Storing generic_array::GenericArray in union triggers ICE

[jgarvin]

Code

typenum="1.12.0"
generic-array="0.14.4"

Playground link

use generic_array::GenericArray;
use typenum::Unsigned;

union Foo<N: Unsigned> {
    data: GenericArray<u8, N>
}

Meta

This bug exists both on current nightly and stable. Nightly output:

rustc --version --verbose:

rustc 1.52.0-nightly

Error output

   Compiling playground v0.0.1 (/playground)
error: internal compiler error: compiler/rustc_traits/src/normalize_erasing_regions.rs:43:32: could not fully normalize `<N as generic_array::ArrayLength<u8>>::ArrayType`

thread 'rustc' panicked at 'Box<Any>', compiler/rustc_errors/src/lib.rs:958:9
note: run with `RUST_BACKTRACE=1` environment variable to display a backtrace

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 1.50.0 (cb75ad5db 2021-02-10) running on x86_64-unknown-linux-gnu

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

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

query stack during panic:
#0 [normalize_generic_arg_after_erasing_regions] normalizing `<N as generic_array::ArrayLength<u8>>::ArrayType`
#1 [needs_drop_raw] computing whether `generic_array::GenericArray<u8, N>` needs drop
end of query stack
error: aborting due to previous error

Backtrace

error: internal compiler error: compiler/rustc_traits/src/normalize_erasing_regions.rs:43:32: could not fully normalize `<N as generic_array::ArrayLength<u8>>::ArrayType`

thread 'rustc' panicked at 'Box<Any>', /rustc/3f5aee2d5241139d808f4fdece0026603489afd1/library/std/src/panic.rs:59:5
stack backtrace:
   0:     0x7fb3e8b1cc70 - std::backtrace_rs::backtrace::libunwind::trace::hb4de9797f80b7b8c
                               at /rustc/3f5aee2d5241139d808f4fdece0026603489afd1/library/std/src/../../backtrace/src/backtrace/libunwind.rs:90:5
   1:     0x7fb3e8b1cc70 - std::backtrace_rs::backtrace::trace_unsynchronized::h59566d0bd20efff7
                               at /rustc/3f5aee2d5241139d808f4fdece0026603489afd1/library/std/src/../../backtrace/src/backtrace/mod.rs:66:5
   2:     0x7fb3e8b1cc70 - std::sys_common::backtrace::_print_fmt::hcfa5ce6be50275d4
                               at /rustc/3f5aee2d5241139d808f4fdece0026603489afd1/library/std/src/sys_common/backtrace.rs:67:5
   3:     0x7fb3e8b1cc70 - <std::sys_common::backtrace::_print::DisplayBacktrace as core::fmt::Display>::fmt::hd8c307a38b9bab04
                               at /rustc/3f5aee2d5241139d808f4fdece0026603489afd1/library/std/src/sys_common/backtrace.rs:46:22
   4:     0x7fb3e8b8deec - core::fmt::write::h3868db8542c90941
                               at /rustc/3f5aee2d5241139d808f4fdece0026603489afd1/library/core/src/fmt/mod.rs:1096:17
   5:     0x7fb3e8b0fba2 - std::io::Write::write_fmt::hab90295d5a0f197d
                               at /rustc/3f5aee2d5241139d808f4fdece0026603489afd1/library/std/src/io/mod.rs:1568:15
   6:     0x7fb3e8b20b55 - std::sys_common::backtrace::_print::h19224910b8700cf1
                               at /rustc/3f5aee2d5241139d808f4fdece0026603489afd1/library/std/src/sys_common/backtrace.rs:49:5
   7:     0x7fb3e8b20b55 - std::sys_common::backtrace::print::h25dedfa68c5fb84a
                               at /rustc/3f5aee2d5241139d808f4fdece0026603489afd1/library/std/src/sys_common/backtrace.rs:36:9
   8:     0x7fb3e8b20b55 - std::panicking::default_hook::{{closure}}::h12c5765653a72a42
                               at /rustc/3f5aee2d5241139d808f4fdece0026603489afd1/library/std/src/panicking.rs:208:50
   9:     0x7fb3e8b206b3 - std::panicking::default_hook::he65cee71c4209f0c
                               at /rustc/3f5aee2d5241139d808f4fdece0026603489afd1/library/std/src/panicking.rs:225:9
  10:     0x7fb3e937b52b - rustc_driver::report_ice::h9bfcf5769c15fbf2
  11:     0x7fb3e8b21456 - std::panicking::rust_panic_with_hook::h01a674d863fe0d8a
                               at /rustc/3f5aee2d5241139d808f4fdece0026603489afd1/library/std/src/panicking.rs:595:17
  12:     0x7fb3eab5337e - std::panicking::begin_panic::{{closure}}::h04d9d59beaf7438f
  13:     0x7fb3eab530b9 - std::sys_common::backtrace::__rust_end_short_backtrace::h91912ecacddbde4e
  14:     0x7fb3eab53322 - std::panicking::begin_panic::h3001af3848957078
  15:     0x7fb3eab46070 - std::panic::panic_any::h4f4426de976e6adf
  16:     0x7fb3eab4947a - rustc_errors::HandlerInner::bug::hdf11185f92e2a22a
  17:     0x7fb3eab48f53 - rustc_errors::Handler::bug::h2dfda4f443e5c9b7
  18:     0x7fb3ea848aaa - rustc_middle::ty::context::tls::with_opt::h931a04da690f236d
  19:     0x7fb3ec15fab0 - rustc_middle::util::bug::opt_span_bug_fmt::h550b33bd70d0f311
  20:     0x7fb3ea84af26 - rustc_middle::util::bug::bug_fmt::h36f36510cd9d6fb0
  21:     0x7fb3ead4b19f - rustc_infer::infer::InferCtxtBuilder::enter::hf940139bf6bfbc27
  22:     0x7fb3ead5420a - rustc_traits::normalize_erasing_regions::normalize_generic_arg_after_erasing_regions::h80e6571a4ee85ad8
  23:     0x7fb3ec1f50a8 - rustc_middle::dep_graph::<impl rustc_query_system::dep_graph::DepKind for rustc_middle::dep_graph::dep_node::DepKind>::with_deps::ha53fe413c90dab6e
  24:     0x7fb3eb61722d - rustc_query_system::dep_graph::graph::DepGraph<K>::with_task_impl::h22198f06d62ce937
  25:     0x7fb3eb57c065 - rustc_data_structures::stack::ensure_sufficient_stack::h661218e91a1b54e9
  26:     0x7fb3eb56e65e - rustc_query_system::query::plumbing::force_query_with_job::h3c8146f2d1f28d43
  27:     0x7fb3eb553b58 - rustc_query_system::query::plumbing::get_query_impl::ha6c6abc347fafc39
  28:     0x7fb3eb59844b - <rustc_middle::ty::normalize_erasing_regions::NormalizeAfterErasingRegionsFolder as rustc_middle::ty::fold::TypeFolder>::fold_ty::hddf16ed3359dbd34
  29:     0x7fb3ead33aa3 - rustc_ty_utils::needs_drop::needs_drop_raw::hf8e0eae2daf84614
  30:     0x7fb3e9ae1a16 - rustc_middle::ty::query::<impl rustc_query_system::query::config::QueryAccessors<rustc_middle::ty::context::TyCtxt> for rustc_middle::ty::query::queries::needs_drop_raw>::compute::h82c0a5ac3f555896
  31:     0x7fb3e9b09c10 - rustc_middle::dep_graph::<impl rustc_query_system::dep_graph::DepKind for rustc_middle::dep_graph::dep_node::DepKind>::with_deps::hf7df7e26f965f6be
  32:     0x7fb3e9af8efd - rustc_query_system::dep_graph::graph::DepGraph<K>::with_task_impl::haae861225e7e67f6
  33:     0x7fb3e9afcf6c - rustc_query_system::dep_graph::graph::DepGraph<K>::with_task::h1207d5165f8894a7
  34:     0x7fb3e9b2c015 - rustc_data_structures::stack::ensure_sufficient_stack::h5929c556f360f9c2
  35:     0x7fb3e9ae79db - rustc_query_system::query::plumbing::force_query_with_job::ha8da147a11595916
  36:     0x7fb3e9ae25dc - rustc_query_system::query::plumbing::get_query_impl::h4b5993c042058290
  37:     0x7fb3e9af0e2f - rustc_query_system::query::plumbing::get_query::h3ab4a250ccb3bbf1
  38:     0x7fb3eafe525f - <rustc_passes::stability::Checker as rustc_hir::intravisit::Visitor>::visit_item::h2bf5d0cf54fef87b
  39:     0x7fb3eafb2162 - rustc_middle::hir::map::Map::visit_item_likes_in_module::h2a479328b3cfc618
  40:     0x7fb3ebbb74e2 - rustc_passes::stability::check_mod_unstable_api_usage::h384a7e0e614a05bd
  41:     0x7fb3eb6eb7fc - rustc_middle::ty::query::<impl rustc_query_system::query::config::QueryAccessors<rustc_middle::ty::context::TyCtxt> for rustc_middle::ty::query::queries::check_mod_unstable_api_usage>::compute::h538c349dade82501
  42:     0x7fb3eb6f6207 - rustc_middle::dep_graph::<impl rustc_query_system::dep_graph::DepKind for rustc_middle::dep_graph::dep_node::DepKind>::with_deps::hb18acbc8e33ea959
  43:     0x7fb3eb6d7f0d - rustc_query_system::dep_graph::graph::DepGraph<K>::with_task_impl::ha27bbe1fb2160242
  44:     0x7fb3eb705005 - rustc_data_structures::stack::ensure_sufficient_stack::h98d3bece40371b3e
  45:     0x7fb3eb6f3761 - rustc_query_system::query::plumbing::force_query_with_job::h3480dbaedc8e4d04
  46:     0x7fb3eb6f1a98 - rustc_query_system::query::plumbing::get_query_impl::hc861c865b8ac055a
  47:     0x7fb3eb6f2d47 - rustc_query_system::query::plumbing::ensure_query_impl::h6c30c930f4936591
  48:     0x7fb3eb6cedbc - <std::panic::AssertUnwindSafe<F> as core::ops::function::FnOnce<()>>::call_once::hf18fa3d3907c9ecd
  49:     0x7fb3eb6f6aac - rustc_session::utils::<impl rustc_session::session::Session>::time::h23248c12f89aea1d
  50:     0x7fb3eb708d91 - rustc_interface::passes::analysis::heddb9cef62da4ab1
  51:     0x7fb3eb6864c9 - rustc_middle::ty::query::<impl rustc_query_system::query::config::QueryAccessors<rustc_middle::ty::context::TyCtxt> for rustc_middle::ty::query::queries::analysis>::compute::hc584fab50c0e9742
  52:     0x7fb3e9337afa - rustc_middle::dep_graph::<impl rustc_query_system::dep_graph::DepKind for rustc_middle::dep_graph::dep_node::DepKind>::with_deps::he189719f47fb03a4
  53:     0x7fb3eb698964 - rustc_query_system::dep_graph::graph::DepGraph<K>::with_task_impl::h90cdb9d4b5390542
  54:     0x7fb3eb6a7855 - rustc_data_structures::stack::ensure_sufficient_stack::hc03964f1cadb8cd3
  55:     0x7fb3eb6871f1 - rustc_query_system::query::plumbing::force_query_with_job::h085fb2f93a800461
  56:     0x7fb3eb686801 - rustc_query_system::query::plumbing::get_query_impl::hc18a830d288c39e4
  57:     0x7fb3eb69faaa - rustc_interface::passes::QueryContext::enter::hf896adfd99e9040f
  58:     0x7fb3eb6a68e4 - rustc_interface::queries::<impl rustc_interface::interface::Compiler>::enter::h2ac7000621882a7f
  59:     0x7fb3eb69f391 - rustc_span::with_source_map::h9c33ff8439fe9783
  60:     0x7fb3eb6a60b3 - scoped_tls::ScopedKey<T>::set::h0eb8893a0191dbc1
  61:     0x7fb3eb6a7ac8 - std::sys_common::backtrace::__rust_begin_short_backtrace::hccc56e59b0e3233c
  62:     0x7fb3eb68619a - core::ops::function::FnOnce::call_once{{vtable.shim}}::h09f6484b7e2514ef
  63:     0x7fb3e8b31dda - <alloc::boxed::Box<F,A> as core::ops::function::FnOnce<Args>>::call_once::h321523073ee11258
                               at /rustc/3f5aee2d5241139d808f4fdece0026603489afd1/library/alloc/src/boxed.rs:1548:9
  64:     0x7fb3e8b31dda - <alloc::boxed::Box<F,A> as core::ops::function::FnOnce<Args>>::call_once::hf0e85e12c83b99b3
                               at /rustc/3f5aee2d5241139d808f4fdece0026603489afd1/library/alloc/src/boxed.rs:1548:9
  65:     0x7fb3e8b31dda - std::sys::unix::thread::Thread::new::thread_start::hba22c7961aa0e2f8
                               at /rustc/3f5aee2d5241139d808f4fdece0026603489afd1/library/std/src/sys/unix/thread.rs:71:17
  66:     0x7fb3e8a4d609 - start_thread
  67:     0x7fb3e8961293 - clone
  68:                0x0 - <unknown>

[Johannesd3]

I think this is a duplicate of #81199.

However, an MCVE would be:

trait Trait {
    type Assoc;
}

struct Struct<T: Trait> {
    data: T::Assoc,
}

union Union<T> {
    data: Struct<T>
}

another example:

union Union<I> {
    data: std::iter::Peekable<I>
}

[Alexendoo]

Fixed by #91462