Array patterns and tuple patterns don't properly check for Sized

The code below shouldn't compile, since it creates a variable y of type &[str; 2]. This type is invalid, since str is not Sized. However, it compiles without errors.

// Compiles without errors
fn main() {
    // y has type &[str; 2]
    let ref y @ [ref x, _];
    x = "";
}

I can also create a variable of type [str; 2] without a reference indirection.

// Compiles without errors
fn main() {
    // y has type [str; 2]
    let [[ref x, _], y];
    x = "";
}

Furthermore, if the array has length 0, I can even initialize the variable, and take its address.

// Compiles without errors
fn main() {
    // y has type [str; 0]
    let [[ref x], [_, y @ ..]];
    x = "";
    y = [];
    let z = &raw const y as *const ();
    println!("{z:p}");
}

Here are some other variants of this weirdness:

Code using tuple patterns instead of array patterns

// Compiles without errors
fn main() {
    // z has type &(str, str)
    let ref z @ (ref x, ref y);
    x = "";
    y = "";
}

Code that prints type information about this invalid type

// Compiles and runs without errors

trait TypeInfo: std::any::Any {
    fn type_name(&self) -> &'static str {
        std::any::type_name::<Self>()
    }
    fn size(&self) -> usize {
        size_of_val(self)
    }
    fn align(&self) -> usize {
        align_of_val(self)
    }
}
impl<T: ?Sized + 'static> TypeInfo for T {}

fn main() {
    // y has type [[i32]; 0]
    let [[ref x], [_, y @ ..]];
    x = &[] as &[i32];
    y = [];
    let z: &dyn TypeInfo = &y;
    assert_eq!("[[i32]; 0]", z.type_name());
    assert_eq!(0, z.size());
    assert_eq!(4, z.align());
    println!("{:?}", z.type_id());
}

Code that stores this invalid type in a const

const A: &dyn Send = {
    // y has type [str; 0]
    let [[ref x], [_, y @ ..]];
    x = "";
    y = [];
    &{y}
};

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Reproducible on the playground with version 1.94.0-nightly (2025-12-14 0208ee09be465f69005a)

We should probably check wf of non-trivial patterns.

Or ideally, just check wf of all let statements 🤷 cc @rust-lang/types if one of u wants to look into this

This can also cause an ICE.

#![expect(unused)]

trait Trait {}
impl<T: ?Sized> Trait for T {}

fn main() {
    // x has type [(str, str); 0]
    let [[(ref a, ref b)], [_, x @ ..]];
    a = "";
    b = "";
    x = [];
    let _: &dyn Trait = &x;
}

Error output

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 (str, str): TyAndLayout {
                                    ty: str,
                                    layout: Layout {
                                        size: Size(0 bytes),
                                        align: AbiAlign {
                                            abi: Align(1 bytes),
                                        },
                                        backend_repr: Memory {
                                            sized: false,
                                        },
                                        fields: Array {
                                            stride: Size(1 bytes),
                                            count: 0,
                                        },
                                        largest_niche: None,
                                        uninhabited: false,
                                        variants: Single {
                                            index: 0,
                                        },
                                        max_repr_align: None,
                                        unadjusted_abi_align: Align(1 bytes),
                                        randomization_seed: 13921294091492507170,
                                    },
                                }
  |
  = note: delayed at /rustc-dev/a293cc4af8b26701c42738381c0c6f9d2ba881e0/compiler/rustc_ty_utils/src/layout.rs:104:32
             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::{closure#3}
             6: rustc_ty_utils::layout::layout_of_uncached
             7: rustc_ty_utils::layout::layout_of
             8: rustc_query_impl::plumbing::__rust_begin_short_backtrace::<rustc_query_impl::query_impl::layout_of::make_query_vtable::{closure#1}::{closure#0}, rustc_middle::query::erase::ErasedData<[u8; 16]>>
             9: rustc_query_system::query::plumbing::try_execute_query::<rustc_query_impl::SemiDynamicQueryDispatcher<rustc_query_system::query::caches::DefaultCache<rustc_middle::ty::PseudoCanonicalInput<rustc_middle::ty::Ty>, rustc_middle::query::erase::ErasedData<[u8; 16]>>, false, true, false>, false>
            10: rustc_query_impl::query_impl::layout_of::get_query_non_incr::__rust_end_short_backtrace
            11: <rustc_middle::ty::layout::LayoutCx as rustc_middle::ty::layout::LayoutOf>::spanned_layout_of
            12: rustc_ty_utils::layout::layout_of_uncached
            13: rustc_ty_utils::layout::layout_of
            14: rustc_query_impl::plumbing::__rust_begin_short_backtrace::<rustc_query_impl::query_impl::layout_of::make_query_vtable::{closure#1}::{closure#0}, rustc_middle::query::erase::ErasedData<[u8; 16]>>
            15: rustc_query_system::query::plumbing::try_execute_query::<rustc_query_impl::SemiDynamicQueryDispatcher<rustc_query_system::query::caches::DefaultCache<rustc_middle::ty::PseudoCanonicalInput<rustc_middle::ty::Ty>, rustc_middle::query::erase::ErasedData<[u8; 16]>>, false, true, false>, false>
            16: rustc_query_impl::query_impl::layout_of::get_query_non_incr::__rust_end_short_backtrace
            17: <rustc_mir_transform::known_panics_lint::KnownPanicsLint as rustc_mir_transform::pass_manager::MirLint>::run_lint
            18: rustc_mir_transform::run_analysis_to_runtime_passes
            19: rustc_mir_transform::mir_drops_elaborated_and_const_checked
            20: rustc_query_impl::plumbing::__rust_begin_short_backtrace::<rustc_query_impl::query_impl::mir_drops_elaborated_and_const_checked::make_query_vtable::{closure#1}::{closure#0}, rustc_middle::query::erase::ErasedData<[u8; 8]>>
            21: rustc_query_system::query::plumbing::try_execute_query::<rustc_query_impl::SemiDynamicQueryDispatcher<rustc_data_structures::vec_cache::VecCache<rustc_span::def_id::LocalDefId, rustc_middle::query::erase::ErasedData<[u8; 8]>, rustc_query_system::dep_graph::graph::DepNodeIndex>, false, false, false>, false>
            22: rustc_query_impl::query_impl::mir_drops_elaborated_and_const_checked::get_query_non_incr::__rust_end_short_backtrace
            23: <rustc_middle::ty::context::TyCtxt>::par_hir_body_owners::<rustc_interface::passes::run_required_analyses::{closure#1}::{closure#0}>::{closure#0}
            24: rustc_interface::passes::analysis
            25: rustc_query_impl::plumbing::__rust_begin_short_backtrace::<rustc_query_impl::query_impl::analysis::make_query_vtable::{closure#1}::{closure#0}, rustc_middle::query::erase::ErasedData<[u8; 0]>>
            26: rustc_query_system::query::plumbing::try_execute_query::<rustc_query_impl::SemiDynamicQueryDispatcher<rustc_query_system::query::caches::SingleCache<rustc_middle::query::erase::ErasedData<[u8; 0]>>, false, false, false>, false>
            27: rustc_query_impl::query_impl::analysis::get_query_non_incr::__rust_end_short_backtrace
            28: <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} as core::ops::function::FnOnce<(&rustc_session::session::Session, rustc_middle::ty::context::CurrentGcx, alloc::sync::Arc<rustc_data_structures::jobserver::Proxy>, &std::sync::once_lock::OnceLock<rustc_middle::ty::context::GlobalCtxt>, &rustc_data_structures::sync::worker_local::WorkerLocal<rustc_middle::arena::Arena>, &rustc_data_structures::sync::worker_local::WorkerLocal<rustc_hir::Arena>, rustc_driver_impl::run_compiler::{closure#0}::{closure#2})>>::call_once::{shim:vtable#0}
            29: rustc_interface::interface::run_compiler::<(), rustc_driver_impl::run_compiler::{closure#0}>::{closure#1}
            30: 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}, ()>
            31: <std::thread::lifecycle::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}
            32: <std::sys::thread::unix::Thread>::new::thread_start
            33: <unknown>
            34: clone
          

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 `/playground/rustc-ice-2026-01-31T04_07_12-50.txt` to your bug report

note: rustc 1.95.0-nightly (a293cc4af 2026-01-30) running on x86_64-unknown-linux-gnu

note: compiler flags: --crate-type bin -C embed-bitcode=no -C codegen-units=1 -C debuginfo=2

note: some of the compiler flags provided by cargo are hidden

query stack during panic:
end of query stack

A slightly smaller code snippet that still causes an ICE:

#[allow(unused)]

fn main() {
    let [(ref a, b), x];
    a = "";
    b = 5;
}

Rollup merge of rust-lang#157013 - s7tya:fix-let-pat-inferred-wf, r=lcnr

Unrolled build for #157013

Reopening due to a revert in #157795

the middle example from #150040 (comment) will crash with --emit=mir

thread 'rustc' (2738477) panicked at /rustc-dev/7608eb7b07eaf93f16d7cf5bcb2098eca87503df/compiler/rustc_const_eval/src/interpret/projection.rs:167:13:
assertion failed: !base.layout().is_sized()

Finally fixed in #157841

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Array patterns and tuple patterns don't properly check for Sized #150040

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Array patterns and tuple patterns don't properly check for Sized #150040

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lcnr commented on Dec 16, 2025

theemathas commented on Jan 31, 2026

s7tya commented on May 27, 2026

theemathas commented on Jun 12, 2026

matthiaskrgr commented on Aug 6, 2026

s7tya commented on Aug 12, 2026

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