treat-err-as-bug

This feature is perma-unstable and has no tracking issue.

This flag converts the selected error to a bug! call, exiting the compiler immediately and allowing you to generate a backtrace of where the error occurred. For full documentation, see the rustc-dev-guide.

Note that the compiler automatically sets RUST_BACKTRACE=1 for itself, and so you do not need to set it yourself when using this flag.