rustdoc: ICE: synthetic auto trait impls: `unexpected result when selecting […]` involving unsatisfied bounds, projections and super trait bounds

[iquerejeta]

Code

This is the least I've managed to reduce the code:

pub trait Foo {
    type FooType;
}

pub trait Bar<const A: usize>: Foo<FooType = <Self as Bar<A>>::BarType> {
    type BarType;
}

pub(crate) const B: usize = 5;

pub trait Tec: Bar<B> {}

pub struct Structure<C: Tec> {
    _field: C::BarType,
}

Meta

rustc --version --verbose:

rustc 1.71.1 (eb26296b5 2023-08-03)
binary: rustc
commit-hash: eb26296b556cef10fb713a38f3d16b9886080f26
commit-date: 2023-08-03
host: aarch64-apple-darwin
release: 1.71.1
LLVM version: 16.0.5

With nightly version

rustc 1.73.0-nightly (f88a8b71c 2023-08-08)
binary: rustc
commit-hash: f88a8b71cebb730cbd5058c45ebcae1d4d9be377
commit-date: 2023-08-08
host: aarch64-apple-darwin
release: 1.73.0-nightly
LLVM version: 17.0.0

the compiler asks me to change the Structure as follows:

pub struct Structure<C: Tec + Bar<5>> {
    _field: <C as Bar<B>>::BarType,
}

and now the error no longer occurs.

Error output

After running the cargo doc command, I get the following:

thread 'rustc' panicked at 'Unexpected result when selecting Structure<C> Obligation(predicate=Binder(ProjectionPredicate(AliasTy { substs: [C, Const { ty: usize, kind: Leaf(0x0000000000000005) }], def_id: DefId(0:7 ~ rust_sodium[23d3]::Bar::BarType) }, Term::Ty(_)), []), depth=2)', compiler/rustc_trait_selection/src/traits/auto_trait.rs:756:33
stack backtrace:
   0:        0x10627acc0 - <std::sys_common::backtrace::_print::DisplayBacktrace as core::fmt::Display>::fmt::hb75be2413dd8ceb3
   1:        0x1062c9a64 - core::fmt::write::h95d50546e769656f
   2:        0x106270e2c - std::io::Write::write_fmt::hce019ca594763835
   3:        0x10627ab14 - std::sys_common::backtrace::print::hae7307dcada41b2a
   4:        0x10627d578 - std::panicking::default_hook::{{closure}}::h30c41986d637ef23
   5:        0x10627d380 - std::panicking::default_hook::h81d03189ef2e7e78
   6:        0x10e72ff98 - rustc_driver_impl[21827c9a287a9f15]::install_ice_hook::{closure#0}
   7:        0x10627dc2c - std::panicking::rust_panic_with_hook::he8360f4d28da55fc
   8:        0x10627da0c - std::panicking::begin_panic_handler::{{closure}}::he9e07d605072520f
   9:        0x10627b0a0 - std::sys_common::backtrace::__rust_end_short_backtrace::he03bf52f9c1eb73a
  10:        0x10627d780 - _rust_begin_unwind
  11:        0x1062f49e0 - core::panicking::panic_fmt::ha5f5ca2311fff2ad
  12:        0x1122eba90 - <rustc_trait_selection[96b496d6d05954f1]::traits::auto_trait::AutoTraitFinder>::evaluate_predicates
  13:        0x1051c41f4 - <rustc_trait_selection[96b496d6d05954f1]::traits::auto_trait::AutoTraitFinder>::find_auto_trait_generics::<rustdoc[426ea5acc7761888]::clean::types::Generics, <rustdoc[426ea5acc7761888]::clean::auto_trait::AutoTraitFinder>::generate_for_trait::{closure#0}>
  14:        0x1050cc2a8 - <rustdoc[426ea5acc7761888]::clean::auto_trait::AutoTraitFinder>::generate_for_trait
  15:        0x105122808 - <alloc[e0f95eb21a34f6a8]::vec::Vec<rustdoc[426ea5acc7761888]::clean::types::Item> as alloc[e0f95eb21a34f6a8]::vec::spec_from_iter::SpecFromIter<rustdoc[426ea5acc7761888]::clean::types::Item, core[6a5f4426c52daa32]::iter::adapters::filter_map::FilterMap<alloc[e0f95eb21a34f6a8]::vec::into_iter::IntoIter<rustc_span[2eda851f0959417e]::def_id::DefId>, <rustdoc[426ea5acc7761888]::clean::auto_trait::AutoTraitFinder>::get_auto_trait_impls::{closure#0}>>>::from_iter
  16:        0x1050cc86c - <rustdoc[426ea5acc7761888]::clean::auto_trait::AutoTraitFinder>::get_auto_trait_impls
  17:        0x10507d76c - rustdoc[426ea5acc7761888]::clean::utils::get_auto_trait_and_blanket_impls
  18:        0x1051fb170 - <rustdoc[426ea5acc7761888]::passes::collect_trait_impls::SyntheticImplCollector as rustdoc[426ea5acc7761888]::visit::DocVisitor>::visit_item
  19:        0x1051fb240 - <rustdoc[426ea5acc7761888]::passes::collect_trait_impls::SyntheticImplCollector as rustdoc[426ea5acc7761888]::visit::DocVisitor>::visit_item
  20:        0x1051fbd34 - <rustdoc[426ea5acc7761888]::passes::collect_trait_impls::SyntheticImplCollector as rustdoc[426ea5acc7761888]::visit::DocVisitor>::visit_crate
  21:        0x105091a30 - <rustc_session[1039b6c2e3771dcd]::session::Session>::time::<alloc[e0f95eb21a34f6a8]::vec::Vec<rustdoc[426ea5acc7761888]::clean::types::Item>, rustdoc[426ea5acc7761888]::passes::collect_trait_impls::collect_trait_impls::{closure#0}>
  22:        0x1051f94cc - rustdoc[426ea5acc7761888]::passes::collect_trait_impls::collect_trait_impls
  23:        0x105091d28 - <rustc_session[1039b6c2e3771dcd]::session::Session>::time::<rustdoc[426ea5acc7761888]::clean::types::Crate, rustdoc[426ea5acc7761888]::core::run_global_ctxt::{closure#7}>
  24:        0x1051a808c - rustdoc[426ea5acc7761888]::core::run_global_ctxt
  25:        0x105092064 - <rustc_session[1039b6c2e3771dcd]::session::Session>::time::<(rustdoc[426ea5acc7761888]::clean::types::Crate, rustdoc[426ea5acc7761888]::config::RenderOptions, rustdoc[426ea5acc7761888]::formats::cache::Cache), rustdoc[426ea5acc7761888]::main_args::{closure#1}::{closure#0}::{closure#0}::{closure#0}>
  26:        0x10523c070 - <rustc_middle[a39402582bfd677]::ty::context::GlobalCtxt>::enter::<rustdoc[426ea5acc7761888]::main_args::{closure#1}::{closure#0}::{closure#0}, core[6a5f4426c52daa32]::result::Result<(), rustc_span[2eda851f0959417e]::ErrorGuaranteed>>
  27:        0x10504f878 - <rustc_interface[df80c09a2aa6fb7f]::interface::Compiler>::enter::<rustdoc[426ea5acc7761888]::main_args::{closure#1}::{closure#0}, core[6a5f4426c52daa32]::result::Result<(), rustc_span[2eda851f0959417e]::ErrorGuaranteed>>
  28:        0x105201938 - rustc_span[2eda851f0959417e]::set_source_map::<core[6a5f4426c52daa32]::result::Result<(), rustc_span[2eda851f0959417e]::ErrorGuaranteed>, rustc_interface[df80c09a2aa6fb7f]::interface::run_compiler<core[6a5f4426c52daa32]::result::Result<(), rustc_span[2eda851f0959417e]::ErrorGuaranteed>, rustdoc[426ea5acc7761888]::main_args::{closure#1}>::{closure#0}::{closure#0}>
  29:        0x104fd0214 - <scoped_tls[80ce123946cbe7a6]::ScopedKey<rustc_span[2eda851f0959417e]::SessionGlobals>>::set::<rustc_interface[df80c09a2aa6fb7f]::interface::run_compiler<core[6a5f4426c52daa32]::result::Result<(), rustc_span[2eda851f0959417e]::ErrorGuaranteed>, rustdoc[426ea5acc7761888]::main_args::{closure#1}>::{closure#0}, core[6a5f4426c52daa32]::result::Result<(), rustc_span[2eda851f0959417e]::ErrorGuaranteed>>
  30:        0x1050b901c - std[12e62f360352ccd]::sys_common::backtrace::__rust_begin_short_backtrace::<rustc_interface[df80c09a2aa6fb7f]::util::run_in_thread_pool_with_globals<rustc_interface[df80c09a2aa6fb7f]::interface::run_compiler<core[6a5f4426c52daa32]::result::Result<(), rustc_span[2eda851f0959417e]::ErrorGuaranteed>, rustdoc[426ea5acc7761888]::main_args::{closure#1}>::{closure#0}, core[6a5f4426c52daa32]::result::Result<(), rustc_span[2eda851f0959417e]::ErrorGuaranteed>>::{closure#0}::{closure#0}, core[6a5f4426c52daa32]::result::Result<(), rustc_span[2eda851f0959417e]::ErrorGuaranteed>>
  31:        0x1051904c0 - <<std[12e62f360352ccd]::thread::Builder>::spawn_unchecked_<rustc_interface[df80c09a2aa6fb7f]::util::run_in_thread_pool_with_globals<rustc_interface[df80c09a2aa6fb7f]::interface::run_compiler<core[6a5f4426c52daa32]::result::Result<(), rustc_span[2eda851f0959417e]::ErrorGuaranteed>, rustdoc[426ea5acc7761888]::main_args::{closure#1}>::{closure#0}, core[6a5f4426c52daa32]::result::Result<(), rustc_span[2eda851f0959417e]::ErrorGuaranteed>>::{closure#0}::{closure#0}, core[6a5f4426c52daa32]::result::Result<(), rustc_span[2eda851f0959417e]::ErrorGuaranteed>>::{closure#1} as core[6a5f4426c52daa32]::ops::function::FnOnce<()>>::call_once::{shim:vtable#0}
  32:        0x106286640 - std::sys::unix::thread::Thread::new::thread_start::h06dea01d0985d944
  33:        0x196397fa8 - __pthread_joiner_wake

error: the compiler unexpectedly panicked. this is a bug.

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

note: rustc 1.71.1 (eb26296b5 2023-08-03) running on aarch64-apple-darwin

note: compiler flags: --crate-type lib

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

query stack during panic:
end of query stack
error: could not document `rust-sodium`

Caused by:
  process didn't exit successfully: `/Users/queremendi/.rustup/toolchains/stable-aarch64-apple-darwin/bin/rustdoc --edition=2018 --crate-type lib --crate-name rust_sodium src/lib.rs -o /Users/queremendi/iohk/CryptoLibs/rust-testing/target/doc --error-format=json --json=diagnostic-rendered-ansi,artifacts,future-incompat --diagnostic-width=244 -C metadata=cfbf9925d0133061 -L dependency=/Users/queremendi/iohk/CryptoLibs/rust-testing/target/debug/deps --crate-version 0.1.0` (exit status: 101)

Backtrace

Output seems the same

thread 'rustc' panicked at 'Unexpected result when selecting Structure<C> Obligation(predicate=Binder(ProjectionPredicate(AliasTy { substs: [C, Const { ty: usize, kind: Leaf(0x0000000000000005) }], def_id: DefId(0:7 ~ rust_sodium[23d3]::Bar::BarType) }, Term::Ty(_)), []), depth=2)', compiler/rustc_trait_selection/src/traits/auto_trait.rs:756:33
stack backtrace:
   0: _rust_begin_unwind
   1: core::panicking::panic_fmt
   2: <rustc_trait_selection::traits::auto_trait::AutoTraitFinder>::evaluate_predicates
   3: <rustc_trait_selection::traits::auto_trait::AutoTraitFinder>::find_auto_trait_generics::<rustdoc::clean::types::Generics, <rustdoc::clean::auto_trait::AutoTraitFinder>::generate_for_trait::{closure#0}>
   4: <rustdoc::clean::auto_trait::AutoTraitFinder>::generate_for_trait
   5: <alloc::vec::Vec<rustdoc::clean::types::Item> as alloc::vec::spec_from_iter::SpecFromIter<rustdoc::clean::types::Item, core::iter::adapters::filter_map::FilterMap<alloc::vec::into_iter::IntoIter<rustc_span::def_id::DefId>, <rustdoc::clean::auto_trait::AutoTraitFinder>::get_auto_trait_impls::{closure#0}>>>::from_iter
   6: <rustdoc::clean::auto_trait::AutoTraitFinder>::get_auto_trait_impls
   7: rustdoc::clean::utils::get_auto_trait_and_blanket_impls
   8: <rustdoc::passes::collect_trait_impls::SyntheticImplCollector as rustdoc::visit::DocVisitor>::visit_item
   9: <rustdoc::passes::collect_trait_impls::SyntheticImplCollector as rustdoc::visit::DocVisitor>::visit_item
  10: <rustdoc::passes::collect_trait_impls::SyntheticImplCollector as rustdoc::visit::DocVisitor>::visit_crate
  11: <rustc_session::session::Session>::time::<alloc::vec::Vec<rustdoc::clean::types::Item>, rustdoc::passes::collect_trait_impls::collect_trait_impls::{closure#0}>
  12: rustdoc::passes::collect_trait_impls::collect_trait_impls
  13: <rustc_session::session::Session>::time::<rustdoc::clean::types::Crate, rustdoc::core::run_global_ctxt::{closure#7}>
  14: rustdoc::core::run_global_ctxt
  15: <rustc_session::session::Session>::time::<(rustdoc::clean::types::Crate, rustdoc::config::RenderOptions, rustdoc::formats::cache::Cache), rustdoc::main_args::{closure#1}::{closure#0}::{closure#0}::{closure#0}>
  16: <rustc_middle::ty::context::GlobalCtxt>::enter::<rustdoc::main_args::{closure#1}::{closure#0}::{closure#0}, core::result::Result<(), rustc_span::ErrorGuaranteed>>
  17: <rustc_interface::interface::Compiler>::enter::<rustdoc::main_args::{closure#1}::{closure#0}, core::result::Result<(), rustc_span::ErrorGuaranteed>>
  18: rustc_span::set_source_map::<core::result::Result<(), rustc_span::ErrorGuaranteed>, rustc_interface::interface::run_compiler<core::result::Result<(), rustc_span::ErrorGuaranteed>, rustdoc::main_args::{closure#1}>::{closure#0}::{closure#0}>
  19: <scoped_tls::ScopedKey<rustc_span::SessionGlobals>>::set::<rustc_interface::interface::run_compiler<core::result::Result<(), rustc_span::ErrorGuaranteed>, rustdoc::main_args::{closure#1}>::{closure#0}, core::result::Result<(), rustc_span::ErrorGuaranteed>>
note: Some details are omitted, run with `RUST_BACKTRACE=full` for a verbose backtrace.

error: the compiler unexpectedly panicked. this is a bug.

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

note: rustc 1.71.1 (eb26296b5 2023-08-03) running on aarch64-apple-darwin

note: compiler flags: --crate-type lib

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

query stack during panic:
end of query stack
error: could not document `rust-sodium`

Caused by:
  process didn't exit successfully: `/Users/queremendi/.rustup/toolchains/stable-aarch64-apple-darwin/bin/rustdoc --edition=2018 --crate-type lib --crate-name rust_sodium src/lib.rs -o /Users/queremendi/iohk/CryptoLibs/rust-testing/target/doc --error-format=json --json=diagnostic-rendered-ansi,artifacts,future-incompat --diagnostic-width=244 -C metadata=cfbf9925d0133061 -L dependency=/Users/queremendi/iohk/CryptoLibs/rust-testing/target/debug/deps --crate-version 0.1.0` (exit status: 101)

[fmease]

Related if not duplicate of one of: #105199, #107715, #114097.

@rustbot label -needs-triage T-rustdoc A-auto-traits A-synthetic-impls

[drahnr]

I can't seem to reproduce the cargo doc ICE with

pub trait Foo {
    type FooType;
}

pub trait Bar<const A: usize>: Foo<FooType = <Self as Bar<A>>::BarType> {
    type BarType;
}

pub(crate) const B: usize = 5;

pub trait Tec: Bar<B> {}

pub struct Structure<C: Tec + Bar<5>> {
    _field: <C as Bar<B>>::BarType,
}

and

rustc 1.73.0 (cc66ad468 2023-10-03)

[fmease]

I can't seem to reproduce the […] ICE […]

Me neither, seems to have been fixed. Potentially by err's “ParamEnv PR” or by one of the PRs that made rustdoc execute more of rustc's stages.

Fixed: ICE → errors (unsatisfied bounds).