rustdoc: ICE: synthetic auto trait impls: index out of bounds, snapshot vec using -Znormalize-docs

Code

rustdoc -Znormalize-docs --edition=2021 file.rs

mod foo {
    pub trait MyTrait<'a> {
        type MyItem: ?Sized;
    }

    pub struct Inner<'a, Q, R: ?Sized> {
        field: Q,
        field3: &'a u8,
        my_foo: Foo<Q>,
        field2: R,
    }

    pub struct Outer<'a, T, K: ?Sized> {
        my_inner: Inner<'a, T, K>,
    }

    pub struct Foo<T> {
        myfield: T,
    }
}

// @has complex/struct.NotOuter.html
// @has - '//*[@id="synthetic-implementations-list"]//*[@class="impl"]//h3[@class="code-header"]' \
// @has complex/struct.NotOuter.html
// -> &'b i8, T: MyTrait<'a>, <T as MyTrait<'a>>::MyItem: Copy, 'a: 'static"

pub use foo::{Foo, Inner as NotInner, MyTrait as NotMyTrait, Outer as NotOuter};

unsafe impl<T> Send for Foo<T>
where
    T: NotMyTrait<'static>,
{
}

unsafe impl<'a, Q, R: ?Sized> Send for NotInner<'static, Q, R>
where
    Q: NotMyTrait<'a>,
    <Q as NotMyTrait<'a>>::MyItem: Copy,
    R: for<'b> Fn((&'b bool, &'a u8)) -> &'b i8,
    Foo<Q>: Send,
{
}

Error output

<output>

Backtrace

thread 'rustc' panicked at 'index out of bounds: the len is 0 but the index is 1', /cargo/registry/src/index.crates.io-6f17d22bba15001f/ena-0.14.2/src/snapshot_vec.rs:199:10
stack backtrace:
   0:     0x7f3621169bb1 - std::backtrace_rs::backtrace::libunwind::trace::hf9423e7319e7b273
                               at /rustc/dd5d7c729d4e8a59708df64002e09dbcbc4005ba/library/std/src/../../backtrace/src/backtrace/libunwind.rs:93:5
   1:     0x7f3621169bb1 - std::backtrace_rs::backtrace::trace_unsynchronized::h66acda1b30f743d6
                               at /rustc/dd5d7c729d4e8a59708df64002e09dbcbc4005ba/library/std/src/../../backtrace/src/backtrace/mod.rs:66:5
   2:     0x7f3621169bb1 - std::sys_common::backtrace::_print_fmt::hd68a2e46e11b4b1a
                               at /rustc/dd5d7c729d4e8a59708df64002e09dbcbc4005ba/library/std/src/sys_common/backtrace.rs:65:5
   3:     0x7f3621169bb1 - <std::sys_common::backtrace::_print::DisplayBacktrace as core::fmt::Display>::fmt::h9597144efc95fd0d
                               at /rustc/dd5d7c729d4e8a59708df64002e09dbcbc4005ba/library/std/src/sys_common/backtrace.rs:44:22
   4:     0x7f36211ca18f - core::fmt::rt::Argument::fmt::h78292bc3d727b7ea
                               at /rustc/dd5d7c729d4e8a59708df64002e09dbcbc4005ba/library/core/src/fmt/rt.rs:138:9
   5:     0x7f36211ca18f - core::fmt::write::h3c0df26dbae30f71
                               at /rustc/dd5d7c729d4e8a59708df64002e09dbcbc4005ba/library/core/src/fmt/mod.rs:1094:21
   6:     0x7f362115ce61 - std::io::Write::write_fmt::h9885b87fb4cdbd4b
                               at /rustc/dd5d7c729d4e8a59708df64002e09dbcbc4005ba/library/std/src/io/mod.rs:1713:15
   7:     0x7f36211699c5 - std::sys_common::backtrace::_print::h8dd7723bf85d46b9
                               at /rustc/dd5d7c729d4e8a59708df64002e09dbcbc4005ba/library/std/src/sys_common/backtrace.rs:47:5
   8:     0x7f36211699c5 - std::sys_common::backtrace::print::h4d1dcd147b97d0e0
                               at /rustc/dd5d7c729d4e8a59708df64002e09dbcbc4005ba/library/std/src/sys_common/backtrace.rs:34:9
   9:     0x7f362116c687 - std::panicking::default_hook::{{closure}}::h77fbf8c391b9b7dc
  10:     0x7f362116c474 - std::panicking::default_hook::h8cf79dcd3fda8d66
                               at /rustc/dd5d7c729d4e8a59708df64002e09dbcbc4005ba/library/std/src/panicking.rs:288:9
  11:     0x7f362436c01b - <rustc_driver_impl[1c1e48d71b0475de]::install_ice_hook::{closure#0} as core[4909aebc30286168]::ops::function::FnOnce<(&core[4909aebc30286168]::panic::panic_info::PanicInfo,)>>::call_once::{shim:vtable#0}
  12:     0x7f362116cdcd - <alloc::boxed::Box<F,A> as core::ops::function::Fn<Args>>::call::hab8947fe39a54f02
                               at /rustc/dd5d7c729d4e8a59708df64002e09dbcbc4005ba/library/alloc/src/boxed.rs:1999:9
  13:     0x7f362116cdcd - std::panicking::rust_panic_with_hook::h499030a402682852
                               at /rustc/dd5d7c729d4e8a59708df64002e09dbcbc4005ba/library/std/src/panicking.rs:709:13
  14:     0x7f362116cb67 - std::panicking::begin_panic_handler::{{closure}}::h6ee14f69855f4395
                               at /rustc/dd5d7c729d4e8a59708df64002e09dbcbc4005ba/library/std/src/panicking.rs:597:13
  15:     0x7f3621169fe6 - std::sys_common::backtrace::__rust_end_short_backtrace::he15120d3b7461309
                               at /rustc/dd5d7c729d4e8a59708df64002e09dbcbc4005ba/library/std/src/sys_common/backtrace.rs:151:18
  16:     0x7f362116c8b2 - rust_begin_unwind
                               at /rustc/dd5d7c729d4e8a59708df64002e09dbcbc4005ba/library/std/src/panicking.rs:593:5
  17:     0x7f36211c6413 - core::panicking::panic_fmt::hc8e9b6dda341d3de
                               at /rustc/dd5d7c729d4e8a59708df64002e09dbcbc4005ba/library/core/src/panicking.rs:67:14
  18:     0x7f36211c6572 - core::panicking::panic_bounds_check::h05862dd3eb969670
                               at /rustc/dd5d7c729d4e8a59708df64002e09dbcbc4005ba/library/core/src/panicking.rs:162:5
  19:     0x7f36223a7876 - <ena[4426b5e329104381]::unify::UnificationTable<ena[4426b5e329104381]::unify::backing_vec::InPlace<rustc_middle[810cd5c852e8362a]::infer::unify_key::RegionVidKey, &mut alloc[c31f8ca689b1ba4a]::vec::Vec<ena[4426b5e329104381]::unify::VarValue<rustc_middle[810cd5c852e8362a]::infer::unify_key::RegionVidKey>>, &mut rustc_infer[631e14d7b7f44c7d]::infer::undo_log::InferCtxtUndoLogs>>>::uninlined_get_root_key
  20:     0x7f362245ba5d - <rustc_infer[631e14d7b7f44c7d]::infer::canonical::canonicalizer::Canonicalizer as rustc_type_ir[924a60b187e3d5f3]::fold::TypeFolder<rustc_middle[810cd5c852e8362a]::ty::context::TyCtxt>>::fold_region
  21:     0x7f3622d0610d - <&rustc_middle[810cd5c852e8362a]::ty::list::List<rustc_middle[810cd5c852e8362a]::ty::subst::GenericArg> as rustc_type_ir[924a60b187e3d5f3]::fold::TypeFoldable<rustc_middle[810cd5c852e8362a]::ty::context::TyCtxt>>::try_fold_with::<rustc_infer[631e14d7b7f44c7d]::infer::canonical::canonicalizer::Canonicalizer>
  22:     0x7f3622d408a0 - <rustc_trait_selection[b17b0dc4b37af673]::traits::query::normalize::QueryNormalizer as rustc_type_ir[924a60b187e3d5f3]::fold::FallibleTypeFolder<rustc_middle[810cd5c852e8362a]::ty::context::TyCtxt>>::try_fold_ty
  23:     0x556ae975b959 - <rustc_infer[631e14d7b7f44c7d]::infer::at::At as rustc_trait_selection[b17b0dc4b37af673]::traits::query::normalize::QueryNormalizeExt>::query_normalize::<rustc_middle[810cd5c852e8362a]::ty::sty::Binder<rustc_middle[810cd5c852e8362a]::ty::Ty>>
  24:     0x556ae99a53e8 - rustdoc[88e8a3041a7fc0e6]::clean::normalize
  25:     0x556ae99d148f - rustdoc[88e8a3041a7fc0e6]::clean::clean_middle_ty
  26:     0x556ae999ce5a - rustdoc[88e8a3041a7fc0e6]::clean::clean_predicate
  27:     0x556ae98270e0 - <rustdoc[88e8a3041a7fc0e6]::clean::auto_trait::AutoTraitFinder>::param_env_to_generics
  28:     0x556ae994a326 - <rustc_trait_selection[b17b0dc4b37af673]::traits::auto_trait::AutoTraitFinder>::find_auto_trait_generics::<rustdoc[88e8a3041a7fc0e6]::clean::types::Generics, <rustdoc[88e8a3041a7fc0e6]::clean::auto_trait::AutoTraitFinder>::generate_for_trait::{closure#0}>
  29:     0x556ae982383f - <rustdoc[88e8a3041a7fc0e6]::clean::auto_trait::AutoTraitFinder>::generate_for_trait
  30:     0x556ae98b5bb0 - <alloc[c31f8ca689b1ba4a]::vec::Vec<rustdoc[88e8a3041a7fc0e6]::clean::types::Item> as alloc[c31f8ca689b1ba4a]::vec::spec_from_iter::SpecFromIter<rustdoc[88e8a3041a7fc0e6]::clean::types::Item, core[4909aebc30286168]::iter::adapters::filter_map::FilterMap<alloc[c31f8ca689b1ba4a]::vec::into_iter::IntoIter<rustc_span[f21e7ea1847889b8]::def_id::DefId>, <rustdoc[88e8a3041a7fc0e6]::clean::auto_trait::AutoTraitFinder>::get_auto_trait_impls::{closure#0}>>>::from_iter
  31:     0x556ae9824061 - <rustdoc[88e8a3041a7fc0e6]::clean::auto_trait::AutoTraitFinder>::get_auto_trait_impls
  32:     0x556ae9867df3 - rustdoc[88e8a3041a7fc0e6]::clean::utils::get_auto_trait_and_blanket_impls
  33:     0x556ae997b083 - <rustdoc[88e8a3041a7fc0e6]::passes::collect_trait_impls::SyntheticImplCollector as rustdoc[88e8a3041a7fc0e6]::visit::DocVisitor>::visit_item
  34:     0x556ae997b18a - <rustdoc[88e8a3041a7fc0e6]::passes::collect_trait_impls::SyntheticImplCollector as rustdoc[88e8a3041a7fc0e6]::visit::DocVisitor>::visit_item
  35:     0x556ae997b18a - <rustdoc[88e8a3041a7fc0e6]::passes::collect_trait_impls::SyntheticImplCollector as rustdoc[88e8a3041a7fc0e6]::visit::DocVisitor>::visit_item
  36:     0x556ae997cc06 - <rustdoc[88e8a3041a7fc0e6]::passes::collect_trait_impls::SyntheticImplCollector as rustdoc[88e8a3041a7fc0e6]::visit::DocVisitor>::visit_crate
  37:     0x556ae97f83a7 - <rustc_session[92d4b519115028ad]::session::Session>::time::<alloc[c31f8ca689b1ba4a]::vec::Vec<rustdoc[88e8a3041a7fc0e6]::clean::types::Item>, rustdoc[88e8a3041a7fc0e6]::passes::collect_trait_impls::collect_trait_impls::{closure#0}>
  38:     0x556ae9978ce3 - rustdoc[88e8a3041a7fc0e6]::passes::collect_trait_impls::collect_trait_impls
  39:     0x556ae97f85b2 - <rustc_session[92d4b519115028ad]::session::Session>::time::<rustdoc[88e8a3041a7fc0e6]::clean::types::Crate, rustdoc[88e8a3041a7fc0e6]::core::run_global_ctxt::{closure#7}>
  40:     0x556ae9973435 - rustdoc[88e8a3041a7fc0e6]::core::run_global_ctxt
  41:     0x556ae97f8831 - <rustc_session[92d4b519115028ad]::session::Session>::time::<(rustdoc[88e8a3041a7fc0e6]::clean::types::Crate, rustdoc[88e8a3041a7fc0e6]::config::RenderOptions, rustdoc[88e8a3041a7fc0e6]::formats::cache::Cache), rustdoc[88e8a3041a7fc0e6]::main_args::{closure#1}::{closure#0}::{closure#0}::{closure#0}>
  42:     0x556ae9742a03 - <rustc_middle[810cd5c852e8362a]::ty::context::GlobalCtxt>::enter::<rustdoc[88e8a3041a7fc0e6]::main_args::{closure#1}::{closure#0}::{closure#0}, core[4909aebc30286168]::result::Result<(), rustc_span[f21e7ea1847889b8]::ErrorGuaranteed>>
  43:     0x556ae97f9bf3 - <rustc_interface[6876b9425c9db921]::interface::Compiler>::enter::<rustdoc[88e8a3041a7fc0e6]::main_args::{closure#1}::{closure#0}, core[4909aebc30286168]::result::Result<(), rustc_span[f21e7ea1847889b8]::ErrorGuaranteed>>
  44:     0x556ae9944502 - rustc_span[f21e7ea1847889b8]::set_source_map::<core[4909aebc30286168]::result::Result<(), rustc_span[f21e7ea1847889b8]::ErrorGuaranteed>, rustc_interface[6876b9425c9db921]::interface::run_compiler<core[4909aebc30286168]::result::Result<(), rustc_span[f21e7ea1847889b8]::ErrorGuaranteed>, rustdoc[88e8a3041a7fc0e6]::main_args::{closure#1}>::{closure#0}::{closure#0}>
  45:     0x556ae9a0a6ca - <scoped_tls[3d28ca529fb5aad6]::ScopedKey<rustc_span[f21e7ea1847889b8]::SessionGlobals>>::set::<rustc_interface[6876b9425c9db921]::interface::run_compiler<core[4909aebc30286168]::result::Result<(), rustc_span[f21e7ea1847889b8]::ErrorGuaranteed>, rustdoc[88e8a3041a7fc0e6]::main_args::{closure#1}>::{closure#0}, core[4909aebc30286168]::result::Result<(), rustc_span[f21e7ea1847889b8]::ErrorGuaranteed>>
  46:     0x556ae96f7409 - std[cde9a7b237b1159]::sys_common::backtrace::__rust_begin_short_backtrace::<rustc_interface[6876b9425c9db921]::util::run_in_thread_pool_with_globals<rustc_interface[6876b9425c9db921]::interface::run_compiler<core[4909aebc30286168]::result::Result<(), rustc_span[f21e7ea1847889b8]::ErrorGuaranteed>, rustdoc[88e8a3041a7fc0e6]::main_args::{closure#1}>::{closure#0}, core[4909aebc30286168]::result::Result<(), rustc_span[f21e7ea1847889b8]::ErrorGuaranteed>>::{closure#0}::{closure#0}, core[4909aebc30286168]::result::Result<(), rustc_span[f21e7ea1847889b8]::ErrorGuaranteed>>
  47:     0x556ae9914301 - <<std[cde9a7b237b1159]::thread::Builder>::spawn_unchecked_<rustc_interface[6876b9425c9db921]::util::run_in_thread_pool_with_globals<rustc_interface[6876b9425c9db921]::interface::run_compiler<core[4909aebc30286168]::result::Result<(), rustc_span[f21e7ea1847889b8]::ErrorGuaranteed>, rustdoc[88e8a3041a7fc0e6]::main_args::{closure#1}>::{closure#0}, core[4909aebc30286168]::result::Result<(), rustc_span[f21e7ea1847889b8]::ErrorGuaranteed>>::{closure#0}::{closure#0}, core[4909aebc30286168]::result::Result<(), rustc_span[f21e7ea1847889b8]::ErrorGuaranteed>>::{closure#1} as core[4909aebc30286168]::ops::function::FnOnce<()>>::call_once::{shim:vtable#0}
  48:     0x7f36211772c5 - <alloc::boxed::Box<F,A> as core::ops::function::FnOnce<Args>>::call_once::h13a60418c9a4d1aa
                               at /rustc/dd5d7c729d4e8a59708df64002e09dbcbc4005ba/library/alloc/src/boxed.rs:1985:9
  49:     0x7f36211772c5 - <alloc::boxed::Box<F,A> as core::ops::function::FnOnce<Args>>::call_once::he4eb541375b2c3d8
                               at /rustc/dd5d7c729d4e8a59708df64002e09dbcbc4005ba/library/alloc/src/boxed.rs:1985:9
  50:     0x7f36211772c5 - std::sys::unix::thread::Thread::new::thread_start::hbdba04d5a7b01509
                               at /rustc/dd5d7c729d4e8a59708df64002e09dbcbc4005ba/library/std/src/sys/unix/thread.rs:108:17
  51:     0x7f3620df1bb5 - <unknown>
  52:     0x7f3620e73d90 - <unknown>
  53:                0x0 - <unknown>

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 1.72.0-nightly (dd5d7c729 2023-06-02) running on x86_64-unknown-linux-gnu

note: compiler flags: -Z normalize-docs

query stack during panic:
end of query stack

reduced a bit

mod foo {
    pub trait MyTrait<'a> {
        type MyItem: ?Sized;
    }

    pub struct Inner<'a, Q, R: ?Sized> {
        field: Q,
        field3: &'a u8,
        my_foo: Foo<Q>,
        field2: R,
    }

    pub struct Outer<'a, T, K: ?Sized> {
        my_inner: Inner<'a, T, K>,
    }

    pub struct Foo<T> {
        myfield: T,
    }
}

pub use foo::{Foo, Inner as NotInner, MyTrait as NotMyTrait};

unsafe impl<'a, Q, R: ?Sized> Send for NotInner<'static, Q, R>
where
    Q: NotMyTrait<'a>,
    <Q as NotMyTrait<'a>>::MyItem: Copy,
    R:,
    Foo<Q>: Send,
{
}

@rustbot

Ah another AutoTraitFinder bug ^^.
@rustbot label T-compiler A-synthetic-impls A-auto-traits

reduce:

rustdoc -Znormalize-docs file.rs

trait MyTrait<'a> {
  type MyItem;
}
struct Inner<Q>(Q);
struct Outer<Q>(Inner<Q>);

unsafe impl<'a, Q> Send for Inner<Q>
where
  Q: MyTrait<'a>,
  <Q as MyTrait<'a>>::MyItem: Copy,
{}

All three reproducers will be fixed by #108503.

./tests/ui/implied-bounds/implied-bounds-unconstrained-2.rs

// check-pass

// Another minimized regression test for #112832.
trait Trait {
    type Assoc;
}

trait Sub<'a>: Trait<Assoc = <Self as Sub<'a>>::SubAssoc> {
    type SubAssoc;
}

// By using the where-clause we normalize `<T as Trait>::Assoc` to
// `<T as Sub<'a>>::SubAssoc` where `'a` is an unconstrained region
// variable.
fn foo<T>(x: <T as Trait>::Assoc)
where
    for<'a> T: Sub<'a>,
{}

fn main() {}

I can no longer reproduce any of these issues.

Auto merge of rust-lang#123348 - fmease:add-synth-auto-trait-impls-te…

Rollup merge of rust-lang#123375 - fmease:rustdoc-sati-re-hotfix, r=G…

Unrolled build for rust-lang#123375

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rustdoc: ICE: synthetic auto trait impls: `index out of bounds, snapshot vec` using `-Znormalize-docs` #112242

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rustdoc: ICE: synthetic auto trait impls: index out of bounds, snapshot vec using -Znormalize-docs #112242

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matthiaskrgr commented on Jun 3, 2023

fmease commented on Jun 7, 2023

bvanjoi commented on Jun 20, 2023

fmease commented on Sep 5, 2023

matthiaskrgr commented on Sep 8, 2023

fmease commented on Mar 31, 2024

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rustdoc: ICE: synthetic auto trait impls: `index out of bounds, snapshot vec` using `-Znormalize-docs` #112242