crash: #[path="/dev/null"] attr

[matthiaskrgr]

This code causes rustfmt to crash

#[path="/dev/null"]
pub mod null;

thread 'main' panicked at 'path is expected to be under the root', /cargo/registry/src/github.com-1ecc6299db9ec823/ignore-0.4.16/src/gitignore.rs:227:9
stack backtrace:
   0:     0x5587c3e2eaa7 - std::backtrace_rs::backtrace::libunwind::trace::h746c3e9529d524bc
                               at /rustc/2225ee1b62ff089917434aefd9b2bf509cfa087f/library/std/src/../../backtrace/src/backtrace/libunwind.rs:90:5
   1:     0x5587c3e2eaa7 - std::backtrace_rs::backtrace::trace_unsynchronized::h86340908ff889faa
                               at /rustc/2225ee1b62ff089917434aefd9b2bf509cfa087f/library/std/src/../../backtrace/src/backtrace/mod.rs:66:5
   2:     0x5587c3e2eaa7 - std::sys_common::backtrace::_print_fmt::h43f85f9b18230404
                               at /rustc/2225ee1b62ff089917434aefd9b2bf509cfa087f/library/std/src/sys_common/backtrace.rs:67:5
   3:     0x5587c3e2eaa7 - <std::sys_common::backtrace::_print::DisplayBacktrace as core::fmt::Display>::fmt::hc132ae1a5b5aa7cd
                               at /rustc/2225ee1b62ff089917434aefd9b2bf509cfa087f/library/std/src/sys_common/backtrace.rs:46:22
   4:     0x5587c3e5283c - core::fmt::write::hdf023a0036d2a25f
                               at /rustc/2225ee1b62ff089917434aefd9b2bf509cfa087f/library/core/src/fmt/mod.rs:1078:17
   5:     0x5587c3e2b462 - std::io::Write::write_fmt::h8580846154bcb66a
                               at /rustc/2225ee1b62ff089917434aefd9b2bf509cfa087f/library/std/src/io/mod.rs:1519:15
   6:     0x5587c3e30a75 - std::sys_common::backtrace::_print::h7ee55fed88d107a3
                               at /rustc/2225ee1b62ff089917434aefd9b2bf509cfa087f/library/std/src/sys_common/backtrace.rs:49:5
   7:     0x5587c3e30a75 - std::sys_common::backtrace::print::h54a7d3e52a524177
                               at /rustc/2225ee1b62ff089917434aefd9b2bf509cfa087f/library/std/src/sys_common/backtrace.rs:36:9
   8:     0x5587c3e30a75 - std::panicking::default_hook::{{closure}}::h60921e857bf55a40
                               at /rustc/2225ee1b62ff089917434aefd9b2bf509cfa087f/library/std/src/panicking.rs:208:50
   9:     0x5587c3e305ca - std::panicking::default_hook::hf0f9afb1017317fc
                               at /rustc/2225ee1b62ff089917434aefd9b2bf509cfa087f/library/std/src/panicking.rs:225:9
  10:     0x5587c3e31211 - std::panicking::rust_panic_with_hook::h8d66bf42b407aaea
                               at /rustc/2225ee1b62ff089917434aefd9b2bf509cfa087f/library/std/src/panicking.rs:591:17
  11:     0x5587c3ae67c4 - std::panicking::begin_panic::{{closure}}::hbe262b95ef2ff8f9
  12:     0x5587c3ae66bc - std::sys_common::backtrace::__rust_end_short_backtrace::hd70d74b6b6dc38ff
  13:     0x5587c3a2ddac - std::panicking::begin_panic::h998094cd3d11af60
  14:     0x5587c3a5e258 - ignore::gitignore::Gitignore::matched_path_or_any_parents::h687892c59c3a1cae
  15:     0x5587c3b66149 - rustfmt_nightly::syntux::session::ParseSess::ignore_file::h60741d92df2c771d
  16:     0x5587c39bfae0 - rustfmt_nightly::formatting::format_project::h75f3cb078ea2edba
  17:     0x5587c39c93ee - scoped_tls::ScopedKey<T>::set::h46570b94864b4223
  18:     0x5587c39c3789 - rustfmt_nightly::Session<T>::format::h16e5c985cca65c6b
  19:     0x5587c39d38fb - rustfmt::format_and_emit_report::h34b4f1b50145fd6f
  20:     0x5587c39c309d - rustfmt_nightly::Session<T>::override_config::h588d4c0abb82dcad
  21:     0x5587c39d0f8d - rustfmt::execute::hbead43f61fce9ab6
  22:     0x5587c39cd9fd - rustfmt::main::hdc579be80dab480f
  23:     0x5587c39c58b3 - std::sys_common::backtrace::__rust_begin_short_backtrace::h425146d795f70aec
  24:     0x5587c39c5c09 - std::rt::lang_start::{{closure}}::h1a880688683e8956
  25:     0x5587c3e31727 - core::ops::function::impls::<impl core::ops::function::FnOnce<A> for &F>::call_once::h54c39b9b8451875a
                               at /rustc/2225ee1b62ff089917434aefd9b2bf509cfa087f/library/core/src/ops/function.rs:259:13
  26:     0x5587c3e31727 - std::panicking::try::do_call::hcdfba51a06e21b42
                               at /rustc/2225ee1b62ff089917434aefd9b2bf509cfa087f/library/std/src/panicking.rs:379:40
  27:     0x5587c3e31727 - std::panicking::try::hb36953ccd24f930d
                               at /rustc/2225ee1b62ff089917434aefd9b2bf509cfa087f/library/std/src/panicking.rs:343:19
  28:     0x5587c3e31727 - std::panic::catch_unwind::hbb374cd03beb3824
                               at /rustc/2225ee1b62ff089917434aefd9b2bf509cfa087f/library/std/src/panic.rs:396:14
  29:     0x5587c3e31727 - std::rt::lang_start_internal::h97dca9624db2aa85
                               at /rustc/2225ee1b62ff089917434aefd9b2bf509cfa087f/library/std/src/rt.rs:51:25
  30:     0x5587c39d4552 - main
  31:     0x7f0254b48152 - __libc_start_main
  32:     0x5587c39b9f59 - <unknown>

rustfmt 1.4.29-nightly (70ce182 2020-12-04)

[calebcartwright]

Admittedly not the most graceful of exits, but I'm also a little puzzled by the use case of the snippet provided in the description.

This isn't reproducible in source though I'm pretty confident that's due to some changes that haven't been backported. Is there a more realistic use case where this is occurring or am I perhaps missing something with the original snippet?

[matthiaskrgr]

The code is from a rustdoc test in the rustc repo src/test/rustdoc/issue-26995.rs
I was running rustfmt on all files in the rustc repo to find crashes. :)

[msrd0]

I just came across a very similar error message in a realistic environment: I have some Rust source code that is not part of any project managed by cargo, but instead used as UI tests with trybuild. This means that cargo fmt does not format the code, but I'd still like it formatted. Hence, I wrote a shell script like this: https://github.com/msrd0/openapi_type/blob/main/tests/fail/rustfmt.sh

This used to work fine, however, on the latest nightly (1.58.0-nightly (c390d69a6 2021-10-28)) it crashes with this error message:

thread 'main' panicked at 'path is expected to be under the root', /cargo/registry/src/github.com-1ecc6299db9ec823/ignore-0.4.17/src/gitignore.rs:227:9
stack backtrace:
   0: std::panicking::begin_panic::<&str>
   1: <ignore::gitignore::Gitignore>::matched_path_or_any_parents::<&std::path::PathBuf>
   2: <rustfmt_nightly::syntux::session::ParseSess>::ignore_file
   3: rustfmt_nightly::formatting::format_project::<rustfmt_nightly::Session<std::io::stdio::Stdout>>
   4: <scoped_tls::ScopedKey<rustc_span::SessionGlobals>>::with::<<rustfmt_nightly::Session<std::io::stdio::Stdout>>::format_input_inner::{closure#0}, core::result::Result<rustfmt_nightly::FormatReport, rustfmt_nightly::ErrorKind>>
   5: <rustfmt_nightly::Session<std::io::stdio::Stdout>>::format
   6: rustfmt::format_and_emit_report::<std::io::stdio::Stdout>
   7: rustfmt::execute
   8: rustfmt::main
note: Some details are omitted, run with `RUST_BACKTRACE=full` for a verbose backtrace.