Poor error in ./miri run --dep when using a wrong -Zmiri flag

[RalfJung]

$ ./miri run tests/fail-dep/libc/socketpair-data-race.rs  -Zmiri-foo --dep
The application panicked (crashed).
Message:  called `Result::unwrap()` on an `Err` value: Errored { command: "\"/home/r/src/rust/miri/target/debug/miri\" \"--edition\" \"2021\" \"--sysroot\" \"/home/r/.cache/miri\" \"tests/fail-dep/libc/socketpair-data-race.rs\" \"-Zmiri-foo\" \"--out-dir\" \"/home/r/src/rust/miri/target/miri_ui\" \"--print=cfg\" \"--target\" \"x86_64-unknown-linux-gnu\"", errors: [], stderr: [101, 114, 114, 111, 114, 58, 32, 117, 110, 107, 110, 111, 119, 110, 32, 117, 110, 115, 116, 97, 98, 108, 101, 32, 111, 112, 116, 105, 111, 110, 58, 32, 96, 109, 105, 114, 105, 45, 102, 111, 111, 96, 10, 10], stdout: [] }
Location: tests/ui.rs:340

Showing stderr as its raw ASCII encoding isn't exactly readable. ;)

Cc @oli-obk

[RalfJung]

This is caused by that unwrap here:

miri/tests/ui.rs

Line 340 in 6636681

test_config.apply_custom(&mut cmd, &build_manager).unwrap();

However, as far as I can see there is no nice way to report a test_result::Errored -- the fields are private and the Debug impl produces the ugly output above. @oli-obk how is this intended to work? I can't quite figure it out...

[oli-obk]

I just need to fix the debug impl.

[RalfJung]

Ideally it can use the already existing reporting logic, would be unfortunate to have the same error reported in two different ways.