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Passing a lifetime GAT to a closure can cause the compiler to run indefinitely #108826

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jihiggins opened this issue Mar 6, 2023 · 11 comments
Open

Passing a lifetime GAT to a closure can cause the compiler to run indefinitely #108826

jihiggins opened this issue Mar 6, 2023 · 11 comments
Labels
C-bug Category: This is a bug. F-generic_associated_types `#![feature(generic_associated_types)]` a.k.a. GATs fixed-by-next-solver Fixed by the next-generation trait solver, `-Znext-solver`. I-hang Issue: The compiler never terminates, due to infinite loops, deadlock, livelock, etc. T-compiler Relevant to the compiler team, which will review and decide on the PR/issue.

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@jihiggins
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Code

I tried to pair it down more, but so far this is the smallest version I could get to cause the issue:

pub trait LendingIterator {
    type Item<'a>
    where
        Self: 'a;

    fn next<'a>(&'a mut self) -> Self::Item<'a>
    where
        Self: 'a;
        
    
    fn filter<P>(self, predicate: P) -> Filter<Self, P>
    where
        Self: Sized,
        for<'a> P: FnMut(&Self::Item<'a>) -> bool,
    {
        Filter {
            stream: self,
            predicate,
        }
    }
}

#[derive(Clone, Debug)]
pub struct Filter<S, P> {
    stream: S,
    predicate: P,
}

impl<S, P> LendingIterator for Filter<S, P>
where
    S: LendingIterator + Unpin,
    for<'a> P: FnMut(&Self::Item<'a>) -> bool,
{
    type Item<'a> = S::Item<'a> where S: 'a;

    fn next<'a>(&'a mut self) -> Self::Item<'a>
    where
        Self: 'a,
    {
        loop {
            let next = self.stream.next()?;
            if (self.predicate)(&next) {
                return Some(());
            }
        }
    }
}

https://play.rust-lang.org/?version=stable&mode=debug&edition=2021&gist=5042463788e49bf6964dfa80dcb5b9bb

Meta

rustc --version --verbose:

rustc 1.70.0-nightly (7820b62d2 2023-03-05)
binary: rustc
commit-hash: 7820b62d20bc548096d4632a3487987308cb4b5d
commit-date: 2023-03-05
host: x86_64-pc-windows-msvc
release: 1.70.0-nightly
LLVM version: 15.0.7

and

rustc 1.67.1 (d5a82bbd2 2023-02-07)
binary: rustc
commit-hash: d5a82bbd26e1ad8b7401f6a718a9c57c96905483
commit-date: 2023-02-07
host: x86_64-pc-windows-gnu
release: 1.67.1
LLVM version: 15.0.6

Error output

There isn't any error output, since the compiler runs indefinitely when encountering this issue.
@jihiggins jihiggins added C-bug Category: This is a bug. 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. labels Mar 6, 2023
@jihiggins jihiggins closed this as not planned Won't fix, can't repro, duplicate, stale Mar 6, 2023
@jihiggins jihiggins reopened this Mar 6, 2023
@jihiggins
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jihiggins commented Mar 6, 2023 •
edited
Loading

It looks like it's not the reference part, I found a case that also causes it where the predicate doesn't take the value by reference, and another case where taking it by reference doesn't cause this behavior

@jihiggins jihiggins changed the title Lifetime GATs passed by reference to a closure cause the compiler to run forever Passing a lifetime GAT to a closure can cause the compiler to run indefinitely Mar 6, 2023
@fmease

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@rustbot rustbot added I-hang Issue: The compiler never terminates, due to infinite loops, deadlock, livelock, etc. and removed I-ICE Issue: The compiler panicked, giving an Internal Compilation Error (ICE) ❄️ labels Mar 6, 2023
@Teapot4195
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Backtrace 
#0  0x00007ff809464ebd in <rustc_middle[ebf260dc149f6367]::traits::ObligationCauseCode as core[20e502c22ca6166f]::cmp::PartialEq>::eq ()
   from C:\usr\local\bin\rustc_driver-eda9524c4e602df3.dll
#1  0x00007ff80946554a in <rustc_middle[ebf260dc149f6367]::traits::ImplDerivedObligationCause as core[20e502c22ca6166f]::cmp::PartialEq>::eq ()
   from C:\usr\local\bin\rustc_driver-eda9524c4e602df3.dll
---collapsed 61 identical stack frames---
#62 0x00007ff80946554a in <rustc_middle[ebf260dc149f6367]::traits::ImplDerivedObligationCause as core[20e502c22ca6166f]::cmp::PartialEq>::eq ()
   from C:\usr\local\bin\rustc_driver-eda9524c4e602df3.dll
#63 0x00007ff809463629 in <hashbrown[a8280373705225ad]::map::HashMap<rustc_infer[f1d617581dd2c354]::traits::Obligation<rustc_middle[ebf260dc149f6367]::ty::Predicate>, (), core[20e502c22ca6166f]::hash::BuildHasherDefault<rustc_hash[c142d14f14395d39]::FxHasher>>>::insert ()
   from C:\usr\local\bin\rustc_driver-eda9524c4e602df3.dll
#64 0x00007ff8093f0df6 in <rustc_data_structures[8c44cb2cf75f2b5c]::sso::map::SsoHashMap<rustc_infer[f1d617581dd2c354]::traits::Obligation<rustc_middle[ebf260dc149f6367]::ty::Predicate>, ()>>::insert ()
   from C:\usr\local\bin\rustc_driver-eda9524c4e602df3.dll
#65 0x00007ff8093cff49 in <alloc[6644710a05fa25bc]::vec::drain_filter::DrainFilter<rustc_infer[f1d617581dd2c354]::traits::Obligation<rustc_middle[ebf260dc149f6367]::ty::Predicate>, rustc_trait_selection[7ec6d0943e96810b]::traits::project::opt_normalize_projection_type::{closure#0}> as core[20e502c22ca6166f]::iter::traits::iterator::Iterator>::next ()
   from C:\usr\local\bin\rustc_driver-eda9524c4e602df3.dll
#66 0x00007ff8093c43fb in core[20e502c22ca6166f]::ptr::drop_in_place::<alloc[6644710a05fa25bc]::vec::drain_filter::DrainFilter<rustc_infer[f1d617581dd2c354]::traits::Obligation<rustc_middle[ebf260dc149f6367]::ty::Predicate>, rustc_trait_selection[7ec6d0943e96810b]::traits::project::opt_normalize_projection_type::{closure#0}>> () from C:\usr\local\bin\rustc_driver-eda9524c4e602df3.dll
#67 0x00007ff80925d9ab in rustc_trait_selection[7ec6d0943e96810b]::traits::project::opt_normalize_projection_type ()
   from C:\usr\local\bin\rustc_driver-eda9524c4e602df3.dll
#68 0x00007ff809254fbb in <rustc_trait_selection[7ec6d0943e96810b]::traits::project::AssocTypeNormalizer as rustc_type_ir[514e0b83b1a29ee1]::fold::TypeFolder<rustc_middle[ebf260dc149f6367]::ty::context::TyCtxt>>::fold_ty ()
   from C:\usr\local\bin\rustc_driver-eda9524c4e602df3.dll
#69 0x00007ff8093aaa9b in <rustc_middle[ebf260dc149f6367]::ty::Ty as rustc_type_ir[514e0b83b1a29ee1]::fold::TypeSuperFoldable<rustc_middle[ebf260dc149f6367]::ty::context::TyCtxt>>::super_fold_with::<rustc_trait_selection[7ec6d0943e96810b]::traits::project::AssocTypeNormalizer> ()
   from C:\usr\local\bin\rustc_driver-eda9524c4e602df3.dll
#70 0x00007ff809254e74 in <rustc_trait_selection[7ec6d0943e96810b]::traits::project::AssocTypeNormalizer as rustc_type_ir[514e0b83b1a29ee1]::fold::TypeFolder<rustc_middle[ebf260dc149f6367]::ty::context::TyCtxt>>::fold_ty ()
   from C:\usr\local\bin\rustc_driver-eda9524c4e602df3.dll
#71 0x00007ff8094030ef in rustc_middle[ebf260dc149f6367]::ty::util::fold_list::<rustc_trait_selection[7ec6d0943e96810b]::traits::project::AssocTypeNormalizer, rustc_middle[ebf260dc149f6367]::ty::Ty, <&rustc_middle[ebf260dc149f6367]::ty::list::List<rustc_middle[ebf260dc149f6367]::ty::Ty> as rustc_type_ir[514e0b83b1a29ee1]::fold::TypeFoldable<rustc_middle[ebf260dc149f6367]::ty::context::TyCtxt>>::try_fold_with<rustc_trait_selection[7ec6d0943e96810b]::traits::project::AssocTypeNormalizer>::{closure#0}> ()
   from C:\usr\local\bin\rustc_driver-eda9524c4e602df3.dll
#72 0x00007ff8093aabd1 in <rustc_middle[ebf260dc149f6367]::ty::Ty as rustc_type_ir[514e0b83b1a29ee1]::fold::TypeSuperFoldable<rustc_middle[ebf260dc149f6367]::ty::context::TyCtxt>>::super_fold_with::<rustc_trait_selection[7ec6d0943e96810b]::traits::project::AssocTypeNormalizer> ()
   from C:\usr\local\bin\rustc_driver-eda9524c4e602df3.dll
#73 0x00007ff809254e74 in <rustc_trait_selection[7ec6d0943e96810b]::traits::project::AssocTypeNormalizer as rustc_type_ir[514e0b83b1a29ee1]::fold::TypeFolder<rustc_middle[ebf260dc149f6367]::ty::context::TyCtxt>>::fold_ty ()
   from C:\usr\local\bin\rustc_driver-eda9524c4e602df3.dll
#74 0x00007ff8092f8cca in <rustc_middle[ebf260dc149f6367]::ty::subst::GenericArg as rustc_type_ir[514e0b83b1a29ee1]::fold::TypeFoldable<rustc_middle[ebf260dc149f6367]::ty::context::TyCtxt>>::try_fold_with::<rustc_trait_selection[7ec6d0943e96810b]::traits::project::AssocTypeNormalizer> ()
   from C:\usr\local\bin\rustc_driver-eda9524c4e602df3.dll
#75 0x00007ff8093b6783 in <&rustc_middle[ebf260dc149f6367]::ty::list::List<rustc_middle[ebf260dc149f6367]::ty::subst::GenericArg> as rustc_type_ir[514e0b83b1a29ee1]::fold::TypeFoldable<rustc_middle[ebf260dc149f6367]::ty::context::TyCtxt>>::try_fold_with::<rustc_trait_selection[7ec6d0943e96810b]::traits::project::AssocTypeNormalizer> () from C:\usr\local\bin\rustc_driver-eda9524c4e602df3.dll
#76 0x00007ff809288e27 in <rustc_middle[ebf260dc149f6367]::ty::sty::AliasTy as rustc_type_ir[514e0b83b1a29ee1]::fold::TypeFoldable<rustc_middle[ebf260dc149f6367]::ty::context::TyCtxt>>::try_fold_with::<rustc_trait_selection[7ec6d0943e96810b]::traits::project::AssocTypeNormalizer> ()
   from C:\usr\local\bin\rustc_driver-eda9524c4e602df3.dll
#77 0x00007ff8093a27b1 in <rustc_middle[ebf260dc149f6367]::ty::PredicateKind as rustc_type_ir[514e0b83b1a29ee1]::fold::TypeFoldable<rustc_middle[ebf260dc149f6367]::ty::context::TyCtxt>>::try_fold_with::<rustc_trait_selection[7ec6d0943e96810b]::traits::project::AssocTypeNormalizer> ()
   from C:\usr\local\bin\rustc_driver-eda9524c4e602df3.dll
#78 0x00007ff80928f38c in <rustc_middle[ebf260dc149f6367]::ty::sty::Binder<rustc_middle[ebf260dc149f6367]::ty::PredicateKind> as rustc_type_ir[514e0b83b1a29ee1]::fold::TypeSuperFoldable<rustc_middle[ebf260dc149f6367]::ty::context::TyCtxt>>::super_fold_with::<rustc_trait_selection[7ec6d0943e96810b]::traits::project::AssocTypeNormalizer> ()
   from C:\usr\local\bin\rustc_driver-eda9524c4e602df3.dll
#79 0x00007ff80933cd22 in <rustc_trait_selection[7ec6d0943e96810b]::traits::project::AssocTypeNormalizer as rustc_type_ir[514e0b83b1a29ee1]::fold::FallibleTypeFolder<rustc_middle[ebf260dc149f6367]::ty::context::TyCtxt>>::try_fold_binder::<rustc_middle[ebf260dc149f6367]::ty::PredicateKind> ()
   from C:\usr\local\bin\rustc_driver-eda9524c4e602df3.dll
#80 0x00007ff8093ac506 in <rustc_middle[ebf260dc149f6367]::ty::Predicate as rustc_type_ir[514e0b83b1a29ee1]::fold::TypeSuperFoldable<rustc_middle[ebf260dc149f6367]::ty::context::TyCtxt>>::super_fold_with::<rustc_trait_selection[7ec6d0943e96810b]::traits::project::AssocTypeNormalizer> ()
   from C:\usr\local\bin\rustc_driver-eda9524c4e602df3.dll
#81 0x00007ff809345426 in <rustc_trait_selection[7ec6d0943e96810b]::traits::project::AssocTypeNormalizer>::fold::<rustc_middle[ebf260dc149f6367]::ty::Predicate> () from C:\usr\local\bin\rustc_driver-eda9524c4e602df3.dll
#82 0x00007ff809348c9e in rustc_trait_selection[7ec6d0943e96810b]::traits::project::normalize_with_depth_to::<rustc_middle[ebf260dc149f6367]::ty::Predicate>
    () from C:\usr\local\bin\rustc_driver-eda9524c4e602df3.dll
#83 0x00007ff809284233 in <rustc_trait_selection[7ec6d0943e96810b]::traits::select::SelectionContext>::impl_or_trait_obligations ()
   from C:\usr\local\bin\rustc_driver-eda9524c4e602df3.dll
#84 0x00007ff809263794 in <rustc_trait_selection[7ec6d0943e96810b]::traits::select::SelectionContext>::vtable_impl ()
   from C:\usr\local\bin\rustc_driver-eda9524c4e602df3.dll
#85 0x00007ff80927284e in <rustc_trait_selection[7ec6d0943e96810b]::traits::select::SelectionContext>::confirm_candidate ()
   from C:\usr\local\bin\rustc_driver-eda9524c4e602df3.dll
---Collapsed 2458 repeating stack frames---
#2543 0x00007ff80927a617 in <rustc_trait_selection[7ec6d0943e96810b]::traits::select::SelectionContext>::select ()
   from C:\usr\local\bin\rustc_driver-eda9524c4e602df3.dll
#2544 0x00007ff8092d4e55 in <rustc_infer[f1d617581dd2c354]::infer::InferCtxt>::commit_if_ok::<(), (), rustc_trait_selection[7ec6d0943e96810b]::traits::project::assemble_candidates_from_impls::{closure#0}> ()
   from C:\usr\local\bin\rustc_driver-eda9524c4e602df3.dll
#2545 0x00007ff80925f2a7 in rustc_trait_selection[7ec6d0943e96810b]::traits::project::opt_normalize_projection_type ()
   from C:\usr\local\bin\rustc_driver-eda9524c4e602df3.dll
#2546 0x00007ff809254fbb in <rustc_trait_selection[7ec6d0943e96810b]::traits::project::AssocTypeNormalizer as rustc_type_ir[514e0b83b1a29ee1]::fold::TypeFolder<rustc_middle[ebf260dc149f6367]::ty::context::TyCtxt>>::fold_ty ()
   from C:\usr\local\bin\rustc_driver-eda9524c4e602df3.dll
#2547 0x00007ff8093aaa9b in <rustc_middle[ebf260dc149f6367]::ty::Ty as rustc_type_ir[514e0b83b1a29ee1]::fold::TypeSuperFoldable<rustc_middle[ebf260dc149f6367]::ty::context::TyCtxt>>::super_fold_with::<rustc_trait_selection[7ec6d0943e96810b]::traits::project::AssocTypeNormalizer> ()
   from C:\usr\local\bin\rustc_driver-eda9524c4e602df3.dll
#2548 0x00007ff809254e74 in <rustc_trait_selection[7ec6d0943e96810b]::traits::project::AssocTypeNormalizer as rustc_type_ir[514e0b83b1a29ee1]::fold::TypeFolder<rustc_middle[ebf260dc149f6367]::ty::context::TyCtxt>>::fold_ty ()
   from C:\usr\local\bin\rustc_driver-eda9524c4e602df3.dll
#2549 0x00007ff8094030ef in rustc_middle[ebf260dc149f6367]::ty::util::fold_list::<rustc_trait_selection[7ec6d0943e96810b]::traits::project::AssocTypeNormalizer, rustc_middle[ebf260dc149f6367]::ty::Ty, <&rustc_middle[ebf260dc149f6367]::ty::list::List<rustc_middle[ebf260dc149f6367]::ty::Ty> as rustc_type_ir[514e0b83b1a29ee1]::fold::TypeFoldable<rustc_middle[ebf260dc149f6367]::ty::context::TyCtxt>>::try_fold_with<rustc_trait_selection[7ec6d0943e96810b]::traits::project::AssocTypeNormalizer>::{closure#0}> ()
   from C:\usr\local\bin\rustc_driver-eda9524c4e602df3.dll
#2550 0x00007ff8093aabd1 in <rustc_middle[ebf260dc149f6367]::ty::Ty as rustc_type_ir[514e0b83b1a29ee1]::fold::TypeSuperFoldable<rustc_middle[ebf260dc149f6367]::ty::context::TyCtxt>>::super_fold_with::<rustc_trait_selection[7ec6d0943e96810b]::traits::project::AssocTypeNormalizer> ()
   from C:\usr\local\bin\rustc_driver-eda9524c4e602df3.dll
#2551 0x00007ff809254e74 in <rustc_trait_selection[7ec6d0943e96810b]::traits::project::AssocTypeNormalizer as rustc_type_ir[514e0b83b1a29ee1]::fold::TypeFolder<rustc_middle[ebf260dc149f6367]::ty::context::TyCtxt>>::fold_ty ()
   from C:\usr\local\bin\rustc_driver-eda9524c4e602df3.dll
#2552 0x00007ff8092f8cca in <rustc_middle[ebf260dc149f6367]::ty::subst::GenericArg as rustc_type_ir[514e0b83b1a29ee1]::fold::TypeFoldable<rustc_middle[ebf260dc149f6367]::ty::context::TyCtxt>>::try_fold_with::<rustc_trait_selection[7ec6d0943e96810b]::traits::project::AssocTypeNormalizer> ()
   from C:\usr\local\bin\rustc_driver-eda9524c4e602df3.dll
#2553 0x00007ff8093b6783 in <&rustc_middle[ebf260dc149f6367]::ty::list::List<rustc_middle[ebf260dc149f6367]::ty::subst::GenericArg> as rustc_type_ir[514e0b83b1a29ee1]::fold::TypeFoldable<rustc_middle[ebf260dc149f6367]::ty::context::TyCtxt>>::try_fold_with::<rustc_trait_selection[7ec6d0943e96810b]::traits::project::AssocTypeNormalizer> ()
   from C:\usr\local\bin\rustc_driver-eda9524c4e602df3.dll
#2554 0x00007ff809289287 in <rustc_middle[ebf260dc149f6367]::ty::sty::TraitRef as rustc_type_ir[514e0b83b1a29ee1]::fold::TypeFoldable<rustc_middle[ebf260dc149f6367]::ty::context::TyCtxt>>::try_fold_with::<rustc_trait_selection[7ec6d0943e96810b]::traits::project::AssocTypeNormalizer> ()
   from C:\usr\local\bin\rustc_driver-eda9524c4e602df3.dll
#2555 0x00007ff8093a2573 in <rustc_middle[ebf260dc149f6367]::ty::PredicateKind as rustc_type_ir[514e0b83b1a29ee1]::fold::TypeFoldable<rustc_middle[ebf260dc149f6367]::ty::context::TyCtxt>>::try_fold_with::<rustc_trait_selection[7ec6d0943e96810b]::traits::project::AssocTypeNormalizer> ()
   from C:\usr\local\bin\rustc_driver-eda9524c4e602df3.dll
#2556 0x00007ff80928f38c in <rustc_middle[ebf260dc149f6367]::ty::sty::Binder<rustc_middle[ebf260dc149f6367]::ty::PredicateKind> as rustc_type_ir[514e0b83b1a29ee1]::fold::TypeSuperFoldable<rustc_middle[ebf260dc149f6367]::ty::context::TyCtxt>>::super_fold_with::<rustc_trait_selection[7ec6d0943e96810b]::traits::project::AssocTypeNormalizer> ()
   from C:\usr\local\bin\rustc_driver-eda9524c4e602df3.dll
#2557 0x00007ff80933cd22 in <rustc_trait_selection[7ec6d0943e96810b]::traits::project::AssocTypeNormalizer as rustc_type_ir[514e0b83b1a29ee1]::fold::FallibleTypeFolder<rustc_middle[ebf260dc149f6367]::ty::context::TyCtxt>>::try_fold_binder::<rustc_middle[ebf260dc149f6367]::ty::PredicateKind> ()
   from C:\usr\local\bin\rustc_driver-eda9524c4e602df3.dll
#2558 0x00007ff8093ac506 in <rustc_middle[ebf260dc149f6367]::ty::Predicate as rustc_type_ir[514e0b83b1a29ee1]::fold::TypeSuperFoldable<rustc_middle[ebf260dc149f6367]::ty::context::TyCtxt>>::super_fold_with::<rustc_trait_selection[7ec6d0943e96810b]::traits::project::AssocTypeNormalizer> ()
   from C:\usr\local\bin\rustc_driver-eda9524c4e602df3.dll
#2559 0x00007ff80933d7e6 in <rustc_trait_selection[7ec6d0943e96810b]::traits::project::AssocTypeNormalizer as rustc_type_ir[514e0b83b1a29ee1]::fold::FallibleTypeFolder<rustc_middle[ebf260dc149f6367]::ty::context::TyCtxt>>::try_fold_predicate () from C:\usr\local\bin\rustc_driver-eda9524c4e602df3.dll
#2560 0x00007ff809366feb in <core[20e502c22ca6166f]::iter::adapters::map::Map<alloc[6644710a05fa25bc]::vec::into_iter::IntoIter<rustc_middle[ebf260dc149f6367]::ty::Predicate>, <alloc[6644710a05fa25bc]::vec::Vec<rustc_middle[ebf260dc149f6367]::ty::Predicate> as rustc_type_ir[514e0b83b1a29ee1]::fold::TypeFoldable<rustc_middle[ebf260dc149f6367]::ty::context::TyCtxt>>::try_fold_with<rustc_trait_selection[7ec6d0943e96810b]::traits::project::AssocTypeNormalizer>::{closure#0}> as core[20e502c22ca6166f]::iter::traits::iterator::Iterator>::try_fold::<alloc[6644710a05fa25bc]::vec::in_place_drop::InPlaceDrop<rustc_middle[ebf260dc149f6367]::ty::Predicate>, <core[20e502c22ca6166f]::iter::adapters::GenericShunt<core[20e502c22ca6166f]::iter::adapters::map::Map<alloc[6644710a05fa25bc]::vec::into_iter::IntoIter<rustc_middle[ebf260dc149f6367]::ty::Predicate>, <alloc[6644710a05fa25bc]::vec::Vec<rustc_middle[ebf260dc149f6367]::ty::Predicate> as rustc_type_ir[514e0b83b1a29ee1]::fold::TypeFoldable<rustc_middle[ebf260dc149f6367]::ty::context::TyCtxt>>::try_fold_with<rustc_trait_selection[7ec6d0943e96810b]::traits::project::AssocTypeNormalizer>::{closure#0}>, core[20e502c22ca6166f]::result::Result<core[20e502c22ca6166f]::convert::Infallible, !>> as core[20e502c22ca6166f]::iter::traits::iterator::Iterator>::try_fold<alloc[6644710a05fa25bc]::vec::in_place_drop::InPlaceDrop<rustc_middle[ebf260dc149f6367]::ty::Predicate>, alloc[6644710a05fa25bc]::vec::in_place_collect::write_in_place_with_drop<rustc_middle[ebf260dc149f6367]::ty::Predicate>::{closure#0}, core[20e502c22ca6166f]::result::Result<alloc[6644710a05fa25bc]::vec::in_place_drop::InPlaceDrop<rustc_middle[ebf260dc149f6367]::ty::Predicate>, !>>::{closure#0}, core[20e502c22ca6166f]::ops::control_flow::ControlFlow<core[20e502c22ca6166f]::result::Result<alloc[6644710a05fa25bc]::vec::in_place_drop::InPlaceDrop<rustc_middle[ebf260dc149f6367]::ty::Predicate>, !>, alloc[6644710a05fa25bc]::vec::in_place_drop::InPlaceDrop<rustc_middle[ebf260dc149f6367]::ty::Predicate>>> ()
   from C:\usr\local\bin\rustc_driver-eda9524c4e602df3.dll
#2561 0x00007ff80940d3e2 in <core[20e502c22ca6166f]::iter::adapters::GenericShunt<core[20e502c22ca6166f]::iter::adapters::map::Map<alloc[6644710a05fa25bc]::vec::into_iter::IntoIter<rustc_middle[ebf260dc149f6367]::ty::Predicate>, <alloc[6644710a05fa25bc]::vec::Vec<rustc_middle[ebf260dc149f6367]::ty::Predicate> as rustc_type_ir[514e0b83b1a29ee1]::fold::TypeFoldable<rustc_middle[ebf260dc149f6367]::ty::context::TyCtxt>>::try_fold_with<rustc_trait_selection[7ec6d0943e96810b]::traits::project::AssocTypeNormalizer>::{closure#0}>, core[20e502c22ca6166f]::result::Result<core[20e502c22ca6166f]::convert::Infallible, !>> as core[20e502c22ca6166f]::iter::traits::iterator::Iterator>::try_fold::<alloc[6644710a05fa25bc]::vec::in_place_drop::InPlaceDrop<rustc_middle[ebf260dc149f6367]::ty::Predicate>, alloc[6644710a05fa25bc]::vec::in_place_collect::write_in_place_with_drop<rustc_middle[ebf260dc149f6367]::ty::Predicate>::{closure#0}, core[20e502c22ca6166f]::result::Result<alloc[6644710a05fa25bc]::vec::in_place_drop::InPlaceDrop<rustc_middle[ebf260dc149f6367]::ty::Predicate>, !>> ()
   from C:\usr\local\bin\rustc_driver-eda9524c4e602df3.dll
#2562 0x00007ff8092a67ea in <alloc[6644710a05fa25bc]::vec::Vec<rustc_middle[ebf260dc149f6367]::ty::Predicate> as alloc[6644710a05fa25bc]::vec::spec_from_iter::SpecFromIter<rustc_middle[ebf260dc149f6367]::ty::Predicate, core[20e502c22ca6166f]::iter::adapters::GenericShunt<core[20e502c22ca6166f]::iter::adapters::map::Map<alloc[6644710a05fa25bc]::vec::into_iter::IntoIter<rustc_middle[ebf260dc149f6367]::ty::Predicate>, <alloc[6644710a05fa25bc]::vec::Vec<rustc_middle[ebf260dc149f6367]::ty::Predicate> as rustc_type_ir[514e0b83b1a29ee1]::fold::TypeFoldable<rustc_middle[ebf260dc149f6367]::ty::context::TyCtxt>>::try_fold_with<rustc_trait_selection[7ec6d0943e96810b]::traits::project::AssocTypeNormalizer>::{closure#0}>, core[20e502c22ca6166f]::result::Result<core[20e502c22ca6166f]::convert::Infallible, !>>>>::from_iter ()
   from C:\usr\local\bin\rustc_driver-eda9524c4e602df3.dll
#2563 0x00007ff80940cdeb in core[20e502c22ca6166f]::iter::adapters::try_process::<core[20e502c22ca6166f]::iter::adapters::map::Map<alloc[6644710a05fa25bc]::vec::into_iter::IntoIter<rustc_middle[ebf260dc149f6367]::ty::Predicate>, <alloc[6644710a05fa25bc]::vec::Vec<rustc_middle[ebf260dc149f6367]::ty::Predicate> as rustc_type_ir[514e0b83b1a29ee1]::fold::TypeFoldable<rustc_middle[ebf260dc149f6367]::ty::context::TyCtxt>>::try_fold_with<rustc_trait_selection[7ec6d0943e96810b]::traits::project::AssocTypeNormalizer>::{closure#0}>, rustc_middle[ebf260dc149f6367]::ty::Predicate, core[20e502c22ca6166f]::result::Result<core[20e502c22ca6166f]::convert::Infallible, !>, <core[20e502c22ca6166f]::result::Result<alloc[6644710a05fa25bc]::vec::Vec<rustc_middle[ebf260dc149f6367]::ty::Predicate>, !> as core[20e502c22ca6166f]::iter::traits::collect::FromIterator<core[20e502c22ca6166f]::result::Result<rustc_middle[ebf260dc149f6367]::ty::Predicate, !>>>::from_iter<core[20e502c22ca6166f]::iter::adapters::map::Map<alloc[6644710a05fa25bc]::vec::into_iter::IntoIter<rustc_middle[ebf260dc149f6367]::ty::Predicate>, <alloc[6644710a05fa25bc]::vec::Vec<rustc_middle[ebf260dc149f6367]::ty::Predicate> as rustc_type_ir[514e0b83b1a29ee1]::fold::TypeFoldable<rustc_middle[ebf260dc149f6367]::ty::context::TyCtxt>>::try_fold_with<rustc_trait_selection[7ec6d0943e96810b]::traits::project::AssocTypeNormalizer>::{closure#0}>>::{closure#0}, alloc[6644710a05fa25bc]::vec::Vec<rustc_middle[ebf260dc149f6367]::ty::Predicate>> ()
   from C:\usr\local\bin\rustc_driver-eda9524c4e602df3.dll
#2564 0x00007ff80929826f in <alloc[6644710a05fa25bc]::vec::Vec<rustc_middle[ebf260dc149f6367]::ty::Predicate> as rustc_type_ir[514e0b83b1a29ee1]::fold::TypeFoldable<rustc_middle[ebf260dc149f6367]::ty::context::TyCtxt>>::fold_with::<rustc_trait_selection[7ec6d0943e96810b]::traits::project::AssocTypeNormalizer> ()
   from C:\usr\local\bin\rustc_driver-eda9524c4e602df3.dll
#2565 0x00007ff809343894 in <rustc_trait_selection[7ec6d0943e96810b]::traits::project::AssocTypeNormalizer>::fold::<alloc[6644710a05fa25bc]::vec::Vec<rustc_middle[ebf260dc149f6367]::ty::Predicate>> ()
   from C:\usr\local\bin\rustc_driver-eda9524c4e602df3.dll
#2566 0x00007ff80933de00 in rustc_trait_selection[7ec6d0943e96810b]::traits::project::normalize_with_depth::<alloc[6644710a05fa25bc]::vec::Vec<rustc_middle[ebf260dc149f6367]::ty::Predicate>> ()
   from C:\usr\local\bin\rustc_driver-eda9524c4e602df3.dll
#2567 0x00007ff8092b1e3c in <rustc_infer[f1d617581dd2c354]::infer::at::At as rustc_trait_selection[7ec6d0943e96810b]::traits::project::NormalizeExt>::normalize::<alloc[6644710a05fa25bc]::vec::Vec<rustc_middle[ebf260dc149f6367]::ty::Predicate>> () from C:\usr\local\bin\rustc_driver-eda9524c4e602df3.dll
#2568 0x00007ff80946a178 in <rustc_trait_selection[7ec6d0943e96810b]::traits::engine::ObligationCtxt>::normalize::<alloc[6644710a05fa25bc]::vec::Vec<rustc_middle[ebf260dc149f6367]::ty::Predicate>> ()
   from C:\usr\local\bin\rustc_driver-eda9524c4e602df3.dll
#2569 0x00007ff80946c72b in rustc_trait_selection[7ec6d0943e96810b]::traits::fully_normalize::<alloc[6644710a05fa25bc]::vec::Vec<rustc_middle[ebf260dc149f6367]::ty::Predicate>> () from C:\usr\local\bin\rustc_driver-eda9524c4e602df3.dll
#2570 0x00007ff809410066 in rustc_trait_selection[7ec6d0943e96810b]::traits::do_normalize_predicates ()
   from C:\usr\local\bin\rustc_driver-eda9524c4e602df3.dll
#2571 0x00007ff80941126f in rustc_trait_selection[7ec6d0943e96810b]::traits::normalize_param_env_or_error ()
   from C:\usr\local\bin\rustc_driver-eda9524c4e602df3.dll
#2572 0x00007ff8073cf44f in rustc_ty_utils[4a5eeb4403464e8c]::ty::param_env ()
   from C:\usr\local\bin\rustc_driver-eda9524c4e602df3.dll
#2573 0x00007ff8089277f3 in rustc_query_system[f1ff4f506666fc4d]::query::plumbing::try_execute_query::<rustc_query_impl[f865b387ba6e061a]::queries::param_env, rustc_query_impl[f865b387ba6e061a]::plumbing::QueryCtxt> ()
   from C:\usr\local\bin\rustc_driver-eda9524c4e602df3.dll
#2574 0x00007ff8089b9a47 in <rustc_query_impl[f865b387ba6e061a]::Queries as rustc_middle[ebf260dc149f6367]::ty::query::QueryEngine>::param_env ()
   from C:\usr\local\bin\rustc_driver-eda9524c4e602df3.dll
#2575 0x00007ff8078650c4 in rustc_hir_analysis[25229fcfe87c7597]::check::wfcheck::enter_wf_checking_ctxt::<rustc_hir_analysis[25229fcfe87c7597]::check::wfcheck::check_impl::{closure#0}> ()
   from C:\usr\local\bin\rustc_driver-eda9524c4e602df3.dll
#2576 0x00007ff807751bc3 in rustc_hir_analysis[25229fcfe87c7597]::check::wfcheck::check_well_formed ()
   from C:\usr\local\bin\rustc_driver-eda9524c4e602df3.dll
#2577 0x00007ff808847295 in rustc_query_system[f1ff4f506666fc4d]::query::plumbing::try_execute_query::<rustc_query_impl[f865b387ba6e061a]::queries::check_well_formed, rustc_query_impl[f865b387ba6e061a]::plumbing::QueryCtxt> ()
   from C:\usr\local\bin\rustc_driver-eda9524c4e602df3.dll
#2578 0x00007ff8089c7506 in <rustc_query_impl[f865b387ba6e061a]::Queries as rustc_middle[ebf260dc149f6367]::ty::query::QueryEngine>::check_well_formed ()
   from C:\usr\local\bin\rustc_driver-eda9524c4e602df3.dll
#2579 0x00007ff8078800b9 in <core[20e502c22ca6166f]::panic::unwind_safe::AssertUnwindSafe<rustc_data_structures[8c44cb2cf75f2b5c]::sync::par_for_each_in<&[rustc_hir[9f049f9ca34b43c2]::hir::ItemId], <rustc_middle[ebf260dc149f6367]::hir::ModuleItems>::par_items<rustc_hir_analysis[25229fcfe87c7597]::check::wfcheck::check_mod_type_wf::{closure#0}>::{closure#0}>::{closure#0}::{closure#0}> as core[20e502c22ca6166f]::ops::function::FnOnce<()>>::call_once ()
   from C:\usr\local\bin\rustc_driver-eda9524c4e602df3.dll
#2580 0x00007ff807870279 in std[6f73a53b78cbdd15]::panicking::try::<(), core[20e502c22ca6166f]::panic::unwind_safe::AssertUnwindSafe<rustc_data_structures[8c44cb2cf75f2b5c]::sync::par_for_each_in<&[rustc_hir[9f049f9ca34b43c2]::hir::ItemId], <rustc_middle[ebf260dc149f6367]::hir::ModuleItems>::par_items<rustc_hir_analysis[25229fcfe87c7597]::check::wfcheck::check_mod_type_wf::{closure#0}>::{closure#0}>::{closure#0}::{closure#0}>> ()
   from C:\usr\local\bin\rustc_driver-eda9524c4e602df3.dll
#2581 0x00007ff80776dfb5 in rustc_data_structures[8c44cb2cf75f2b5c]::sync::par_for_each_in::<&[rustc_hir[9f049f9ca34b43c2]::hir::ItemId], <rustc_middle[ebf260dc149f6367]::hir::ModuleItems>::par_items<rustc_hir_analysis[25229fcfe87c7597]::check::wfcheck::check_mod_type_wf::{closure#0}>::{closure#0}> ()
   from C:\usr\local\bin\rustc_driver-eda9524c4e602df3.dll
#2582 0x00007ff8077547b8 in rustc_hir_analysis[25229fcfe87c7597]::check::wfcheck::check_mod_type_wf ()
   from C:\usr\local\bin\rustc_driver-eda9524c4e602df3.dll
#2583 0x00007ff808846359 in rustc_query_system[f1ff4f506666fc4d]::query::plumbing::try_execute_query::<rustc_query_impl[f865b387ba6e061a]::queries::check_mod_type_wf, rustc_query_impl[f865b387ba6e061a]::plumbing::QueryCtxt> ()
   from C:\usr\local\bin\rustc_driver-eda9524c4e602df3.dll
#2584 0x00007ff80899d776 in <rustc_query_impl[f865b387ba6e061a]::Queries as rustc_middle[ebf260dc149f6367]::ty::query::QueryEngine>::check_mod_type_wf ()
   from C:\usr\local\bin\rustc_driver-eda9524c4e602df3.dll
#2585 0x00007ff8078801b9 in <core[20e502c22ca6166f]::panic::unwind_safe::AssertUnwindSafe<rustc_data_structures[8c44cb2cf75f2b5c]::sync::par_for_each_in<&[rustc_hir[9f049f9ca34b43c2]::hir_id::OwnerId], <rustc_middle[ebf260dc149f6367]::hir::map::Map>::par_for_each_module<rustc_hir_analysis[25229fcfe87c7597]::check_crate::{closure#5}::{closure#0}::{closure#0}>::{closure#0}>::{closure#0}::{closure#0}> as core[20e502c22ca6166f]::ops::function::FnOnce<()>>::call_once ()
   from C:\usr\local\bin\rustc_driver-eda9524c4e602df3.dll
#2586 0x00007ff807870299 in std[6f73a53b78cbdd15]::panicking::try::<(), core[20e502c22ca6166f]::panic::unwind_safe::AssertUnwindSafe<rustc_data_structures[8c44cb2cf75f2b5c]::sync::par_for_each_in<&[rustc_hir[9f049f9ca34b43c2]::hir_id::OwnerId], <rustc_middle[ebf260dc149f6367]::hir::map::Map>::par_for_each_module<rustc_hir_analysis[25229fcfe87c7597]::check_crate::{closure#5}::{closure#0}::{closure#0}>::{closure#0}>::{closure#0}::{closure#0}>> ()
   from C:\usr\local\bin\rustc_driver-eda9524c4e602df3.dll
#2587 0x00007ff80776e085 in rustc_data_structures[8c44cb2cf75f2b5c]::sync::par_for_each_in::<&[rustc_hir[9f049f9ca34b43c2]::hir_id::OwnerId], <rustc_middle[ebf260dc149f6367]::hir::map::Map>::par_for_each_module<rustc_hir_analysis[25229fcfe87c7597]::check_crate::{closure#5}::{closure#0}::{closure#0}>::{closure#0}>
    () from C:\usr\local\bin\rustc_driver-eda9524c4e602df3.dll
#2588 0x00007ff80780f0dc in <rustc_session[94c1e885e8c82419]::session::Session>::track_errors::<rustc_hir_analysis[25229fcfe87c7597]::check_crate::{closure#5}, ()> () from C:\usr\local\bin\rustc_driver-eda9524c4e602df3.dll
#2589 0x00007ff80784bb93 in rustc_hir_analysis[25229fcfe87c7597]::check_crate
    () from C:\usr\local\bin\rustc_driver-eda9524c4e602df3.dll
#2590 0x00007ff8071e7d41 in rustc_interface[1496720bf34f4141]::passes::analysis () from C:\usr\local\bin\rustc_driver-eda9524c4e602df3.dll
#2591 0x00007ff8089169b1 in rustc_query_system[f1ff4f506666fc4d]::query::plumbing::try_execute_query::<rustc_query_impl[f865b387ba6e061a]::queries::analysis, rustc_query_impl[f865b387ba6e061a]::plumbing::QueryCtxt> ()
   from C:\usr\local\bin\rustc_driver-eda9524c4e602df3.dll
#2592 0x00007ff808976882 in <rustc_query_impl[f865b387ba6e061a]::Queries as rustc_middle[ebf260dc149f6367]::ty::query::QueryEngine>::analysis ()
   from C:\usr\local\bin\rustc_driver-eda9524c4e602df3.dll
#2593 0x00007ff8071714ea in <rustc_middle[ebf260dc149f6367]::ty::context::GlobalCtxt>::enter::<rustc_driver_impl[137639c14726341]::run_compiler::{closure#1}::{closure#2}::{closure#4}, core[20e502c22ca6166f]::result::Result<(), rustc_span[65f57099d4b96856]::ErrorGuaranteed>> ()
   from C:\usr\local\bin\rustc_driver-eda9524c4e602df3.dll
#2594 0x00007ff80716d8fe in <rustc_interface[1496720bf34f4141]::interface::Compiler>::enter::<rustc_driver_impl[137639c14726341]::run_compiler::{closure#1}::{closure#2}, core[20e502c22ca6166f]::result::Result<core[20e502c22ca6166f]::option::Option<rustc_interface[1496720bf34f4141]::queries::Linker>, rustc_span[65f57099d4b96856]::ErrorGuaranteed>> ()
   from C:\usr\local\bin\rustc_driver-eda9524c4e602df3.dll
#2595 0x00007ff807160a96 in rustc_span[65f57099d4b96856]::with_source_map::<core[20e502c22ca6166f]::result::Result<(), rustc_span[65f57099d4b96856]::ErrorGuaranteed>, rustc_interface[1496720bf34f4141]::interface::run_compiler<core[20e502c22ca6166f]::result::Result<(), rustc_span[65f57099d4b96856]::ErrorGuaranteed>, rustc_driver_impl[137639c14726341]::run_compiler::{closure#1}>::{closure#0}::{closure#0}> () from C:\usr\local\bin\rustc_driver-eda9524c4e602df3.dll
#2596 0x00007ff807157387 in <scoped_tls[c8b2a3d21b60c86d]::ScopedKey<rustc_span[65f57099d4b96856]::SessionGlobals>>::set::<rustc_interface[1496720bf34f4141]::interface::run_compiler<core[20e502c22ca6166f]::result::Result<(), rustc_span[65f57099d4b96856]::ErrorGuaranteed>, rustc_driver_impl[137639c14726341]::run_compiler::{closure#1}>::{closure#0}, core[20e502c22ca6166f]::result::Result<(), rustc_span[65f57099d4b96856]::ErrorGuaranteed>> ()
   from C:\usr\local\bin\rustc_driver-eda9524c4e602df3.dll
#2597 0x00007ff807171cfd in std[6f73a53b78cbdd15]::sys_common::backtrace::__rust_begin_short_backtrace::<rustc_interface[1496720bf34f4141]::util::run_in_thread_pool_with_globals<rustc_interface[1496720bf34f4141]::interface::run_compiler<core[20e502c22ca6166f]::result::Result<(), rustc_span[65f57099d4b96856]::ErrorGuaranteed>, rustc_driver_impl[137639c14726341]::run_compiler::{closure#1}>::{closure#0}, core[20e502c22ca6166f]::result::Result<(), rustc_span[65f57099d4b96856]::ErrorGuaranteed>>::{closure#0}::{closure#0}, core[20e502c22ca6166f]::result::Result<(), rustc_span[65f57099d4b96856]::ErrorGuaranteed>> ()
   from C:\usr\local\bin\rustc_driver-eda9524c4e602df3.dll
#2598 0x00007ff80716ce31 in std[6f73a53b78cbdd15]::panicking::try::<core[20e502c22ca6166f]::result::Result<(), rustc_span[65f57099d4b96856]::ErrorGuaranteed>, core[20e502c22ca6166f]::panic::unwind_safe::AssertUnwindSafe<<std[6f73a53b78cbdd15]::thread::Builder>::spawn_unchecked_<rustc_interface[1496720bf34f4141]::util::run_in_thread_pool_with_globals<rustc_interface[1496720bf34f4141]::interface::run_compiler<core[20e502c22ca6166f]::result::Result<(), rustc_span[65f57099d4b96856]::ErrorGuaranteed>, rustc_driver_impl[137639c14726341]::run_compiler::{closure#1}>::{closure#0}, core[20e502c22ca6166f]::result::Result<(), rustc_span[65f57099d4b96856]::ErrorGuaranteed>>::{closure#0}::{closure#0}, core[20e502c22ca6166f]::result::Result<(), rustc_span[65f57099d4b96856]::ErrorGuaranteed>>::{closure#1}::{closure#0}>> ()
   from C:\usr\local\bin\rustc_driver-eda9524c4e602df3.dll
#2599 0x00007ff807174282 in <<std[6f73a53b78cbdd15]::thread::Builder>::spawn_unchecked_<rustc_interface[1496720bf34f4141]::util::run_in_thread_pool_with_globals<rustc_interface[1496720bf34f4141]::interface::run_compiler<core[20e502c22ca6166f]::result::Result<(), rustc_span[65f57099d4b96856]::ErrorGuaranteed>, rustc_driver_impl[137639c14726341]::run_compiler::{closure#1}>::{closure#0}, core[20e502c22ca6166f]::result::Result<(), rustc_span[65f57099d4b96856]::ErrorGuaranteed>>::{closure#0}::{closure#0}, core[20e502c22ca6166f]::result::Result<(), rustc_span[65f57099d4b96856]::ErrorGuaranteed>>::{closure#1} as core[20e502c22ca6166f]::ops::function::FnOnce<()>>::call_once::{shim:vtable#0} ()
   from C:\usr\local\bin\rustc_driver-eda9524c4e602df3.dll
#2600 0x00007ff83375da69 in <alloc::boxed::Box<F,A> as core::ops::function::FnOnce<Args>>::call_once::h7fd5a5c69811f34a ()
   from C:\usr\local\bin\std-a84f40a7e9b3ae6c.dll

repeating stack is frame 62 to 85 + select() call @ 2543
2544+ is probably unnesesary but I included it anyways.

@jackh726 jackh726 added the F-generic_associated_types `#![feature(generic_associated_types)]` a.k.a. GATs label Mar 8, 2023
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fmease commented Mar 10, 2023 •
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Alright, I've investigated this a bit. This regressed in #81055 which set out to make some overflow errors recoverable (undoing parts of #80246). If I locally revert the change made in #81055, the modified compiler correctly bails out early and reports the following overflow error:

error[E0601]: `main` function not found in crate `hang`
  --> hang.rs:47:2
   |
47 | }
   |  ^ consider adding a `main` function to `hang.rs`

error[E0275]: overflow evaluating the requirement `<Filter<S, P> as LendingIterator>::Item<'a>`
  --> hang.rs:29:1
   |
29 | impl<S, P> LendingIterator for Filter<S, P>
   | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
   |
   = help: consider increasing the recursion limit by adding a `#![recursion_limit = "256"]` attribute to your crate (`hang`)

error: aborting due to 2 previous errors

Some errors have detailed explanations: E0275, E0601.
For more information about an error, try `rustc --explain E0275`.

Issue #81091 seems very relevant here (if a PR implements the proposal in #81091, I assume this issue will be fixed by it, too).

@fmease fmease mentioned this issue Mar 10, 2023
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fmease commented Mar 11, 2023 •
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Further minimized:

trait LendingIterator {
    type Item<'a>
    where
        Self: 'a;
}

struct Filter<S, P>(S, P);

impl<S, P> LendingIterator for Filter<S, P>
where
    S: LendingIterator,
    P: FnMut(&Self::Item<'_>),
{
    type Item<'a> = S::Item<'a> where S: 'a;
}

@jihiggins
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Sorry if this is the wrong place to ask, but is there a way to accomplish a similar thing without running into the trait evaluation recursion?

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fmease commented Mar 13, 2023 •
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is there a way to accomplish a similar thing without running into the trait evaluation recursion?

To make it compile, LendingIterator::next needs to return an Option.

- fn next<'a>(&'a mut self) -> Self::Item<'a>
+ fn next<'a>(&'a mut self) -> Option<Self::Item<'a>>

Here is a link to a working version.

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fmease commented Mar 13, 2023 •
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Here is a link to a working version.

And to work around the borrow checker limitation mentioned on that playground, you may want to consider using polonius-the-crab.

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Awesome, thanks!

@fmease fmease mentioned this issue Mar 17, 2023
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fmease commented Aug 21, 2023 •
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Fixed by next solver (-Zsolver=next):

error[E0275]: overflow evaluating the requirement `Filter<S, P>: LendingIterator`
 --> eh.rs:9:32
  |
9 | impl<S, P> LendingIterator for Filter<S, P>
  |                                ^^^^^^^^^^^^
  |
  = help: consider increasing the recursion limit by adding a `#![recursion_limit = "256"]` attribute to your crate (`eh`)

@rustbot label fixed-by-next-solver

@rustbot rustbot added the fixed-by-next-solver Fixed by the next-generation trait solver, `-Znext-solver`. label Aug 29, 2023
@martinjrobins martinjrobins mentioned this issue Mar 21, 2024
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@matthiaskrgr matthiaskrgr mentioned this issue Jun 15, 2024
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Found a similar issue that doesn't use GATs directly, in case that's useful:

pub trait LendingIteratorItem<'item> {
    type Item;
}

impl<'item, F> LendingIteratorItem<'item> for (F,)
where
    F: for<'a> FnMut(<Self as LendingIteratorItem<'a>>::Item),
{
    type Item = ();
}

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C-bug Category: This is a bug. F-generic_associated_types `#![feature(generic_associated_types)]` a.k.a. GATs fixed-by-next-solver Fixed by the next-generation trait solver, `-Znext-solver`. I-hang Issue: The compiler never terminates, due to infinite loops, deadlock, livelock, etc. T-compiler Relevant to the compiler team, which will review and decide on the PR/issue.
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