ICE on higher-trait bounds

[agalakhov]

The following code:

use std::iter::Map;

trait Foo { }

impl<T> Foo for &'_ T where T: Foo { }
impl<T> Foo for Option<T> where T: Foo { }

impl Foo for u32 { }

fn trigger_error<I, F>(iterable: I, functor: F)
where
    for<'t> &'t I: IntoIterator,
    for<'t> Map<<&'t I as IntoIterator>::IntoIter, F>: Iterator,
    for<'t> <Map<<&'t I as IntoIterator>::IntoIter, F> as Iterator>::Item: Foo,
{
    
}

fn main() {
    trigger_error(Vec::<u32>::new(), |x: &u32| Some(x))
}

results in an ICE

error: internal compiler error: src/librustc/infer/lexical_region_resolve/mod.rs:632: collect_error_for_expanding_node() could not find error for var '_#2r in universe U11, lower_bounds=[
    RegionAndOrigin(RePlaceholder(Placeholder { universe: U1, name: BrNamed(crate0:DefIndex(1:14), 't) }),Subtype(TypeTrace(ObligationCause { span: src/main.rs:20:5: 20:18, body_id: HirId { owner: DefIndex(0:9), local_id: 24 }, code: ImplDerivedObligation(DerivedObligationCause { parent_trait_ref: Binder(<std::iter::Map<<&'t _ as std::iter::IntoIterator>::IntoIter, _> as std::iter::Iterator>), parent_code: ItemObligation(DefId(0/0:8 ~ playground[b1a9]::trigger_error[0])) }) }))),
    RegionAndOrigin(RePlaceholder(Placeholder { universe: U1, name: BrNamed(crate0:DefIndex(1:14), 't) }),Subtype(TypeTrace(ObligationCause { span: src/main.rs:20:5: 20:18, body_id: HirId { owner: DefIndex(0:9), local_id: 24 }, code: ImplDerivedObligation(DerivedObligationCause { parent_trait_ref: Binder(<std::iter::Map<<&'t _ as std::iter::IntoIterator>::IntoIter, _> as std::iter::Iterator>), parent_code: ItemObligation(DefId(0/0:8 ~ playground[b1a9]::trigger_error[0])) }) })))
], upper_bounds=[
    RegionAndOrigin(RePlaceholder(Placeholder { universe: U1, name: BrNamed(crate0:DefIndex(1:14), 't) }),Subtype(TypeTrace(ObligationCause { span: src/main.rs:20:5: 20:18, body_id: HirId { owner: DefIndex(0:9), local_id: 24 }, code: ImplDerivedObligation(DerivedObligationCause { parent_trait_ref: Binder(<std::iter::Map<<&'t _ as std::iter::IntoIterator>::IntoIter, _> as std::iter::Iterator>), parent_code: ItemObligation(DefId(0/0:8 ~ playground[b1a9]::trigger_error[0])) }) }))),
    RegionAndOrigin(RePlaceholder(Placeholder { universe: U1, name: BrNamed(crate0:DefIndex(1:14), 't) }),Subtype(TypeTrace(ObligationCause { span: src/main.rs:20:5: 20:18, body_id: HirId { owner: DefIndex(0:9), local_id: 24 }, code: ImplDerivedObligation(DerivedObligationCause { parent_trait_ref: Binder(<std::iter::Map<<&'t _ as std::iter::IntoIterator>::IntoIter, _> as std::iter::Iterator>), parent_code: ItemObligation(DefId(0/0:8 ~ playground[b1a9]::trigger_error[0])) }) })))
]

Tested this on stable and nightly. May be somehow related to #60070.

[hellow554]

Backtrace:

thread 'rustc' panicked at 'Box<Any>', src/librustc_errors/lib.rs:558:9
stack backtrace:
   0: std::sys::unix::backtrace::tracing::imp::unwind_backtrace
             at src/libstd/sys/unix/backtrace/tracing/gcc_s.rs:39
   1: std::sys_common::backtrace::_print
             at src/libstd/sys_common/backtrace.rs:70
   2: std::panicking::default_hook::{{closure}}
             at src/libstd/sys_common/backtrace.rs:58
             at src/libstd/panicking.rs:200
   3: std::panicking::default_hook
             at src/libstd/panicking.rs:215
   4: rustc::util::common::panic_hook
   5: std::panicking::rust_panic_with_hook
             at src/libstd/panicking.rs:482
   6: std::panicking::begin_panic
   7: rustc_errors::Handler::span_bug
   8: rustc::util::bug::opt_span_bug_fmt::{{closure}}
   9: rustc::ty::context::tls::with_opt::{{closure}}
  10: rustc::ty::context::tls::with_context_opt
  11: rustc::ty::context::tls::with_opt
  12: rustc::util::bug::opt_span_bug_fmt
  13: rustc::util::bug::span_bug_fmt
  14: rustc::infer::lexical_region_resolve::resolve
  15: rustc::infer::InferCtxt::resolve_regions_and_report_errors
  16: rustc_typeck::check::regionck::<impl rustc_typeck::check::FnCtxt<'a, 'gcx, 'tcx>>::regionck_fn
  17: rustc::ty::context::GlobalCtxt::enter_local
  18: rustc_typeck::check::typeck_tables_of
  19: rustc::ty::query::__query_compute::typeck_tables_of
  20: rustc::ty::query::<impl rustc::ty::query::config::QueryAccessors<'tcx> for rustc::ty::query::queries::typeck_tables_of<'tcx>>::compute
  21: rustc::dep_graph::graph::DepGraph::with_task_impl
  22: rustc::ty::query::plumbing::<impl rustc::ty::context::TyCtxt<'a, 'gcx, 'tcx>>::get_query
  23: rustc::ty::<impl rustc::ty::context::TyCtxt<'a, 'gcx, 'tcx>>::par_body_owners
  24: rustc_typeck::check::typeck_item_bodies
  25: rustc::ty::query::__query_compute::typeck_item_bodies
  26: rustc::ty::query::<impl rustc::ty::query::config::QueryAccessors<'tcx> for rustc::ty::query::queries::typeck_item_bodies<'tcx>>::compute
  27: rustc::dep_graph::graph::DepGraph::with_task_impl
  28: rustc::ty::query::plumbing::<impl rustc::ty::context::TyCtxt<'a, 'gcx, 'tcx>>::get_query
  29: rustc::util::common::time
  30: rustc_typeck::check_crate
  31: <std::thread::local::LocalKey<T>>::with
  32: rustc::ty::context::TyCtxt::create_and_enter
  33: rustc_driver::driver::compile_input
  34: rustc_driver::run_compiler_with_pool
  35: <scoped_tls::ScopedKey<T>>::set
  36: rustc_driver::run_compiler
  37: syntax::with_globals
  38: __rust_maybe_catch_panic
             at src/libpanic_unwind/lib.rs:87
  39: <F as alloc::boxed::FnBox<A>>::call_box
  40: std::sys::unix::thread::Thread::new::thread_start
             at /rustc/91856ed52c58aa5ba66a015354d1cc69e9779bdf/src/liballoc/boxed.rs:759
             at src/libstd/sys_common/thread.rs:14
             at src/libstd/sys/unix/thread.rs:81
  41: start_thread
  42: __clone
query stack during panic:
#0 [typeck_tables_of] processing `main`
#1 [typeck_item_bodies] type-checking all item bodies
end of query stack
error: aborting due to 2 previous errors

Happens on stable, beta, nightly

[hellow554]

Litte bit simplified:

use std::iter::Map;

pub trait Foo {}

pub fn trigger_error<I, F>(iterable: I, functor: F)
where
    for<'t> &'t I: IntoIterator,
    for<'t> Map<<&'t I as IntoIterator>::IntoIter, F>: Iterator,
    for<'t> <Map<<&'t I as IntoIterator>::IntoIter, F> as Iterator>::Item: Foo,
{
}

fn main() {
    trigger_error(vec![], |x: &u32| x)
}

[hellow554]

Bisection show ICE was introduced in c0bbc39, but I'm not sure how related that is, because it's a very very big PR.
CC #55517 @nikomatsakis

[nikomatsakis]

I will investigate.

[pnkfelix]

ping @nikomatsakis , any progress here?

[nikomatsakis]

I did some investigation. This bugs turns out to have been fixed -- well, more likely it was worked around by #58592. I'm going to land a test for it so that when I get around to reversing #58592, I can fix it then.