ICE when using nalgebra type in impl Trait type alias.

[connerebbinghaus]

Code

src/lib.rs

#![feature(type_alias_impl_trait)]
use nalgebra::Vector3;

pub type A = impl Fn(Vector3<f64>);

pub fn foo() -> A {
    |_| ()
}

Cargo.toml

[package]
name = "bug"
version = "0.1.0"
edition = "2018"

[dependencies]
nalgebra = "0.21"

Meta

rustc --version --verbose:

rustc 1.46.0-nightly (daecab3a7 2020-07-10)
binary: rustc
commit-hash: daecab3a784f28082df90cebb204998051f3557d
commit-date: 2020-07-10
host: x86_64-unknown-linux-gnu
release: 1.46.0-nightly
LLVM version: 10.0

Error output

error: internal compiler error: src/librustc_mir/borrow_check/type_check/free_region_relations.rs:324:33: failed to compute implied bounds impl std::ops::Fn<(nalgebra::Matrix<f64, nalgebra::U3, nalgebra::U1, <nalgebra::DefaultAllocator as nalgebra::allocator::Allocator<f64, nalgebra::U3>>::Buffer>,)>

thread 'rustc' panicked at 'Box<Any>', src/librustc_errors/lib.rs:916:9
note: run with `RUST_BACKTRACE=1` environment variable to display a 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 1.46.0-nightly (daecab3a7 2020-07-10) 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

error: aborting due to previous error

error: could not compile `bug`.

To learn more, run the command again with --verbose.

Backtrace

error: internal compiler error: src/librustc_mir/borrow_check/type_check/free_region_relations.rs:324:33: failed to compute implied bounds impl std::ops::Fn<(nalgebra::Matrix<f64, nalgebra::U3, nalgebra::U1, <nalgebra::DefaultAllocator as nalgebra::allocator::Allocator<f64, nalgebra::U3>>::Buffer>,)>

thread 'rustc' panicked at 'Box<Any>', src/librustc_errors/lib.rs:916:9
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:217
  10: rustc_driver::report_ice
  11: std::panicking::rust_panic_with_hook
             at src/libstd/panicking.rs:530
  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_mir::borrow_check::type_check::free_region_relations::UniversalRegionRelationsBuilder::add_implied_bounds::{{closure}}
  21: core::ops::function::impls::<impl core::ops::function::FnOnce<A> for &mut F>::call_once
  22: <core::iter::adapters::flatten::FlatMap<I,U,F> as core::iter::traits::iterator::Iterator>::next
  23: <alloc::vec::Vec<T> as alloc::vec::SpecExtend<T,I>>::from_iter
  24: rustc_mir::borrow_check::type_check::free_region_relations::create
  25: rustc_mir::borrow_check::type_check::type_check
  26: rustc_mir::borrow_check::nll::compute_regions
  27: rustc_mir::borrow_check::do_mir_borrowck
  28: rustc_infer::infer::InferCtxtBuilder::enter
  29: rustc_mir::borrow_check::mir_borrowck
  30: rustc_middle::ty::query::<impl rustc_query_system::query::config::QueryAccessors<rustc_middle::ty::context::TyCtxt> for rustc_middle::ty::query::queries::mir_borrowck>::compute
  31: rustc_middle::dep_graph::<impl rustc_query_system::dep_graph::DepKind for rustc_middle::dep_graph::dep_node::DepKind>::with_deps
  32: rustc_query_system::dep_graph::graph::DepGraph<K>::with_task_impl
  33: rustc_data_structures::stack::ensure_sufficient_stack
  34: rustc_query_system::query::plumbing::get_query_impl
  35: rustc_typeck::collect::type_of::find_opaque_ty_constraints::ConstraintLocator::check
  36: rustc_hir::intravisit::Visitor::visit_nested_item
  37: rustc_typeck::collect::type_of::type_of
  38: rustc_middle::ty::query::<impl rustc_query_system::query::config::QueryAccessors<rustc_middle::ty::context::TyCtxt> for rustc_middle::ty::query::queries::type_of>::compute
  39: rustc_middle::dep_graph::<impl rustc_query_system::dep_graph::DepKind for rustc_middle::dep_graph::dep_node::DepKind>::with_deps
  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_query_system::query::plumbing::ensure_query_impl
  44: <rustc_typeck::collect::CollectItemTypesVisitor as rustc_hir::intravisit::Visitor>::visit_item
  45: rustc_middle::hir::map::Map::visit_item_likes_in_module
  46: rustc_typeck::collect::collect_mod_item_types
  47: rustc_middle::ty::query::<impl rustc_query_system::query::config::QueryAccessors<rustc_middle::ty::context::TyCtxt> for rustc_middle::ty::query::queries::collect_mod_item_types>::compute
  48: rustc_middle::dep_graph::<impl rustc_query_system::dep_graph::DepKind for rustc_middle::dep_graph::dep_node::DepKind>::with_deps
  49: rustc_query_system::dep_graph::graph::DepGraph<K>::with_task_impl
  50: rustc_data_structures::stack::ensure_sufficient_stack
  51: rustc_query_system::query::plumbing::get_query_impl
  52: rustc_query_system::query::plumbing::ensure_query_impl
  53: rustc_session::session::Session::track_errors
  54: rustc_typeck::check_crate
  55: rustc_interface::passes::analysis
  56: rustc_middle::ty::query::<impl rustc_query_system::query::config::QueryAccessors<rustc_middle::ty::context::TyCtxt> for rustc_middle::ty::query::queries::analysis>::compute
  57: rustc_middle::dep_graph::<impl rustc_query_system::dep_graph::DepKind for rustc_middle::dep_graph::dep_node::DepKind>::with_deps
  58: rustc_query_system::dep_graph::graph::DepGraph<K>::with_task_impl
  59: rustc_query_system::query::plumbing::get_query_impl
  60: rustc_middle::ty::context::tls::enter_global
  61: rustc_interface::queries::<impl rustc_interface::interface::Compiler>::enter
  62: rustc_span::with_source_map
  63: rustc_interface::interface::run_compiler_in_existing_thread_pool
  64: scoped_tls::ScopedKey<T>::set
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 1.46.0-nightly (daecab3a7 2020-07-10) 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 [mir_borrowck] borrow-checking `foo`
#1 [type_of] computing type of `A::{{opaque}}#0`
#2 [collect_mod_item_types] collecting item types in top-level module
#3 [analysis] running analysis passes on this crate
end of query stack
error: aborting due to previous error

error: could not compile `bug`.

To learn more, run the command again with --verbose.

Bisection

searched nightlies: from nightly-2019-10-03 to nightly-2020-07-05
regressed nightly: nightly-2020-02-16
searched commits: from 433aae9 to 61d9231
regressed commit: 19288dd

bisected with cargo-bisect-rustc v0.5.1

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

cargo bisect-rustc --start 2019-10-03 --end 2020-07-05 --with-cargo --prompt -- check 

[connorskees]

Minified,

trait Allocator {
    type Buffer;
}

struct DefaultAllocator;

impl<T> Allocator for DefaultAllocator {
    type Buffer = ();
}

type A = impl Fn(<DefaultAllocator as Allocator>::Buffer);

fn foo() -> A {
    |_| ()
}

playground

It seems possible to ICE on stable, though I'm not sure if it counts?

Stable error

rustc --version --verbose
rustc 1.44.1 (c7087fe00 2020-06-17)
binary: rustc
commit-hash: c7087fe00d2ba919df1d813c040a5d47e43b0fe7
commit-date: 2020-06-17
host: x86_64-unknown-linux-gnu
release: 1.44.1
LLVM version: 9.0

error[E0658]: `impl Trait` in type aliases is unstable
  --> src/lib.rs:15:10
   |
15 | type A = impl Fn(Matrix<<DefaultAllocator as Allocator<()>>::Buffer>);
   |          ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
   |
   = note: see issue #63063 <https://github.com/rust-lang/rust/issues/63063> for more information

error: internal compiler error: src/librustc_mir/borrow_check/type_check/free_region_relations.rs:318: failed to compute implied bounds A

thread 'rustc' panicked at 'Box<Any>', src/librustc_errors/lib.rs:904:9
note: run with `RUST_BACKTRACE=1` environment variable to display a 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 1.44.1 (c7087fe00 2020-06-17) running on x86_64-unknown-linux-gnu

note: compiler flags: -C debuginfo=2 -C incremental --crate-type lib

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

error: aborting due to 2 previous errors

For more information about this error, try `rustc --explain E0658`.
error: could not compile `ice`.

[JohnTitor]

The ICE is fixed in the latest nightly, marking as E-needs-test.