thread 'main' panicked at 'internal error: entered unreachable code', src/tools/rustfmt/src/types.rs:764:59

[tronta]

Problem
When executing a cargo fmt on my code I get the following backtrace
thread 'main' panicked at 'internal error: entered unreachable code', src/tools/rustfmt/src/types.rs:764:59
stack backtrace:
0: backtrace::backtrace::libunwind::trace
at /cargo/registry/src/jackfan.us.kg-1ecc6299db9ec823/backtrace-0.3.46/src/backtrace/libunwind.rs:86
1: backtrace::backtrace::trace_unsynchronized
at /cargo/registry/src/jackfan.us.kg-1ecc6299db9ec823/backtrace-0.3.46/src/backtrace/mod.rs:66
2: std::sys_common::backtrace::_print_fmt
at src/libstd/sys_common/backtrace.rs:78
3: <std::sys_common::backtrace::_print::DisplayBacktrace as core::fmt::Display>::fmt
at src/libstd/sys_common/backtrace.rs:59
4: core::fmt::write
at src/libcore/fmt/mod.rs:1069
5: std::io::Write::write_fmt
at src/libstd/io/mod.rs:1504
6: std::sys_common::backtrace::_print
at src/libstd/sys_common/backtrace.rs:62
7: std::sys_common::backtrace::print
at src/libstd/sys_common/backtrace.rs:49
8: std::panicking::default_hook::{{closure}}
at src/libstd/panicking.rs:198
9: std::panicking::default_hook
at src/libstd/panicking.rs:218
10: std::panicking::rust_panic_with_hook
at src/libstd/panicking.rs:511
11: std::panicking::begin_panic
12: rustfmt_nightly::types::::rewrite
13: rustfmt_nightly::items::::rewrite
14: <rustfmt_nightly::lists::ListItems<I,F1,F2,F3> as core::iter::traits::iterator::Iterator>::next
15: <alloc::vec::Vec as alloc::vec::SpecExtend<T,I>>::from_iter
16: rustfmt_nightly::items::rewrite_fn_base
17: rustfmt_nightly::visitor::FmtVisitor::visit_fn
18: rustfmt_nightly::visitor::FmtVisitor::visit_impl_item
19: rustfmt_nightly::items::::visit_impl_items
20: rustfmt_nightly::items::format_impl
21: rustfmt_nightly::visitor::FmtVisitor::visit_item
22: rustfmt_nightly::reorder::::visit_items_with_reordering
23: rustfmt_nightly::visitor::FmtVisitor::format_separate_mod
24: rustfmt_nightly::formatting::format_project
25: rustc_ap_rustc_ast::attr::with_globals
26: rustfmt_nightly::Session::format
27: rustfmt::format_and_emit_report
28: rustfmt_nightly::Session::override_config
29: rustfmt::execute
30: rustfmt::main
31: std::rt::lang_start::{{closure}}
32: std::rt::lang_start_internal::{{closure}}
at src/libstd/rt.rs:52
33: std::panicking::try::do_call
at src/libstd/panicking.rs:331
34: std::panicking::try
at src/libstd/panicking.rs:274
35: std::panic::catch_unwind
at src/libstd/panic.rs:394
36: std::rt::lang_start_internal
at src/libstd/rt.rs:51
37: main
38: __libc_start_main
39:

Steps

As it is proprietary software, I hestate to paste code in here.
If you need sth special, I'm happy to help.

Possible Solution(s)

Notes

Output of cargo version:
cargo 1.44.1 (88ba857 2020-06-11)

[ehuss]

Thanks for the report. This looks like a rustfmt bug. Can you move this issue over to https://github.com/rust-lang/rustfmt/issues?

It looks like it is hitting this line. Looks like the typeof keyword can trigger it. I'm not sure what the other scenarios are, though.

[ehuss]

Moved to rust-lang/rustfmt#4357