Stable ICE: assertion failed: (left == right)

[DutchGhost]

Code

fn bug<T>() -> impl Iterator<Item = [(); { |x: [u8]| { x } }]> {
    std::iter::empty()
}

Meta

rustc --version --verbose:

rustc 1.46.0 (04488afe3 2020-08-24)
rustc 1.47.0-beta.5 (9f0e6fa94 2020-09-29)
rustc 1.48.0-nightly (fc2daaae6 2020-09-28)

Error output

thread 'rustc' panicked at 'assertion failed: `(left == right)`
  left: `DefId(0:5 ~ playground[6bea]::bug[0]::{{opaque}}[0])`,
 right: `DefId(0:3 ~ playground[6bea]::bug[0])`', src/librustc_middle/hir/map/collector.rs:226:13

Backtrace

  Compiling playground v0.0.1 (/playground)
stack backtrace:
   0: backtrace::backtrace::libunwind::trace
             at /cargo/registry/src/github.com-1ecc6299db9ec823/backtrace-0.3.46/src/backtrace/libunwind.rs:86
   1: backtrace::backtrace::trace_unsynchronized
             at /cargo/registry/src/github.com-1ecc6299db9ec823/backtrace-0.3.46/src/backtrace/mod.rs:66
   2: std::sys_common::backtrace::_print_fmt
             at src/libstd/sys_common/backtrace.rs:78
   3: <std::sys_common::backtrace::_print::DisplayBacktrace as core::fmt::Display>::fmt
             at src/libstd/sys_common/backtrace.rs:59
   4: core::fmt::write
             at src/libcore/fmt/mod.rs:1076
   5: std::io::Write::write_fmt
             at src/libstd/io/mod.rs:1537
   6: std::sys_common::backtrace::_print
             at src/libstd/sys_common/backtrace.rs:62
   7: std::sys_common::backtrace::print
             at src/libstd/sys_common/backtrace.rs:49
   8: std::panicking::default_hook::{{closure}}
             at src/libstd/panicking.rs:198
   9: std::panicking::default_hook
             at src/libstd/panicking.rs:217
  10: rustc_driver::report_ice
  11: std::panicking::rust_panic_with_hook
             at src/libstd/panicking.rs:530
  12: rust_begin_unwind
             at src/libstd/panicking.rs:437
  13: std::panicking::begin_panic_fmt
             at src/libstd/panicking.rs:391
  14: rustc_middle::hir::map::collector::NodeCollector::insert_entry
  15: <rustc_middle::hir::map::collector::NodeCollector as rustc_hir::intravisit::Visitor>::visit_param
  16: rustc_hir::intravisit::walk_body
  17: rustc_hir::intravisit::walk_expr
  18: rustc_hir::intravisit::walk_block
  19: rustc_hir::intravisit::walk_expr
  20: rustc_hir::intravisit::walk_body
  21: rustc_hir::intravisit::walk_ty
  22: rustc_hir::intravisit::walk_assoc_type_binding
  23: rustc_hir::intravisit::walk_path
  24: rustc_hir::intravisit::Visitor::visit_param_bound
  25: rustc_hir::intravisit::walk_item
  26: <rustc_middle::hir::map::collector::NodeCollector as rustc_hir::intravisit::Visitor>::visit_item
  27: rustc_hir::intravisit::walk_ty
  28: rustc_hir::intravisit::walk_fn
  29: <rustc_middle::hir::map::collector::NodeCollector as rustc_hir::intravisit::Visitor>::visit_fn
  30: rustc_hir::intravisit::walk_item
  31: <rustc_middle::hir::map::collector::NodeCollector as rustc_hir::intravisit::Visitor>::visit_item
  32: rustc_middle::hir::map::index_hir
  33: rustc_query_system::dep_graph::graph::DepGraph<K>::with_task_impl
  34: rustc_data_structures::stack::ensure_sufficient_stack
  35: rustc_query_system::query::plumbing::get_query_impl
  36: core::ops::function::FnOnce::call_once
  37: rustc_query_system::dep_graph::graph::DepGraph<K>::with_task_impl
  38: rustc_data_structures::stack::ensure_sufficient_stack
  39: rustc_query_system::query::plumbing::get_query_impl
  40: rustc_middle::hir::map::Map::expect_item
  41: rustc_middle::hir::map::Map::visit_item_likes_in_module
  42: rustc_passes::hir_id_validator::check_crate
  43: rustc_interface::passes::analysis
  44: rustc_middle::ty::query::<impl rustc_query_system::query::config::QueryAccessors<rustc_middle::ty::context::TyCtxt> for rustc_middle::ty::query::queries::analysis>::compute
  45: rustc_query_system::dep_graph::graph::DepGraph<K>::with_task_impl
  46: rustc_query_system::query::plumbing::get_query_impl
  47: rustc_middle::ty::context::tls::enter_global
  48: rustc_interface::queries::<impl rustc_interface::interface::Compiler>::enter
  49: rustc_span::with_source_map
  50: rustc_interface::interface::create_compiler_and_run
  51: 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/blob/master/CONTRIBUTING.md#bug-reports

note: rustc 1.46.0 (04488afe3 2020-08-24) 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 [index_hir] index HIR
#1 [hir_owner] HIR owner of `{{misc}}#0`
#2 [analysis] running analysis passes on this crate
end of query stack
error: could not compile `playground`.

[DutchGhost]

This started happening on stable 1.36

[DutchGhost]

I'm realy unsure on how much this bisect can be trusted, I'm happy to run other ones with a little bit of help, this is the best I got.

searched nightlies: from nightly-2020-04-30 to nightly-2020-08-28
regressed nightly: nightly-2020-05-03
searched commits: from 7f65393 to f05a524
regressed commit: dae90c1

bisected with cargo-bisect-rustc v0.5.2

Host triple: x86_64-unknown-linux-gnu
Reproduce with:

cargo bisect-rustc --regress=non-error 

[tesuji]

My bisect:
ERROR: no commits between e4c66af...aa99abe within last 167 days

git lg --author=bors e4c66afba5d69356879570aeff22db5a38566a86...aa99abeb262307d5e9aa11a792312fd620b7f89a

• aa99abe - Auto merge of Properly parse '--extern-private' with name and path #59335 - Aaron1011:fix/extern-priv-final, r=Aaron1011 (1 year, 6 months ago)
• 9cd61f0 - Auto merge of Rollup of 7 pull requests #59967 - Centril:rollup-bdqq7ux, r=Centril (1 year, 6 months ago)
• d70c5a9 - Auto merge of update miri #59929 - RalfJung:miri, r=oli-obk (1 year, 6 months ago)
• 60076bb - Auto merge of Increase Span from 4 bytes to 8 bytes. #59693 - nnethercote:64-bit-Spans, r=petrochenkov (1 year, 6 months ago)
• 464473a - Auto merge of Improvement for comparision against fn #59798 - rchaser53:issue-59488, r=estebank (1 year, 6 months ago)
• ee621f4 - Auto merge of Rollup of 6 pull requests #59950 - Centril:rollup-hpmr62i, r=Centril (1 year, 6 months ago)
• 0085672 - Auto merge of Rollup of 16 pull requests #59949 - Centril:rollup-lsiqq1g, r=Centril (1 year, 6 months ago)

Command: cargo-bisect-rustc --start 2019-02-28 --end 2019-07-01 --preserve --regress=ice

[tamuhey]

Smaller example:

trait Foo {}
fn bug() -> impl Foo<[(); |_: ()| {}]> {}

playground

Something wrong with the inference when iml trait and array expression are used together

[frxstrem]

Using regular const generics on nightly produces the same error, so it's probably related:

#![feature(min_const_generics)]

trait Foo {}
struct Bar<const N: usize>;

fn bug() -> impl Foo<Bar<{|_: ()| {}}>> {}

playground

[tesuji]

All example include closure. So I don't think it is particular bug for const generics.

[lcnr]

Looks like something blocking const generics, even if it's not directly caused by it.

Also something I want to look into myself, so @rustbot claim

[lcnr]

This also breaks code which, if nonsensical, should be working. Don't think we have to increase the priority because of this though.

fn bug<T>() -> impl Iterator<Item = [(); { |x: u32| { x }; 4 }]> {
    std::iter::empty()
}

fn ok<T>() -> Box<dyn Iterator<Item = [(); { |x: u32| { x }; 4 }]>> {
    Box::new(std::iter::empty())
}

[tamuhey]

It is a regression - stable 1.26.0 correctly outputs a compile error

[lcnr]

Not something I can fix myself, releasing assignment.

[lcnr]

Something I can fix myself, #77546 (with a lot of guidance by eddyb)