}, !>
  10:     0x7bcb7786c55d - std[8bfb91823dd31ae1]::panicking::begin_panic::<rustc_errors[bdbedb9356ccbc6e]::ExplicitBug>
  11:     0x7bcb77884611 - <rustc_errors[bdbedb9356ccbc6e]::diagnostic::BugAbort as rustc_errors[bdbedb9356ccbc6e]::diagnostic::EmissionGuarantee>::emit_producing_guarantee
  12:     0x7bcb77e648e3 - rustc_middle[1fd816385aa193f]::util::bug::opt_span_bug_fmt::<rustc_span[af3532371e21fe]::span_encoding::Span>::{closure#0}
  13:     0x7bcb77e4998a - rustc_middle[1fd816385aa193f]::ty::context::tls::with_opt::<rustc_middle[1fd816385aa193f]::util::bug::opt_span_bug_fmt<rustc_span[af3532371e21fe]::span_encoding::Span>::{closure#0}, !>::{closure#0}
  14:     0x7bcb77e4981b - rustc_middle[1fd816385aa193f]::ty::context::tls::with_context_opt::<rustc_middle[1fd816385aa193f]::ty::context::tls::with_opt<rustc_middle[1fd816385aa193f]::util::bug::opt_span_bug_fmt<rustc_span[af3532371e21fe]::span_encoding::Span>::{closure#0}, !>::{closure#0}, !>
  15:     0x7bcb761a9e50 - rustc_middle[1fd816385aa193f]::util::bug::bug_fmt
  16:     0x7bcb7a7e5043 - <rustc_const_eval[180ac8504a62d3dd]::interpret::operand::Immediate>::assert_matches_abi::<rustc_const_eval[180ac8504a62d3dd]::interpret::eval_context::InterpCx<rustc_const_eval[180ac8504a62d3dd]::const_eval::dummy_machine::DummyMachine>>.cold
  17:     0x7bcb79930cf8 - <rustc_const_eval[180ac8504a62d3dd]::interpret::operand::ImmTy>::offset_::<rustc_const_eval[180ac8504a62d3dd]::interpret::eval_context::InterpCx<rustc_const_eval[180ac8504a62d3dd]::const_eval::dummy_machine::DummyMachine>>
  18:     0x7bcb7992ef0d - <rustc_const_eval[180ac8504a62d3dd]::interpret::operand::OpTy as rustc_const_eval[180ac8504a62d3dd]::interpret::projection::Projectable<rustc_middle[1fd816385aa193f]::mir::interpret::pointer::CtfeProvenance>>::offset_with_meta::<rustc_const_eval[180ac8504a62d3dd]::const_eval::dummy_machine::DummyMachine>
  19:     0x7bcb7a11b8a7 - <rustc_const_eval[180ac8504a62d3dd]::interpret::eval_context::InterpCx<rustc_const_eval[180ac8504a62d3dd]::const_eval::dummy_machine::DummyMachine>>::project_downcast::<rustc_const_eval[180ac8504a62d3dd]::interpret::operand::OpTy>
  20:     0x7bcb78048e2e - <rustc_mir_transform[3a0403f4a2d1bba5]::dataflow_const_prop::ConstAnalysis>::assign_constant::{closure#0}
  21:     0x7bcb77f532bf - <rustc_mir_dataflow[f45e8f9b9136a50b]::value_analysis::Map>::for_each_projection_value::<rustc_const_eval[180ac8504a62d3dd]::interpret::operand::OpTy, <rustc_mir_transform[3a0403f4a2d1bba5]::dataflow_const_prop::ConstAnalysis>::assign_constant::{closure#0}, <rustc_mir_transform[3a0403f4a2d1bba5]::dataflow_const_prop::ConstAnalysis>::assign_constant::{closure#1}>
  22:     0x7bcb78048d5e - <rustc_mir_transform[3a0403f4a2d1bba5]::dataflow_const_prop::ConstAnalysis>::assign_constant
  23:     0x7bcb7800d1a6 - <rustc_mir_transform[3a0403f4a2d1bba5]::dataflow_const_prop::ConstAnalysis>::assign_operand
  24:     0x7bcb7800bc1f - <rustc_mir_transform[3a0403f4a2d1bba5]::dataflow_const_prop::ConstAnalysis as rustc_mir_dataflow[f45e8f9b9136a50b]::framework::Analysis>::apply_primary_statement_effect
  25:     0x7bcb78049a6c - <rustc_mir_transform[3a0403f4a2d1bba5]::dataflow_const_prop::DataflowConstProp as rustc_mir_transform[3a0403f4a2d1bba5]::pass_manager::MirPass>::run_pass
  26:     0x7bcb78e0eeee - rustc_mir_transform[3a0403f4a2d1bba5]::pass_manager::run_passes_inner
  27:     0x7bcb78f3be9f - rustc_mir_transform[3a0403f4a2d1bba5]::optimized_mir
  28:     0x7bcb78f3b75f - rustc_query_impl[5253828023562b54]::plumbing::__rust_begin_short_backtrace::<rustc_query_impl[5253828023562b54]::query_impl::optimized_mir::dynamic_query::{closure#2}::{closure#0}, rustc_middle[1fd816385aa193f]::query::erase::Erased<[u8; 8usize]>>
  29:     0x7bcb78f0419f - rustc_query_system[b85e5bdbcfc10045]::query::plumbing::try_execute_query::<rustc_query_impl[5253828023562b54]::DynamicConfig<rustc_query_system[b85e5bdbcfc10045]::query::caches::DefIdCache<rustc_middle[1fd816385aa193f]::query::erase::Erased<[u8; 8usize]>>, false, false, false>, rustc_query_impl[5253828023562b54]::plumbing::QueryCtxt, false>
  30:     0x7bcb78f0365f - rustc_query_impl[5253828023562b54]::query_impl::optimized_mir::get_query_non_incr::__rust_end_short_backtrace
  31:     0x7bcb75d7e8c9 - <rustc_middle[1fd816385aa193f]::ty::context::TyCtxt>::instance_mir
  32:     0x7bcb7925a912 - rustc_interface[15f87623c1d0da48]::passes::run_required_analyses
  33:     0x7bcb79d4479e - rustc_interface[15f87623c1d0da48]::passes::analysis
  34:     0x7bcb79d4476f - rustc_query_impl[5253828023562b54]::plumbing::__rust_begin_short_backtrace::<rustc_query_impl[5253828023562b54]::query_impl::analysis::dynamic_query::{closure#2}::{closure#0}, rustc_middle[1fd816385aa193f]::query::erase::Erased<[u8; 0usize]>>
  35:     0x7bcb79da1815 - rustc_query_system[b85e5bdbcfc10045]::query::plumbing::try_execute_query::<rustc_query_impl[5253828023562b54]::DynamicConfig<rustc_query_system[b85e5bdbcfc10045]::query::caches::SingleCache<rustc_middle[1fd816385aa193f]::query::erase::Erased<[u8; 0usize]>>, false, false, false>, rustc_query_impl[5253828023562b54]::plumbing::QueryCtxt, false>
  36:     0x7bcb79da154e - rustc_query_impl[5253828023562b54]::query_impl::analysis::get_query_non_incr::__rust_end_short_backtrace
  37:     0x7bcb79df445e - rustc_interface[15f87623c1d0da48]::passes::create_and_enter_global_ctxt::<core[d95970c0d684ac01]::option::Option<rustc_interface[15f87623c1d0da48]::queries::Linker>, rustc_driver_impl[a4f26dc2be1bc8fc]::run_compiler::{closure#0}::{closure#2}>::{closure#2}::{closure#0}
  38:     0x7bcb79dcec96 - rustc_interface[15f87623c1d0da48]::interface::run_compiler::<(), rustc_driver_impl[a4f26dc2be1bc8fc]::run_compiler::{closure#0}>::{closure#1}
  39:     0x7bcb79cfe85b - std[8bfb91823dd31ae1]::sys::backtrace::__rust_begin_short_backtrace::<rustc_interface[15f87623c1d0da48]::util::run_in_thread_with_globals<rustc_interface[15f87623c1d0da48]::util::run_in_thread_pool_with_globals<rustc_interface[15f87623c1d0da48]::interface::run_compiler<(), rustc_driver_impl[a4f26dc2be1bc8fc]::run_compiler::{closure#0}>::{closure#1}, ()>::{closure#0}, ()>::{closure#0}::{closure#0}, ()>
  40:     0x7bcb79cfed18 - <<std[8bfb91823dd31ae1]::thread::Builder>::spawn_unchecked_<rustc_interface[15f87623c1d0da48]::util::run_in_thread_with_globals<rustc_interface[15f87623c1d0da48]::util::run_in_thread_pool_with_globals<rustc_interface[15f87623c1d0da48]::interface::run_compiler<(), rustc_driver_impl[a4f26dc2be1bc8fc]::run_compiler::{closure#0}>::{closure#1}, ()>::{closure#0}, ()>::{closure#0}::{closure#0}, ()>::{closure#1} as core[d95970c0d684ac01]::ops::function::FnOnce<()>>::call_once::{shim:vtable#0}
  41:     0x7bcb79d002ef - std::sys::pal::unix::thread::Thread::new::thread_start::hf62fdb37efc5763b
  42:     0x7bcb740a339d - <unknown>
  43:     0x7bcb7412849c - <unknown>
  44:                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: please attach the file at `/tmp/im/rustc-ice-2025-01-02T11_44_39-1308394.txt` to your bug report

note: compiler flags: --crate-type lib -Z mir-opt-level=3 -Z validate-mir

query stack during panic:
#0 [optimized_mir] optimizing MIR for `problem_thingy`
#1 [analysis] running analysis passes on this crate
end of query stack
error: aborting due to 1 previous error

[cyrgani]

reduced:

fn problem_thingy(items: &mut impl Iterator<Item = str>) {
    items.peekable();
}

and without any external items:

struct Wrap<T>(T);

struct Peekable<I: Iterator>(Wrap<I::Item>);

fn problem_thingy(items: impl Iterator<Item = str>) {
    p(items);
}

trait Iterator {
    type Item;
}

fn p<I: Iterator>(_: I) -> Peekable<I> {
    loop {}
}

[apiraino]

thanks @cyrgani for reducing the sample.

I've run your code and run a bisection (without the additional compile flags mentioned in this comment) and I was taken to #129970, so cc @compiler-errors @lukas-code for an opinion here.

searched nightlies: from nightly-2024-07-20 to nightly-2025-01-02
regressed nightly: nightly-2024-09-18
searched commit range: c52c23b...28e8f01
regressed commit: e2dc1a1

bisected with cargo-bisect-rustc v0.6.9

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

cargo bisect-rustc --without-cargo --preserve --start 1.81.0 --script test.sh 

[lukas-code]

Looks like this assertion is actually wrong:

rust/compiler/rustc_ty_utils/src/layout.rs

Lines 107 to 111 in 6ca6659

	if !field.ty.is_sized(cx.tcx(), cx.typing_env) {
	cx.tcx().dcx().delayed_bug(format!(
	"encountered unexpected unsized field in layout of {ty:?}: {field:#?}"
	));
	}

Currently T: Iterator<Item = str> does not imply str: Sized (in either solver) and we eagerly normalize Wrap<I::Item> to Wrap<str> in the layout_of query.

When we compute the layout of Wrap<str> and find the unsized type str in a field that is expected to be sized, the layout computation returns LayoutCalculatorError::UnexpectedUnsized and the assertion then checks for a str: Sized bound, but in this case we only know I::Item: Sized and not str: Sized even though I::Item normalizes to str.

Keeping this assertion in some sensible manner seems like it would be more effort than it's worth, so I'm inclined to just remove it.