ICE: rustdoc on ./src/test/ui/traits/trait-object-vs-lifetime-2.rs: index OOB

[matthiaskrgr]

Code

code from ./src/test/ui/traits/trait-object-vs-lifetime-2.rs

// A few contrived examples where lifetime should (or should not) be parsed as an object type.
// Lifetimes parsed as types are still rejected later by semantic checks.

// `'static` is a lifetime, `'static +` is a type, `'a` is a type
fn g() where
    'static: 'static,
    dyn 'static +: 'static + Copy,
    //~^ ERROR at least one trait is required for an object type
{}

fn main() {}

Meta

rustc --version --verbose:

rustdoc 1.50.0-nightly (1c389ffef 2020-11-24)
binary: rustdoc
commit-hash: 1c389ffeff814726dec325f0f2b0c99107df2673
commit-date: 2020-11-24
host: x86_64-unknown-linux-gnu
release: 1.50.0-nightly

Error output

error[E0224]: at least one trait is required for an object type
 --> ./src/test/ui/traits/trait-object-vs-lifetime-2.rs:7:5
  |
7 |     dyn 'static +: 'static + Copy,
  |     ^^^^^^^^^^^^^

thread 'rustc' panicked at 'index out of bounds: the len is 0 but the index is 0', src/librustdoc/clean/mod.rs:1461:23
note: run with `RUST_BACKTRACE=1` environment variable to display a backtrace

error: internal compiler error: unexpected panic

note: 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-compiler&template=ice.md

note: rustc 1.50.0-nightly (1c389ffef 2020-11-24) running on x86_64-unknown-linux-gnu

query stack during panic:
end of query stack

Backtrace

error[E0224]: at least one trait is required for an object type
 --> ./src/test/ui/traits/trait-object-vs-lifetime-2.rs:7:5
  |
7 |     dyn 'static +: 'static + Copy,
  |     ^^^^^^^^^^^^^

thread 'rustc' panicked at 'index out of bounds: the len is 0 but the index is 0', src/librustdoc/clean/mod.rs:1461:23
stack backtrace:
   0:     0x7f152b646e30 - std::backtrace_rs::backtrace::libunwind::trace::h746c3e9529d524bc
                               at /rustc/1c389ffeff814726dec325f0f2b0c99107df2673/library/std/src/../../backtrace/src/backtrace/libunwind.rs:90:5
   1:     0x7f152b646e30 - std::backtrace_rs::backtrace::trace_unsynchronized::h86340908ff889faa
                               at /rustc/1c389ffeff814726dec325f0f2b0c99107df2673/library/std/src/../../backtrace/src/backtrace/mod.rs:66:5
   2:     0x7f152b646e30 - std::sys_common::backtrace::_print_fmt::h43f85f9b18230404
                               at /rustc/1c389ffeff814726dec325f0f2b0c99107df2673/library/std/src/sys_common/backtrace.rs:67:5
   3:     0x7f152b646e30 - <std::sys_common::backtrace::_print::DisplayBacktrace as core::fmt::Display>::fmt::hc132ae1a5b5aa7cd
                               at /rustc/1c389ffeff814726dec325f0f2b0c99107df2673/library/std/src/sys_common/backtrace.rs:46:22
   4:     0x7f152b6b9c4c - core::fmt::write::hdf023a0036d2a25f
                               at /rustc/1c389ffeff814726dec325f0f2b0c99107df2673/library/core/src/fmt/mod.rs:1078:17
   5:     0x7f152b6389a2 - std::io::Write::write_fmt::h8580846154bcb66a
                               at /rustc/1c389ffeff814726dec325f0f2b0c99107df2673/library/std/src/io/mod.rs:1519:15
   6:     0x7f152b64aa95 - std::sys_common::backtrace::_print::h7ee55fed88d107a3
                               at /rustc/1c389ffeff814726dec325f0f2b0c99107df2673/library/std/src/sys_common/backtrace.rs:49:5
   7:     0x7f152b64aa95 - std::sys_common::backtrace::print::h54a7d3e52a524177
                               at /rustc/1c389ffeff814726dec325f0f2b0c99107df2673/library/std/src/sys_common/backtrace.rs:36:9
   8:     0x7f152b64aa95 - std::panicking::default_hook::{{closure}}::h60921e857bf55a40
                               at /rustc/1c389ffeff814726dec325f0f2b0c99107df2673/library/std/src/panicking.rs:208:50
   9:     0x7f152b64a5ea - std::panicking::default_hook::hf0f9afb1017317fc
                               at /rustc/1c389ffeff814726dec325f0f2b0c99107df2673/library/std/src/panicking.rs:225:9
  10:     0x7f152bed7bb8 - rustc_driver::report_ice::ha25ae86a5858acc3
  11:     0x7f152b64b396 - std::panicking::rust_panic_with_hook::h8d66bf42b407aaea
                               at /rustc/1c389ffeff814726dec325f0f2b0c99107df2673/library/std/src/panicking.rs:595:17
  12:     0x7f152b64aeb7 - std::panicking::begin_panic_handler::{{closure}}::hde71edcd925d0c5e
                               at /rustc/1c389ffeff814726dec325f0f2b0c99107df2673/library/std/src/panicking.rs:497:13
  13:     0x7f152b6472ec - std::sys_common::backtrace::__rust_end_short_backtrace::h8a3c7d6cea578919
                               at /rustc/1c389ffeff814726dec325f0f2b0c99107df2673/library/std/src/sys_common/backtrace.rs:141:18
  14:     0x7f152b64ae19 - rust_begin_unwind
                               at /rustc/1c389ffeff814726dec325f0f2b0c99107df2673/library/std/src/panicking.rs:493:5
  15:     0x7f152b6b6031 - core::panicking::panic_fmt::h20225113c4a2f8fd
                               at /rustc/1c389ffeff814726dec325f0f2b0c99107df2673/library/core/src/panicking.rs:92:14
  16:     0x7f152b6b5ff2 - core::panicking::panic_bounds_check::h5752306d250b5620
                               at /rustc/1c389ffeff814726dec325f0f2b0c99107df2673/library/core/src/panicking.rs:69:5
  17:     0x5633d2986e7a - <rustc_hir::hir::Ty as rustdoc::clean::Clean<rustdoc::clean::types::Type>>::clean::h7e12b892841ced7b
  18:     0x5633d298118b - <rustc_hir::hir::WherePredicate as rustdoc::clean::Clean<rustdoc::clean::types::WherePredicate>>::clean::hf2e322efaf06dc70
  19:     0x5633d298232f - <rustc_hir::hir::Generics as rustdoc::clean::Clean<rustdoc::clean::types::Generics>>::clean::hc30c3f91e19a62bf
  20:     0x5633d2a12168 - rustdoc::clean::utils::enter_impl_trait::h89ecd5f85c6cf117
  21:     0x5633d298a339 - <(&rustc_hir::hir::Item,core::option::Option<rustc_span::symbol::Ident>) as rustdoc::clean::Clean<alloc::vec::Vec<rustdoc::clean::types::Item>>>::clean::h6efe2622d62f0879
  22:     0x5633d2a9601f - <alloc::vec::Vec<T,A> as alloc::vec::SpecExtend<T,I>>::spec_extend::hbf27f2437fec8031
  23:     0x5633d2a12de8 - <rustdoc::doctree::Module as rustdoc::clean::Clean<rustdoc::clean::types::Item>>::clean::hee8955bac14e83bc
  24:     0x5633d2a0c153 - rustdoc::clean::utils::krate::h68bb50ab032123ce
  25:     0x5633d2787b3b - rustdoc::core::run_global_ctxt::h7cf39be6ea65128e
  26:     0x5633d2801ece - rustc_interface::passes::QueryContext::enter::hedb615e17429b641
  27:     0x5633d28f7917 - rustc_interface::interface::create_compiler_and_run::h25fa5935e40978f2
  28:     0x5633d279e0d3 - rustdoc::main_options::h8a5cda9c1c8c625b
  29:     0x5633d28e8a68 - rustc_span::with_session_globals::h7a83fbbd64fb6823
  30:     0x5633d27cf30e - std::sys_common::backtrace::__rust_begin_short_backtrace::h50722f4a01515f7b
  31:     0x5633d290103a - core::ops::function::FnOnce::call_once{{vtable.shim}}::h22276985fb540191
  32:     0x7f152b65a65a - <alloc::boxed::Box<F,A> as core::ops::function::FnOnce<Args>>::call_once::hea1090dbdcecbf5a
                               at /rustc/1c389ffeff814726dec325f0f2b0c99107df2673/library/alloc/src/boxed.rs:1318:9
  33:     0x7f152b65a65a - <alloc::boxed::Box<F,A> as core::ops::function::FnOnce<Args>>::call_once::h8d5723d3912bd325
                               at /rustc/1c389ffeff814726dec325f0f2b0c99107df2673/library/alloc/src/boxed.rs:1318:9
  34:     0x7f152b65a65a - std::sys::unix::thread::Thread::new::thread_start::hc17a425ca2995724
                               at /rustc/1c389ffeff814726dec325f0f2b0c99107df2673/library/std/src/sys/unix/thread.rs:71:17
  35:     0x7f152b5363e9 - start_thread
  36:     0x7f152b31c293 - __GI___clone
  37:                0x0 - <unknown>

error: internal compiler error: unexpected panic

note: 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-compiler&template=ice.md

note: rustc 1.50.0-nightly (1c389ffef 2020-11-24) running on x86_64-unknown-linux-gnu

query stack during panic:
end of query stack
error: aborting due to previous error

For more information about this error, try `rustc --explain E0224`.

[jyn514]

I think this is the code crashing:

rust/src/librustdoc/clean/mod.rs

Line 1467 in 0c11b93

match bounds[0].clean(cx).trait_ {

Assigning P-low by the same rationale as #79496 (comment), but I expect this to be much easier to fix than #79495, #79494, or #79468.

[matthiaskrgr]

No longer crashing:

error[E0224]: at least one trait is required for an object type
 --> out.rs:7:5
  |
7 |     dyn 'static +: 'static + Copy,
  |     ^^^^^^^^^^^^^

error: aborting due to previous error