Fix suggestion-causes-error of manual_swap

[relaxcn]

Fixes: #14931

changelog: Fix [manual_swap]'s suggestion-causes-error when the variable is mutable or as loop variable.

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[samueltardieu]

I don't think you need to introduce a new get_res_span() method.

Suggested change

	|| self
	.get_res_span(expr)
	.is_some_and(|span| !self.suggest_span.contains(span))
	|| path_to_local(expr)
	.is_some_and(|hir_id| !self.suggest_span.contains(self.cx.tcx.hir_span(hir_id)))

[samueltardieu]

Suggested change

	fn get_res_span(&self, expr: &'tcx Expr<'tcx>) -> Option<Span> {
	if let ExprKind::Path(QPath::Resolved(
	_,
	Path {
	res: rustc_hir::def::Res::Local(hir_id),
	..
	},
	)) = expr.kind
	{
	Some(self.cx.tcx.hir_span(*hir_id))
	} else {
	None
	}
	}

[samueltardieu]

This test seems more costly than the new one (declaration outside the suggestion span), maybe you should move it in last position.

[samueltardieu]

Thanks for adding documentation here. I would not repeat the negation of previous conditions, this seems simpler and is logically equivalent:

Suggested change

	// We skip suggesting a variable binding in any of these cases:
	// 1. Variable initialization is outside the suggestion span
	// 2. Variable initialization is inside the suggestion span but the variable is not used as an index
	// or elsewhere later
	// 3. Variable initialization is inside the suggestion span and the variable is used as an
	// index/elsewhere later, but its declaration is outside the suggestion span
	// We skip suggesting a variable binding in any of these cases:
	// - Variable initialization is outside the suggestion span
	// - Variable declaration is outside the suggestion span
	// - Variable is not used as an index or elsewhere later

(see below for the ordering)

[samueltardieu]

r? @samueltardieu
@rustbot author

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