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Preserve brackets around if-lets and skip while-lets r? `@jieyouxu` Tracked by #124085 Fresh out of #129466, we have discovered 9 crates that the lint did not successfully migrate because the span of `if let` includes the surrounding brackets `(..)` like the following, which surprised me a bit. ```rust if (if let .. { .. } else { .. }) { // ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ // the span somehow includes the surrounding brackets } ``` There is one crate that failed the migration because some suggestion spans cross the macro expansion boundaries. Surely there is no way to patch them with `match` rewrite. To handle this case, we will instead require all spans to be tested for admissibility as suggestion spans. Besides, there are 4 false negative cases discovered with desugared-`while let`. We don't need to lint them, because the `else` branch surely contains exactly one statement because the drop order is not changed whatsoever in this case. ```rust while let Some(value) = droppy().get() { .. } // is desugared into loop { if let Some(value) = droppy().get() { .. } else { break; // here can be nothing observable in this block } } ``` I believe this is the one and only false positive that I have found. I think we have finally nailed all the corner cases this time.