ICE with GATs #50115

Boscop · 2018-04-20T13:36:21Z

What is the right way to do this?

pub trait ChanFx2: Clone + Default {
	type Ctx<'a> = ChannelProcessParams<'a>; // GAT with default type
	fn process<'a>(&mut self, msgs: Vec<MidiMsg>, params: &ChannelProcessParams<'a>, ctx: &Self::Ctx<'a>) -> Vec<MidiMsg>;
}

error: lifetime parameters are not allowed on this type

It's underlinining &Self::Ctx<'a> but how else am I supposed to instantiate the GAT with a lifetime?
Now I tried to omit the <'a>:

pub trait ChanFx2: Clone + Default {
	type Ctx<'a> = ChannelProcessParams<'a>;
	fn process<'a>(&mut self, msgs: Vec<MidiMsg>, params: &ChannelProcessParams<'a>, ctx: &Self::Ctx/*<'a>*/) -> Vec<MidiMsg>;
}

struct MidiMerger {}

struct SidechainCtx<'a> {
	inherited: ChannelProcessParams<'a>,
	sc_msgs: Vec<MidiMsg>,
}

impl ChanFx2 for MidiMerger {
	type Ctx<'a> = SidechainCtx<'a>;
	fn process<'a>(&mut self, mut msgs: Vec<MidiMsg>, params: &ChannelProcessParams<'a>, ctx: &Self::Ctx/*<'a>*/) -> Vec<MidiMsg> {
		msgs.extend(ctx.sc_msgs);
		msgs
	}
}

But I get this (ICE):

error: internal compiler error: src\main.rs:1: librustc\ty\subst.rs:427: Region parameter out of range when substituting in region 'a (root type=Some(fx::multichanfx::SidechainCtx<'a>)) (index=0)
thread 'rustc' panicked at 'Box<Any>', librustc_errors\lib.rs:482:9
stack backtrace:
   0: _rdl_shrink_in_place
   1: std::panicking::take_hook
   2: std::panicking::take_hook
   3: <unknown>
   4: std::panicking::rust_panic_with_hook
   5: <unknown>
   6: <unknown>
   7: rustc::session::bug_fmt
   8: rustc::ty::context::tls::span_debug
   9: rustc::ty::context::tls::span_debug
  10: <unknown>
  11: <unknown>
  12: rustc::ty::context::tls::span_debug
  13: rustc::ty::context::tls::span_debug
  14: rustc::session::bug_fmt
  15: rustc::session::bug_fmt
  16: <rustc::ty::subst::SubstFolder<'a, 'gcx, 'tcx> as rustc::ty::fold::TypeFolder<'gcx, 'tcx>>::fold_region
  17: rustc::ty::subst::<impl rustc::ty::Slice<rustc::ty::subst::Kind<'tcx>>>::truncate_to
  18: <rustc::ty::subst::SubstFolder<'a, 'gcx, 'tcx> as rustc::ty::fold::TypeFolder<'gcx, 'tcx>>::fold_ty
  19: rustc::traits::project::normalize_projection_type
  20: rustc::traits::project::normalize_projection_type
  21: rustc::traits::project::normalize_projection_type
  22: rustc::traits::project::normalize_projection_type
  23: <rustc::traits::project::AssociatedTypeNormalizer<'a, 'b, 'gcx, 'tcx> as rustc::ty::fold::TypeFolder<'gcx, 'tcx>>::fold_ty
  24: rustc::ty::subst::<impl rustc::ty::Slice<rustc::ty::subst::Kind<'tcx>>>::truncate_to
  25: rustc::ty::structural_impls::<impl rustc::ty::context::Lift<'tcx> for rustc::ty::layout::LayoutError<'a>>::lift_to_tcx
  26: rustc::traits::project::poly_project_and_unify_type
  27: rustc::ty::wf::predicate_obligations
  28: <unknown>
  29: <unknown>
  30: rustc::ty::wf::trait_obligations
  31: <rustc_typeck::check::upvar::InferBorrowKind<'a, 'gcx, 'tcx> as rustc::middle::expr_use_visitor::Delegate<'tcx>>::mutate
  32: <rustc_typeck::check::wfcheck::CheckTypeWellFormedVisitor<'a, 'tcx> as rustc::hir::intravisit::Visitor<'v>>::visit_item
  33: rustc_typeck::check_crate
  34: rustc_typeck::check_crate
  35: <rustc_driver::derive_registrar::Finder as rustc::hir::itemlikevisit::ItemLikeVisitor<'v>>::visit_impl_item
  36: rustc_driver::driver::compile_input
  37: rustc_driver::run_compiler
  38: <unknown>
  39: _rust_maybe_catch_panic
  40: <rustc_driver::derive_registrar::Finder as rustc::hir::itemlikevisit::ItemLikeVisitor<'v>>::visit_impl_item
  41: std::sys::windows::thread::Thread::new
  42: BaseThreadInitThunk
  43: RtlUserThreadStart

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 1.26.0-nightly (2789b067d 2018-03-06) running on x86_64-pc-windows-msvc

note: compiler flags: -C opt-level=1 -C debuginfo=2 -C debug-assertions=on -C incremental -C target-cpu=native --crate-type bin

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

What is the correct way to instantiate the GAT with a lifetime here?

The text was updated successfully, but these errors were encountered:

Boscop · 2018-04-20T13:42:29Z

Similar situation with this, what's the right way to instantiate the GAT (with types this time)?

pub trait ToOther {
	type Other<P: AsPitch, V: AsVal, B: AsPitchBend>;

	fn to_other<Pitch: AsPitch, Val: AsVal, Pb: AsPitchBend>(&self) -> Self::Other/*<Pitch, Val, Pb>*/;
}

impl<Pitch: AsPitch, Val: AsVal, Pb: AsPitchBend> ToOther for HighLvlMsg<Pitch, Val, Pb> {
	type Other<P, V, B> = HighLvlMsg<P, V, B>;

	fn to_other<Pitch2: AsPitch, Val2: AsVal, Pb2: AsPitchBend>(&self) -> Self::Other/*<Pitch2, Val2, Pb2>*/ {
		use HighLvlMsg::*;

		match *self {
			NoteOn { pitch, vel, len } => NoteOn { pitch: AsPitch::conv(pitch), vel, len },
			NoteOff { pitch, vel } => NoteOff { pitch: AsPitch::conv(pitch), vel },
			ControlChange { cc, val } => ControlChange { cc, val: AsVal::conv(val) },
			ProgramChange { prog } => ProgramChange { prog },
			PitchBend { semitones } => PitchBend { semitones: AsPitchBend::conv(semitones) },
			PolyphonicAftertouch { pitch, val } => PolyphonicAftertouch { pitch: AsPitch::conv(pitch), val: AsVal::conv(val) },
			ChannelAftertouch { val } => ChannelAftertouch { val: AsVal::conv(val) },
		}
	}
}

error: internal compiler error: src\lib.rs:1: librustc\ty\subst.rs:481: Type parameter `P/#3` (P/3) out of range when substituting (root type=Some(highlvl::HighLvlMsg<P, V, B>)) substs=[_, _, _]
thread 'rustc' panicked at 'Box<Any>', librustc_errors\lib.rs:482:9
stack backtrace:
   0: _rdl_shrink_in_place
   1: std::panicking::take_hook
   2: std::panicking::take_hook
   3: <unknown>
   4: std::panicking::rust_panic_with_hook
   5: <unknown>
   6: <unknown>
   7: rustc::session::bug_fmt
   8: rustc::ty::context::tls::span_debug
   9: rustc::ty::context::tls::span_debug
  10: <unknown>
  11: <unknown>
  12: rustc::ty::context::tls::span_debug
  13: rustc::ty::context::tls::span_debug
  14: rustc::session::bug_fmt
  15: rustc::session::bug_fmt
  16: <rustc::ty::subst::SubstFolder<'a, 'gcx, 'tcx> as rustc::ty::fold::TypeFolder<'gcx, 'tcx>>::fold_ty
  17: rustc::ty::subst::<impl rustc::ty::Slice<rustc::ty::subst::Kind<'tcx>>>::truncate_to
  18: <rustc::ty::subst::SubstFolder<'a, 'gcx, 'tcx> as rustc::ty::fold::TypeFolder<'gcx, 'tcx>>::fold_ty
  19: rustc::traits::project::normalize_projection_type
  20: rustc::traits::project::normalize_projection_type
  21: rustc::traits::project::normalize_projection_type
  22: rustc::traits::project::normalize_projection_type
  23: <rustc::traits::project::AssociatedTypeNormalizer<'a, 'b, 'gcx, 'tcx> as rustc::ty::fold::TypeFolder<'gcx, 'tcx>>::fold_ty
  24: rustc::ty::subst::<impl rustc::ty::Slice<rustc::ty::subst::Kind<'tcx>>>::truncate_to
  25: rustc::ty::structural_impls::<impl rustc::ty::context::Lift<'tcx> for rustc::ty::layout::LayoutError<'a>>::lift_to_tcx
  26: rustc::traits::project::poly_project_and_unify_type
  27: rustc::ty::wf::predicate_obligations
  28: <unknown>
  29: <unknown>
  30: rustc::ty::wf::trait_obligations
  31: <rustc_typeck::check::upvar::InferBorrowKind<'a, 'gcx, 'tcx> as rustc::middle::expr_use_visitor::Delegate<'tcx>>::mutate
  32: <rustc_typeck::check::wfcheck::CheckTypeWellFormedVisitor<'a, 'tcx> as rustc::hir::intravisit::Visitor<'v>>::visit_item
  33: rustc_typeck::check_crate
  34: rustc_typeck::check_crate
  35: <rustc_driver::derive_registrar::Finder as rustc::hir::itemlikevisit::ItemLikeVisitor<'v>>::visit_impl_item
  36: rustc_driver::driver::compile_input
  37: rustc_driver::run_compiler
  38: <unknown>
  39: _rust_maybe_catch_panic
  40: <rustc_driver::derive_registrar::Finder as rustc::hir::itemlikevisit::ItemLikeVisitor<'v>>::visit_impl_item
  41: std::sys::windows::thread::Thread::new
  42: BaseThreadInitThunk
  43: RtlUserThreadStart

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 1.26.0-nightly (2789b067d 2018-03-06) running on x86_64-pc-windows-msvc

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

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

pietroalbini · 2018-04-20T20:26:57Z

Thanks for reporting this! Can you provide a small example to reproduce the ICE? With the custom types you used it's difficult for us to bisect/reproduce ourself :)

Boscop · 2018-04-20T22:50:06Z

#![feature(generic_associated_types)]
#![feature(associated_type_defaults)]

struct Foo;
struct Bar;
struct Baz;

struct A<'a> {
	foo: &'a Foo,
}

struct B<'a> {
	inherited: A<'a>,
	own: Bar,
}

trait Trait: Clone + Default {
	type Ctx<'a> = A<'a>;
	fn process<'a>(&mut self, ctx: &Self::Ctx/*<'a>*/);
}

impl Trait for Baz {
	type Ctx<'a> = B<'a>;
	fn process<'a>(&mut self, ctx: &Self::Ctx/*<'a>*/) {}
}

fn main() {}

https://play.rust-lang.org/?gist=5fc07e14a633f3ec4db4de1c421053ff&version=nightly

sinkuu · 2018-04-21T00:41:19Z

This seems to be a known issue. GAT (#44265) is a WIP feature and probably not supposed to be usable yet.

rust/src/test/ui/rfc1598-generic-associated-types/streaming_iterator.rs

Lines 13 to 14 in a10bb6b

    
           //FIXME(#44265): "lifetime parameter not allowed on this type" errors will be addressed in a 
        
           // follow-up PR

dtolnay · 2018-06-16T15:44:03Z

Closing as a duplicate of #49362.

pietroalbini added I-ICE Issue: The compiler panicked, giving an Internal Compilation Error (ICE) ❄️ T-compiler Relevant to the compiler team, which will review and decide on the PR/issue. C-bug Category: This is a bug. labels Apr 20, 2018

This was referenced Apr 21, 2018

Generic associated types (associated type constructors) rust-lang/rfcs#1598

Merged

Rustc should be able to unify <T as A<'static>>::B> with <T as A<'a>>::B> for all 'a, given A::B: 'static #50166

Open

dtolnay closed this as completed Jun 16, 2018

Centril added the F-generic_associated_types `#![feature(generic_associated_types)]` a.k.a. GATs label Aug 5, 2019

fmease added the A-GATs Area: Generic associated types (GATs) label Nov 2, 2024

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ICE with GATs #50115

ICE with GATs #50115

Boscop commented Apr 20, 2018 •

edited

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Boscop commented Apr 20, 2018

pietroalbini commented Apr 20, 2018

Boscop commented Apr 20, 2018

sinkuu commented Apr 21, 2018

dtolnay commented Jun 16, 2018

ICE with GATs #50115

ICE with GATs #50115

Comments

Boscop commented Apr 20, 2018 • edited Loading

Boscop commented Apr 20, 2018

pietroalbini commented Apr 20, 2018

Boscop commented Apr 20, 2018

sinkuu commented Apr 21, 2018

dtolnay commented Jun 16, 2018

Boscop commented Apr 20, 2018 •

edited

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