ICE using `repr(align(…))` type as trait object receiver (arbitrary `self`-type)

[steffahn]

Code

#![feature(unsize, dispatch_from_dyn, arbitrary_self_types)]

use std::marker::Unsize;
use std::ops::{Deref, DispatchFromDyn};

#[repr(align(16))]
pub struct MyPointer<T: ?Sized>(*const T);

impl<T: ?Sized + Unsize<U>, U: ?Sized> DispatchFromDyn<MyPointer<U>> for MyPointer<T> {}
impl<T: ?Sized> Deref for MyPointer<T> {
    type Target = T;
    fn deref(&self) -> &T {
        unimplemented!()
    }
}

pub trait Trait {
    fn foo(self: MyPointer<Self>) {}
}

// make sure some usage of `<dyn Trait>::foo` makes it to codegen
pub fn user() -> *const () {
    <dyn Trait>::foo as *const ()
}

(playground)

Error output

error: internal compiler error: compiler/rustc_ty_utils/src/abi.rs:740:18: receiver type has unsupported layout: TyAndLayout { ty: MyPointer<dyn Trait>, layout: Layout { size: Size(16 bytes), align: AbiAndPrefAlign { abi: Align(16 bytes), pref: Align(16 bytes) }, backend_repr: Memory { sized: true }, fields: Arbitrary { offsets: [Size(0 bytes)], memory_index: [0] }, largest_niche: Some(Niche { offset: Size(8 bytes), value: Pointer(AddressSpace(0)), valid_range: 1..=18446744073709551615 }), uninhabited: false, variants: Single { index: 0 }, max_repr_align: Some(Align(16 bytes)), unadjusted_abi_align: Align(8 bytes), randomization_seed: 7312131278044645289 } }


thread 'rustc' panicked at compiler/rustc_ty_utils/src/abi.rs:740:18:
Box<dyn Any>
stack backtrace:
   0:     0x770c57633893 - <std::sys::backtrace::BacktraceLock::print::DisplayBacktrace as core::fmt::Display>::fmt::h2fbd06f1ad558926
   1:     0x770c57e05a58 - core::fmt::write::he613d79b06f4b50b
   2:     0x770c5913a2d1 - std::io::Write::write_fmt::h2d558f8849cee296
   3:     0x770c576336f2 - std::sys::backtrace::BacktraceLock::print::h980245f16d2e53c5
   4:     0x770c57635faa - std::panicking::default_hook::{{closure}}::ha8e1870143bb4424
   5:     0x770c57635b2f - std::panicking::default_hook::h510c7e30611e55b6
   6:     0x770c566991ff - std[9e04a37a0a8a4f45]::panicking::update_hook::<alloc[324835f0a3c901e2]::boxed::Box<rustc_driver_impl[8fdf64b2f913ec67]::install_ice_hook::{closure#1}>>::{closure#0}
   7:     0x770c57636823 - std::panicking::rust_panic_with_hook::hf32ade211372445e
   8:     0x770c566d66c1 - std[9e04a37a0a8a4f45]::panicking::begin_panic::<rustc_errors[1bf8457a84dc8be7]::ExplicitBug>::{closure#0}
   9:     0x770c566ca8b6 - std[9e04a37a0a8a4f45]::sys::backtrace::__rust_end_short_backtrace::<std[9e04a37a0a8a4f45]::panicking::begin_panic<rustc_errors[1bf8457a84dc8be7]::ExplicitBug>::{closure#0}, !>
  10:     0x770c566ca89b - std[9e04a37a0a8a4f45]::panicking::begin_panic::<rustc_errors[1bf8457a84dc8be7]::ExplicitBug>
  11:     0x770c566e0071 - <rustc_errors[1bf8457a84dc8be7]::diagnostic::BugAbort as rustc_errors[1bf8457a84dc8be7]::diagnostic::EmissionGuarantee>::emit_producing_guarantee
  12:     0x770c56d1e56a - rustc_middle[77f5a5ad0a03fbe5]::util::bug::opt_span_bug_fmt::<rustc_span[616a7760585f005b]::span_encoding::Span>::{closure#0}
  13:     0x770c56cf97da - rustc_middle[77f5a5ad0a03fbe5]::ty::context::tls::with_opt::<rustc_middle[77f5a5ad0a03fbe5]::util::bug::opt_span_bug_fmt<rustc_span[616a7760585f005b]::span_encoding::Span>::{closure#0}, !>::{closure#0}
  14:     0x770c56cf966b - rustc_middle[77f5a5ad0a03fbe5]::ty::context::tls::with_context_opt::<rustc_middle[77f5a5ad0a03fbe5]::ty::context::tls::with_opt<rustc_middle[77f5a5ad0a03fbe5]::util::bug::opt_span_bug_fmt<rustc_span[616a7760585f005b]::span_encoding::Span>::{closure#0}, !>::{closure#0}, !>
  15:     0x770c5497a4c0 - rustc_middle[77f5a5ad0a03fbe5]::util::bug::bug_fmt
  16:     0x770c58697fd7 - <core[1a8e3f3c1152e72c]::iter::adapters::enumerate::Enumerate<_> as core[1a8e3f3c1152e72c]::iter::traits::iterator::Iterator>::try_fold::enumerate::<rustc_middle[77f5a5ad0a03fbe5]::ty::Ty, (), core[1a8e3f3c1152e72c]::ops::control_flow::ControlFlow<core[1a8e3f3c1152e72c]::ops::control_flow::ControlFlow<rustc_target[f1139571c8f7483e]::callconv::ArgAbi<rustc_middle[77f5a5ad0a03fbe5]::ty::Ty>>>, core[1a8e3f3c1152e72c]::iter::adapters::map::map_try_fold<(usize, rustc_middle[77f5a5ad0a03fbe5]::ty::Ty), core[1a8e3f3c1152e72c]::result::Result<rustc_target[f1139571c8f7483e]::callconv::ArgAbi<rustc_middle[77f5a5ad0a03fbe5]::ty::Ty>, &rustc_middle[77f5a5ad0a03fbe5]::ty::layout::FnAbiError>, (), core[1a8e3f3c1152e72c]::ops::control_flow::ControlFlow<core[1a8e3f3c1152e72c]::ops::control_flow::ControlFlow<rustc_target[f1139571c8f7483e]::callconv::ArgAbi<rustc_middle[77f5a5ad0a03fbe5]::ty::Ty>>>, rustc_ty_utils[7aab6de42c66b8b6]::abi::fn_abi_new_uncached::{closure#3}, <core[1a8e3f3c1152e72c]::iter::adapters::GenericShunt<core[1a8e3f3c1152e72c]::iter::adapters::map::Map<core[1a8e3f3c1152e72c]::iter::adapters::enumerate::Enumerate<core[1a8e3f3c1152e72c]::iter::adapters::chain::Chain<core[1a8e3f3c1152e72c]::iter::adapters::chain::Chain<core[1a8e3f3c1152e72c]::iter::adapters::copied::Copied<core[1a8e3f3c1152e72c]::slice::iter::Iter<rustc_middle[77f5a5ad0a03fbe5]::ty::Ty>>, core[1a8e3f3c1152e72c]::iter::adapters::copied::Copied<core[1a8e3f3c1152e72c]::slice::iter::Iter<rustc_middle[77f5a5ad0a03fbe5]::ty::Ty>>>, core[1a8e3f3c1152e72c]::option::IntoIter<rustc_middle[77f5a5ad0a03fbe5]::ty::Ty>>>, rustc_ty_utils[7aab6de42c66b8b6]::abi::fn_abi_new_uncached::{closure#3}>, core[1a8e3f3c1152e72c]::result::Result<core[1a8e3f3c1152e72c]::convert::Infallible, &rustc_middle[77f5a5ad0a03fbe5]::ty::layout::FnAbiError>> as core[1a8e3f3c1152e72c]::iter::traits::iterator::Iterator>::try_fold<(), core[1a8e3f3c1152e72c]::iter::traits::iterator::Iterator::try_for_each::call<rustc_target[f1139571c8f7483e]::callconv::ArgAbi<rustc_middle[77f5a5ad0a03fbe5]::ty::Ty>, core[1a8e3f3c1152e72c]::ops::control_flow::ControlFlow<rustc_target[f1139571c8f7483e]::callconv::ArgAbi<rustc_middle[77f5a5ad0a03fbe5]::ty::Ty>>, core[1a8e3f3c1152e72c]::ops::control_flow::ControlFlow<rustc_target[f1139571c8f7483e]::callconv::ArgAbi<rustc_middle[77f5a5ad0a03fbe5]::ty::Ty>>::Break>::{closure#0}, core[1a8e3f3c1152e72c]::ops::control_flow::ControlFlow<rustc_target[f1139571c8f7483e]::callconv::ArgAbi<rustc_middle[77f5a5ad0a03fbe5]::ty::Ty>>>::{closure#0}>::{closure#0}>::{closure#0}
  17:     0x770c587c4ee8 - rustc_ty_utils[7aab6de42c66b8b6]::abi::fn_abi_new_uncached
  18:     0x770c587bf392 - rustc_ty_utils[7aab6de42c66b8b6]::abi::fn_abi_of_instance
  19:     0x770c587be818 - rustc_query_impl[fc8387517396db3d]::plumbing::__rust_begin_short_backtrace::<rustc_query_impl[fc8387517396db3d]::query_impl::fn_abi_of_instance::dynamic_query::{closure#2}::{closure#0}, rustc_middle[77f5a5ad0a03fbe5]::query::erase::Erased<[u8; 16usize]>>
  20:     0x770c587bb563 - rustc_query_system[3b7ccee9954445dd]::query::plumbing::try_execute_query::<rustc_query_impl[fc8387517396db3d]::DynamicConfig<rustc_query_system[3b7ccee9954445dd]::query::caches::DefaultCache<rustc_middle[77f5a5ad0a03fbe5]::ty::PseudoCanonicalInput<(rustc_middle[77f5a5ad0a03fbe5]::ty::instance::Instance, &rustc_middle[77f5a5ad0a03fbe5]::ty::list::RawList<(), rustc_middle[77f5a5ad0a03fbe5]::ty::Ty>)>, rustc_middle[77f5a5ad0a03fbe5]::query::erase::Erased<[u8; 16usize]>>, false, false, false>, rustc_query_impl[fc8387517396db3d]::plumbing::QueryCtxt, false>
  21:     0x770c587bb107 - rustc_query_impl[fc8387517396db3d]::query_impl::fn_abi_of_instance::get_query_non_incr::__rust_end_short_backtrace
  22:     0x770c54cfaf46 - <rustc_codegen_ssa[99f2d35fcd5a252c]::mir::FunctionCx<rustc_codegen_llvm[ddc53a90a6190b8a]::builder::GenericBuilder<rustc_codegen_llvm[ddc53a90a6190b8a]::context::FullCx>>>::codegen_terminator
  23:     0x770c58ea9195 - rustc_codegen_ssa[99f2d35fcd5a252c]::mir::codegen_mir::<rustc_codegen_llvm[ddc53a90a6190b8a]::builder::GenericBuilder<rustc_codegen_llvm[ddc53a90a6190b8a]::context::FullCx>>
  24:     0x770c58e8cc9b - rustc_codegen_llvm[ddc53a90a6190b8a]::base::compile_codegen_unit::module_codegen
  25:     0x770c58fbf715 - <rustc_codegen_llvm[ddc53a90a6190b8a]::LlvmCodegenBackend as rustc_codegen_ssa[99f2d35fcd5a252c]::traits::backend::ExtraBackendMethods>::compile_codegen_unit
  26:     0x770c58fc1017 - <rustc_codegen_llvm[ddc53a90a6190b8a]::LlvmCodegenBackend as rustc_codegen_ssa[99f2d35fcd5a252c]::traits::backend::CodegenBackend>::codegen_crate
  27:     0x770c59177345 - <rustc_interface[3173e466a85c5e7c]::queries::Linker>::codegen_and_build_linker
  28:     0x770c59174bf0 - rustc_interface[3173e466a85c5e7c]::passes::create_and_enter_global_ctxt::<core[1a8e3f3c1152e72c]::option::Option<rustc_interface[3173e466a85c5e7c]::queries::Linker>, rustc_driver_impl[8fdf64b2f913ec67]::run_compiler::{closure#0}::{closure#2}>::{closure#2}::{closure#0}
  29:     0x770c58f80b20 - rustc_interface[3173e466a85c5e7c]::interface::run_compiler::<(), rustc_driver_impl[8fdf64b2f913ec67]::run_compiler::{closure#0}>::{closure#1}
  30:     0x770c58ca4412 - std[9e04a37a0a8a4f45]::sys::backtrace::__rust_begin_short_backtrace::<rustc_interface[3173e466a85c5e7c]::util::run_in_thread_with_globals<rustc_interface[3173e466a85c5e7c]::util::run_in_thread_pool_with_globals<rustc_interface[3173e466a85c5e7c]::interface::run_compiler<(), rustc_driver_impl[8fdf64b2f913ec67]::run_compiler::{closure#0}>::{closure#1}, ()>::{closure#0}, ()>::{closure#0}::{closure#0}, ()>
  31:     0x770c58ca4cf4 - <<std[9e04a37a0a8a4f45]::thread::Builder>::spawn_unchecked_<rustc_interface[3173e466a85c5e7c]::util::run_in_thread_with_globals<rustc_interface[3173e466a85c5e7c]::util::run_in_thread_pool_with_globals<rustc_interface[3173e466a85c5e7c]::interface::run_compiler<(), rustc_driver_impl[8fdf64b2f913ec67]::run_compiler::{closure#0}>::{closure#1}, ()>::{closure#0}, ()>::{closure#0}::{closure#0}, ()>::{closure#1} as core[1a8e3f3c1152e72c]::ops::function::FnOnce<()>>::call_once::{shim:vtable#0}
  32:     0x770c58ca60eb - std::sys::pal::unix::thread::Thread::new::thread_start::h907dccd2cf29cc8f
  33:     0x770c5a4f4a94 - <unknown>
  34:     0x770c5a581a34 - clone
  35:                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 `/playground/rustc-ice-2025-03-16T17_35_25-24.txt` to your bug report

note: compiler flags: --crate-type lib -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:
#0 [fn_abi_of_instance] computing call ABI of `<dyn Trait as Trait>::foo - virtual#3`
end of query stack
error: could not compile `playground` (lib)

@rustbot label F-arbitrary_self_types, F-dispatch_from_dyn, requires-nightly, A-trait-objects, A-layout

[compiler-errors]

Yeah, the implementation of DispatchFromDyn in codegen is really sensitive about the specifics of layout. This is internal layout jargon, but it expects the pointee to be Scalar-shaped but an alignment attr causes this to have a Memory backend. For now we probably just need to strengthen the checks for self type type validity for DispatchFromDyn.