rust-lang / rust

Code

#![crate_type = "lib"]
#![feature(transmutability)]
#![allow(dead_code)]

mod assert {
    use std::mem::{Assume, BikeshedIntrinsicFrom};
    pub struct Context;
    pub fn is_maybe_transmutable<Src, Dst>()
    where
        Dst: BikeshedIntrinsicFrom<Src, Context, {
            Assume {
                alignment: false,
                lifetimes: false,
                safety: false,
                validity: false,
            }
        }>
    {}
}

fn test() {
    pub union U {
        a: [u16; 0],
        b: u8,
    }

    #[repr(C)]
    struct S(
        U, 
        u8,
    );

    assert::is_maybe_transmutable::<S, u128>();
}

Found with a modified fuzz-rustc

About this testcase

Origin:

Found by fuzzer mutating src/test/ui/transmutability/unions/repr/should_handle_packed.rs
I tried to reduce the test function while keeping the assert module normal-ish

Elements that seem necessary:

In the union, the zero-length array seems necessary
In the union, a and b mentioning different size things (u16 vs u8) seems necessary
The union's lack of #[repr(C)] seems necessary

ICE output

In a compiler with debug assertions enabled, this trips: "size mismatch between ABI and layout in TyAndLayout".

Output including layouts, backtraces, and query stack

thread 'rustc' panicked at 'assertion failed: `(left == right)`
  left: `Size(2 bytes)`,
 right: `Size(1 bytes)`: size mismatch between ABI and layout in TyAndLayout {
    ty: test::U,
    layout: Layout {
        size: Size(2 bytes),
        align: AbiAndPrefAlign {
            abi: Align(2 bytes),
            pref: Align(8 bytes),
        },
        abi: Scalar(
            Union {
                value: Int(
                    I8,
                    false,
                ),
            },
        ),
        fields: Union(
            2,
        ),
        largest_niche: None,
        variants: Single {
            index: 0,
        },
    },
}', compiler/rustc_ty_utils/src/layout_sanity_check.rs:72:21
stack backtrace:
   0:        0x1106b5291 - <std::sys_common::backtrace::_print::DisplayBacktrace as core::fmt::Display>::fmt::ha861de675ede8b0c
   1:        0x110739448 - core::fmt::write::hda6b0e10b55724fb
   2:        0x1106c3f28 - std::io::Write::write_fmt::hdf206c4f52d49905
   3:        0x1106b5082 - std::sys_common::backtrace::print::h34f569a9c7a99a9f
   4:        0x1106ba405 - std::panicking::default_hook::{{closure}}::hda4eceb51b014a4b
   5:        0x1106ba1e7 - std::panicking::default_hook::he3b91b4302671d36
   6:        0x11fee8fa8 - rustc_driver[800c97195df9dd7a]::DEFAULT_HOOK::{closure#0}::{closure#0}
   7:        0x1106baac6 - std::panicking::rust_panic_with_hook::he8e29b5de756633a
   8:        0x1106c6dc3 - std::panicking::begin_panic_handler::{{closure}}::hdf4593bcdd333004
   9:        0x1106c6cf8 - std::sys_common::backtrace::__rust_end_short_backtrace::h574e2faa7e4a189e
  10:        0x1106ba4d8 - _rust_begin_unwind
  11:        0x110756ca3 - core::panicking::panic_fmt::h852bdf3f14372e73
  12:        0x110738325 - core::panicking::assert_failed_inner::h6aa04f268f2607ae
  13:        0x124f7363e - core[63810368375d8c35]::panicking::assert_failed::<rustc_target[44d477e4461259e2]::abi::Size, rustc_target[44d477e4461259e2]::abi::Size>
  14:        0x122730731 - rustc_ty_utils[335bf625919b7879]::layout_sanity_check::sanity_check_layout
  15:        0x1226e6341 - rustc_ty_utils[335bf625919b7879]::layout::layout_of
  16:        0x123b77537 - rustc_query_system[9c2b8b59a29958f0]::query::plumbing::get_query::<rustc_query_impl[e3f63d70ae94933f]::queries::layout_of, rustc_query_impl[e3f63d70ae94933f]::plumbing::QueryCtxt>
  17:        0x123e5c721 - <rustc_query_impl[e3f63d70ae94933f]::Queries as rustc_middle[8a1cca0694b55532]::ty::query::QueryEngine>::layout_of
  18:        0x122702dfb - <rustc_middle[8a1cca0694b55532]::ty::layout::LayoutCx<rustc_middle[8a1cca0694b55532]::ty::context::TyCtxt> as rustc_middle[8a1cca0694b55532]::ty::layout::LayoutOf>::layout_of
  19:        0x122701c71 - <core[63810368375d8c35]::iter::adapters::map::Map<core[63810368375d8c35]::slice::iter::Iter<rustc_middle[8a1cca0694b55532]::ty::FieldDef>, rustc_ty_utils[335bf625919b7879]::layout::layout_of_uncached::{closure#5}::{closure#0}> as core[63810368375d8c35]::iter::traits::iterator::Iterator>::try_fold::<(), <core[63810368375d8c35]::iter::adapters::GenericShunt<core[63810368375d8c35]::iter::adapters::map::Map<core[63810368375d8c35]::slice::iter::Iter<rustc_middle[8a1cca0694b55532]::ty::FieldDef>, rustc_ty_utils[335bf625919b7879]::layout::layout_of_uncached::{closure#5}::{closure#0}>, core[63810368375d8c35]::result::Result<core[63810368375d8c35]::convert::Infallible, rustc_middle[8a1cca0694b55532]::ty::layout::LayoutError>> as core[63810368375d8c35]::iter::traits::iterator::Iterator>::try_fold<(), core[63810368375d8c35]::iter::traits::iterator::Iterator::try_for_each::call<rustc_target[44d477e4461259e2]::abi::TyAndLayout<rustc_middle[8a1cca0694b55532]::ty::Ty>, core[63810368375d8c35]::ops::control_flow::ControlFlow<rustc_target[44d477e4461259e2]::abi::TyAndLayout<rustc_middle[8a1cca0694b55532]::ty::Ty>>, core[63810368375d8c35]::ops::control_flow::ControlFlow<rustc_target[44d477e4461259e2]::abi::TyAndLayout<rustc_middle[8a1cca0694b55532]::ty::Ty>>::Break>::{closure#0}, core[63810368375d8c35]::ops::control_flow::ControlFlow<rustc_target[44d477e4461259e2]::abi::TyAndLayout<rustc_middle[8a1cca0694b55532]::ty::Ty>>>::{closure#0}, core[63810368375d8c35]::ops::control_flow::ControlFlow<core[63810368375d8c35]::ops::control_flow::ControlFlow<rustc_target[44d477e4461259e2]::abi::TyAndLayout<rustc_middle[8a1cca0694b55532]::ty::Ty>>>>
  20:        0x1226cea5c - <core[63810368375d8c35]::iter::adapters::GenericShunt<core[63810368375d8c35]::iter::adapters::map::Map<core[63810368375d8c35]::slice::iter::Iter<rustc_middle[8a1cca0694b55532]::ty::FieldDef>, rustc_ty_utils[335bf625919b7879]::layout::layout_of_uncached::{closure#5}::{closure#0}>, core[63810368375d8c35]::result::Result<core[63810368375d8c35]::convert::Infallible, rustc_middle[8a1cca0694b55532]::ty::layout::LayoutError>> as core[63810368375d8c35]::iter::traits::iterator::Iterator>::next
  21:        0x12273929e - <alloc[9c4954bf8315fe26]::vec::Vec<rustc_target[44d477e4461259e2]::abi::TyAndLayout<rustc_middle[8a1cca0694b55532]::ty::Ty>> as alloc[9c4954bf8315fe26]::vec::spec_from_iter::SpecFromIter<rustc_target[44d477e4461259e2]::abi::TyAndLayout<rustc_middle[8a1cca0694b55532]::ty::Ty>, core[63810368375d8c35]::iter::adapters::GenericShunt<core[63810368375d8c35]::iter::adapters::map::Map<core[63810368375d8c35]::slice::iter::Iter<rustc_middle[8a1cca0694b55532]::ty::FieldDef>, rustc_ty_utils[335bf625919b7879]::layout::layout_of_uncached::{closure#5}::{closure#0}>, core[63810368375d8c35]::result::Result<core[63810368375d8c35]::convert::Infallible, rustc_middle[8a1cca0694b55532]::ty::layout::LayoutError>>>>::from_iter
  22:        0x1226ce089 - core[63810368375d8c35]::iter::adapters::try_process::<core[63810368375d8c35]::iter::adapters::map::Map<core[63810368375d8c35]::slice::iter::Iter<rustc_middle[8a1cca0694b55532]::ty::FieldDef>, rustc_ty_utils[335bf625919b7879]::layout::layout_of_uncached::{closure#5}::{closure#0}>, rustc_target[44d477e4461259e2]::abi::TyAndLayout<rustc_middle[8a1cca0694b55532]::ty::Ty>, core[63810368375d8c35]::result::Result<core[63810368375d8c35]::convert::Infallible, rustc_middle[8a1cca0694b55532]::ty::layout::LayoutError>, <core[63810368375d8c35]::result::Result<alloc[9c4954bf8315fe26]::vec::Vec<rustc_target[44d477e4461259e2]::abi::TyAndLayout<rustc_middle[8a1cca0694b55532]::ty::Ty>>, rustc_middle[8a1cca0694b55532]::ty::layout::LayoutError> as core[63810368375d8c35]::iter::traits::collect::FromIterator<core[63810368375d8c35]::result::Result<rustc_target[44d477e4461259e2]::abi::TyAndLayout<rustc_middle[8a1cca0694b55532]::ty::Ty>, rustc_middle[8a1cca0694b55532]::ty::layout::LayoutError>>>::from_iter<core[63810368375d8c35]::iter::adapters::map::Map<core[63810368375d8c35]::slice::iter::Iter<rustc_middle[8a1cca0694b55532]::ty::FieldDef>, rustc_ty_utils[335bf625919b7879]::layout::layout_of_uncached::{closure#5}::{closure#0}>>::{closure#0}, alloc[9c4954bf8315fe26]::vec::Vec<rustc_target[44d477e4461259e2]::abi::TyAndLayout<rustc_middle[8a1cca0694b55532]::ty::Ty>>>
  23:        0x122701b61 - <core[63810368375d8c35]::iter::adapters::map::Map<core[63810368375d8c35]::slice::iter::Iter<rustc_middle[8a1cca0694b55532]::ty::VariantDef>, rustc_ty_utils[335bf625919b7879]::layout::layout_of_uncached::{closure#5}> as core[63810368375d8c35]::iter::traits::iterator::Iterator>::try_fold::<(), <core[63810368375d8c35]::iter::adapters::GenericShunt<core[63810368375d8c35]::iter::adapters::map::Map<core[63810368375d8c35]::slice::iter::Iter<rustc_middle[8a1cca0694b55532]::ty::VariantDef>, rustc_ty_utils[335bf625919b7879]::layout::layout_of_uncached::{closure#5}>, core[63810368375d8c35]::result::Result<core[63810368375d8c35]::convert::Infallible, rustc_middle[8a1cca0694b55532]::ty::layout::LayoutError>> as core[63810368375d8c35]::iter::traits::iterator::Iterator>::try_fold<(), core[63810368375d8c35]::iter::traits::iterator::Iterator::try_for_each::call<alloc[9c4954bf8315fe26]::vec::Vec<rustc_target[44d477e4461259e2]::abi::TyAndLayout<rustc_middle[8a1cca0694b55532]::ty::Ty>>, core[63810368375d8c35]::ops::control_flow::ControlFlow<alloc[9c4954bf8315fe26]::vec::Vec<rustc_target[44d477e4461259e2]::abi::TyAndLayout<rustc_middle[8a1cca0694b55532]::ty::Ty>>>, core[63810368375d8c35]::ops::control_flow::ControlFlow<alloc[9c4954bf8315fe26]::vec::Vec<rustc_target[44d477e4461259e2]::abi::TyAndLayout<rustc_middle[8a1cca0694b55532]::ty::Ty>>>::Break>::{closure#0}, core[63810368375d8c35]::ops::control_flow::ControlFlow<alloc[9c4954bf8315fe26]::vec::Vec<rustc_target[44d477e4461259e2]::abi::TyAndLayout<rustc_middle[8a1cca0694b55532]::ty::Ty>>>>::{closure#0}, core[63810368375d8c35]::ops::control_flow::ControlFlow<core[63810368375d8c35]::ops::control_flow::ControlFlow<alloc[9c4954bf8315fe26]::vec::Vec<rustc_target[44d477e4461259e2]::abi::TyAndLayout<rustc_middle[8a1cca0694b55532]::ty::Ty>>>>>
  24:        0x1226ce9bd - <core[63810368375d8c35]::iter::adapters::GenericShunt<core[63810368375d8c35]::iter::adapters::map::Map<core[63810368375d8c35]::slice::iter::Iter<rustc_middle[8a1cca0694b55532]::ty::VariantDef>, rustc_ty_utils[335bf625919b7879]::layout::layout_of_uncached::{closure#5}>, core[63810368375d8c35]::result::Result<core[63810368375d8c35]::convert::Infallible, rustc_middle[8a1cca0694b55532]::ty::layout::LayoutError>> as core[63810368375d8c35]::iter::traits::iterator::Iterator>::next
  25:        0x1227387a8 - <alloc[9c4954bf8315fe26]::vec::Vec<alloc[9c4954bf8315fe26]::vec::Vec<rustc_target[44d477e4461259e2]::abi::TyAndLayout<rustc_middle[8a1cca0694b55532]::ty::Ty>>> as alloc[9c4954bf8315fe26]::vec::spec_from_iter::SpecFromIter<alloc[9c4954bf8315fe26]::vec::Vec<rustc_target[44d477e4461259e2]::abi::TyAndLayout<rustc_middle[8a1cca0694b55532]::ty::Ty>>, core[63810368375d8c35]::iter::adapters::GenericShunt<core[63810368375d8c35]::iter::adapters::map::Map<core[63810368375d8c35]::slice::iter::Iter<rustc_middle[8a1cca0694b55532]::ty::VariantDef>, rustc_ty_utils[335bf625919b7879]::layout::layout_of_uncached::{closure#5}>, core[63810368375d8c35]::result::Result<core[63810368375d8c35]::convert::Infallible, rustc_middle[8a1cca0694b55532]::ty::layout::LayoutError>>>>::from_iter
  26:        0x1226cdfb9 - core[63810368375d8c35]::iter::adapters::try_process::<core[63810368375d8c35]::iter::adapters::map::Map<core[63810368375d8c35]::slice::iter::Iter<rustc_middle[8a1cca0694b55532]::ty::VariantDef>, rustc_ty_utils[335bf625919b7879]::layout::layout_of_uncached::{closure#5}>, alloc[9c4954bf8315fe26]::vec::Vec<rustc_target[44d477e4461259e2]::abi::TyAndLayout<rustc_middle[8a1cca0694b55532]::ty::Ty>>, core[63810368375d8c35]::result::Result<core[63810368375d8c35]::convert::Infallible, rustc_middle[8a1cca0694b55532]::ty::layout::LayoutError>, <core[63810368375d8c35]::result::Result<rustc_index[79a26d8f822ca42d]::vec::IndexVec<rustc_target[44d477e4461259e2]::abi::VariantIdx, alloc[9c4954bf8315fe26]::vec::Vec<rustc_target[44d477e4461259e2]::abi::TyAndLayout<rustc_middle[8a1cca0694b55532]::ty::Ty>>>, rustc_middle[8a1cca0694b55532]::ty::layout::LayoutError> as core[63810368375d8c35]::iter::traits::collect::FromIterator<core[63810368375d8c35]::result::Result<alloc[9c4954bf8315fe26]::vec::Vec<rustc_target[44d477e4461259e2]::abi::TyAndLayout<rustc_middle[8a1cca0694b55532]::ty::Ty>>, rustc_middle[8a1cca0694b55532]::ty::layout::LayoutError>>>::from_iter<core[63810368375d8c35]::iter::adapters::map::Map<core[63810368375d8c35]::slice::iter::Iter<rustc_middle[8a1cca0694b55532]::ty::VariantDef>, rustc_ty_utils[335bf625919b7879]::layout::layout_of_uncached::{closure#5}>>::{closure#0}, rustc_index[79a26d8f822ca42d]::vec::IndexVec<rustc_target[44d477e4461259e2]::abi::VariantIdx, alloc[9c4954bf8315fe26]::vec::Vec<rustc_target[44d477e4461259e2]::abi::TyAndLayout<rustc_middle[8a1cca0694b55532]::ty::Ty>>>>
  27:        0x1226dc9cb - rustc_ty_utils[335bf625919b7879]::layout::layout_of_uncached
  28:        0x1226e6290 - rustc_ty_utils[335bf625919b7879]::layout::layout_of
  29:        0x123b77537 - rustc_query_system[9c2b8b59a29958f0]::query::plumbing::get_query::<rustc_query_impl[e3f63d70ae94933f]::queries::layout_of, rustc_query_impl[e3f63d70ae94933f]::plumbing::QueryCtxt>
  30:        0x123e5c721 - <rustc_query_impl[e3f63d70ae94933f]::Queries as rustc_middle[8a1cca0694b55532]::ty::query::QueryEngine>::layout_of
  31:        0x124854b58 - <rustc_transmute[32bd9b76539f9694]::layout::tree::rustc::LayoutSummary>::from_ty
  32:        0x124860ccd - <rustc_transmute[32bd9b76539f9694]::layout::tree::Tree<rustc_transmute[32bd9b76539f9694]::layout::rustc::Def, rustc_transmute[32bd9b76539f9694]::layout::rustc::Ref>>::from_ty
  33:        0x12486f9ae - <rustc_transmute[32bd9b76539f9694]::maybe_transmutable::MaybeTransmutableQuery<rustc_middle[8a1cca0694b55532]::ty::Ty, rustc_middle[8a1cca0694b55532]::ty::context::TyCtxt>>::map_layouts::<<rustc_transmute[32bd9b76539f9694]::maybe_transmutable::MaybeTransmutableQuery<rustc_middle[8a1cca0694b55532]::ty::Ty, rustc_middle[8a1cca0694b55532]::ty::context::TyCtxt>>::answer::{closure#0}, rustc_transmute[32bd9b76539f9694]::layout::tree::Tree<rustc_transmute[32bd9b76539f9694]::layout::rustc::Def, rustc_transmute[32bd9b76539f9694]::layout::rustc::Ref>>
  34:        0x124867f15 - <rustc_transmute[32bd9b76539f9694]::maybe_transmutable::MaybeTransmutableQuery<rustc_middle[8a1cca0694b55532]::ty::Ty, rustc_middle[8a1cca0694b55532]::ty::context::TyCtxt>>::answer
  35:        0x124864f01 - <rustc_transmute[32bd9b76539f9694]::rustc::TransmuteTypeEnv>::is_transmutable
  36:        0x1246a3416 - <rustc_trait_selection[96165f1221266323]::traits::select::SelectionContext>::confirm_candidate
  37:        0x1246674d5 - <rustc_infer[8f07edc99fd14f09]::infer::InferCtxt>::probe::<core[63810368375d8c35]::result::Result<rustc_middle[8a1cca0694b55532]::traits::select::EvaluationResult, rustc_middle[8a1cca0694b55532]::traits::select::OverflowError>, <rustc_trait_selection[96165f1221266323]::traits::select::SelectionContext>::evaluation_probe<<rustc_trait_selection[96165f1221266323]::traits::select::SelectionContext>::evaluate_candidate::{closure#0}::{closure#0}>::{closure#0}>
  38:        0x1247faed3 - <rustc_trait_selection[96165f1221266323]::traits::select::SelectionContext>::evaluation_probe::<<rustc_trait_selection[96165f1221266323]::traits::select::SelectionContext>::evaluate_candidate::{closure#0}::{closure#0}>
  39:        0x1246b438b - <rustc_trait_selection[96165f1221266323]::traits::select::SelectionContext>::evaluate_candidate
  40:        0x124699810 - <rustc_trait_selection[96165f1221266323]::traits::select::SelectionContext>::evaluate_stack
  41:        0x1247ad3a4 - <rustc_query_system[9c2b8b59a29958f0]::dep_graph::graph::DepGraph<rustc_middle[8a1cca0694b55532]::dep_graph::dep_node::DepKind>>::with_anon_task::<rustc_middle[8a1cca0694b55532]::ty::context::TyCtxt, <rustc_trait_selection[96165f1221266323]::traits::select::SelectionContext>::in_task<<rustc_trait_selection[96165f1221266323]::traits::select::SelectionContext>::evaluate_trait_predicate_recursively::{closure#0}::{closure#2}, core[63810368375d8c35]::result::Result<rustc_middle[8a1cca0694b55532]::traits::select::EvaluationResult, rustc_middle[8a1cca0694b55532]::traits::select::OverflowError>>::{closure#0}, core[63810368375d8c35]::result::Result<rustc_middle[8a1cca0694b55532]::traits::select::EvaluationResult, rustc_middle[8a1cca0694b55532]::traits::select::OverflowError>>
  42:        0x1247fb0cb - <rustc_trait_selection[96165f1221266323]::traits::select::SelectionContext>::in_task::<<rustc_trait_selection[96165f1221266323]::traits::select::SelectionContext>::evaluate_trait_predicate_recursively::{closure#0}::{closure#2}, core[63810368375d8c35]::result::Result<rustc_middle[8a1cca0694b55532]::traits::select::EvaluationResult, rustc_middle[8a1cca0694b55532]::traits::select::OverflowError>>
  43:        0x1246b210b - <rustc_trait_selection[96165f1221266323]::traits::select::SelectionContext>::evaluate_trait_predicate_recursively
  44:        0x1246af940 - <rustc_trait_selection[96165f1221266323]::traits::select::SelectionContext>::evaluate_predicate_recursively
  45:        0x124667f49 - <rustc_infer[8f07edc99fd14f09]::infer::InferCtxt>::probe::<core[63810368375d8c35]::result::Result<rustc_middle[8a1cca0694b55532]::traits::select::EvaluationResult, rustc_middle[8a1cca0694b55532]::traits::select::OverflowError>, <rustc_trait_selection[96165f1221266323]::traits::select::SelectionContext>::evaluation_probe<<rustc_trait_selection[96165f1221266323]::traits::select::SelectionContext>::evaluate_root_obligation::{closure#0}>::{closure#0}>
  46:        0x12469945f - <rustc_trait_selection[96165f1221266323]::traits::select::SelectionContext>::evaluate_root_obligation
  47:        0x1235a16ce - rustc_traits[16c39305a736ba01]::evaluate_obligation::evaluate_obligation
  48:        0x123ea5ae6 - <rustc_query_system[9c2b8b59a29958f0]::query::config::QueryVTable<rustc_query_impl[e3f63d70ae94933f]::plumbing::QueryCtxt, rustc_middle[8a1cca0694b55532]::infer::canonical::Canonical<rustc_middle[8a1cca0694b55532]::ty::ParamEnvAnd<rustc_middle[8a1cca0694b55532]::ty::Predicate>>, core[63810368375d8c35]::result::Result<rustc_middle[8a1cca0694b55532]::traits::select::EvaluationResult, rustc_middle[8a1cca0694b55532]::traits::select::OverflowError>>>::compute
  49:        0x123b3c971 - rustc_query_system[9c2b8b59a29958f0]::query::plumbing::get_query::<rustc_query_impl[e3f63d70ae94933f]::queries::evaluate_obligation, rustc_query_impl[e3f63d70ae94933f]::plumbing::QueryCtxt>
  50:        0x123e7f1a4 - <rustc_query_impl[e3f63d70ae94933f]::Queries as rustc_middle[8a1cca0694b55532]::ty::query::QueryEngine>::evaluate_obligation
  51:        0x124805917 - <rustc_infer[8f07edc99fd14f09]::infer::InferCtxt as rustc_trait_selection[96165f1221266323]::traits::query::evaluate_obligation::InferCtxtExt>::evaluate_obligation
  52:        0x124805a6f - <rustc_infer[8f07edc99fd14f09]::infer::InferCtxt as rustc_trait_selection[96165f1221266323]::traits::query::evaluate_obligation::InferCtxtExt>::evaluate_obligation_no_overflow
  53:        0x1247f64e8 - <rustc_trait_selection[96165f1221266323]::traits::fulfill::FulfillProcessor>::process_trait_obligation
  54:        0x1247f4e0f - <rustc_trait_selection[96165f1221266323]::traits::fulfill::FulfillProcessor as rustc_data_structures[8a51262431e07920]::obligation_forest::ObligationProcessor>::process_obligation
  55:        0x1246e69ed - <rustc_data_structures[8a51262431e07920]::obligation_forest::ObligationForest<rustc_trait_selection[96165f1221266323]::traits::fulfill::PendingPredicateObligation>>::process_obligations::<rustc_trait_selection[96165f1221266323]::traits::fulfill::FulfillProcessor>
  56:        0x1247f2e42 - <rustc_trait_selection[96165f1221266323]::traits::fulfill::FulfillmentContext as rustc_infer[8f07edc99fd14f09]::traits::engine::TraitEngine>::select_where_possible
  57:        0x1227b4e73 - <rustc_hir_typeck[5ebbf62125a398cb]::fn_ctxt::FnCtxt>::select_obligations_where_possible::<rustc_hir_typeck[5ebbf62125a398cb]::typeck_with_fallback<rustc_hir_typeck[5ebbf62125a398cb]::typeck_const_arg::{closure#0}>::{closure#1}::{closure#2}>
  58:        0x1228289ff - <rustc_hir_typeck[5ebbf62125a398cb]::fn_ctxt::FnCtxt>::check_argument_types
  59:        0x122807e58 - <rustc_hir_typeck[5ebbf62125a398cb]::fn_ctxt::FnCtxt>::confirm_builtin_call
  60:        0x1228058ad - <rustc_hir_typeck[5ebbf62125a398cb]::fn_ctxt::FnCtxt>::check_call
  61:        0x12286c65f - <rustc_hir_typeck[5ebbf62125a398cb]::fn_ctxt::FnCtxt>::check_expr_kind
  62:        0x12281564f - <rustc_hir_typeck[5ebbf62125a398cb]::fn_ctxt::FnCtxt>::check_expr_with_expectation_and_args
  63:        0x12286b6e4 - <rustc_hir_typeck[5ebbf62125a398cb]::fn_ctxt::FnCtxt>::check_expr_with_expectation
  64:        0x12282ef02 - <rustc_hir_typeck[5ebbf62125a398cb]::fn_ctxt::FnCtxt>::check_stmt
  65:        0x1227b53df - <rustc_hir_typeck[5ebbf62125a398cb]::fn_ctxt::FnCtxt>::with_breakable_ctxt::<<rustc_hir_typeck[5ebbf62125a398cb]::fn_ctxt::FnCtxt>::check_block_with_expected::{closure#0}, ()>
  66:        0x12282f1e0 - <rustc_hir_typeck[5ebbf62125a398cb]::fn_ctxt::FnCtxt>::check_block_with_expected
  67:        0x12286ca41 - <rustc_hir_typeck[5ebbf62125a398cb]::fn_ctxt::FnCtxt>::check_expr_kind
  68:        0x12281564f - <rustc_hir_typeck[5ebbf62125a398cb]::fn_ctxt::FnCtxt>::check_expr_with_expectation_and_args
  69:        0x12286b6e4 - <rustc_hir_typeck[5ebbf62125a398cb]::fn_ctxt::FnCtxt>::check_expr_with_expectation
  70:        0x122816997 - <rustc_hir_typeck[5ebbf62125a398cb]::fn_ctxt::FnCtxt>::check_return_expr
  71:        0x122777c47 - rustc_hir_typeck[5ebbf62125a398cb]::check::check_fn
  72:        0x1227c3710 - <rustc_hir_typeck[5ebbf62125a398cb]::inherited::InheritedBuilder>::enter::<rustc_hir_typeck[5ebbf62125a398cb]::typeck_with_fallback<rustc_hir_typeck[5ebbf62125a398cb]::typeck::{closure#0}>::{closure#1}, &rustc_middle[8a1cca0694b55532]::ty::context::TypeckResults>
  73:        0x1227c66c2 - rustc_hir_typeck[5ebbf62125a398cb]::typeck_with_fallback::<rustc_hir_typeck[5ebbf62125a398cb]::typeck::{closure#0}>
  74:        0x12292d3f9 - rustc_hir_typeck[5ebbf62125a398cb]::typeck
  75:        0x123a49bca - rustc_query_system[9c2b8b59a29958f0]::query::plumbing::try_execute_query::<rustc_query_impl[e3f63d70ae94933f]::plumbing::QueryCtxt, rustc_query_system[9c2b8b59a29958f0]::query::caches::DefaultCache<rustc_span[2af9326393a24b2a]::def_id::LocalDefId, &rustc_middle[8a1cca0694b55532]::ty::context::TypeckResults>>
  76:        0x123b75c7a - rustc_query_system[9c2b8b59a29958f0]::query::plumbing::get_query::<rustc_query_impl[e3f63d70ae94933f]::queries::typeck, rustc_query_impl[e3f63d70ae94933f]::plumbing::QueryCtxt>
  77:        0x123e4047f - <rustc_query_impl[e3f63d70ae94933f]::Queries as rustc_middle[8a1cca0694b55532]::ty::query::QueryEngine>::typeck
  78:        0x1228dd7df - <core[63810368375d8c35]::panic::unwind_safe::AssertUnwindSafe<rustc_data_structures[8a51262431e07920]::sync::par_for_each_in<&[rustc_span[2af9326393a24b2a]::def_id::LocalDefId], <rustc_middle[8a1cca0694b55532]::hir::map::Map>::par_body_owners<rustc_hir_typeck[5ebbf62125a398cb]::typeck_item_bodies::{closure#0}>::{closure#0}>::{closure#0}::{closure#0}> as core[63810368375d8c35]::ops::function::FnOnce<()>>::call_once
  79:        0x1227717e9 - std[6a7b9961a507fa09]::panicking::try::<(), core[63810368375d8c35]::panic::unwind_safe::AssertUnwindSafe<rustc_data_structures[8a51262431e07920]::sync::par_for_each_in<&[rustc_span[2af9326393a24b2a]::def_id::LocalDefId], <rustc_middle[8a1cca0694b55532]::hir::map::Map>::par_body_owners<rustc_hir_typeck[5ebbf62125a398cb]::typeck_item_bodies::{closure#0}>::{closure#0}>::{closure#0}::{closure#0}>>
  80:        0x12292e713 - rustc_data_structures[8a51262431e07920]::sync::par_for_each_in::<&[rustc_span[2af9326393a24b2a]::def_id::LocalDefId], <rustc_middle[8a1cca0694b55532]::hir::map::Map>::par_body_owners<rustc_hir_typeck[5ebbf62125a398cb]::typeck_item_bodies::{closure#0}>::{closure#0}>
  81:        0x12292d22f - rustc_hir_typeck[5ebbf62125a398cb]::typeck_item_bodies
  82:        0x123a9efe3 - rustc_query_system[9c2b8b59a29958f0]::query::plumbing::try_execute_query::<rustc_query_impl[e3f63d70ae94933f]::plumbing::QueryCtxt, rustc_query_system[9c2b8b59a29958f0]::query::caches::DefaultCache<(), ()>>
  83:        0x123b3b779 - rustc_query_system[9c2b8b59a29958f0]::query::plumbing::get_query::<rustc_query_impl[e3f63d70ae94933f]::queries::typeck_item_bodies, rustc_query_impl[e3f63d70ae94933f]::plumbing::QueryCtxt>
  84:        0x123e3fe17 - <rustc_query_impl[e3f63d70ae94933f]::Queries as rustc_middle[8a1cca0694b55532]::ty::query::QueryEngine>::typeck_item_bodies
  85:        0x122aa37a8 - <rustc_session[3422556dcb6df88d]::session::Session>::time::<(), rustc_hir_analysis[e4fb2be97854ccf3]::check_crate::{closure#7}>
  86:        0x122a53f7e - rustc_hir_analysis[e4fb2be97854ccf3]::check_crate
  87:        0x120093e6a - rustc_interface[2b9f011c4a1d6882]::passes::analysis
  88:        0x123a935cd - rustc_query_system[9c2b8b59a29958f0]::query::plumbing::try_execute_query::<rustc_query_impl[e3f63d70ae94933f]::plumbing::QueryCtxt, rustc_query_system[9c2b8b59a29958f0]::query::caches::DefaultCache<(), core[63810368375d8c35]::result::Result<(), rustc_errors[8c17e79fb1f0a5e4]::ErrorGuaranteed>>>
  89:        0x123b76029 - rustc_query_system[9c2b8b59a29958f0]::query::plumbing::get_query::<rustc_query_impl[e3f63d70ae94933f]::queries::analysis, rustc_query_impl[e3f63d70ae94933f]::plumbing::QueryCtxt>
  90:        0x123e1be17 - <rustc_query_impl[e3f63d70ae94933f]::Queries as rustc_middle[8a1cca0694b55532]::ty::query::QueryEngine>::analysis
  91:        0x11ff5f658 - <rustc_interface[2b9f011c4a1d6882]::passes::QueryContext>::enter::<rustc_driver[800c97195df9dd7a]::run_compiler::{closure#1}::{closure#2}::{closure#3}, core[63810368375d8c35]::result::Result<(), rustc_errors[8c17e79fb1f0a5e4]::ErrorGuaranteed>>
  92:        0x11ff52ff8 - <rustc_interface[2b9f011c4a1d6882]::interface::Compiler>::enter::<rustc_driver[800c97195df9dd7a]::run_compiler::{closure#1}::{closure#2}, core[63810368375d8c35]::result::Result<core[63810368375d8c35]::option::Option<rustc_interface[2b9f011c4a1d6882]::queries::Linker>, rustc_errors[8c17e79fb1f0a5e4]::ErrorGuaranteed>>
  93:        0x11ff4a7db - rustc_span[2af9326393a24b2a]::with_source_map::<core[63810368375d8c35]::result::Result<(), rustc_errors[8c17e79fb1f0a5e4]::ErrorGuaranteed>, rustc_interface[2b9f011c4a1d6882]::interface::run_compiler<core[63810368375d8c35]::result::Result<(), rustc_errors[8c17e79fb1f0a5e4]::ErrorGuaranteed>, rustc_driver[800c97195df9dd7a]::run_compiler::{closure#1}>::{closure#0}::{closure#1}>
  94:        0x11ff5109a - <scoped_tls[a4e3500caacc884c]::ScopedKey<rustc_span[2af9326393a24b2a]::SessionGlobals>>::set::<rustc_interface[2b9f011c4a1d6882]::interface::run_compiler<core[63810368375d8c35]::result::Result<(), rustc_errors[8c17e79fb1f0a5e4]::ErrorGuaranteed>, rustc_driver[800c97195df9dd7a]::run_compiler::{closure#1}>::{closure#0}, core[63810368375d8c35]::result::Result<(), rustc_errors[8c17e79fb1f0a5e4]::ErrorGuaranteed>>
  95:        0x11ff6b260 - std[6a7b9961a507fa09]::sys_common::backtrace::__rust_begin_short_backtrace::<rustc_interface[2b9f011c4a1d6882]::util::run_in_thread_pool_with_globals<rustc_interface[2b9f011c4a1d6882]::interface::run_compiler<core[63810368375d8c35]::result::Result<(), rustc_errors[8c17e79fb1f0a5e4]::ErrorGuaranteed>, rustc_driver[800c97195df9dd7a]::run_compiler::{closure#1}>::{closure#0}, core[63810368375d8c35]::result::Result<(), rustc_errors[8c17e79fb1f0a5e4]::ErrorGuaranteed>>::{closure#0}::{closure#0}, core[63810368375d8c35]::result::Result<(), rustc_errors[8c17e79fb1f0a5e4]::ErrorGuaranteed>>
  96:        0x11ff4550d - std[6a7b9961a507fa09]::panicking::try::<core[63810368375d8c35]::result::Result<(), rustc_errors[8c17e79fb1f0a5e4]::ErrorGuaranteed>, core[63810368375d8c35]::panic::unwind_safe::AssertUnwindSafe<<std[6a7b9961a507fa09]::thread::Builder>::spawn_unchecked_<rustc_interface[2b9f011c4a1d6882]::util::run_in_thread_pool_with_globals<rustc_interface[2b9f011c4a1d6882]::interface::run_compiler<core[63810368375d8c35]::result::Result<(), rustc_errors[8c17e79fb1f0a5e4]::ErrorGuaranteed>, rustc_driver[800c97195df9dd7a]::run_compiler::{closure#1}>::{closure#0}, core[63810368375d8c35]::result::Result<(), rustc_errors[8c17e79fb1f0a5e4]::ErrorGuaranteed>>::{closure#0}::{closure#0}, core[63810368375d8c35]::result::Result<(), rustc_errors[8c17e79fb1f0a5e4]::ErrorGuaranteed>>::{closure#1}::{closure#0}>>
  97:        0x11ff6cd90 - <<std[6a7b9961a507fa09]::thread::Builder>::spawn_unchecked_<rustc_interface[2b9f011c4a1d6882]::util::run_in_thread_pool_with_globals<rustc_interface[2b9f011c4a1d6882]::interface::run_compiler<core[63810368375d8c35]::result::Result<(), rustc_errors[8c17e79fb1f0a5e4]::ErrorGuaranteed>, rustc_driver[800c97195df9dd7a]::run_compiler::{closure#1}>::{closure#0}, core[63810368375d8c35]::result::Result<(), rustc_errors[8c17e79fb1f0a5e4]::ErrorGuaranteed>>::{closure#0}::{closure#0}, core[63810368375d8c35]::result::Result<(), rustc_errors[8c17e79fb1f0a5e4]::ErrorGuaranteed>>::{closure#1} as core[63810368375d8c35]::ops::function::FnOnce<()>>::call_once::{shim:vtable#0}
  98:        0x110692adb - <alloc::boxed::Box<F,A> as core::ops::function::FnOnce<Args>>::call_once::hdf7bfd1e0a7b9c83
  99:        0x1106a7d5f - std::sys::unix::thread::Thread::new::thread_start::h5ad5524ac09352ab
 100:     0x7ff81000f4e1 - __pthread_start

error: internal compiler error: unexpected panic

note: 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: rustc 1.66.0-dev running on x86_64-apple-darwin

query stack during panic:
#0 [layout_of] computing layout of `test::U`
#1 [layout_of] computing layout of `test::S`
#2 [evaluate_obligation] evaluating trait selection obligation `u128: core::mem::transmutability::BikeshedIntrinsicFrom<test::S, assert::Context, core::mem::transmutability::Assume { alignment: false, lifetimes: false, safety: false, validity: false }>`
#3 [typeck] type-checking `test`
#4 [typeck_item_bodies] type-checking all item bodies
#5 [analysis] running analysis passes on this crate
end of query stack

Version

Built from 44fcfb0 (master some time yesterday, 2022-10-26)

config.toml

# Includes one of the default files in src/bootstrap/defaults
profile = "compiler"
changelog-seen = 2

[llvm]
download-ci-llvm = true     # Download a pre-built LLVM?
assertions = true           # LLVM assertions on?

[rust]
incremental = true          # Build rustc with incremental compilation?
debug-assertions = true

CC @jswrenn, who might understand the BikeshedIntrinsicFrom parts of the testcase

CC @RalfJung, who added the assertion

Yeah that's definitely an incorrect layout -- Scalar ABI types may not have padding.

This is unrelated to BikeshedIntrinsicFrom, the following already shows a bad layout:

#![feature(rustc_attrs)]

#[rustc_layout(debug)]
pub union U {
    a: [u16; 0],
    b: u8,
}

Cc @eddyb @oli-obk

Indeed, the assertion trips with that smaller input as well.

Yeah this is bad, basically another misuse of is_zst...

rust/compiler/rustc_ty_utils/src/layout.rs

Lines 674 to 678 in dc05f60

    
           // If all non-ZST fields have the same ABI, forward this ABI 
        
           if optimize && !field.is_zst() { 
        
               // Discard valid range information and allow undef 
        
               let field_abi = match field.abi { 
        
                   Abi::Scalar(x) => Abi::Scalar(x.to_union()),

(it should either be size=0 align=1 or check that the ZSTs being ignored don't raise the alignment beyond the single-non-ZST-field, but that's harder to get right)

	// If all non-ZST fields have the same ABI, forward this ABI
	if optimize && !field.is_zst() {
	// Discard valid range information and allow undef
	let field_abi = match field.abi {
	Abi::Scalar(x) => Abi::Scalar(x.to_union()),

Layout sanity failed check: "size mismatch between ABI and layout in TyAndLayout". Zero size array in union.

Code

ICE output

Version