ICE: You can't project to field 0 of `DynMetadata` because layout is weird and thinks it doesn't have fields.

[matthiaskrgr]

auto-reduced (treereduce-rust):

#![feature(ptr_metadata)]

trait Foo {}

struct Bar;

impl Foo for Bar {}

fn main() {
    let a: *mut dyn Foo = &mut Bar;

    let d = a.to_raw_parts().0 as usize;
}

original:

// run-pass

#![feature(ptr_metadata)]

trait Foo {
    fn foo(&self) {}
}

struct Bar;

impl Foo for Bar {}

fn main() {
    // Test we can turn a fat pointer to array back into a thin pointer.
    let a: *const [i32] = &[1, 2, 3];
    let b = a as *const [i32; 2];
    unsafe {
        assert_eq!(*b, [1, 2]);
    }

    // Test conversion to an address (usize).
    let a: *const [i32; 3] = &[1, 2, 3];
    let b: *const [i32] = a;
    assert_eq!(a as usize, b as *const () as usize);

    // And conversion to a void pointer/address for trait objects too.
    let a: *mut dyn Foo = &mut Bar;
    let b = a as *mut () as usize;
    let c = a as *const () as usize;
    let d = a.to_raw_parts().0 as usize;

    assert_eq!(b, d);
    assert_eq!(c, d);
}

Version information

rustc 1.80.0-nightly (213ad10c8 2024-05-24)
binary: rustc
commit-hash: 213ad10c8f0fc275648552366275dc4e07f97462
commit-date: 2024-05-24
host: x86_64-unknown-linux-gnu
release: 1.80.0-nightly
LLVM version: 18.1.6

Command:
/home/matthias/.rustup/toolchains/master/bin/rustc -Zmir-opt-level=5 -Zvalidate-mir

Program output

warning: unused variable: `d`
  --> /tmp/icemaker_global_tempdir.MOmdI3aUIa6V/rustc_testrunner_tmpdir_reporting.HOhhbRhhlSye/mvce.rs:12:9
   |
12 |     let d = a.to_raw_parts().0 as usize;
   |         ^ help: if this is intentional, prefix it with an underscore: `_d`
   |
   = note: `#[warn(unused_variables)]` on by default

thread 'rustc' panicked at compiler/rustc_const_eval/src/transform/validate.rs:90:25:
broken MIR in Item(DefId(0:7 ~ mvce[a8d7]::main)) (after pass ScalarReplacementOfAggregates) at bb0[6]:
You can't project to field 0 of `DynMetadata` because layout is weird and thinks it doesn't have fields.
stack backtrace:
   0:     0x7d28bd152a15 - std::backtrace_rs::backtrace::libunwind::trace::ha14a3c487f1e072b
                               at /rustc/213ad10c8f0fc275648552366275dc4e07f97462/library/std/src/../../backtrace/src/backtrace/libunwind.rs:105:5
   1:     0x7d28bd152a15 - std::backtrace_rs::backtrace::trace_unsynchronized::hf4889a75ccd505ee
                               at /rustc/213ad10c8f0fc275648552366275dc4e07f97462/library/std/src/../../backtrace/src/backtrace/mod.rs:66:5
   2:     0x7d28bd152a15 - std::sys_common::backtrace::_print_fmt::h9590c8d63b078677
                               at /rustc/213ad10c8f0fc275648552366275dc4e07f97462/library/std/src/sys_common/backtrace.rs:68:5
   3:     0x7d28bd152a15 - <std::sys_common::backtrace::_print::DisplayBacktrace as core::fmt::Display>::fmt::hd126fab93aa88efe
                               at /rustc/213ad10c8f0fc275648552366275dc4e07f97462/library/std/src/sys_common/backtrace.rs:44:22
   4:     0x7d28bd1a1aeb - core::fmt::rt::Argument::fmt::hf17f29f90df880a1
                               at /rustc/213ad10c8f0fc275648552366275dc4e07f97462/library/core/src/fmt/rt.rs:165:63
   5:     0x7d28bd1a1aeb - core::fmt::write::h0ebd95f36610e669
                               at /rustc/213ad10c8f0fc275648552366275dc4e07f97462/library/core/src/fmt/mod.rs:1172:21
   6:     0x7d28bd14776f - std::io::Write::write_fmt::h3eef362c47ded0c4
                               at /rustc/213ad10c8f0fc275648552366275dc4e07f97462/library/std/src/io/mod.rs:1835:15
   7:     0x7d28bd1527ee - std::sys_common::backtrace::_print::h6ff81878b57bf5c8
                               at /rustc/213ad10c8f0fc275648552366275dc4e07f97462/library/std/src/sys_common/backtrace.rs:47:5
   8:     0x7d28bd1527ee - std::sys_common::backtrace::print::hdc5e68f22314f4a9
                               at /rustc/213ad10c8f0fc275648552366275dc4e07f97462/library/std/src/sys_common/backtrace.rs:34:9
   9:     0x7d28bd155219 - std::panicking::default_hook::{{closure}}::h03d46e664671b447
  10:     0x7d28bd154fba - std::panicking::default_hook::h1ae40dc0fea72a33
                               at /rustc/213ad10c8f0fc275648552366275dc4e07f97462/library/std/src/panicking.rs:298:9
  11:     0x7d28b9b1709f - std[b9bb1320dc5ae1a4]::panicking::update_hook::<alloc[b0def3f22af53808]::boxed::Box<rustc_driver_impl[9effea81b954d024]::install_ice_hook::{closure#0}>>::{closure#0}
  12:     0x7d28bd15594b - <alloc::boxed::Box<F,A> as core::ops::function::Fn<Args>>::call::h00416b40e105786e
                               at /rustc/213ad10c8f0fc275648552366275dc4e07f97462/library/alloc/src/boxed.rs:2077:9
  13:     0x7d28bd15594b - std::panicking::rust_panic_with_hook::h7af4ff1dc1e8071b
                               at /rustc/213ad10c8f0fc275648552366275dc4e07f97462/library/std/src/panicking.rs:799:13
  14:     0x7d28bd1556c4 - std::panicking::begin_panic_handler::{{closure}}::heb4d90acdc12b443
                               at /rustc/213ad10c8f0fc275648552366275dc4e07f97462/library/std/src/panicking.rs:664:13
  15:     0x7d28bd152ed9 - std::sys_common::backtrace::__rust_end_short_backtrace::h533bec95ab2736b2
                               at /rustc/213ad10c8f0fc275648552366275dc4e07f97462/library/std/src/sys_common/backtrace.rs:171:18
  16:     0x7d28bd1553f7 - rust_begin_unwind
                               at /rustc/213ad10c8f0fc275648552366275dc4e07f97462/library/std/src/panicking.rs:652:5
  17:     0x7d28bd19e0b3 - core::panicking::panic_fmt::h71bc10306699fad0
                               at /rustc/213ad10c8f0fc275648552366275dc4e07f97462/library/core/src/panicking.rs:72:14
  18:     0x7d28b8ed02b9 - <rustc_const_eval[9b69744695b0afef]::transform::validate::CfgChecker>::fail::<alloc[b0def3f22af53808]::string::String>
  19:     0x7d28b8ecef04 - <rustc_const_eval[9b69744695b0afef]::transform::validate::Validator as rustc_middle[c8c87ebb1fd33f9c]::mir::MirPass>::run_pass
  20:     0x7d28b9546940 - rustc_mir_transform[250cc2f4a89ad9b0]::pass_manager::validate_body
  21:     0x7d28bae01d45 - rustc_mir_transform[250cc2f4a89ad9b0]::pass_manager::run_passes_inner
  22:     0x7d28bb914b26 - rustc_mir_transform[250cc2f4a89ad9b0]::optimized_mir
  23:     0x7d28bb913c6b - rustc_query_impl[91ea4ef0d9b42432]::plumbing::__rust_begin_short_backtrace::<rustc_query_impl[91ea4ef0d9b42432]::query_impl::optimized_mir::dynamic_query::{closure#2}::{closure#0}, rustc_middle[c8c87ebb1fd33f9c]::query::erase::Erased<[u8; 8usize]>>
  24:     0x7d28baf91da7 - rustc_query_system[442df03e8028498c]::query::plumbing::try_execute_query::<rustc_query_impl[91ea4ef0d9b42432]::DynamicConfig<rustc_query_system[442df03e8028498c]::query::caches::DefIdCache<rustc_middle[c8c87ebb1fd33f9c]::query::erase::Erased<[u8; 8usize]>>, false, false, false>, rustc_query_impl[91ea4ef0d9b42432]::plumbing::QueryCtxt, false>
  25:     0x7d28baf915a0 - rustc_query_impl[91ea4ef0d9b42432]::query_impl::optimized_mir::get_query_non_incr::__rust_end_short_backtrace
  26:     0x7d28baf995b7 - <rustc_middle[c8c87ebb1fd33f9c]::ty::context::TyCtxt>::instance_mir
  27:     0x7d28bbb8e29a - rustc_monomorphize[5c6307a2377ff607]::collector::collect_items_rec::{closure#0}
  28:     0x7d28baf6208d - rustc_monomorphize[5c6307a2377ff607]::collector::collect_items_rec
  29:     0x7d28bb1cb391 - rustc_monomorphize[5c6307a2377ff607]::partitioning::collect_and_partition_mono_items
  30:     0x7d28bb1ca9d6 - rustc_query_impl[91ea4ef0d9b42432]::plumbing::__rust_begin_short_backtrace::<rustc_query_impl[91ea4ef0d9b42432]::query_impl::collect_and_partition_mono_items::dynamic_query::{closure#2}::{closure#0}, rustc_middle[c8c87ebb1fd33f9c]::query::erase::Erased<[u8; 24usize]>>
  31:     0x7d28bb1ca9a9 - <rustc_query_impl[91ea4ef0d9b42432]::query_impl::collect_and_partition_mono_items::dynamic_query::{closure#2} as core[a480ab4ddb292070]::ops::function::FnOnce<(rustc_middle[c8c87ebb1fd33f9c]::ty::context::TyCtxt, ())>>::call_once
  32:     0x7d28bbc70fc8 - rustc_query_system[442df03e8028498c]::query::plumbing::try_execute_query::<rustc_query_impl[91ea4ef0d9b42432]::DynamicConfig<rustc_query_system[442df03e8028498c]::query::caches::SingleCache<rustc_middle[c8c87ebb1fd33f9c]::query::erase::Erased<[u8; 24usize]>>, false, false, false>, rustc_query_impl[91ea4ef0d9b42432]::plumbing::QueryCtxt, false>
  33:     0x7d28bbc70ce1 - rustc_query_impl[91ea4ef0d9b42432]::query_impl::collect_and_partition_mono_items::get_query_non_incr::__rust_end_short_backtrace
  34:     0x7d28bbc35c94 - rustc_codegen_ssa[786e474d3d8fe57a]::base::codegen_crate::<rustc_codegen_llvm[b358019a521b9791]::LlvmCodegenBackend>
  35:     0x7d28bbc296cc - <rustc_codegen_llvm[b358019a521b9791]::LlvmCodegenBackend as rustc_codegen_ssa[786e474d3d8fe57a]::traits::backend::CodegenBackend>::codegen_crate
  36:     0x7d28bbc2905f - rustc_interface[90b491fb83b45114]::passes::start_codegen
  37:     0x7d28bbc286da - <rustc_interface[90b491fb83b45114]::queries::Queries>::codegen_and_build_linker
  38:     0x7d28bb9c19ee - rustc_interface[90b491fb83b45114]::interface::run_compiler::<core[a480ab4ddb292070]::result::Result<(), rustc_span[c256c11c98aa3170]::ErrorGuaranteed>, rustc_driver_impl[9effea81b954d024]::run_compiler::{closure#0}>::{closure#1}
  39:     0x7d28bb9b5fe7 - std[b9bb1320dc5ae1a4]::sys_common::backtrace::__rust_begin_short_backtrace::<rustc_interface[90b491fb83b45114]::util::run_in_thread_with_globals<rustc_interface[90b491fb83b45114]::util::run_in_thread_pool_with_globals<rustc_interface[90b491fb83b45114]::interface::run_compiler<core[a480ab4ddb292070]::result::Result<(), rustc_span[c256c11c98aa3170]::ErrorGuaranteed>, rustc_driver_impl[9effea81b954d024]::run_compiler::{closure#0}>::{closure#1}, core[a480ab4ddb292070]::result::Result<(), rustc_span[c256c11c98aa3170]::ErrorGuaranteed>>::{closure#0}, core[a480ab4ddb292070]::result::Result<(), rustc_span[c256c11c98aa3170]::ErrorGuaranteed>>::{closure#0}::{closure#0}, core[a480ab4ddb292070]::result::Result<(), rustc_span[c256c11c98aa3170]::ErrorGuaranteed>>
  40:     0x7d28bb9b5daa - <<std[b9bb1320dc5ae1a4]::thread::Builder>::spawn_unchecked_<rustc_interface[90b491fb83b45114]::util::run_in_thread_with_globals<rustc_interface[90b491fb83b45114]::util::run_in_thread_pool_with_globals<rustc_interface[90b491fb83b45114]::interface::run_compiler<core[a480ab4ddb292070]::result::Result<(), rustc_span[c256c11c98aa3170]::ErrorGuaranteed>, rustc_driver_impl[9effea81b954d024]::run_compiler::{closure#0}>::{closure#1}, core[a480ab4ddb292070]::result::Result<(), rustc_span[c256c11c98aa3170]::ErrorGuaranteed>>::{closure#0}, core[a480ab4ddb292070]::result::Result<(), rustc_span[c256c11c98aa3170]::ErrorGuaranteed>>::{closure#0}::{closure#0}, core[a480ab4ddb292070]::result::Result<(), rustc_span[c256c11c98aa3170]::ErrorGuaranteed>>::{closure#2} as core[a480ab4ddb292070]::ops::function::FnOnce<()>>::call_once::{shim:vtable#0}
  41:     0x7d28bd15f72b - <alloc::boxed::Box<F,A> as core::ops::function::FnOnce<Args>>::call_once::h89a54a9f8510c705
                               at /rustc/213ad10c8f0fc275648552366275dc4e07f97462/library/alloc/src/boxed.rs:2063:9
  42:     0x7d28bd15f72b - <alloc::boxed::Box<F,A> as core::ops::function::FnOnce<Args>>::call_once::h195cf2ba72e01fdb
                               at /rustc/213ad10c8f0fc275648552366275dc4e07f97462/library/alloc/src/boxed.rs:2063:9
  43:     0x7d28bd15f72b - std::sys::pal::unix::thread::Thread::new::thread_start::h98d3876c0f9ad401
                               at /rustc/213ad10c8f0fc275648552366275dc4e07f97462/library/std/src/sys/pal/unix/thread.rs:108:17
  44:     0x7d28bcefd1cf - <unknown>
  45:     0x7d28bcf7e6ec - <unknown>
  46:                0x0 - <unknown>

error: 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: please make sure that you have updated to the latest nightly

note: rustc 1.80.0-nightly (213ad10c8 2024-05-24) running on x86_64-unknown-linux-gnu

note: compiler flags: -Z mir-opt-level=5 -Z validate-mir -Z dump-mir-dir=dir

query stack during panic:
#0 [optimized_mir] optimizing MIR for `main`
#1 [collect_and_partition_mono_items] collect_and_partition_mono_items
end of query stack
warning: 1 warning emitted

@rustbot label +F-ptr_metadata

[matthiaskrgr]

#125479 cc @scottmcm

[scottmcm]

Thanks!

I have a fix for this in #124251 -- I didn't know it was possible without that change. I'll pull it out to a separate PR.