assertion failed: !value.has_escaping_bound_vars() with trait A where for<'a> Self: 'a{}

[mixal-iirec]

Code

trait A where
    for<'a> Self: 'a,
{
}

Meta

Stable (1.54.0) works correctly(?) (E0311 the parameter type `Self` may not live long enough with nonsensical help consider adding an explicit lifetime bound `Self: 'a` ).

rustc --version --verbose:

rustc 1.56.0-nightly (50171c310 2021-09-01)
binary: rustc
commit-hash: 50171c310cd15e1b2d3723766ce64e2e4d6696fc
commit-date: 2021-09-01
host: x86_64-unknown-linux-gnu
release: 1.56.0-nightly
LLVM version: 13.0.0

Error output

thread 'rustc' panicked at 'assertion failed: !value.has_escaping_bound_vars()', /rustc/50171c310cd15e1b2d3723766ce64e2e4d6696fc/compiler/rustc_middle/src/ty/sty.rs:971:9
note: run with `RUST_BACKTRACE=1` environment variable to display a backtrace

error: internal compiler error: unexpected panic

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 1.56.0-nightly (50171c310 2021-09-01) running on x86_64-unknown-linux-gnu

note: compiler flags: -C embed-bitcode=no -C debuginfo=2 -C incremental --crate-type lib

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

query stack during panic:
#0 [super_predicates_that_define_assoc_type] computing the super traits of `A`
#1 [super_predicates_of] computing the super predicates of `A`
end of query stack

Backtrace

thread 'rustc' panicked at 'assertion failed: !value.has_escaping_bound_vars()', /rustc/50171c310cd15e1b2d3723766ce64e2e4d6696fc/compiler/rustc_middle/src/ty/sty.rs:971:9
stack backtrace:
   0: rust_begin_unwind
             at /rustc/50171c310cd15e1b2d3723766ce64e2e4d6696fc/library/std/src/panicking.rs:517:5
   1: core::panicking::panic_fmt
             at /rustc/50171c310cd15e1b2d3723766ce64e2e4d6696fc/library/core/src/panicking.rs:101:14
   2: core::panicking::panic
             at /rustc/50171c310cd15e1b2d3723766ce64e2e4d6696fc/library/core/src/panicking.rs:50:5
   3: rustc_typeck::collect::predicates_from_bound
   4: <core::iter::adapters::chain::Chain<A,B> as core::iter::traits::iterator::Iterator>::next
   5: <alloc::vec::Vec<T> as alloc::vec::spec_from_iter::SpecFromIter<T,I>>::from_iter
   6: rustc_typeck::collect::super_predicates_that_define_assoc_type
   7: rustc_query_system::dep_graph::graph::DepGraph<K>::with_task_impl
   8: rustc_data_structures::stack::ensure_sufficient_stack
   9: rustc_query_system::query::plumbing::get_query_impl
  10: <rustc_query_impl::Queries as rustc_middle::ty::query::QueryEngine>::super_predicates_that_define_assoc_type
  11: rustc_typeck::collect::super_predicates_of
  12: rustc_query_system::dep_graph::graph::DepGraph<K>::with_task_impl
  13: rustc_query_system::query::plumbing::force_query_with_job
  14: rustc_query_system::query::plumbing::get_query_impl
  15: <rustc_query_impl::Queries as rustc_middle::ty::query::QueryEngine>::super_predicates_of
  16: rustc_typeck::collect::convert_item
  17: <rustc_typeck::collect::CollectItemTypesVisitor as rustc_hir::intravisit::Visitor>::visit_item
  18: rustc_typeck::collect::collect_mod_item_types
  19: rustc_query_system::dep_graph::graph::DepGraph<K>::with_task_impl
  20: rustc_data_structures::stack::ensure_sufficient_stack
  21: rustc_query_system::query::plumbing::force_query_with_job
  22: rustc_query_system::query::plumbing::get_query_impl
  23: <rustc_query_impl::Queries as rustc_middle::ty::query::QueryEngine>::collect_mod_item_types
  24: rustc_session::session::Session::track_errors
  25: rustc_typeck::check_crate
  26: rustc_interface::passes::analysis
  27: rustc_query_system::dep_graph::graph::DepGraph<K>::with_task_impl
  28: rustc_data_structures::stack::ensure_sufficient_stack
  29: rustc_query_system::query::plumbing::force_query_with_job
  30: rustc_query_system::query::plumbing::get_query_impl
  31: <rustc_query_impl::Queries as rustc_middle::ty::query::QueryEngine>::analysis
  32: rustc_interface::passes::QueryContext::enter
  33: rustc_interface::queries::<impl rustc_interface::interface::Compiler>::enter
  34: rustc_span::with_source_map
  35: scoped_tls::ScopedKey<T>::set
note: Some details are omitted, run with `RUST_BACKTRACE=full` for a verbose backtrace.

error: internal compiler error: unexpected panic

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 1.56.0-nightly (50171c310 2021-09-01) running on x86_64-unknown-linux-gnu

note: compiler flags: -C embed-bitcode=no -C debuginfo=2 -C incremental --crate-type lib

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

query stack during panic:
#0 [super_predicates_that_define_assoc_type] computing the super traits of `A`
#1 [super_predicates_of] computing the super predicates of `A`
#2 [collect_mod_item_types] collecting item types in top-level module
#3 [analysis] running analysis passes on this crate
end of query stack

[apiraino]

Assigning priority as discussed in the Zulip thread of the Prioritization Working Group.

@rustbot label -I-prioritize +P-medium

[Alexendoo]

No longer ICEs since #88061

[jackh726]

Wait really? Neat.

[JohnTitor]

This triggers another ICE with debug_assertions as described in #89803.

The relevant part is:

rust/compiler/rustc_middle/src/ty/sty.rs

Lines 979 to 982 in 4626184

	if cfg!(debug_assertions) {
	let mut validator = ValidateBoundVars::new(vars);
	value.visit_with(&mut validator);
	}

And bound_vars is prepared here:

rust/compiler/rustc_typeck/src/collect.rs

Lines 2438 to 2443 in 4626184

	astconv.add_bounds(
	param_ty,
	std::array::IntoIter::new([bound]),
	&mut bounds,
	ty::List::empty(),
	);

So if I understand correctly, since it's empty, it won't pass the assertion, and validating it doesn't make sense here currently. @jackh726 could we just remove the validation or should we have something in bound_vars?

[jackh726]

I very briefly looked at this a few days ago.

We most certainly should be validating here; this is precisely the case that we want to catch. The problem really comes down to

rust/compiler/rustc_typeck/src/astconv/mod.rs

Lines 999 to 1004 in 4626184

	hir::GenericBound::Outlives(lifetime) => {
	let region = self.ast_region_to_region(lifetime, None);
	bounds
	.region_bounds
	.push((ty::Binder::bind_with_vars(region, bound_vars), lifetime.span));
	}

I think the correct fix here is to just make GenericBound::Outlives have a Binder<Lifetime>. I'm definitely willing to mentor someone here, but don't have time currently to work on this.

[BGR360]

I'd like to take a stab at this. @jackh726 I started a thread on zulip to track mentoring questions. You've given a very good starting point so I'll start reading code to see if it doesn't just click.