Uplift clippy::mem_discriminant_non_enum into rustc

[Flying-Toast]

The clippy::mem_discriminant_non_enum lint seems like it should be directly in rustc. The lint prevents doing something like:

core::mem::discriminant::<i32>(&4)

which causes unspecified behavior.

[Flying-Toast]

I'd like to try implementing this myself, if would be likely to be accepted - do people think this would this be useful?

[jyn514]

I think this is a great idea, it's clearly wrong code with no false positives.

[Flying-Toast]

Should I make this a hard error instead of a lint?

[jyn514]

No, I think this should be a lint. Hard errors are a breaking change and are almost never accepted except at edition boundaries, and the 2021 edition is not taking new ideas right now.