#[rustc_layout(debug)] ICEs when applied to some type aliases #85103
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#![feature(rustc_attrs)] use std::borrow::Cow; #[rustc_layout(debug)] type Edges<'a, E> = Cow<'a, [E]>;ICE
error: internal compiler error: compiler/rustc_traits/src/normalize_erasing_regions.rs:54:32: could not fully normalize `<[E] as std::borrow::ToOwned>::Owned` thread 'rustc' panicked at 'Box<Any>', /rustc/770792ff8d1ec542e78e77876ac936f43ffb8e05/library/std/src/panic.rs:59:5 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 1.54.0-nightly (770792ff8 2021-05-07) 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 `<[E] as std::borrow::ToOwned>::Owned` #1 [layout_raw] computing layout of `std::borrow::Cow<[E]>` end of query stack error: aborting due to previous error error: could not compile `playground` To learn more, run the command again with --verbose. Backtrace
thread 'rustc' panicked at 'Box<Any>', /rustc/770792ff8d1ec542e78e77876ac936f43ffb8e05/library/std/src/panic.rs:59:5 stack backtrace: 0: std::panicking::begin_panic 1: std::panic::panic_any 2: rustc_errors::HandlerInner::bug 3: rustc_errors::Handler::bug 4: rustc_middle::ty::context::tls::with_opt 5: rustc_middle::util::bug::opt_span_bug_fmt 6: rustc_middle::util::bug::bug_fmt 7: rustc_infer::infer::InferCtxtBuilder::enter 8: core::ops::function::FnOnce::call_once 9: rustc_query_system::dep_graph::graph::DepGraph<K>::with_task_impl 10: rustc_data_structures::stack::ensure_sufficient_stack 11: rustc_query_system::query::plumbing::force_query_with_job 12: rustc_query_system::query::plumbing::get_query_impl 13: <rustc_query_impl::Queries as rustc_middle::ty::query::QueryEngine>::normalize_generic_arg_after_erasing_regions 14: <rustc_middle::ty::normalize_erasing_regions::NormalizeAfterErasingRegionsFolder as rustc_middle::ty::fold::TypeFolder>::fold_ty 15: <rustc_middle::ty::layout::LayoutCx<rustc_middle::ty::context::TyCtxt> as rustc_target::abi::LayoutOf>::layout_of 16: <alloc::vec::Vec<T> as alloc::vec::spec_from_iter::SpecFromIter<T,I>>::from_iter 17: <alloc::vec::Vec<T> as alloc::vec::spec_from_iter::SpecFromIter<T,I>>::from_iter 18: core::iter::adapters::process_results 19: rustc_middle::ty::layout::LayoutCx<rustc_middle::ty::context::TyCtxt>::layout_raw_uncached 20: rustc_middle::ty::layout::layout_raw 21: rustc_query_impl::<impl rustc_query_system::query::config::QueryAccessors<rustc_query_impl::plumbing::QueryCtxt> for rustc_query_impl::queries::layout_raw>::compute 22: rustc_query_system::dep_graph::graph::DepGraph<K>::with_task_impl 23: rustc_data_structures::stack::ensure_sufficient_stack 24: rustc_query_system::query::plumbing::force_query_with_job 25: rustc_query_system::query::plumbing::get_query_impl 26: <rustc_query_impl::Queries as rustc_middle::ty::query::QueryEngine>::layout_raw 27: <rustc_middle::ty::layout::LayoutCx<rustc_middle::ty::context::TyCtxt> as rustc_target::abi::LayoutOf>::layout_of 28: <rustc_passes::layout_test::LayoutTest as rustc_hir::itemlikevisit::ItemLikeVisitor>::visit_item 29: rustc_hir::hir::Crate::visit_all_item_likes 30: rustc_passes::layout_test::test_layout 31: rustc_interface::passes::analysis 32: rustc_query_system::dep_graph::graph::DepGraph<K>::with_task_impl 33: rustc_data_structures::stack::ensure_sufficient_stack 34: rustc_query_system::query::plumbing::force_query_with_job 35: rustc_query_system::query::plumbing::get_query_impl 36: <rustc_query_impl::Queries as rustc_middle::ty::query::QueryEngine>::analysis 37: rustc_interface::passes::QueryContext::enter 38: rustc_interface::queries::<impl rustc_interface::interface::Compiler>::enter 39: rustc_span::with_source_map 40: rustc_interface::interface::create_compiler_and_run 41: scoped_tls::ScopedKey<T>::set Background information
This is a minimization of a bug encountered in #83501. Rustdoc wants to show memory layout info for type aliases (see 78d4b453ad2e19d44011b26fc55c949bff5dba3d for an explanation of why we want to show it for type aliases in particular), but building the compiler docs failed (which probably means that many other crates would fail as well). The type alias that caused the ICE is rustc_graphviz::Edges, which (fortunately) can be extracted into an MCVE without any other dependencies. That is the MCVE that I used for this issue.
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Area: Memory layout of typesCategory: This is a bug.Internal rustc attributes gated on the `#[rustc_attrs]` feature gate.Issue: The compiler panicked, giving an Internal Compilation Error (ICE) ❄️Medium priorityRelevant to the compiler team, which will review and decide on the PR/issue.ICE tracked in rust-lang/glacier.This issue requires a nightly compiler in some way.