ICE on experimental feature fn delegation (`reuse`) in associated item position

[fmease]

Disclaimer: This has a very low priority given feature fn_delegation (rust-lang/rust#118212) is highly experimental and since it's not guaranteed that this feature will persist. Still, for the sake of coverage, I've decided to report it.

Reproducers

#![feature(fn_delegation)]

struct Ty;
impl Ty {
    reuse std::convert::identity;
}

rustfmt output

thread 'main' panicked at src/tools/rustfmt/src/visitor.rs:677:18:
internal error: entered unreachable code
stack backtrace:
   0:     0x74ee55bbea64 - <std::sys::backtrace::BacktraceLock::print::DisplayBacktrace as core::fmt::Display>::fmt::hd9fc6a39ec3df3d1
   1:     0x74ee564057e2 - core::fmt::write::h73a1e37ddefe0a4f
   2:     0x74ee57427c91 - std::io::Write::write_fmt::h12f84d1a8e648b12
   3:     0x74ee55bbe8c2 - std::sys::backtrace::BacktraceLock::print::h91fc82fbc6b056a6
   4:     0x74ee55bc11a2 - std::panicking::default_hook::{{closure}}::hebc0ecceade2cd26
   5:     0x74ee55bc0d94 - std::panicking::default_hook::h82ddd3fdf5856794
   6:     0x74ee54d19277 - std[20d29db3e999c305]::panicking::update_hook::<alloc[e1570dfcc331507b]::boxed::Box<rustc_driver_impl[633be37e059aaf16]::install_ice_hook::{closure#1}>>::{closure#0}
   7:     0x74ee55bc1a13 - std::panicking::rust_panic_with_hook::hb92b3172308f4e8b
   8:     0x74ee55bc16d6 - std::panicking::begin_panic_handler::{{closure}}::hbf0e4f1d78818dec
   9:     0x74ee55bbef39 - std::sys::backtrace::__rust_end_short_backtrace::hfc58a21f6afae4ae
  10:     0x74ee55bc13cd - rust_begin_unwind
  11:     0x74ee5285be40 - core::panicking::panic_fmt::h52a3de72b5c008c5
  12:     0x74ee532ebf7c - core::panicking::panic::h968935f54951f8e4
  13:     0x60e9f23eaa7f - <rustfmt_nightly[8bef2c5348bbd989]::visitor::FmtVisitor>::visit_assoc_item
  14:     0x60e9f23764c4 - <rustfmt_nightly[8bef2c5348bbd989]::visitor::FmtVisitor>::visit_impl_items
  15:     0x60e9f23e8109 - <rustfmt_nightly[8bef2c5348bbd989]::visitor::FmtVisitor>::visit_item
  16:     0x60e9f23bdd58 - <rustfmt_nightly[8bef2c5348bbd989]::visitor::FmtVisitor>::visit_items_with_reordering
  17:     0x60e9f23ede2b - <rustfmt_nightly[8bef2c5348bbd989]::visitor::FmtVisitor>::format_separate_mod
  18:     0x60e9f224e7c9 - <scoped_tls[bb4943a609257807]::ScopedKey<rustc_span[142d3b94b336956b]::SessionGlobals>>::with::<<rustfmt_nightly[8bef2c5348bbd989]::Session<std[20d29db3e999c305]::io::stdio::Stdout>>::format_input_inner::{closure#0}, core[7509374bb9bacf81]::result::Result<rustfmt_nightly[8bef2c5348bbd989]::FormatReport, rustfmt_nightly[8bef2c5348bbd989]::ErrorKind>>
  19:     0x60e9f2267067 - rustfmt[ce1aaa3c9c957e5c]::format_and_emit_report::<std[20d29db3e999c305]::io::stdio::Stdout>
  20:     0x60e9f2264bb9 - rustfmt[ce1aaa3c9c957e5c]::execute
  21:     0x60e9f2260bdf - rustfmt[ce1aaa3c9c957e5c]::main
  22:     0x60e9f2257443 - std[20d29db3e999c305]::sys::backtrace::__rust_begin_short_backtrace::<fn(), ()>
  23:     0x60e9f22579b9 - std[20d29db3e999c305]::rt::lang_start::<()>::{closure#0}
  24:     0x74ee5732699e - std::rt::lang_start_internal::h71fef5e5f25ac3f5
  25:     0x60e9f2268278 - main
  26:     0x74ee512f1e08 - <unknown>
  27:     0x74ee512f1ecc - __libc_start_main
  28:     0x60e9f2248cf9 - <unknown>
  29:                0x0 - <unknown>

error: the compiler unexpectedly panicked. this is a bug.

note: we would appreciate a bug report: https://github.com/rust-lang/rustfmt/issues/new?labels=bug

note: please make sure that you have updated to the latest nightly

note: rustc 1.87.0-nightly (e16a049ad 2025-03-03) running on x86_64-unknown-linux-gnu

query stack during panic:
end of query stack

#![feature(fn_delegation)]

trait Trait {
    reuse std::convert::identity;
}

rustfmt output

thread 'main' panicked at src/tools/rustfmt/src/visitor.rs:677:18:
internal error: entered unreachable code
stack backtrace:
   0:     0x775a063bea64 - <std::sys::backtrace::BacktraceLock::print::DisplayBacktrace as core::fmt::Display>::fmt::hd9fc6a39ec3df3d1
   1:     0x775a06c057e2 - core::fmt::write::h73a1e37ddefe0a4f
   2:     0x775a07c27c91 - std::io::Write::write_fmt::h12f84d1a8e648b12
   3:     0x775a063be8c2 - std::sys::backtrace::BacktraceLock::print::h91fc82fbc6b056a6
   4:     0x775a063c11a2 - std::panicking::default_hook::{{closure}}::hebc0ecceade2cd26
   5:     0x775a063c0d94 - std::panicking::default_hook::h82ddd3fdf5856794
   6:     0x775a05519277 - std[20d29db3e999c305]::panicking::update_hook::<alloc[e1570dfcc331507b]::boxed::Box<rustc_driver_impl[633be37e059aaf16]::install_ice_hook::{closure#1}>>::{closure#0}
   7:     0x775a063c1a13 - std::panicking::rust_panic_with_hook::hb92b3172308f4e8b
   8:     0x775a063c16d6 - std::panicking::begin_panic_handler::{{closure}}::hbf0e4f1d78818dec
   9:     0x775a063bef39 - std::sys::backtrace::__rust_end_short_backtrace::hfc58a21f6afae4ae
  10:     0x775a063c13cd - rust_begin_unwind
  11:     0x775a0305be40 - core::panicking::panic_fmt::h52a3de72b5c008c5
  12:     0x775a03aebf7c - core::panicking::panic::h968935f54951f8e4
  13:     0x6132bd533a7f - <rustfmt_nightly[8bef2c5348bbd989]::visitor::FmtVisitor>::visit_assoc_item
  14:     0x6132bd5306cf - <rustfmt_nightly[8bef2c5348bbd989]::visitor::FmtVisitor>::visit_item
  15:     0x6132bd506d58 - <rustfmt_nightly[8bef2c5348bbd989]::visitor::FmtVisitor>::visit_items_with_reordering
  16:     0x6132bd536e2b - <rustfmt_nightly[8bef2c5348bbd989]::visitor::FmtVisitor>::format_separate_mod
  17:     0x6132bd3977c9 - <scoped_tls[bb4943a609257807]::ScopedKey<rustc_span[142d3b94b336956b]::SessionGlobals>>::with::<<rustfmt_nightly[8bef2c5348bbd989]::Session<std[20d29db3e999c305]::io::stdio::Stdout>>::format_input_inner::{closure#0}, core[7509374bb9bacf81]::result::Result<rustfmt_nightly[8bef2c5348bbd989]::FormatReport, rustfmt_nightly[8bef2c5348bbd989]::ErrorKind>>
  18:     0x6132bd3b0067 - rustfmt[ce1aaa3c9c957e5c]::format_and_emit_report::<std[20d29db3e999c305]::io::stdio::Stdout>
  19:     0x6132bd3adbb9 - rustfmt[ce1aaa3c9c957e5c]::execute
  20:     0x6132bd3a9bdf - rustfmt[ce1aaa3c9c957e5c]::main
  21:     0x6132bd3a0443 - std[20d29db3e999c305]::sys::backtrace::__rust_begin_short_backtrace::<fn(), ()>
  22:     0x6132bd3a09b9 - std[20d29db3e999c305]::rt::lang_start::<()>::{closure#0}
  23:     0x775a07b2699e - std::rt::lang_start_internal::h71fef5e5f25ac3f5
  24:     0x6132bd3b1278 - main
  25:     0x775a01b45e08 - <unknown>
  26:     0x775a01b45ecc - __libc_start_main
  27:     0x6132bd391cf9 - <unknown>
  28:                0x0 - <unknown>

error: the compiler unexpectedly panicked. this is a bug.

note: we would appreciate a bug report: https://github.com/rust-lang/rustfmt/issues/new?labels=bug

note: please make sure that you have updated to the latest nightly

note: rustc 1.87.0-nightly (e16a049ad 2025-03-03) running on x86_64-unknown-linux-gnu

query stack during panic:
end of query stack

Meta

rustfmt -V:

rustfmt 1.8.0-nightly (e16a049adb 2025-03-03)

[ytmimi]

@fmease looks like we're not handling the AssocItemKind::Delegation and AssocItemKind::DelegationMac variants here:

rustfmt/src/visitor.rs

Line 668 in ee329d3

_ => unreachable!(),