Existential type doc example ICE

[DutchGhost]

Trying to run 'cargo test' on https://github.com/DutchGhost/rust_fun/blob/master/src/lib.rs, ICE's on the compose documentation example.

Backtrace:

---- src\lib.rs - compose (line 12) stdout ----
thread 'src\lib.rs - compose (line 12)' panicked at 'librustc_resolve\build_reduced_graph.rs:741: unexpected definition: Existential(DefId(9/0:3))', librustc\util\bug.rs:47:26
stack backtrace:
   0: <std::sys::windows::args::Args as core::ops::drop::Drop>::drop
   1: <std::sys::windows::dynamic_lib::DynamicLibrary as core::ops::drop::Drop>::drop
   2: std::panicking::take_hook
   3: std::panicking::take_hook
   4: <rustc::ty::sty::Binder<rustc::ty::ProjectionPredicate<'tcx>> as rustc::ty::ToPredicate<'tcx>>::to_predicate
   5: std::panicking::rust_panic_with_hook
   6: <rustc::hir::intravisit::IdRange as core::fmt::Debug>::fmt
   7: rustc::util::bug::bug_fmt
   8: rustc::ty::context::tls::track_diagnostic
   9: rustc::ty::context::tls::track_diagnostic
  10: rustc::ty::context::tls::track_diagnostic
  11: rustc::util::bug::bug_fmt
  12: rustc::util::bug::bug_fmt
  13: rustc_resolve::build_reduced_graph::<impl rustc_resolve::Resolver<'a, 'cl>>::populate_module_if_necessary
  14: rustc_resolve::build_reduced_graph::<impl rustc_resolve::ToNameBinding<'a> for (&'a rustc_resolve::ModuleData<'a>, rustc::ty::Visibility, syntax_pos::span_encoding::Span, syntax_pos::hygiene::Mark)>::to_name_binding
  15: <rustc_resolve::build_reduced_graph::BuildReducedGraphVisitor<'a, 'b, 'cl> as syntax::visit::Visitor<'a>>::visit_item
  16: <rustc_resolve::BindingError as core::cmp::PartialOrd>::partial_cmp
  17: <rustc_resolve::build_reduced_graph::BuildReducedGraphVisitor<'a, 'b, 'cl> as syntax::visit::Visitor<'a>>::visit_item
  18: <rustc_resolve::BindingError as core::cmp::PartialOrd>::partial_cmp
  19: rustc_resolve::macros::<impl syntax::ext::base::Resolver for rustc_resolve::Resolver<'a, 'crateloader>>::visit_ast_fragment_with_placeholders
  20: syntax::ext::expand::MacroExpander::expand_crate
  21: syntax::ext::expand::MacroExpander::expand_crate
  22: syntax::ext::expand::MacroExpander::expand_crate
  23: <unknown>
  24: <unknown>
  25: rustc_driver::driver::count_nodes
  26: rustc_driver::driver::compile_input
  27: <unknown>
  28: _rust_maybe_catch_panic
  29: <unknown>
  30: <unknown>
  31: <unknown>
  32: <unknown>
  33: <unknown>
  34: _rust_maybe_catch_panic
  35: <unknown>
  36: <unknown>
  37: test::Metric::new
  38: _rust_maybe_catch_panic
  39: <test::TestOpts as core::fmt::Debug>::fmt
  40: test::stats::winsorize
  41: _rust_maybe_catch_panic
  42: test::stats::winsorize
  43: std::process::id
  44: std::sys::windows::thread::Thread::new
  45: BaseThreadInitThunk
  46: RtlUserThreadStart
query stack during panic:
end of query stack
thread 'src\lib.rs - compose (line 12)' panicked at 'couldn't compile the test', librustdoc\test.rs:333:13
stack backtrace:
   0: <std::sys::windows::args::Args as core::ops::drop::Drop>::drop
   1: <std::sys::windows::dynamic_lib::DynamicLibrary as core::ops::drop::Drop>::drop
   2: std::panicking::take_hook
   3: std::panicking::take_hook
   4: <rustc::ty::sty::Binder<rustc::ty::ProjectionPredicate<'tcx>> as rustc::ty::ToPredicate<'tcx>>::to_predicate
   5: std::panicking::rust_panic_with_hook
   6: <unknown>
   7: <unknown>
   8: <unknown>
   9: <unknown>
  10: <unknown>
  11: _rust_maybe_catch_panic
  12: <unknown>
  13: <unknown>
  14: test::Metric::new
  15: _rust_maybe_catch_panic
  16: <test::TestOpts as core::fmt::Debug>::fmt
  17: test::stats::winsorize
  18: _rust_maybe_catch_panic
  19: test::stats::winsorize
  20: std::process::id
  21: std::sys::windows::thread::Thread::new
  22: BaseThreadInitThunk
  23: RtlUserThreadStart
query stack during panic:
end of query stack

Playground: https://play.rust-lang.org/?version=nightly&mode=debug&edition=2015

[Arnavion]

Duplicate of #53443