`Map::find` should not index, but call `get` instead to prevent ICEs

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Assessment

Difficulty
2/5
Estimated time
1-3 hours
Newbie friendliness
62/100
Issue type
Bug
Clarity
Clearly specified
Activity status
Stale
Tech stack
rust
Domain
compilers

Research direction

Start in compiler/rustc_middle/src/hir/map/mod.rs at the Map::find implementation and review the failing call path from the backtrace. Reproduce the missing-HirId case, then verify that Map::find returns None rather than panicking when the ID is out of bounds, including through the reported Clippy visitor scenario.

Written by the indexing model from the issue text.

Description

C-bug I-ICE T-compiler

rustc_middle::hir::map::Map::find will panic even though it's meant to return None, since it uses indexing instead of get.

This was ran into while writing a clippy lint. This visited every HirId using visit_id. It would be expected that if it failed to find it, it would ignore that id. Instead, it panics. For now, a reimplementation has been created.

Code

https://github.com/Centri3/rust-clippy/blob/676ad8d65cfc5c9c383c7dcde30026ad7152cf88/clippy_lints/src/min_ident_chars.rs#L85-L87, not really applicable.

Backtrace 

thread 'rustc' panicked at 'index out of bounds: the len is 3 but the index is 3', compiler/rustc_middle/src/hir/map/mod.rs:322:24
stack backtrace:
   0:     0x7fd35bbc5bb1 - std::backtrace_rs::backtrace::libunwind::trace::h4e09b4719f180222
                               at /rustc/d59363ad0b6391b7fc5bbb02c9ccf9300eef3753/library/std/src/../../backtrace/src/backtrace/libunwind.rs:93:5
   1:     0x7fd35bbc5bb1 - std::backtrace_rs::backtrace::trace_unsynchronized::hd7cdeae81cc896d9
                               at /rustc/d59363ad0b6391b7fc5bbb02c9ccf9300eef3753/library/std/src/../../backtrace/src/backtrace/mod.rs:66:5
   2:     0x7fd35bbc5bb1 - std::sys_common::backtrace::_print_fmt::hd49c3b478db8c635
                               at /rustc/d59363ad0b6391b7fc5bbb02c9ccf9300eef3753/library/std/src/sys_common/backtrace.rs:65:5
   3:     0x7fd35bbc5bb1 - <std::sys_common::backtrace::_print::DisplayBacktrace as core::fmt::Display>::fmt::h59edacfaa3bc83ad
                               at /rustc/d59363ad0b6391b7fc5bbb02c9ccf9300eef3753/library/std/src/sys_common/backtrace.rs:44:22
   4:     0x7fd35bc2619f - core::fmt::rt::Argument::fmt::h4d6e5a3b8dd7874d
                               at /rustc/d59363ad0b6391b7fc5bbb02c9ccf9300eef3753/library/core/src/fmt/rt.rs:138:9
   5:     0x7fd35bc2619f - core::fmt::write::haf2f7e5235ba578a
                               at /rustc/d59363ad0b6391b7fc5bbb02c9ccf9300eef3753/library/core/src/fmt/mod.rs:1094:21
   6:     0x7fd35bbb8dc1 - std::io::Write::write_fmt::h4a6949a8bf6e6368
                               at /rustc/d59363ad0b6391b7fc5bbb02c9ccf9300eef3753/library/std/src/io/mod.rs:1713:15
   7:     0x7fd35bbc59c5 - std::sys_common::backtrace::_print::hff5de9ef9631778c
                               at /rustc/d59363ad0b6391b7fc5bbb02c9ccf9300eef3753/library/std/src/sys_common/backtrace.rs:47:5
   8:     0x7fd35bbc59c5 - std::sys_common::backtrace::print::he929539ea17f974e
                               at /rustc/d59363ad0b6391b7fc5bbb02c9ccf9300eef3753/library/std/src/sys_common/backtrace.rs:34:9
   9:     0x7fd35bbc8687 - std::panicking::default_hook::{{closure}}::hf81d17fa0bdad902
  10:     0x7fd35bbc8474 - std::panicking::default_hook::hf7cf1a888245839f
                               at /rustc/d59363ad0b6391b7fc5bbb02c9ccf9300eef3753/library/std/src/panicking.rs:288:9
  11:     0x7fd35ed9c92b - rustc_driver_impl[56cae5af60b3bf59]::install_ice_hook::{closure#0}
  12:     0x7fd35bbc8dcd - <alloc::boxed::Box<F,A> as core::ops::function::Fn<Args>>::call::h15d48301475b02a0
                               at /rustc/d59363ad0b6391b7fc5bbb02c9ccf9300eef3753/library/alloc/src/boxed.rs:1999:9
  13:     0x7fd35bbc8dcd - std::panicking::rust_panic_with_hook::h057616b5a1d41480
                               at /rustc/d59363ad0b6391b7fc5bbb02c9ccf9300eef3753/library/std/src/panicking.rs:709:13
  14:     0x7fd35bbc8b67 - std::panicking::begin_panic_handler::{{closure}}::h5ec862423d83e4d3
                               at /rustc/d59363ad0b6391b7fc5bbb02c9ccf9300eef3753/library/std/src/panicking.rs:597:13
  15:     0x7fd35bbc5fe6 - std::sys_common::backtrace::__rust_end_short_backtrace::h4c1dca17bc43c37e
                               at /rustc/d59363ad0b6391b7fc5bbb02c9ccf9300eef3753/library/std/src/sys_common/backtrace.rs:151:18
  16:     0x7fd35bbc88b2 - rust_begin_unwind
                               at /rustc/d59363ad0b6391b7fc5bbb02c9ccf9300eef3753/library/std/src/panicking.rs:593:5
  17:     0x7fd35bc22423 - core::panicking::panic_fmt::h704203a971c03be5
                               at /rustc/d59363ad0b6391b7fc5bbb02c9ccf9300eef3753/library/core/src/panicking.rs:67:14
  18:     0x7fd35bc22582 - core::panicking::panic_bounds_check::hd086f175ae4832c3
                               at /rustc/d59363ad0b6391b7fc5bbb02c9ccf9300eef3753/library/core/src/panicking.rs:162:5
  19:     0x7fd35cf4f934 - <rustc_middle[4f6cb0c16f06e5a5]::hir::map::Map>::find
  20:     0x55c159342b13 - <clippy_lints::min_ident_chars::IdentVisitor as rustc_hir::intravisit::Visitor>::visit_id::ha653009bcd00a3b1
                               at /home/centri/GitHub/rust-clippy/clippy_lints/src/min_ident_chars.rs:88:26
  21:     0x55c15905e75f - rustc_hir::intravisit::walk_param_bound::hcf81da3ee637b560
                               at /rustc/d59363ad0b6391b7fc5bbb02c9ccf9300eef3753/compiler/rustc_hir/src/intravisit.rs:1065:13
  22:     0x55c158ce1a34 - rustc_hir::intravisit::Visitor::visit_param_bound::h094792a64fd53dd6
                               at /rustc/d59363ad0b6391b7fc5bbb02c9ccf9300eef3753/compiler/rustc_hir/src/intravisit.rs:393:9
  23:     0x55c159169fe1 - rustc_hir::intravisit::walk_item::h270fa81635496322
                               at /rustc/d59363ad0b6391b7fc5bbb02c9ccf9300eef3753/compiler/rustc_hir/src/intravisit.rs:505:13
  24:     0x55c1593428d2 - <clippy_lints::min_ident_chars::MinIdentChars as rustc_lint::passes::LateLintPass>::check_item::hfe7d6c5b6b848b08
                               at /home/centri/GitHub/rust-clippy/clippy_lints/src/min_ident_chars.rs:57:9
  25:     0x7fd35f155eb3 - <rustc_lint[427e7e775f1dde36]::early::RuntimeCombinedEarlyLintPass as rustc_lint[427e7e775f1dde36]::passes::EarlyLintPass>::check_local
  26:     0x7fd35f13fa17 - <rustc_lint[427e7e775f1dde36]::late::LateContextAndPass<rustc_lint[427e7e775f1dde36]::late::RuntimeCombinedLateLintPass> as rustc_hir[55fad958df311873]::intravisit::Visitor>::visit_nested_item
  27:     0x7fd35f118eee - rustc_hir[55fad958df311873]::intravisit::walk_ty::<rustc_lint[427e7e775f1dde36]::late::LateContextAndPass<rustc_lint[427e7e775f1dde36]::late::RuntimeCombinedLateLintPass>>
  28:     0x7fd35f118e4a - rustc_hir[55fad958df311873]::intravisit::walk_fn::<rustc_lint[427e7e775f1dde36]::late::LateContextAndPass<rustc_lint[427e7e775f1dde36]::late::RuntimeCombinedLateLintPass>>
  29:     0x7fd35f13f37a - <rustc_lint[427e7e775f1dde36]::late::LateContextAndPass<rustc_lint[427e7e775f1dde36]::late::RuntimeCombinedLateLintPass> as rustc_hir[55fad958df311873]::intravisit::Visitor>::visit_fn
  30:     0x7fd35f119843 - rustc_hir[55fad958df311873]::intravisit::walk_item::<rustc_lint[427e7e775f1dde36]::late::LateContextAndPass<rustc_lint[427e7e775f1dde36]::late::RuntimeCombinedLateLintPass>>
  31:     0x7fd35f13fa22 - <rustc_lint[427e7e775f1dde36]::late::LateContextAndPass<rustc_lint[427e7e775f1dde36]::late::RuntimeCombinedLateLintPass> as rustc_hir[55fad958df311873]::intravisit::Visitor>::visit_nested_item
  32:     0x7fd35f1190c8 - rustc_hir[55fad958df311873]::intravisit::walk_mod::<rustc_lint[427e7e775f1dde36]::late::LateContextAndPass<rustc_lint[427e7e775f1dde36]::late::RuntimeCombinedLateLintPass>>
  33:     0x7fd35e451cfb - rustc_lint[427e7e775f1dde36]::late::late_lint_crate::<rustc_lint[427e7e775f1dde36]::BuiltinCombinedLateLintPass>
  34:     0x7fd35e451168 - <rustc_session[bd1b384f0d262623]::session::Session>::time::<(), rustc_lint[427e7e775f1dde36]::late::check_crate<rustc_lint[427e7e775f1dde36]::BuiltinCombinedLateLintPass, rustc_interface[f00e945cb6d9f8c2]::passes::analysis::{closure#5}::{closure#1}::{closure#2}::{closure#0}::{closure#0}>::{closure#0}::{closure#0}>
  35:     0x7fd35e25d163 - <rustc_session[bd1b384f0d262623]::session::Session>::time::<(), rustc_interface[f00e945cb6d9f8c2]::passes::analysis::{closure#5}::{closure#1}::{closure#2}::{closure#0}>
  36:     0x7fd35e25ccde - <core[6c80c2e01350ba19]::panic::unwind_safe::AssertUnwindSafe<rustc_interface[f00e945cb6d9f8c2]::passes::analysis::{closure#5}::{closure#1}> as core[6c80c2e01350ba19]::ops::function::FnOnce<()>>::call_once
  37:     0x7fd35e25c7d8 - <rustc_session[bd1b384f0d262623]::session::Session>::time::<(), rustc_interface[f00e945cb6d9f8c2]::passes::analysis::{closure#5}>
  38:     0x7fd35e25bf4d - rustc_interface[f00e945cb6d9f8c2]::passes::analysis
  39:     0x7fd35e2c4efa - rustc_query_impl[d4eb4aa411611910]::plumbing::__rust_begin_short_backtrace::<rustc_query_impl[d4eb4aa411611910]::query_impl::analysis::dynamic_query::{closure#2}::{closure#0}, rustc_middle[4f6cb0c16f06e5a5]::query::erase::Erased<[u8; 1usize]>>
  40:     0x7fd35e2c4ee9 - <rustc_query_impl[d4eb4aa411611910]::query_impl::analysis::dynamic_query::{closure#2} as core[6c80c2e01350ba19]::ops::function::FnOnce<(rustc_middle[4f6cb0c16f06e5a5]::ty::context::TyCtxt, ())>>::call_once
  41:     0x7fd35e47b1c8 - rustc_query_system[9ea2071ffed97fb3]::query::plumbing::try_execute_query::<rustc_query_impl[d4eb4aa411611910]::DynamicConfig<rustc_query_system[9ea2071ffed97fb3]::query::caches::SingleCache<rustc_middle[4f6cb0c16f06e5a5]::query::erase::Erased<[u8; 1usize]>>, false, false, false>, rustc_query_impl[d4eb4aa411611910]::plumbing::QueryCtxt, false>
  42:     0x7fd35e47af99 - rustc_query_impl[d4eb4aa411611910]::query_impl::analysis::get_query_non_incr::__rust_end_short_backtrace
  43:     0x7fd35e4529f5 - <rustc_middle[4f6cb0c16f06e5a5]::ty::context::GlobalCtxt>::enter::<rustc_driver_impl[56cae5af60b3bf59]::run_compiler::{closure#1}::{closure#2}::{closure#4}, core[6c80c2e01350ba19]::result::Result<(), rustc_span[9ffd76ecb71b4ec4]::ErrorGuaranteed>>
  44:     0x7fd35e001800 - <rustc_interface[f00e945cb6d9f8c2]::interface::Compiler>::enter::<rustc_driver_impl[56cae5af60b3bf59]::run_compiler::{closure#1}::{closure#2}, core[6c80c2e01350ba19]::result::Result<core[6c80c2e01350ba19]::option::Option<rustc_interface[f00e945cb6d9f8c2]::queries::Linker>, rustc_span[9ffd76ecb71b4ec4]::ErrorGuaranteed>>
  45:     0x7fd35dfff39f - <scoped_tls[eca48f4274888ca2]::ScopedKey<rustc_span[9ffd76ecb71b4ec4]::SessionGlobals>>::set::<rustc_interface[f00e945cb6d9f8c2]::interface::run_compiler<core[6c80c2e01350ba19]::result::Result<(), rustc_span[9ffd76ecb71b4ec4]::ErrorGuaranteed>, rustc_driver_impl[56cae5af60b3bf59]::run_compiler::{closure#1}>::{closure#0}, core[6c80c2e01350ba19]::result::Result<(), rustc_span[9ffd76ecb71b4ec4]::ErrorGuaranteed>>
  46:     0x7fd35dffe806 - std[cd42f2f269856667]::sys_common::backtrace::__rust_begin_short_backtrace::<rustc_interface[f00e945cb6d9f8c2]::util::run_in_thread_pool_with_globals<rustc_interface[f00e945cb6d9f8c2]::interface::run_compiler<core[6c80c2e01350ba19]::result::Result<(), rustc_span[9ffd76ecb71b4ec4]::ErrorGuaranteed>, rustc_driver_impl[56cae5af60b3bf59]::run_compiler::{closure#1}>::{closure#0}, core[6c80c2e01350ba19]::result::Result<(), rustc_span[9ffd76ecb71b4ec4]::ErrorGuaranteed>>::{closure#0}::{closure#0}, core[6c80c2e01350ba19]::result::Result<(), rustc_span[9ffd76ecb71b4ec4]::ErrorGuaranteed>>
  47:     0x7fd35dffe5b5 - <<std[cd42f2f269856667]::thread::Builder>::spawn_unchecked_<rustc_interface[f00e945cb6d9f8c2]::util::run_in_thread_pool_with_globals<rustc_interface[f00e945cb6d9f8c2]::interface::run_compiler<core[6c80c2e01350ba19]::result::Result<(), rustc_span[9ffd76ecb71b4ec4]::ErrorGuaranteed>, rustc_driver_impl[56cae5af60b3bf59]::run_compiler::{closure#1}>::{closure#0}, core[6c80c2e01350ba19]::result::Result<(), rustc_span[9ffd76ecb71b4ec4]::ErrorGuaranteed>>::{closure#0}::{closure#0}, core[6c80c2e01350ba19]::result::Result<(), rustc_span[9ffd76ecb71b4ec4]::ErrorGuaranteed>>::{closure#1} as core[6c80c2e01350ba19]::ops::function::FnOnce<()>>::call_once::{shim:vtable#0}
  48:     0x7fd35bbd32d5 - <alloc::boxed::Box<F,A> as core::ops::function::FnOnce<Args>>::call_once::h04ff4859749c6ea9
                               at /rustc/d59363ad0b6391b7fc5bbb02c9ccf9300eef3753/library/alloc/src/boxed.rs:1985:9
  49:     0x7fd35bbd32d5 - <alloc::boxed::Box<F,A> as core::ops::function::FnOnce<Args>>::call_once::hc63f4d2c9651d617
                               at /rustc/d59363ad0b6391b7fc5bbb02c9ccf9300eef3753/library/alloc/src/boxed.rs:1985:9
  50:     0x7fd35bbd32d5 - std::sys::unix::thread::Thread::new::thread_start::h5594a02e634c76b0
                               at /rustc/d59363ad0b6391b7fc5bbb02c9ccf9300eef3753/library/std/src/sys/unix/thread.rs:108:17
  51:     0x7fd352785b43 - start_thread
                               at ./nptl/pthread_create.c:442:8
  52:     0x7fd352817a00 - clone3
                               at ./misc/../sysdeps/unix/sysv/linux/x86_64/clone3.S:81
  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-clippy/issues/new

note: rustc 1.72.0-nightly (d59363ad0 2023-06-01) running on x86_64-unknown-linux-gnu

note: compiler flags: -C prefer-dynamic -Z ui-testing

query stack during panic:
#0 [analysis] running analysis passes on this crate
end of query stack
note: Clippy version: clippy 0.1.72 (7f43e0f10 2023-06-09)

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