Combining `default impl` with associated type projections leads to `delay_span_bug` ICE

[CAD97]

Code

[playground] (requires release mode)

#![no_std]
#![feature(specialization)]
#![allow(incomplete_features)]

pub unsafe trait Storage {
    type Handle;
}

pub unsafe trait MultipleStorage: Storage {}

default unsafe impl<S> Storage for S
where
    S: MultipleStorage,
{
}

// the tuple (or any compound type) is required to get an ICE
pub fn ice<S: Storage>(boxed: (S::Handle,)) -> (S::Handle,) {
    boxed
}

Meta

rustc --version: 1.70.0-nightly (2023-04-02 3a8a131)

rustc 1.70.0-nightly (3a8a131e9 2023-04-02)
binary: rustc
commit-hash: 3a8a131e9509c478ece1c58fe0ea2d49463d2300
commit-date: 2023-04-02
host: x86_64-pc-windows-msvc
release: 1.70.0-nightly
LLVM version: 16.0.0

Error output

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

error: internal compiler error: TyKind::Error constructed but no error reported
  |
  = note: delayed at    (snip)

Backtrace

  = note: delayed at    0: <rustc_errors::HandlerInner>::emit_diagnostic
             1: <rustc_errors::Handler>::delay_span_bug::<rustc_span::span_encoding::Span, &str>
             2: <rustc_middle::ty::context::TyCtxt>::ty_error_misc
             3: rustc_trait_selection::traits::project::normalize_projection_type
             4: <rustc_trait_selection::traits::project::AssocTypeNormalizer as rustc_type_ir::fold::TypeFolder<rustc_middle::ty::context::TyCtxt>>::fold_ty
             5: <rustc_trait_selection::traits::project::AssocTypeNormalizer as rustc_type_ir::fold::TypeFolder<rustc_middle::ty::context::TyCtxt>>::fold_ty
             6: rustc_trait_selection::traits::project::normalize_with_depth_to::<rustc_middle::ty::Predicate>
             7: <rustc_trait_selection::traits::select::SelectionContext>::impl_or_trait_obligations
             8: <rustc_trait_selection::traits::select::SelectionContext>::confirm_candidate
             9: <rustc_trait_selection::traits::select::SelectionContext>::evaluate_stack
            10: <rustc_trait_selection::traits::select::SelectionContext>::evaluate_predicate_recursively
            11: rustc_traits::evaluate_obligation::evaluate_obligation
            12: rustc_query_system::query::plumbing::try_execute_query::<rustc_query_impl::queries::evaluate_obligation, rustc_query_impl::plumbing::QueryCtxt>
            13: <rustc_infer::infer::InferCtxt as rustc_trait_selection::traits::query::evaluate_obligation::InferCtxtExt>::evaluate_obligation_no_overflow
            14: rustc_ty_utils::common_traits::is_item_raw
            15: rustc_query_system::query::plumbing::try_execute_query::<rustc_query_impl::queries::is_freeze_raw, rustc_query_impl::plumbing::QueryCtxt>
            16: <rustc_query_impl::Queries as rustc_middle::ty::query::QueryEngine>::is_freeze_raw
            17: <rustc_middle::ty::Ty>::is_freeze
            18: rustc_mir_transform::deduce_param_attrs::deduced_param_attrs
            19: rustc_query_system::query::plumbing::try_execute_query::<rustc_query_impl::queries::deduced_param_attrs, rustc_query_impl::plumbing::QueryCtxt>
            20: <rustc_query_impl::Queries as rustc_middle::ty::query::QueryEngine>::deduced_param_attrs
            21: <rustc_metadata::rmeta::encoder::EncodeContext>::encode_crate_root
            22: rustc_metadata::rmeta::encoder::encode_metadata_impl
            23: rustc_data_structures::sync::join::<rustc_metadata::rmeta::encoder::encode_metadata::{closure#0}, rustc_metadata::rmeta::encoder::encode_metadata::{closure#1}, (), ()>
            24: rustc_metadata::rmeta::encoder::encode_metadata
            25: rustc_metadata::fs::encode_and_write_metadata
            26: rustc_interface::passes::start_codegen
            27: <rustc_middle::ty::context::GlobalCtxt>::enter::<<rustc_interface::queries::Queries>::ongoing_codegen::{closure#0}::{closure#0}, core::result::Result<alloc::boxed::Box<dyn core::any::Any>, rustc_span::ErrorGuaranteed>>
            28: <rustc_interface::queries::Queries>::ongoing_codegen
            29: <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>>
            30: rustc_span::set_source_map::<core::result::Result<(), rustc_span::ErrorGuaranteed>, rustc_interface::interface::run_compiler<core::result::Result<(), rustc_span::ErrorGuaranteed>, rustc_driver_impl::run_compiler::{closure#1}>::{closure#0}::{closure#0}>
            31: 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>>
            32: <<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}
            33: <alloc::boxed::Box<F,A> as core::ops::function::FnOnce<Args>>::call_once
                       at /rustc/3a8a131e9509c478ece1c58fe0ea2d49463d2300/library/alloc/src/boxed.rs:1976:9
            34: <alloc::boxed::Box<F,A> as core::ops::function::FnOnce<Args>>::call_once
                       at /rustc/3a8a131e9509c478ece1c58fe0ea2d49463d2300/library/alloc/src/boxed.rs:1976:9
            35: std::sys::unix::thread::Thread::new::thread_start
                       at /rustc/3a8a131e9509c478ece1c58fe0ea2d49463d2300/library/std/src/sys/unix/thread.rs:108:17
            36: start_thread
            37: clone

@rustbot labels modify +F-specialization +requires-nightly +requires-incomplete-features

[compiler-errors]

I understand how this ICE can come about, but I frankly cannot reproduce this. @CAD97, can you help out?

[CAD97]

Ah, I apparently forgot to list that the ICE requires build --release; building without optimizations doesn't ICE. Reproduces on playground.

[CAD97]

@rustbot label +F-specialization +requires-nightly +requires-incomplete-features