ICE: unnested_or_patterns while checking rustc_typeck

[matthiaskrgr]

Clippy crashes while checking rustcs rustc_typeck crate.
clippy 0.0.212 (8aa18cb 2020-07-08)

Backtrace:

thread 'rustc' panicked at 'index out of bounds: the len is 0 but the index is 0', src/tools/clippy/clippy_lints/src/unnested_or_patterns.rs:403:27
stack backtrace:
   0:     0x7fc4bdcb58a5 - backtrace::backtrace::libunwind::trace::h34afbfad7fd770fc
                               at /cargo/registry/src/github.com-1ecc6299db9ec823/backtrace-0.3.46/src/backtrace/libunwind.rs:86
   1:     0x7fc4bdcb58a5 - backtrace::backtrace::trace_unsynchronized::h460d522b1619a600
                               at /cargo/registry/src/github.com-1ecc6299db9ec823/backtrace-0.3.46/src/backtrace/mod.rs:66
   2:     0x7fc4bdcb58a5 - std::sys_common::backtrace::_print_fmt::ha45fac10086813b4
                               at src/libstd/sys_common/backtrace.rs:78
   3:     0x7fc4bdcb58a5 - <std::sys_common::backtrace::_print::DisplayBacktrace as core::fmt::Display>::fmt::hde84f63fcfd0e6de
                               at src/libstd/sys_common/backtrace.rs:59
   4:     0x7fc4bdcf232c - core::fmt::write::h540ac4a6a1232abc
                               at src/libcore/fmt/mod.rs:1076
   5:     0x7fc4bdca7622 - std::io::Write::write_fmt::hc344eafd6e850b4d
                               at src/libstd/io/mod.rs:1537
   6:     0x7fc4bdcba740 - std::sys_common::backtrace::_print::h4db88ff15cb5d61d
                               at src/libstd/sys_common/backtrace.rs:62
   7:     0x7fc4bdcba740 - std::sys_common::backtrace::print::h5fc39e1b1f610bd3
                               at src/libstd/sys_common/backtrace.rs:49
   8:     0x7fc4bdcba740 - std::panicking::default_hook::{{closure}}::h59e55edacb1d974a
                               at src/libstd/panicking.rs:198
   9:     0x7fc4bdcba48c - std::panicking::default_hook::heee4c8016dfbf328
                               at src/libstd/panicking.rs:217
  10:     0x55613a432c61 - clippy_driver::report_clippy_ice::h0e13321a0601dc3a
  11:     0x7fc4bdcbaeb8 - std::panicking::rust_panic_with_hook::h8405b6301c79fb5a
                               at src/libstd/panicking.rs:530
  12:     0x7fc4bdcbaa8b - rust_begin_unwind
                               at src/libstd/panicking.rs:437
  13:     0x7fc4bdceeed1 - core::panicking::panic_fmt::h78830ea6a34e7206
                               at src/libcore/panicking.rs:85
  14:     0x7fc4bdceee92 - core::panicking::panic_bounds_check::hdef4fff11e167a6a
                               at src/libcore/panicking.rs:62
  15:     0x55613a4daa87 - clippy_lints::unnested_or_patterns::eq_pre_post::hc91d82b8fff79e75
  16:     0x55613a57baeb - <alloc::vec::DrainFilter<T,F> as core::iter::traits::iterator::Iterator>::next::h3d1fe73d02a8b853
  17:     0x55613a4d87b9 - <clippy_lints::unnested_or_patterns::unnest_or_patterns::Visitor as rustc_ast::mut_visit::MutVisitor>::visit_pat::hf6ef0e32dca88cc5
  18:     0x55613a4d7c89 - <clippy_lints::unnested_or_patterns::unnest_or_patterns::Visitor as rustc_ast::mut_visit::MutVisitor>::visit_pat::hf6ef0e32dca88cc5
  19:     0x55613a62cfdd - rustc_ast::mut_visit::noop_visit_pat::h00ccb57e0a7e0c92
  20:     0x55613a4d9d83 - <clippy_lints::unnested_or_patterns::unnest_or_patterns::Visitor as rustc_ast::mut_visit::MutVisitor>::visit_pat::hf6ef0e32dca88cc5
  21:     0x55613a4d78b9 - clippy_lints::unnested_or_patterns::lint_unnested_or_patterns::hed89529dfabfc49d
  22:     0x7fc4c0385da3 - <rustc_lint::early::EarlyLintPassObjects as rustc_lint::passes::EarlyLintPass>::check_arm::h702c4cfb2d5a0003
  23:     0x7fc4be66525c - rustc_ast::visit::walk_expr::hc6f2fa2739b5bd44
  24:     0x7fc4be60a90d - <rustc_lint::early::EarlyContextAndPass<T> as rustc_ast::visit::Visitor>::visit_expr::h1ec66f13d405e19d
  25:     0x7fc4be60b4ed - <rustc_lint::early::EarlyContextAndPass<T> as rustc_ast::visit::Visitor>::visit_local::h8fe4e8c834fcace8
  26:     0x7fc4be665152 - rustc_ast::visit::walk_expr::hc6f2fa2739b5bd44
  27:     0x7fc4be60a90d - <rustc_lint::early::EarlyContextAndPass<T> as rustc_ast::visit::Visitor>::visit_expr::h1ec66f13d405e19d
  28:     0x7fc4be660db1 - rustc_ast::visit::walk_fn::hb33763d93347ea2c
  29:     0x7fc4be65bffd - rustc_ast::visit::walk_assoc_item::hf809cdfa669afdd4
  30:     0x7fc4be666ac7 - rustc_ast::visit::walk_item::hadb85d96c7e22896
  31:     0x7fc4be661f57 - rustc_ast::visit::walk_mod::h44239b070db7d8eb
  32:     0x7fc4be665e92 - rustc_ast::visit::walk_item::hadb85d96c7e22896
  33:     0x7fc4be661f57 - rustc_ast::visit::walk_mod::h44239b070db7d8eb
  34:     0x7fc4be665e92 - rustc_ast::visit::walk_item::hadb85d96c7e22896
  35:     0x7fc4be661f57 - rustc_ast::visit::walk_mod::h44239b070db7d8eb
  36:     0x7fc4be5e353e - rustc_lint::early::early_lint_crate::h69be7315dc13e506
  37:     0x7fc4be5e2cb9 - rustc_lint::early::check_ast_crate::he9606f65d602b3ad
  38:     0x7fc4be66cb3e - rustc_session::utils::<impl rustc_session::session::Session>::time::hb9014418586e5e41
  39:     0x7fc4be5c5388 - rustc_interface::passes::BoxedResolver::access::{{closure}}::h86171b927fa2cfca
  40:     0x7fc4be62b10b - rustc_interface::passes::configure_and_expand::{{closure}}::hd6cfede8be3ee7f8
  41:     0x7fc4be5c5164 - rustc_interface::passes::BoxedResolver::access::h689cbc08776fdcff
  42:     0x7fc4be5df367 - rustc_interface::queries::Queries::lower_to_hir::h84562e3bfbe512f1
  43:     0x7fc4be5dffe7 - rustc_interface::queries::Queries::global_ctxt::h534722f6d7513c5d
  44:     0x7fc4be3df3ab - rustc_interface::queries::<impl rustc_interface::interface::Compiler>::enter::hfbc63b8f1bb864b3
  45:     0x7fc4be47f787 - rustc_span::with_source_map::h57513f6df947164e
  46:     0x7fc4be3e0aa6 - rustc_interface::interface::run_compiler_in_existing_thread_pool::ha77eec52fccd45a0
  47:     0x7fc4be40b31d - scoped_tls::ScopedKey<T>::set::hf9bed68bfc8ed2b7
  48:     0x7fc4be42d420 - std::sys_common::backtrace::__rust_begin_short_backtrace::ha0325e6c1df2523d
  49:     0x7fc4be3ee98e - core::ops::function::FnOnce::call_once{{vtable.shim}}::hb9561786ae71a4d6
  50:     0x7fc4bdcc9c7a - <alloc::boxed::Box<F> as core::ops::function::FnOnce<A>>::call_once::h13d34828db364579
                               at /rustc/8aa18cbdc5d4bc33bd61e2d9a4b643d87f5d21de/src/liballoc/boxed.rs:1081
  51:     0x7fc4bdcc9c7a - <alloc::boxed::Box<F> as core::ops::function::FnOnce<A>>::call_once::hd51b619e0f884abf
                               at /rustc/8aa18cbdc5d4bc33bd61e2d9a4b643d87f5d21de/src/liballoc/boxed.rs:1081
  52:     0x7fc4bdcc9c7a - std::sys::unix::thread::Thread::new::thread_start::h02c6e34c2c73f344
                               at src/libstd/sys/unix/thread.rs:87
  53:     0x7fc4bdbde422 - start_thread
  54:     0x7fc4bdaf3bf3 - __GI___clone
  55:                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-clippy/issues/new

note: Clippy version: clippy 0.0.212 (8aa18cb 2020-07-08)

query stack during panic:
end of query stack
warning: 1 warning emitted

error: could not compile `rustc_typeck`.

To learn more, run the command again with --verbose.
command did not execute successfully: "/home/matthias/vcs/github/rust/build/x86_64-unknown-linux-gnu/stage0/bin/cargo" "clippy" "--target" "x86_64-unknown-linux-gnu" "-Zbinary-dep-depinfo" "-j" "1" "--release" "--features" " llvm" "--manifest-path" "/home/matthias/vcs/github/rust/src/rustc/Cargo.toml" "--message-format" "json-render-diagnostics" "--" "--cap-lints" "warn" "-Aclippy::too_many_arguments" "-Aclippy::many_single_char_names" "-Aclippy::unreadable_literal" "-Aclippy::missing_safety_doc" "-Aclippy::collapsible_if" "-Aclippy::excessive_precision" "-Aclippy::wrong_self_convention" "-Aclippy::cognitive_complexity" "-Aclippy::trivially_copy_pass_by_ref" "-Aclippy::eval_order_dependence" "-Aclippy::partialeq_ne_impl" "-Aclippy::declare_interior_mutable_const" "-Aclippy::new_without_default" "-Aclippy::len_without_is_empty" "-Aclippy::should_implement_trait" "-Aclippy::transmute_float_to_int" "-Aclippy::mut_from_ref" "-Aclippy::deref_addrof" "-Aclippy::transmute_int_to_float" "-Aclippy::float_cmp" "-Aclippy::mem_replace_with_default" "-Aclippy::not_unsafe_ptr_arg_deref" "-Aclippy::needless_doctest_main" "-Aclippy::transmute_ptr_to_ptr" "-Aclippy::type_complexity" "-Aclippy::ptr_offset_with_cast" "-Aclippy::or_fun_call" "-Aclippy::manual_saturating_arithmetic" "-Aclippy::ptr_arg" "-Aclippy::derive_hash_xor_eq" "-Aclippy::drop_copy" "-Aclippy::diverging_sub_expression" "-Aclippy::just_underscores_and_digits" "-Aclippy::boxed_local" "-Aclippy::vec_box" "-Aclippy::drop_ref" "-Aclippy::match_bool" "-Aclippy::range_plus_one" "-Aclippy::to_digit_is_some" "-Aclippy::absurd_extreme_comparisons" "-Aclippy::assign_op_pattern" "-Aclippy::box_vec" "-Aclippy::cast_ptr_alignment" "-Aclippy::cmp_null" "-Aclippy::enum_variant_names" "-Aclippy::extra_unused_lifetimes" "-Aclippy::identity_op" "-Aclippy::implicit_hasher" "-Aclippy::inconsistent_digit_grouping" "-Aclippy::inherent_to_string" "-Aclippy::inherent_to_string_shadow_display" "-Aclippy::large_enum_variant" "-Aclippy::let_unit_value" "-Aclippy::match_as_ref" "-Aclippy::match_overlapping_arm" "-Aclippy::module_inception" "-Aclippy::modulo_one" "-Aclippy::mutable_key_type" "-Aclippy::option_option" "-Aclippy::range_minus_one" "-Aclippy::transmute_int_to_char" "-Aclippy::transmute_ptr_to_ref" "-Aclippy::option_map_unit_fn" "-Aclippy::comparison_chain" "-Aclippy::write_literal" "-Aclippy::write_with_newline" "-Aclippy::needless_lifetimes"
expected success, got: exit code: 101
failed to run: /home/matthias/vcs/github/rust/build/bootstrap/debug/bootstrap clippy -j 1
Build completed unsuccessfully in 0:00:02

[matthiaskrgr]

I believe the problem is we access by index BEFORE doing the length check here:

fn eq_pre_post(ps1: &[P<Pat>], ps2: &[P<Pat>], idx: usize) -> bool {
    ps1[idx].is_rest() == ps2[idx].is_rest() // Avoid `[x, ..] | [x, 0]` => `[x, .. | 0]`.
        && ps1.len() == ps2.len()         // this should come first
        && over(&ps1[..idx], &ps2[..idx], |l, r| eq_pat(l, r))
        && over(&ps1[idx + 1..], &ps2[idx + 1..], |l, r| eq_pat(l, r))
}