Compiler panic with generic_associated_types

[Vrixyz]

Hello, while attempting to use a lifetime bound to a generic associated type, the compiler ended up in panicking.

I tried this code (roughly 80 lines of Rust, but with specs and nphysics dependencies...)

Vrixyz/testbed-callback#2

I expected to see this happen: Not a compiler panic, I guess "You are not correctly using generic_associated_types"

Meta

All details are in my repository linked above, but for convenience, I'll paste my output :

cargo run --verbose

Compiling testbed_callback v0.1.0 (file:///Users/***/Documents/perso/testbed-callback)
     Running `rustc --crate-name testbed_callback src/main.rs --crate-type bin --emit=dep-info,link -C debuginfo=2 -C metadata=8c68544d0e3087a8 -C extra-filename=-8c68544d0e3087a8 --out-dir /Users/***/Documents/perso/testbed-callback/target/debug/deps -C incremental=/Users/***/Documents/perso/testbed-callback/target/debug/incremental -L dependency=/Users/***/Documents/perso/testbed-callback/target/debug/deps --extern nalgebra=/Users/***/Documents/perso/testbed-callback/target/debug/deps/libnalgebra-a27da1ab88af398c.rlib --extern ncollide2d=/Users/***/Documents/perso/testbed-callback/target/debug/deps/libncollide2d-c5db2bf8d498f1fe.rlib --extern nphysics2d=/Users/***/Documents/perso/testbed-callback/target/debug/deps/libnphysics2d-fab013328e575c2c.rlib --extern nphysics_testbed2d=/Users/***/Documents/perso/testbed-callback/target/debug/deps/libnphysics_testbed2d-fd50d71f04d30a0f.rlib --extern specs=/Users/***/Documents/perso/testbed-callback/target/debug/deps/libspecs-2561d670a586ca05.rlib`
error: internal compiler error: librustc/ty/subst.rs:425: Region parameter out of range when substituting in region 'b (root type=Some((specs::Write<'a, PhysicsWorld<'b>>,))) (index=2)

thread 'main' panicked at 'Box<Any>', librustc_errors/lib.rs:517:9
note: Run with `RUST_BACKTRACE=1` for a backtrace.
error: aborting due to previous error


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 1.30.0-nightly (d5a448b3f 2018-08-13) running on x86_64-apple-darwin

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

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

error: Could not compile `testbed_callback`.

Caused by:
  process didn't exit successfully: `rustc --crate-name testbed_callback src/main.rs --crate-type bin --emit=dep-info,link -C debuginfo=2 -C metadata=8c68544d0e3087a8 -C extra-filename=-8c68544d0e3087a8 --out-dir /Users/***/Documents/perso/testbed-callback/target/debug/deps -C incremental=/Users/***/Documents/perso/testbed-callback/target/debug/incremental -L dependency=/Users/***/Documents/perso/testbed-callback/target/debug/deps --extern nalgebra=/Users/***/Documents/perso/testbed-callback/target/debug/deps/libnalgebra-a27da1ab88af398c.rlib --extern ncollide2d=/Users/***/Documents/perso/testbed-callback/target/debug/deps/libncollide2d-c5db2bf8d498f1fe.rlib --extern nphysics2d=/Users/***/Documents/perso/testbed-callback/target/debug/deps/libnphysics2d-fab013328e575c2c.rlib --extern nphysics_testbed2d=/Users/***/Documents/perso/testbed-callback/target/debug/deps/libnphysics_testbed2d-fd50d71f04d30a0f.rlib --extern specs=/Users/***/Documents/perso/testbed-callback/target/debug/deps/libspecs-2561d670a586ca05.rlib` (exit code: 101)

Backtrace

stack backtrace:
   0: std::sys::unix::backtrace::tracing::imp::unwind_backtrace
   1: std::sys_common::backtrace::print
   2: std::panicking::default_hook::{{closure}}
   3: std::panicking::default_hook
   4: rustc::util::common::panic_hook
   5: std::panicking::rust_panic_with_hook
   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::ty::subst::SubstFolder<'a, 'gcx, 'tcx> as rustc::ty::fold::TypeFolder<'gcx, 'tcx>>::fold_region
  15: rustc::ty::fold::TypeFoldable::fold_with
  16: rustc::ty::structural_impls::<impl rustc::ty::fold::TypeFoldable<'tcx> for &'tcx rustc::ty::TyS<'tcx>>::super_fold_with
  17: <rustc::ty::subst::SubstFolder<'a, 'gcx, 'tcx> as rustc::ty::fold::TypeFolder<'gcx, 'tcx>>::fold_ty
  18: rustc::ty::fold::TypeFoldable::fold_with
  19: rustc::ty::structural_impls::<impl rustc::ty::fold::TypeFoldable<'tcx> for &'tcx rustc::ty::TyS<'tcx>>::super_fold_with
  20: <rustc::ty::subst::SubstFolder<'a, 'gcx, 'tcx> as rustc::ty::fold::TypeFolder<'gcx, 'tcx>>::fold_ty
  21: rustc::ty::fold::TypeFoldable::fold_with
  22: rustc::ty::structural_impls::<impl rustc::ty::fold::TypeFoldable<'tcx> for &'tcx rustc::ty::TyS<'tcx>>::super_fold_with
  23: <rustc::ty::subst::SubstFolder<'a, 'gcx, 'tcx> as rustc::ty::fold::TypeFolder<'gcx, 'tcx>>::fold_ty
  24: rustc::traits::project::opt_normalize_projection_type
  25: rustc::traits::project::normalize_projection_type
  26: <rustc::traits::project::AssociatedTypeNormalizer<'a, 'b, 'gcx, 'tcx> as rustc::ty::fold::TypeFolder<'gcx, 'tcx>>::fold_ty
  27: rustc::ty::fold::TypeFoldable::fold_with
  28: rustc::ty::fold::TypeFoldable::fold_with
  29: rustc::traits::project::normalize
  30: core::ops::function::impls::<impl core::ops::function::FnOnce<A> for &'a mut F>::call_once
  31: <core::iter::FlatMap<I, U, F> as core::iter::iterator::Iterator>::next
  32: <alloc::vec::Vec<T> as alloc::vec::SpecExtend<T, I>>::from_iter
  33: rustc::ty::wf::WfPredicates::normalize
  34: rustc::ty::wf::trait_obligations
  35: rustc::ty::context::tls::with_related_context
  36: rustc::infer::InferCtxtBuilder::enter
  37: rustc_typeck::check::wfcheck::check_item_well_formed
  38: rustc::ty::query::<impl rustc::ty::query::config::QueryAccessors<'tcx> for rustc::ty::query::queries::check_item_well_formed<'tcx>>::compute
  39: rustc::ty::context::tls::with_context
  40: rustc::dep_graph::graph::DepGraph::with_task_impl
  41: <rustc::ty::query::plumbing::JobOwner<'a, 'tcx, Q>>::start
  42: rustc::ty::query::plumbing::<impl rustc::ty::context::TyCtxt<'a, 'gcx, 'tcx>>::force_query_with_job
  43: rustc::ty::query::plumbing::<impl rustc::ty::context::TyCtxt<'a, 'gcx, 'tcx>>::get_query
  44: rustc::ty::query::plumbing::<impl rustc::ty::context::TyCtxt<'a, 'gcx, 'tcx>>::ensure_query
  45: rustc::hir::Crate::visit_all_item_likes
  46: rustc::session::Session::track_errors
  47: rustc_typeck::check_crate
  48: rustc::ty::context::tls::enter_context
  49: <std::thread::local::LocalKey<T>>::with
  50: rustc::ty::context::TyCtxt::create_and_enter
  51: rustc_driver::driver::compile_input
  52: rustc_driver::run_compiler_with_pool
  53: syntax::with_globals
  54: <std::panic::AssertUnwindSafe<F> as core::ops::function::FnOnce<()>>::call_once
  55: __rust_maybe_catch_panic
  56: rustc_driver::run
  57: rustc_driver::main
  58: std::rt::lang_start::{{closure}}
  59: std::panicking::try::do_call
  60: __rust_maybe_catch_panic
  61: std::rt::lang_start_internal
  62: main
query stack during panic:
#0 [check_item_well_formed] processing `<DummySystem as specs::System<'a>>`
end of query stack
error: aborting due to previous error

[varkor]

Generic associated types haven't been implemented yet, despite there being a feature flag for them, so this error is actually expected. Closing this as a duplicate of #49362.