In the suggestion machinery for borrowing expressions and types, always use the available obligation `Span` to find the appropriate `Expr` to perform appropriateness checks no the `ExprKind` instead of on the textual snippet corresponding to the `Span`.
Unify the logic for the case where `&` *and* `&mut` are appropriate with the logic for only one of those cases.
Handle the case when `S::foo()` should have been `<&S>::foo()` (instead of suggesting the prior `&S::foo()`.
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