error: internal compiler error: no errors encountered even though delay_span_bug issued

[lukin35]

can't compile linfa, please show me how to fix

Code

<code>

Meta

rustc --version --verbose:

rustc 1.73.0-nightly (6ef7d16be 2023-08-19)
binary: rustc
commit-hash: 6ef7d16be0fb9d6ecf300c27990f4bff49d22d46
commit-date: 2023-08-19
host: x86_64-unknown-linux-gnu
release: 1.73.0-nightly
LLVM version: 17.0.0

Error output

error: internal compiler error: no errors encountered even though `delay_span_bug` issued

Backtrace

      error: internal compiler error: no errors encountered even though `delay_span_bug` issued

      error: internal compiler error: unresolved inference variable in outlives: ?4t
        --> /public/home/litz/.cargo/registry/src/mirrors.sjtug.sjtu.edu.cn-4f7dbcce21e258a2/linfa-0.6.1/src/dataset/iter.rs:72:5
         |
      72 |     fn next(&mut self) -> Option<Self::Item> {
         |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
         |
      note: delayed at compiler/rustc_infer/src/infer/outlives/obligations.rs:254:35
               0: <rustc_errors::HandlerInner>::emit_diagnostic
               1: <rustc_errors::Handler>::delay_span_bug::<rustc_span::span_encoding::Span, alloc::string::String>
               2: <rustc_infer::infer::outlives::obligations::TypeOutlives<&rustc_infer::infer::InferCtxt>>::components_must_outlive
               3: <rustc_infer::infer::InferCtxt>::resolve_regions
               4: rustc_hir_analysis::check::compare_impl_item::compare_method_predicate_entailment
               5: rustc_hir_analysis::check::check::check_mod_item_types
               6: rustc_query_impl::plumbing::__rust_begin_short_backtrace::<rustc_query_impl::query_impl::check_mod_item_types::dynamic_query::{closure#2}::{closure#0}, rustc_middle::query::erase::Erased<[u8; 0]>>
               7: <rustc_query_impl::query_impl::check_mod_item_types::dynamic_query::{closure#2} as core::ops::function::FnOnce<(rustc_middle::ty::context::TyCtxt, rustc_span::def_id::LocalModDefId)>>::call_once
               8: rustc_query_system::query::plumbing::try_execute_query::<rustc_query_impl::DynamicConfig<rustc_query_system::query::caches::DefaultCache<rustc_span::def_id::LocalModDefId, rustc_middle::query::erase::Erased<[u8; 0]>>, false, false, false>, rustc_query_impl::plumbing::QueryCtxt, false>
               9: rustc_query_impl::query_impl::check_mod_item_types::get_query_non_incr::__rust_end_short_backtrace
              10: <rustc_middle::hir::map::Map>::for_each_module::<rustc_hir_analysis::check_crate::{closure#6}::{closure#0}>
              11: rustc_hir_analysis::check_crate
              12: rustc_interface::passes::analysis
              13: rustc_query_impl::plumbing::__rust_begin_short_backtrace::<rustc_query_impl::query_impl::analysis::dynamic_query::{closure#2}::{closure#0}, rustc_middle::query::erase::Erased<[u8; 1]>>
              14: <rustc_query_impl::query_impl::analysis::dynamic_query::{closure#2} as core::ops::function::FnOnce<(rustc_middle::ty::context::TyCtxt, ())>>::call_once
              15: rustc_query_system::query::plumbing::try_execute_query::<rustc_query_impl::DynamicConfig<rustc_query_system::query::caches::SingleCache<rustc_middle::query::erase::Erased<[u8; 1]>>, false, false, false>, rustc_query_impl::plumbing::QueryCtxt, false>
              16: rustc_query_impl::query_impl::analysis::get_query_non_incr::__rust_end_short_backtrace
              17: <rustc_interface::queries::QueryResult<&rustc_middle::ty::context::GlobalCtxt>>::enter::<core::result::Result<(), rustc_span::ErrorGuaranteed>, rustc_driver_impl::run_compiler::{closure#1}::{closure#2}::{closure#6}>
              18: <rustc_interface::interface::Compiler>::enter::<rustc_driver_impl::run_compiler::{closure#1}::{closure#2}, core::result::Result<core::option::Option<rustc_interface::queries::Linker>, rustc_span::ErrorGuaranteed>>
              19: std::sys_common::backtrace::__rust_begin_short_backtrace::<rustc_interface::util::run_in_thread_pool_with_globals<rustc_interface::interface::run_compiler<core::result::Result<(), rustc_span::ErrorGuaranteed>, rustc_driver_impl::run_compiler::{closure#1}>::{closure#0}, core::result::Result<(), rustc_span::ErrorGuaranteed>>::{closure#0}::{closure#0}, core::result::Result<(), rustc_span::ErrorGuaranteed>>
              20: <<std::thread::Builder>::spawn_unchecked_<rustc_interface::util::run_in_thread_pool_with_globals<rustc_interface::interface::run_compiler<core::result::Result<(), rustc_span::ErrorGuaranteed>, rustc_driver_impl::run_compiler::{closure#1}>::{closure#0}, core::result::Result<(), rustc_span::ErrorGuaranteed>>::{closure#0}::{closure#0}, core::result::Result<(), rustc_span::ErrorGuaranteed>>::{closure#1} as core::ops::function::FnOnce<()>>::call_once::{shim:vtable#0}
              21: <alloc::boxed::Box<F,A> as core::ops::function::FnOnce<Args>>::call_once
                         at /rustc/6ef7d16be0fb9d6ecf300c27990f4bff49d22d46/library/alloc/src/boxed.rs:2007:9
              22: <alloc::boxed::Box<F,A> as core::ops::function::FnOnce<Args>>::call_once
                         at /rustc/6ef7d16be0fb9d6ecf300c27990f4bff49d22d46/library/alloc/src/boxed.rs:2007:9
              23: std::sys::unix::thread::Thread::new::thread_start
                         at /rustc/6ef7d16be0fb9d6ecf300c27990f4bff49d22d46/library/std/src/sys/unix/thread.rs:108:17
              24: start_thread
              25: clone
        --> /public/home/litz/.cargo/registry/src/mirrors.sjtug.sjtu.edu.cn-4f7dbcce21e258a2/linfa-0.6.1/src/dataset/iter.rs:72:5
         |
      72 |     fn next(&mut self) -> Option<Self::Item> {
         |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^

      note: we would appreciate a bug report: https://github.com/rust-lang/rust/issues/new?labels=C-bug%2C+I-ICE%2C+T-compiler&template=ice.md

      note: please attach the file at `/public/home/litz/.cargo/registry/src/mirrors.sjtug.sjtu.edu.cn-4f7dbcce21e258a2/linfa-0.6.1/rustc-ice-2023-08-20T17:30:52.267253091Z-814448.txt` to your bug report

      note: compiler flags: --crate-type lib -C opt-level=3 -C embed-bitcode=no

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

      query stack during panic:
      end of query stack
      error: could not compile `linfa` (lib)

[lukin35]

rustc-ice-2023-08-20T17_30_52.267253091Z-814448.txt

[compiler-errors]

@jackh726 this is due to #109356. It turns out that skipping over projection goals that we get back from wf::obligations leads to unconstrained infer vars. It's pretty difficult to create a minimal repro of this, though.

This isn't fixed by #114787 because the infer var is coming from within wf::obligations's own normalization.

[jackh726]

I'll take a look.

[jackh726]

Pretty rough, but here's an MCVE. Still can probably minimize a bit more:

use std::marker::PhantomData;

trait Data {
    type Elem;
}

struct DatasetBase<R, T> {
    pub records: R,
    pub targets: T,
}

trait Records: Sized {
    type Elem;
}

trait AsTargets {
    type Elem;
}

impl<F, S: Data<Elem = F>> Records for ArrayBase<S> {
    type Elem = F;
}

impl<R, T: AsTargets> AsTargets for DatasetBase<R, T> {
    type Elem = T::Elem;
}

struct DatasetIter<'a, R: Records, T> {
    dataset: T,
    phantom: PhantomData<&'a R::Elem>,
}

pub struct ArrayBase<S> {
    data: S,
}

impl<'a, F, D, T: AsTargets> Iterator for DatasetIter<'a, ArrayBase<D>, T>
where
    D: Data<Elem = F>,
{
    type Item = DatasetBase<F, T::Elem>;

    fn next(&mut self) -> Option<Self::Item> {
        panic!();
    }
}

(edit: updating as I minimize a bit more)

[jackh726]

Okay, here's the simplest MCVE I can make:

trait Data {
    type Elem;
}

impl<F, S: Data<Elem = F>> Data for ArrayBase<S> {
    type Elem = F;
}

struct DatasetIter<'a, R: Data> {
    data: &'a R::Elem,
}

pub struct ArrayBase<S> {
    data: S,
}

trait Trait {
    type Item;
    fn next() -> Option<Self::Item>;
}

impl<'a, D: Data> Trait for DatasetIter<'a, ArrayBase<D>> {
    type Item = ();

    fn next() -> Option<Self::Item> {
        None
    }
}

[apiraino]

WG-prioritization assigning priority (Zulip discussion).

@rustbot label -I-prioritize +P-high -needs-triage