ICE: compiler/rustc_middle/src/ty/normalize_erasing_regions.rs:169:13: Failed to normalize Alias(...

[theemathas]

Code

trait Trait {
    type Output;
}

impl<O, F: Fn() -> O> Trait for F {
    type Output = O;
}

struct Wrap<P>(P);
struct WrapOutput<O>(O);

impl<P: Trait> Trait for Wrap<P> {
    type Output = WrapOutput<P::Output>;
}

fn wrap<P: Trait>(x: P) -> impl Trait {
    Wrap(x)
}

fn consume<P: Trait>(_: P) -> P::Output {
    unimplemented!()
}

pub fn recurse() -> impl Sized {
    consume(wrap(recurse))
}

Note: Reproducing this ICE requires cargo build. Using cargo check compiles fine.

Minimized from real code written by fearless_process on the rust community discord.

Very similar to #139658, which instead gives "overflow evaluating the requirement".

Meta

rustc --version --verbose:

rustc 1.86.0 (05f9846f8 2025-03-31)
binary: rustc
commit-hash: 05f9846f893b09a1be1fc8560e33fc3c815cfecb
commit-date: 2025-03-31
host: aarch64-apple-darwin
release: 1.86.0
LLVM version: 19.1.7

The issue also reproduces on rustc 1.88.0-nightly (0fe8f3454 2025-04-10).

Error output

error: internal compiler error: compiler/rustc_middle/src/ty/normalize_erasing_regions.rs:169:13: Failed to normalize Alias(Opaque, AliasTy { args: [], def_id: DefId(0:26 ~ foo[b3e3]::recurse::{opaque#0}), .. }) in typing_env=TypingEnv { typing_mode: PostAnalysis, param_env: ParamEnv { caller_bounds: [] } }, maybe try to call `try_normalize_erasing_regions` instead

Backtrace

thread 'rustc' panicked at compiler/rustc_middle/src/ty/normalize_erasing_regions.rs:169:13:
Box<dyn Any>
stack backtrace:
   0: std::panicking::begin_panic::<rustc_errors::ExplicitBug>
   1: <rustc_errors::diagnostic::BugAbort as rustc_errors::diagnostic::EmissionGuarantee>::emit_producing_guarantee
   2: rustc_middle::util::bug::opt_span_bug_fmt::<rustc_span::span_encoding::Span>::{closure#0}
   3: rustc_middle::ty::context::tls::with_opt::<rustc_middle::util::bug::opt_span_bug_fmt<rustc_span::span_encoding::Span>::{closure#0}, !>::{closure#0}
   4: rustc_middle::ty::context::tls::with_context_opt::<rustc_middle::ty::context::tls::with_opt<rustc_middle::util::bug::opt_span_bug_fmt<rustc_span::span_encoding::Span>::{closure#0}, !>::{closure#0}, !>
   5: rustc_middle::util::bug::bug_fmt
   6: rustc_ty_utils::abi::fn_abi_new_uncached
   7: rustc_ty_utils::abi::fn_abi_of_instance
      [... omitted 2 frames ...]
   8: rustc_middle::query::plumbing::query_get_at::<rustc_query_system::query::caches::DefaultCache<rustc_middle::ty::PseudoCanonicalInput<(rustc_middle::ty::instance::Instance, &rustc_middle::ty::list::RawList<(), rustc_middle::ty::Ty>)>, rustc_middle::query::erase::Erased<[u8; 16]>>>
   9: rustc_monomorphize::mono_checks::check_mono_item
      [... omitted 2 frames ...]
  10: rustc_monomorphize::collector::items_of_instance
      [... omitted 2 frames ...]
  11: rustc_monomorphize::collector::collect_items_rec::{closure#0}
  12: rustc_monomorphize::collector::collect_items_rec
  13: rustc_monomorphize::collector::collect_crate_mono_items
  14: rustc_monomorphize::partitioning::collect_and_partition_mono_items
      [... omitted 5 frames ...]
  15: <rustc_metadata::rmeta::encoder::EncodeContext>::encode_crate_root
  16: rustc_metadata::rmeta::encoder::encode_metadata
  17: rustc_metadata::fs::encode_and_write_metadata
  18: <rustc_interface::queries::Linker>::codegen_and_build_linker
  19: rustc_interface::passes::create_and_enter_global_ctxt::<core::option::Option<rustc_interface::queries::Linker>, rustc_driver_impl::run_compiler::{closure#0}::{closure#2}>
  20: rustc_interface::interface::run_compiler::<(), rustc_driver_impl::run_compiler::{closure#0}>::{closure#1}
note: Some details are omitted, run with `RUST_BACKTRACE=full` for a verbose backtrace.

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 1.86.0 (05f9846f8 2025-03-31) running on aarch64-apple-darwin

note: compiler flags: --crate-type lib -C embed-bitcode=no -C debuginfo=2 -C split-debuginfo=unpacked -C incremental=[REDACTED]

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

query stack during panic:
#0 [fn_abi_of_instance] computing call ABI of `recurse`
#1 [check_mono_item] monomorphization-time checking
#2 [items_of_instance] collecting items used by `recurse`
#3 [collect_and_partition_mono_items] collect_and_partition_mono_items
#4 [exported_symbols] collecting exported symbols for crate `0`
end of query stack
there was a panic while trying to force a dep node
try_mark_green dep node stack:
#0 exported_symbols(foo[b3e3])
end of try_mark_green dep node stack
error: could not compile `foo` (lib)

Caused by:
  process didn't exit successfully: `/Users/timch/.rustup/toolchains/stable-aarch64-apple-darwin/bin/rustc --crate-name foo --edition=2024 src/lib.rs --error-format=json --json=diagnostic-rendered-ansi,artifacts,future-incompat --diagnostic-width=204 --crate-type lib --emit=dep-info,metadata,link -C embed-bitcode=no -C debuginfo=2 -C split-debuginfo=unpacked --check-cfg 'cfg(docsrs,test)' --check-cfg 'cfg(feature, values())' -C metadata=61fd0e4f3351c637 -C extra-filename=-2bc4f207b16319e9 --out-dir /Users/timch/foo/target/debug/deps -C incremental=/Users/timch/foo/target/debug/incremental -L dependency=/Users/timch/foo/target/debug/deps` (exit status: 101)

[theemathas]

I think this looks related to #139406, since I can't figure out what type is recurse() supposed to be returning.

cc @lcnr