Bootstrap panics when running `x fmt --check`

[camelid]

I ran x fmt --check and got this panic, although the rustfmt output had already been printed:

If you're running `tidy`, try again with `--bless`. Or, if you just want to format code, run `./x.py fmt` instead.
thread 'thread '<unnamed><unnamed>' panicked at '' panicked at 'tx.send(entry.into_path()) failed with sending on a closed channeltx.send(entry.into_path()) failed with sending on a closed channel', ', format.rsformat.rs::166166::1717

note: run with `RUST_BACKTRACE=1` environment variable to display a backtrace
thread 'main' panicked at 'called `Result::unwrap()` on an `Err` value: Any { .. }', /Users/noahlev/.cargo/registry/src/github.com-1ecc6299db9ec823/ignore-0.4.18/src/walk.rs:1302:31
Build completed unsuccessfully in 0:00:07

Notably after running x fmt, the panic stops (and x fmt doesn't panic either). But reintroducing something where rustfmt will suggest changes brings the panic in --check back.

See previous discussion at this Zulip thread.

cc @jyn514

[jyn514]

This is a regression from #98994. resume_unwind only exits the process when run from the main thread.

[jyn514]

The fix is to use process::exit instead.

[shourya5]

@rustbot claim

[shourya5]

So, to be clear, the fix is to replace the detail::exit with process::exit right?

[jyn514]

@shourya5 no - within detail_exit, change resume_unwind to process::exit