ICE: non-Aggregate field with matching ABI but differing alignment

[matthiaskrgr]

auto-reduced (treereduce-rust):

mod assert {
    use std::mem::{Assume, BikeshedIntrinsicFrom};

    pub fn is_transmutable<Src, Dst>()
    where
        Dst: BikeshedIntrinsicFrom<Src>,
    {
    }
}

#[repr(u32)]
enum Ox00 {
    V = 0x00,
}
enum Ox01 {
    V = 0x01,
}
#[repr(C, packed(2))]
enum OxFF {
    V = 0xFF,
}

fn test() {
    #[derive]

    union Superset {
        a: Ox00,
        b: OxFF,
        b: Ox01,
    }

    assert::is_transmutable::<Superset, Subset>();
}

original:

#![crate_type = "lib"]
#![feature(allow)]
#![allow(dead_code, incomplete_features, non_camel_case_types)]

mod assert {
    use std::mem::{Assume, BikeshedIntrinsicFrom};

    pub fn is_transmutable<Src, Dst>()
    where
        Dst: BikeshedIntrinsicFrom<Src, { Assume::SAFETY.and(Assume::VALIDITY) }>
    {}
}

#[derive(Clone, Copy)] #[repr(u32)] enum Ox00 { V = 0x00 }
#[derive(Clone, Copy)] #[repr(u8)] enum Ox01 { V = 0x01 }
#[derive(Clone, Copy)] #[repr(C, packed(2))] enum OxFF { V = 0xFF }

fn test() {
    #[derive]
    union Subset {
        a: (),
        b: V1u8,
    }

    #[packed(C)]
    union Superset {
        a: Ox00,
        b: OxFF,
        b: Ox01,
    }

    assert::is_transmutable::<Superset, Subset>(); //~ ERROR cannot be safely transmuted
}

Version information

rustc 1.81.0-nightly (d929a42a6 2024-06-25)
binary: rustc
commit-hash: d929a42a664c026167800801b26d734db925314f
commit-date: 2024-06-25
host: x86_64-unknown-linux-gnu
release: 1.81.0-nightly
LLVM version: 18.1.7

Command:
/home/matthias/.rustup/toolchains/master/bin/rustc

Program output

error: malformed `derive` attribute input
  --> /tmp/icemaker_global_tempdir.WonAMZI2vcAF/rustc_testrunner_tmpdir_reporting.xuyJdDymg62q/mvce.rs:24:5
   |
24 |     #[derive]
   |     ^^^^^^^^^ help: must be of the form: `#[derive(Trait1, Trait2, ...)]`

error[E0412]: cannot find type `Subset` in this scope
  --> /tmp/icemaker_global_tempdir.WonAMZI2vcAF/rustc_testrunner_tmpdir_reporting.xuyJdDymg62q/mvce.rs:32:41
   |
32 |     assert::is_transmutable::<Superset, Subset>();
   |                                         ^^^^^^ not found in this scope
   |
help: you might be missing a type parameter
   |
23 | fn test<Subset>() {
   |        ++++++++

warning: unused import: `Assume`
 --> /tmp/icemaker_global_tempdir.WonAMZI2vcAF/rustc_testrunner_tmpdir_reporting.xuyJdDymg62q/mvce.rs:2:20
  |
2 |     use std::mem::{Assume, BikeshedIntrinsicFrom};
  |                    ^^^^^^
  |
  = note: `#[warn(unused_imports)]` on by default

error[E0601]: `main` function not found in crate `mvce`
  --> /tmp/icemaker_global_tempdir.WonAMZI2vcAF/rustc_testrunner_tmpdir_reporting.xuyJdDymg62q/mvce.rs:33:2
   |
33 | }
   |  ^ consider adding a `main` function to `/tmp/icemaker_global_tempdir.WonAMZI2vcAF/rustc_testrunner_tmpdir_reporting.xuyJdDymg62q/mvce.rs`

error[E0517]: attribute should be applied to a struct or union
  --> /tmp/icemaker_global_tempdir.WonAMZI2vcAF/rustc_testrunner_tmpdir_reporting.xuyJdDymg62q/mvce.rs:18:11
   |
18 |   #[repr(C, packed(2))]
   |             ^^^^^^^^^
19 | / enum OxFF {
20 | |     V = 0xFF,
21 | | }
   | |_- not a struct or union

error[E0658]: use of unstable library feature 'transmutability'
 --> /tmp/icemaker_global_tempdir.WonAMZI2vcAF/rustc_testrunner_tmpdir_reporting.xuyJdDymg62q/mvce.rs:2:20
  |
2 |     use std::mem::{Assume, BikeshedIntrinsicFrom};
  |                    ^^^^^^
  |
  = note: see issue #99571 <https://github.com/rust-lang/rust/issues/99571> for more information
  = help: add `#![feature(transmutability)]` to the crate attributes to enable
  = note: this compiler was built on 2024-06-25; consider upgrading it if it is out of date

error[E0658]: use of unstable library feature 'transmutability'
 --> /tmp/icemaker_global_tempdir.WonAMZI2vcAF/rustc_testrunner_tmpdir_reporting.xuyJdDymg62q/mvce.rs:2:28
  |
2 |     use std::mem::{Assume, BikeshedIntrinsicFrom};
  |                            ^^^^^^^^^^^^^^^^^^^^^
  |
  = note: see issue #99571 <https://github.com/rust-lang/rust/issues/99571> for more information
  = help: add `#![feature(transmutability)]` to the crate attributes to enable
  = note: this compiler was built on 2024-06-25; consider upgrading it if it is out of date

error[E0658]: use of unstable library feature 'transmutability'
 --> /tmp/icemaker_global_tempdir.WonAMZI2vcAF/rustc_testrunner_tmpdir_reporting.xuyJdDymg62q/mvce.rs:6:14
  |
6 |         Dst: BikeshedIntrinsicFrom<Src>,
  |              ^^^^^^^^^^^^^^^^^^^^^^^^^^
  |
  = note: see issue #99571 <https://github.com/rust-lang/rust/issues/99571> for more information
  = help: add `#![feature(transmutability)]` to the crate attributes to enable
  = note: this compiler was built on 2024-06-25; consider upgrading it if it is out of date

error[E0124]: field `b` is already declared
  --> /tmp/icemaker_global_tempdir.WonAMZI2vcAF/rustc_testrunner_tmpdir_reporting.xuyJdDymg62q/mvce.rs:29:9
   |
28 |         b: OxFF,
   |         ------- `b` first declared here
29 |         b: Ox01,
   |         ^^^^^^^ field already declared

error[E0740]: field must implement `Copy` or be wrapped in `ManuallyDrop<...>` to be used in a union
  --> /tmp/icemaker_global_tempdir.WonAMZI2vcAF/rustc_testrunner_tmpdir_reporting.xuyJdDymg62q/mvce.rs:27:9
   |
27 |         a: Ox00,
   |         ^^^^^^^
   |
   = note: union fields must not have drop side-effects, which is currently enforced via either `Copy` or `ManuallyDrop<...>`
help: wrap the field type in `ManuallyDrop<...>`
   |
27 |         a: std::mem::ManuallyDrop<Ox00>,
   |            +++++++++++++++++++++++    +

thread 'rustc' panicked at /rustc/d929a42a664c026167800801b26d734db925314f/compiler/rustc_abi/src/layout.rs:289:29:
assertion `left == right` failed: non-Aggregate field with matching ABI but differing alignment
  left: Align(4 bytes)
 right: Align(2 bytes)
stack backtrace:
   0:     0x777bc94142e5 - std::backtrace_rs::backtrace::libunwind::trace::h3816f17667167091
                               at /rustc/d929a42a664c026167800801b26d734db925314f/library/std/src/../../backtrace/src/backtrace/libunwind.rs:116:5
   1:     0x777bc94142e5 - std::backtrace_rs::backtrace::trace_unsynchronized::h05c1a74390e79138
                               at /rustc/d929a42a664c026167800801b26d734db925314f/library/std/src/../../backtrace/src/backtrace/mod.rs:66:5
   2:     0x777bc94142e5 - std::sys::backtrace::_print_fmt::hf9f67f450e2340b3
                               at /rustc/d929a42a664c026167800801b26d734db925314f/library/std/src/sys/backtrace.rs:68:5
   3:     0x777bc94142e5 - <std::sys::backtrace::_print::DisplayBacktrace as core::fmt::Display>::fmt::hd0470f4740d6f066
                               at /rustc/d929a42a664c026167800801b26d734db925314f/library/std/src/sys/backtrace.rs:44:22
   4:     0x777bc9463ceb - core::fmt::rt::Argument::fmt::h70b8a6b09781c530
                               at /rustc/d929a42a664c026167800801b26d734db925314f/library/core/src/fmt/rt.rs:165:63
   5:     0x777bc9463ceb - core::fmt::write::hafea0839d2bbb3f2
                               at /rustc/d929a42a664c026167800801b26d734db925314f/library/core/src/fmt/mod.rs:1168:21
   6:     0x777bc9408f6f - std::io::Write::write_fmt::h781fa7911c53c2fa
                               at /rustc/d929a42a664c026167800801b26d734db925314f/library/std/src/io/mod.rs:1835:15
   7:     0x777bc94140be - std::sys::backtrace::_print::h864675b81ca0e917
                               at /rustc/d929a42a664c026167800801b26d734db925314f/library/std/src/sys/backtrace.rs:47:5
   8:     0x777bc94140be - std::sys::backtrace::print::h077604854516c949
                               at /rustc/d929a42a664c026167800801b26d734db925314f/library/std/src/sys/backtrace.rs:34:9
   9:     0x777bc9416a09 - std::panicking::default_hook::{{closure}}::h0655bbcac1b3559e
  10:     0x777bc94167ac - std::panicking::default_hook::ha9e013cc76e074dd
                               at /rustc/d929a42a664c026167800801b26d734db925314f/library/std/src/panicking.rs:292:9
  11:     0x777bc59eac90 - std[e6dd88f179d4d596]::panicking::update_hook::<alloc[7519215c1642967c]::boxed::Box<rustc_driver_impl[6d6094f07793e4a9]::install_ice_hook::{closure#0}>>::{closure#0}
  12:     0x777bc94172df - <alloc::boxed::Box<F,A> as core::ops::function::Fn<Args>>::call::haac7baf64299a07d
                               at /rustc/d929a42a664c026167800801b26d734db925314f/library/alloc/src/boxed.rs:2078:9
  13:     0x777bc94172df - std::panicking::rust_panic_with_hook::h9bfa469549e655b8
                               at /rustc/d929a42a664c026167800801b26d734db925314f/library/std/src/panicking.rs:804:13
  14:     0x777bc9416f07 - std::panicking::begin_panic_handler::{{closure}}::h4a967f6ef7ab4640
                               at /rustc/d929a42a664c026167800801b26d734db925314f/library/std/src/panicking.rs:670:13
  15:     0x777bc94147a9 - std::sys::backtrace::__rust_end_short_backtrace::h6bde84250dc9cd8b
                               at /rustc/d929a42a664c026167800801b26d734db925314f/library/std/src/sys/backtrace.rs:171:18
  16:     0x777bc9416be4 - rust_begin_unwind
                               at /rustc/d929a42a664c026167800801b26d734db925314f/library/std/src/panicking.rs:661:5
  17:     0x777bc94602a3 - core::panicking::panic_fmt::h036234c821d91466
                               at /rustc/d929a42a664c026167800801b26d734db925314f/library/core/src/panicking.rs:74:14
  18:     0x777bc946087f - core::panicking::assert_failed_inner::h6886c5ce8b27c112
                               at /rustc/d929a42a664c026167800801b26d734db925314f/library/core/src/panicking.rs:405:23
  19:     0x777bc6742f17 - core[672c7616ff9a88f5]::panicking::assert_failed::<rustc_abi[75a4f7491f97790a]::Align, rustc_abi[75a4f7491f97790a]::Align>
  20:     0x777bc775ea4e - rustc_ty_utils[91a81cae3f51d4c]::layout::layout_of_uncached
  21:     0x777bc774ce0b - rustc_ty_utils[91a81cae3f51d4c]::layout::layout_of
  22:     0x777bc774cd91 - rustc_query_impl[b034b92d40b1d47d]::plumbing::__rust_begin_short_backtrace::<rustc_query_impl[b034b92d40b1d47d]::query_impl::layout_of::dynamic_query::{closure#2}::{closure#0}, rustc_middle[e321b4b4f2134162]::query::erase::Erased<[u8; 16usize]>>
  23:     0x777bc774c0b6 - rustc_query_system[4a94863d7e85f976]::query::plumbing::try_execute_query::<rustc_query_impl[b034b92d40b1d47d]::DynamicConfig<rustc_query_system[4a94863d7e85f976]::query::caches::DefaultCache<rustc_middle[e321b4b4f2134162]::ty::ParamEnvAnd<rustc_middle[e321b4b4f2134162]::ty::Ty>, rustc_middle[e321b4b4f2134162]::query::erase::Erased<[u8; 16usize]>>, false, true, false>, rustc_query_impl[b034b92d40b1d47d]::plumbing::QueryCtxt, false>
  24:     0x777bc774bd45 - rustc_query_impl[b034b92d40b1d47d]::query_impl::layout_of::get_query_non_incr::__rust_end_short_backtrace
  25:     0x777bc671d5cc - rustc_middle[e321b4b4f2134162]::query::plumbing::query_get_at::<rustc_query_system[4a94863d7e85f976]::query::caches::DefaultCache<rustc_middle[e321b4b4f2134162]::ty::ParamEnvAnd<rustc_middle[e321b4b4f2134162]::ty::Ty>, rustc_middle[e321b4b4f2134162]::query::erase::Erased<[u8; 16usize]>>>
  26:     0x777bc6734531 - <rustc_transmute[483028c4aa667a77]::rustc::TransmuteTypeEnv>::is_transmutable
  27:     0x777bc79db58f - <rustc_trait_selection[acad18ec578eab22]::traits::select::SelectionContext>::confirm_candidate
  28:     0x777bc7472f11 - <rustc_trait_selection[acad18ec578eab22]::traits::select::SelectionContext>::evaluate_trait_predicate_recursively
  29:     0x777bc746ce97 - <rustc_trait_selection[acad18ec578eab22]::traits::select::SelectionContext>::evaluate_root_obligation
  30:     0x777bc746b215 - rustc_traits[8a90ea068024d15f]::evaluate_obligation::evaluate_obligation
  31:     0x777bc746aba9 - rustc_query_impl[b034b92d40b1d47d]::plumbing::__rust_begin_short_backtrace::<rustc_query_impl[b034b92d40b1d47d]::query_impl::evaluate_obligation::dynamic_query::{closure#2}::{closure#0}, rustc_middle[e321b4b4f2134162]::query::erase::Erased<[u8; 2usize]>>
  32:     0x777bc746a10f - rustc_query_system[4a94863d7e85f976]::query::plumbing::try_execute_query::<rustc_query_impl[b034b92d40b1d47d]::DynamicConfig<rustc_query_system[4a94863d7e85f976]::query::caches::DefaultCache<rustc_type_ir[567596a8266d8233]::canonical::Canonical<rustc_middle[e321b4b4f2134162]::ty::context::TyCtxt, rustc_middle[e321b4b4f2134162]::ty::ParamEnvAnd<rustc_middle[e321b4b4f2134162]::ty::predicate::Predicate>>, rustc_middle[e321b4b4f2134162]::query::erase::Erased<[u8; 2usize]>>, false, false, false>, rustc_query_impl[b034b92d40b1d47d]::plumbing::QueryCtxt, false>
  33:     0x777bc7469d64 - rustc_query_impl[b034b92d40b1d47d]::query_impl::evaluate_obligation::get_query_non_incr::__rust_end_short_backtrace
  34:     0x777bc38caa92 - <rustc_trait_selection[acad18ec578eab22]::traits::fulfill::FulfillProcessor as rustc_data_structures[66d2db66d3aeea18]::obligation_forest::ObligationProcessor>::process_obligation
  35:     0x777bc70081e7 - <rustc_data_structures[66d2db66d3aeea18]::obligation_forest::ObligationForest<rustc_trait_selection[acad18ec578eab22]::traits::fulfill::PendingPredicateObligation>>::process_obligations::<rustc_trait_selection[acad18ec578eab22]::traits::fulfill::FulfillProcessor>
  36:     0x777bc3bbbfea - <rustc_hir_typeck[673ed4476fae1319]::fn_ctxt::FnCtxt>::confirm_builtin_call
  37:     0x777bc7bb4c5d - <rustc_hir_typeck[673ed4476fae1319]::fn_ctxt::FnCtxt>::check_expr_with_expectation_and_args
  38:     0x777bc7baedf6 - <rustc_hir_typeck[673ed4476fae1319]::fn_ctxt::FnCtxt>::check_block_with_expected
  39:     0x777bc7bb5760 - <rustc_hir_typeck[673ed4476fae1319]::fn_ctxt::FnCtxt>::check_expr_with_expectation_and_args
  40:     0x777bc72f91f6 - rustc_hir_typeck[673ed4476fae1319]::check::check_fn
  41:     0x777bc72ed054 - rustc_hir_typeck[673ed4476fae1319]::typeck
  42:     0x777bc72eca9d - rustc_query_impl[b034b92d40b1d47d]::plumbing::__rust_begin_short_backtrace::<rustc_query_impl[b034b92d40b1d47d]::query_impl::typeck::dynamic_query::{closure#2}::{closure#0}, rustc_middle[e321b4b4f2134162]::query::erase::Erased<[u8; 8usize]>>
  43:     0x777bc736a073 - rustc_query_system[4a94863d7e85f976]::query::plumbing::try_execute_query::<rustc_query_impl[b034b92d40b1d47d]::DynamicConfig<rustc_query_system[4a94863d7e85f976]::query::caches::VecCache<rustc_span[31538c27a715cd64]::def_id::LocalDefId, rustc_middle[e321b4b4f2134162]::query::erase::Erased<[u8; 8usize]>>, false, false, false>, rustc_query_impl[b034b92d40b1d47d]::plumbing::QueryCtxt, false>
  44:     0x777bc736924d - rustc_query_impl[b034b92d40b1d47d]::query_impl::typeck::get_query_non_incr::__rust_end_short_backtrace
  45:     0x777bc7368e44 - <rustc_middle[e321b4b4f2134162]::hir::map::Map>::par_body_owners::<rustc_hir_analysis[6239ffc5e5ec24c9]::check_crate::{closure#4}>::{closure#0}
  46:     0x777bc73671c1 - rustc_hir_analysis[6239ffc5e5ec24c9]::check_crate
  47:     0x777bc735cf15 - rustc_interface[73bd107be0165211]::passes::analysis
  48:     0x777bc735cad9 - rustc_query_impl[b034b92d40b1d47d]::plumbing::__rust_begin_short_backtrace::<rustc_query_impl[b034b92d40b1d47d]::query_impl::analysis::dynamic_query::{closure#2}::{closure#0}, rustc_middle[e321b4b4f2134162]::query::erase::Erased<[u8; 1usize]>>
  49:     0x777bc7e50825 - rustc_query_system[4a94863d7e85f976]::query::plumbing::try_execute_query::<rustc_query_impl[b034b92d40b1d47d]::DynamicConfig<rustc_query_system[4a94863d7e85f976]::query::caches::SingleCache<rustc_middle[e321b4b4f2134162]::query::erase::Erased<[u8; 1usize]>>, false, false, false>, rustc_query_impl[b034b92d40b1d47d]::plumbing::QueryCtxt, false>
  50:     0x777bc7e5058f - rustc_query_impl[b034b92d40b1d47d]::query_impl::analysis::get_query_non_incr::__rust_end_short_backtrace
  51:     0x777bc7d77e3f - rustc_interface[73bd107be0165211]::interface::run_compiler::<core[672c7616ff9a88f5]::result::Result<(), rustc_span[31538c27a715cd64]::ErrorGuaranteed>, rustc_driver_impl[6d6094f07793e4a9]::run_compiler::{closure#0}>::{closure#1}
  52:     0x777bc7c37e89 - std[e6dd88f179d4d596]::sys::backtrace::__rust_begin_short_backtrace::<rustc_interface[73bd107be0165211]::util::run_in_thread_with_globals<rustc_interface[73bd107be0165211]::util::run_in_thread_pool_with_globals<rustc_interface[73bd107be0165211]::interface::run_compiler<core[672c7616ff9a88f5]::result::Result<(), rustc_span[31538c27a715cd64]::ErrorGuaranteed>, rustc_driver_impl[6d6094f07793e4a9]::run_compiler::{closure#0}>::{closure#1}, core[672c7616ff9a88f5]::result::Result<(), rustc_span[31538c27a715cd64]::ErrorGuaranteed>>::{closure#0}, core[672c7616ff9a88f5]::result::Result<(), rustc_span[31538c27a715cd64]::ErrorGuaranteed>>::{closure#0}::{closure#0}, core[672c7616ff9a88f5]::result::Result<(), rustc_span[31538c27a715cd64]::ErrorGuaranteed>>
  53:     0x777bc7c37c3a - <<std[e6dd88f179d4d596]::thread::Builder>::spawn_unchecked_<rustc_interface[73bd107be0165211]::util::run_in_thread_with_globals<rustc_interface[73bd107be0165211]::util::run_in_thread_pool_with_globals<rustc_interface[73bd107be0165211]::interface::run_compiler<core[672c7616ff9a88f5]::result::Result<(), rustc_span[31538c27a715cd64]::ErrorGuaranteed>, rustc_driver_impl[6d6094f07793e4a9]::run_compiler::{closure#0}>::{closure#1}, core[672c7616ff9a88f5]::result::Result<(), rustc_span[31538c27a715cd64]::ErrorGuaranteed>>::{closure#0}, core[672c7616ff9a88f5]::result::Result<(), rustc_span[31538c27a715cd64]::ErrorGuaranteed>>::{closure#0}::{closure#0}, core[672c7616ff9a88f5]::result::Result<(), rustc_span[31538c27a715cd64]::ErrorGuaranteed>>::{closure#2} as core[672c7616ff9a88f5]::ops::function::FnOnce<()>>::call_once::{shim:vtable#0}
  54:     0x777bc942116b - <alloc::boxed::Box<F,A> as core::ops::function::FnOnce<Args>>::call_once::hcfcb27dcb2ebeeb7
                               at /rustc/d929a42a664c026167800801b26d734db925314f/library/alloc/src/boxed.rs:2064:9
  55:     0x777bc942116b - <alloc::boxed::Box<F,A> as core::ops::function::FnOnce<Args>>::call_once::h7d3cd9c06edd61cc
                               at /rustc/d929a42a664c026167800801b26d734db925314f/library/alloc/src/boxed.rs:2064:9
  56:     0x777bc942116b - std::sys::pal::unix::thread::Thread::new::thread_start::h082ffbd0fcdeae0d
                               at /rustc/d929a42a664c026167800801b26d734db925314f/library/std/src/sys/pal/unix/thread.rs:108:17
  57:     0x777bc24a6ded - <unknown>
  58:     0x777bc252a0dc - <unknown>
  59:                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 1.81.0-nightly (d929a42a6 2024-06-25) running on x86_64-unknown-linux-gnu

query stack during panic:
#0 [layout_of] computing layout of `test::Superset`
#1 [evaluate_obligation] evaluating trait selection obligation `{type error}: core::mem::transmutability::BikeshedIntrinsicFrom<test::Superset, core::mem::transmutability::Assume { alignment: false, lifetimes: false, safety: false, validity: false }>`
end of query stack
error: aborting due to 9 previous errors; 1 warning emitted

Some errors have detailed explanations: E0124, E0412, E0517, E0601, E0658, E0740.
For more information about an error, try `rustc --explain E0124`.

@rustbot label +F-allow

[matthiaskrgr]

bisects to #123367 cc @jswrenn

[matthiaskrgr]

bit smaller

mod assert {
    use std::mem::{Assume, BikeshedIntrinsicFrom};

    pub fn is_transmutable<Src, Dst>()
    where
        Dst: BikeshedIntrinsicFrom<Src>,
    {
    }
}

#[repr(u32)]
enum Ox00 {
    V = 0x00,
}

#[repr(C, packed(2))]
enum OxFF {
    V = 0xFF,
}

fn test() {
    union Superset {
        a: Ox00,
        b: OxFF,
    }

    assert::is_transmutable::<Superset, Subset>();
}