Fix: avoid changing drop order

[koka831]

Fixes #11599

changelog: [redundant_locals] No longer lints which implements Drop trait to avoid reordering

[rustbot]

r? @giraffate

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[y21]

This looks like it won't work if the type is composed of other types implementing Drop.

struct WithDrop(usize);
impl Drop for WithDrop {..}

struct V(WithDrop);

let first = V(WithDrop(1));
let second = WithDrop(2);
let first = first;

clippy_utils::ty::needs_ordered_drop would be better.

But also, the lint already has a bit of logic for checking if it affects drop behavior further down and it already checks if the type has a significant dtor that affects drop ordering:

rust-clippy/clippy_lints/src/redundant_locals.rs

Lines 108 to 116 in 81400e2

	/// Check if a rebinding of a local affects the code's drop behavior.
	fn affects_drop_behavior<'tcx>(cx: &LateContext<'tcx>, bind: HirId, rebind: HirId, rebind_expr: &Expr<'tcx>) -> bool {
	let hir = cx.tcx.hir();
	// the rebinding is in a different scope than the original binding
	// and the type of the binding cares about drop order
	hir.get_enclosing_scope(bind) != hir.get_enclosing_scope(rebind)
	&& needs_ordered_drop(cx, cx.typeck_results().expr_ty(rebind_expr))
	}

We should probably just remove the get_enclosing_scope(bind) != get_enclosing_scope(rebind) check in there

[koka831]

Thanks, I couldn't figure out why affects_drop_behavior wasn't working. 😅

We should probably just remove the get_enclosing_scope(bind) != get_enclosing_scope(rebind) check from there.

Yes, it works perfectly.

[koka831]

I've addressed them. could you r? @y21

[rustbot]

Failed to set assignee to y21: invalid assignee

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[Alexendoo]

Thanks! @bors r=y21

[bors]

📌 Commit c715267 has been approved by y21

It is now in the queue for this repository.

[bors]

⌛ Testing commit c715267 with merge b437069...

[bors]

☀️ Test successful - checks-action_dev_test, checks-action_remark_test, checks-action_test
Approved by: y21
Pushing b437069 to master...