Add enum_intrinsics_non_enums lint

[Flying-Toast]

There is a clippy lint to prevent calling mem::discriminant with a non-enum type. I think the lint is worthy of being included in rustc, given that discriminant::<T>() where T is a non-enum has an unspecified return value, and there are no valid use cases where you'd actually want this.

I've also made the lint check variant_count (#73662).

closes #83899

[rust-highfive]

r? @estebank

(rust-highfive has picked a reviewer for you, use r? to override)

[Flying-Toast]

While I'm at it, I made the lint also check variant_count

[davidtwco]

@Flying-Toast GitHub is still reporting your branch as having conflicts, have you been able to rebase?

[JohnCSimon]

Ping again from triage:
@Flying-Toast GitHub is still reporting your branch as having conflicts, have you been able to rebase?

[Flying-Toast]

@JohnCSimon @davidtwco I've rebased the PR, sorry for the delay - I've been busy with school. @flip1995: The patch doesn't apply very well anymore by now - could you make the patch again?

[camelid]

@Flying-Toast rust-lang/rust follows a "No-Merge Policy". Could you please rebase over upstream changes instead of merging? Thanks!

[flip1995]

I updated the gist. This is based on a rebased version of this branch ontop of the current master branch.

I also pushed a already rebased version with this patch applied here: https://github.com/flip1995/rust/tree/enum_intrinsics_non_enums You can just force push this to your branch:

git remote add flip1995 https://github.com/flip1995/rust --fetch
# The next command assumes, that `origin` is the remote of your fork.
git push origin enum_intrinsics_non_enums:master --force-with-lease

[Flying-Toast]

@flip1995 thanks :) I've pushed from your branch.

[davidtwco]

LGTM!

[davidtwco]

@bors r+

[bors]

📌 Commit f483676 has been approved by davidtwco

[bors]

⌛ Testing commit f483676 with merge 5b21064...

[bors]

☀️ Test successful - checks-actions
Approved by: davidtwco
Pushing 5b21064 to master...

[rust-timer]

Finished benchmarking commit (5b21064): comparison url.

Summary: This benchmark run did not return any relevant changes.

If you disagree with this performance assessment, please file an issue in rust-lang/rustc-perf.

@rustbot label: -perf-regression