ICE (OutputTypeParameterMismatch) with type_alias_impl_trait

[SNCPlay42]

Code

Here's MCVE: #72793 (comment) (Edited by JohnTitor)

#![feature(type_alias_impl_trait)]

type FilteredIter<'a> = impl Iterator<Item = &'a i32> + 'a;

fn filter_positive<'a>(vals: &'a [i32]) -> FilteredIter<'a> {
    vals.iter().filter(|x| **x >= 0)
}

fn with_positive<F>(vals: &[i32], fun: F)
where
    F: Fn(FilteredIter<'_>),
{
    fun(filter_positive(vals));
}

fn main() {
    let x = vec![-1, 1, -2, 2, -3, 3];

    with_positive(&x, |iter| {
        iter.for_each(|x| println!("{}", x));
    });
}

Playground

Error output

error: internal compiler error: src/librustc_trait_selection/traits/codegen/mod.rs:62: Encountered error `OutputTypeParameterMismatch(Binder(<[closure@src/main.rs:19:23: 21:6] as std::ops::Fn<(FilteredIter::<'_>,)>>), Binder(<[closure@src/main.rs:19:23: 21:6] as std::ops::Fn<(std::iter::Filter<std::slice::Iter<i32>, [closure@src/main.rs:6:24: 6:36]>,)>>), Sorts(ExpectedFound { expected: std::iter::Filter<std::slice::Iter<i32>, [closure@src/main.rs:6:24: 6:36]>, found: FilteredIter::<'_> }))` selecting `Binder(<[closure@src/main.rs:19:23: 21:6] as std::ops::Fn<(std::iter::Filter<std::slice::Iter<i32>, [closure@src/main.rs:6:24: 6:36]>,)>>)` during codegen

Prettied a bit:

error: internal compiler error: 
src/librustc_trait_selection/traits/codegen/mod.rs:62: 
Encountered error
`OutputTypeParameterMismatch(
	Binder(<[closure@src/main.rs:19:23: 21:6] as std::ops::Fn<(FilteredIter::<'_>,)>>),
	Binder(<[closure@src/main.rs:19:23: 21:6] as std::ops::Fn<(std::iter::Filter<std::slice::Iter<i32>, [closure@src/main.rs:6:24: 6:36]>,)>>),
	Sorts(ExpectedFound {
		expected: std::iter::Filter<std::slice::Iter<i32>, [closure@src/main.rs:6:24: 6:36]>,
		found: FilteredIter::<'_>
	})
)`
selecting `Binder(<[closure@src/main.rs:19:23: 21:6] as std::ops::Fn<(std::iter::Filter<std::slice::Iter<i32>, [closure@src/main.rs:6:24: 6:36]>,)>>)`
during codegen

Backtrace

thread 'rustc' panicked at 'Box<Any>', src/librustc_errors/lib.rs:907:9
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:218
  10: rustc_driver::report_ice
  11: std::panicking::rust_panic_with_hook
             at src/libstd/panicking.rs:490
  12: std::panicking::begin_panic
  13: rustc_errors::HandlerInner::bug
  14: rustc_errors::Handler::bug
  15: rustc_middle::util::bug::opt_span_bug_fmt::{{closure}}
  16: rustc_middle::ty::context::tls::with_opt::{{closure}}
  17: rustc_middle::ty::context::tls::with_opt
  18: rustc_middle::util::bug::opt_span_bug_fmt
  19: rustc_middle::util::bug::bug_fmt
  20: rustc_middle::ty::context::tls::with_context::{{closure}}
  21: rustc_trait_selection::traits::codegen::codegen_fulfill_obligation
  22: rustc_middle::ty::query::<impl rustc_query_system::query::config::QueryAccessors<rustc_middle::ty::context::TyCtxt> for rustc_middle::ty::query::queries::codegen_fulfill_obligation>::compute
  23: rustc_query_system::dep_graph::graph::DepGraph<K>::with_task_impl
  24: rustc_data_structures::stack::ensure_sufficient_stack
  25: rustc_query_system::query::plumbing::get_query_impl
  26: rustc_ty::instance::resolve_instance
  27: rustc_middle::ty::query::<impl rustc_query_system::query::config::QueryAccessors<rustc_middle::ty::context::TyCtxt> for rustc_middle::ty::query::queries::resolve_instance>::compute
  28: rustc_query_system::dep_graph::graph::DepGraph<K>::with_task_impl
  29: rustc_data_structures::stack::ensure_sufficient_stack
  30: rustc_query_system::query::plumbing::get_query_impl
  31: rustc_middle::ty::instance::Instance::resolve
  32: <rustc_mir::monomorphize::collector::MirNeighborCollector as rustc_middle::mir::visit::Visitor>::visit_terminator_kind
  33: rustc_mir::monomorphize::collector::collect_neighbours
  34: rustc_data_structures::stack::ensure_sufficient_stack
  35: rustc_mir::monomorphize::collector::collect_items_rec
  36: rustc_mir::monomorphize::collector::collect_items_rec
  37: rustc_mir::monomorphize::collector::collect_crate_mono_items
  38: rustc_mir::monomorphize::partitioning::collect_and_partition_mono_items
  39: rustc_middle::ty::query::<impl rustc_query_system::query::config::QueryAccessors<rustc_middle::ty::context::TyCtxt> for rustc_middle::ty::query::queries::collect_and_partition_mono_items>::compute
  40: rustc_query_system::dep_graph::graph::DepGraph<K>::with_task_impl
  41: rustc_data_structures::stack::ensure_sufficient_stack
  42: rustc_query_system::query::plumbing::get_query_impl
  43: rustc_codegen_ssa::base::codegen_crate
  44: <rustc_codegen_llvm::LlvmCodegenBackend as rustc_codegen_ssa::traits::backend::CodegenBackend>::codegen_crate
  45: rustc_interface::passes::start_codegen
  46: rustc_middle::ty::context::tls::enter_global
  47: rustc_interface::queries::Queries::ongoing_codegen
  48: rustc_interface::interface::run_compiler_in_existing_thread_pool
  49: rustc_ast::attr::with_globals
note: Some details are omitted, run with `RUST_BACKTRACE=full` for a verbose backtrace.

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 1.45.0-nightly (4bd32c980 2020-05-29) running on x86_64-unknown-linux-gnu

note: compiler flags: -C embed-bitcode=no -C codegen-units=1 -C debuginfo=2 --crate-type bin

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

query stack during panic:
#0 [codegen_fulfill_obligation] checking if `std::ops::Fn` fulfills its obligations
#1 [resolve_instance] resolving instance `<[closure@src/main.rs:19:23: 21:6] as std::ops::Fn<(std::iter::Filter<std::slice::Iter<i32>, [closure@src/main.rs:6:24: 6:36]>,)>>::call`
#2 [collect_and_partition_mono_items] collect_and_partition_mono_items
end of query stack

[Patryk27]

Just for reference - works fine with explicit lifetimes:

fn with_positive<'a, F>(vals: &'a [i32], fun: F)
where
    F: Fn(FilteredIter<'a>),
{
    fun(filter_positive(vals));
}

[SNCPlay42]

@rustbot modify labels: +requires-nightly +F-type_alias_impl_trait

[hellow554]

Smaller:

#![feature(type_alias_impl_trait)]

trait T { type Item; }

type Alias<'a> = impl T<Item = &'a ()>;

struct S;
impl<'a> T for &'a S {
    type Item = &'a ();
}

fn filter_positive<'a>() -> Alias<'a> {
    &S
}

fn with_positive(fun: impl Fn(Alias<'_>)) {
    fun(filter_positive());
}

fn main() {
    with_positive(|_| ());
}

[JohnTitor]

Seems this is fixed in the latest nightly (not bisected yet). Marking as E-needs-test and will try to bisect later.

[matthiaskrgr]

Still crashes with -Zmir-opt-level=2

error: internal compiler error: Encountered error `Unimplemented` selecting `Binder(<impl Fn(Alias<'_>) as std::ops::Fn<(impl T,)>>)` during codegen
  |
  = note: delayed at /home/matthias/vcs/github/rust/src/librustc_session/session.rs:441:27

thread 'rustc' panicked at 'no errors encountered even though `delay_span_bug` issued', src/librustc_errors/lib.rs:366:17
stack backtrace:
   0:     0x7f6662e2ae31 - <std::sys_common::backtrace::_print::DisplayBacktrace as core::fmt::Display>::fmt::h9a65342185cb7022
   1:     0x7f6662e999dd - core::fmt::write::hc3de054a6627b208
   2:     0x7f6662e0ab53 - std::io::Write::write_fmt::h64bd8d8dca95fd5c
   3:     0x7f6662e03bb0 - std::panicking::default_hook::{{closure}}::ha9c6947a872dc513
   4:     0x7f6662e037ed - std::panicking::default_hook::h3e5e46d076456208
   5:     0x7f6663ef0269 - rustc_driver::report_ice::he0572c9ff71e0a8c
   6:     0x7f6662e041f6 - std::panicking::rust_panic_with_hook::h30c558028146672c
   7:     0x7f6666991a56 - std::panicking::begin_panic::{{closure}}::h62cde3015c32ea83
   8:     0x7f666699191e - std::sys_common::backtrace::__rust_end_short_backtrace::h8d34e3f6f4e20c59
   9:     0x7f666696859c - std::panicking::begin_panic::h6e7f1f8f159dddb1
  10:     0x7f6666971dae - <rustc_errors::HandlerInner as core::ops::drop::Drop>::drop::h5013360fb564f32c
  11:     0x7f6663d4a3d6 - core::ptr::drop_in_place::h4e9bf5d5a9a1b0b3
  12:     0x7f6663d6dad0 - <alloc::rc::Rc<T> as core::ops::drop::Drop>::drop::h0ba476d8189f3dd5
  13:     0x7f6663ec6a4d - core::ptr::drop_in_place::hb83cdb4088f009cf
  14:     0x7f6663eacc92 - rustc_span::with_source_map::hdfa547cd4d1341a2
  15:     0x7f6663d24038 - rustc_interface::interface::create_compiler_and_run::h10b475d531695c0e
  16:     0x7f6663eb7bfd - std::sys_common::backtrace::__rust_begin_short_backtrace::h4c9162f49c0dc935
  17:     0x7f6663eba9be - core::ops::function::FnOnce::call_once{{vtable.shim}}::hbba71a1842b71242
  18:     0x7f6662e05cda - std::sys::unix::thread::Thread::new::thread_start::hdc96d124dc384f80
  19:     0x7f665fc04422 - start_thread
  20:     0x7f6662c07bf3 - __clone
  21:                0x0 - <unknown>

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 1.47.0-dev running on x86_64-unknown-linux-gnu

note: compiler flags: -Z mir-opt-level=2

query stack during panic:
end of query stack

[JohnTitor]

Ohh, good catch! Still, the regression test here is useful but let's keep this open then :)

Oops, closed by mistake XD