-Z treat-err-as-bug panics even when no errors occur

[nagisa]

echo 'fn test(){} fn main() {}' | rustc - -Z treat-err-as-bug
<anon>:1:1: 1:12 warning: function is never used: `test`, #[warn(dead_code)] on by default 
<anon>:1 fn test(){} fn main() {}
         ^~~~~~~~~~~
error: internal compiler error: unexpected panic 
note: the compiler unexpectedly panicked. this is a bug. 
note: we would appreciate a bug report: https://github.com/rust-lang/rust/blob/master/CONTRIBUTING.md#bug-reports 
note: run with `RUST_BACKTRACE=1` for a backtrace 
thread 'rustc' panicked at 'encountered error with `-Z treat_err_as_bug', ../src/librustc_errors/lib.rs:546

[durka]

This is because of this line added in #33137. I'm guessing it needs a conditional to check whether self.level == Level::Error.

[Mark-Simulacrum]

Marking as E-easy and E-mentor. @durka's fix (adding self.level == Level::Error) seems to be still correct, but needs to be added around this line:

rust/src/librustc_errors/diagnostic_builder.rs

Line 102 in e40beb3

self.handler.panic_if_treat_err_as_bug();

.

Let me know if you'd like to do this, and please ask if you have any questions. If you file a PR, please cc or r? me on it.

[tommyip]

I would like to take this issue.