add ptr_offset_by_literal lint

[folkertdev]

Related to https://rust-lang.github.io/rust-clippy/master/index.html#ptr_offset_with_cast (and very much modelled off of its implementation).

This lint is motivated by cleaning up the output of c2rust, which contains many .offset calls with by literal. The lint also nicely handles offsets by zero, which are unnecessary.

I'm aware that the feature freeze is still in place, but this was top-of-mind now. I'll patiently wait until the freeze is lifted.

changelog: [ptr_offset_by_literal]: add ptr_offset_by_literal lint

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[github-actions]

Lintcheck changes for b0e37f3

Lint	Added	Removed	Changed
clippy::ptr_offset_by_literal	41	0	0

This comment will be updated if you push new changes

[ada4a]

nit: a let-chain is a bit more concise

Suggested change

	let ExprKind::Lit(lit) = expr.kind else {
	if let ExprKind::Lit(lit) = expr.kind
	&& let LitKind::Int(packed_u128, _) = lit.node
	{
	Some(packed_u128.get())
	} else {
	None
	}

(the suggestion seems to be formatted weirdly, but it should (?) work correctly)

[ada4a]

This case looks a bit surprising, maybe add a short comment to it? Something like:

Suggested change

	Ordering::Equal => return Some(format!("{receiver}")),
	// `ptr.offset(0)` is equivalent to `ptr`, so no adjustment is needed
	Ordering::Equal => return Some(format!("{receiver}")),

(why on earth do the suggestions look like this)

[rustbot]

This PR was rebased onto a different master commit. Here's a range-diff highlighting what actually changed.

Rebasing is a normal part of keeping PRs up to date, so no action is needed—this note is just to help reviewers.

[folkertdev]

CI fails on an invalid version attribute, I'm using #[clippy::version = "CURRENT_RUSTC_VERSION"] because it's unclear when this will be merged exactly. What is the intended approach here?

[samueltardieu]

CI fails on an invalid version attribute, I'm using #[clippy::version = "CURRENT_RUSTC_VERSION"] because it's unclear when this will be merged exactly. What is the intended approach here?

1.92.0

It will be fixed if necessary.

[folkertdev]

@rustbot ready