Fix use <2024 identifier sorting transitivity
#6786
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There's also a chance this might not be a breaking change at all, but I think this would be an acceptable one if it were since there's no other way to resolve the panic that I can think of. Running our Diff Check shows that the current |
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After the tests are updated we can get this merged. @rustbot author |
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The sorting tries to create a lowercase>Capital>SCREAMING relation, but does this in a way that causes non-transitive behavior for identifiers starting with `_`. These identifiers are neither Capital nor SCREAMING so they are always compared via lexicographic ASCII matching. This causes a problem, because `A < _ < a` lexicographically in ASCII. But `A > a` with our special case rules! When doing these manual comparisons, hitting these issues is very easy. To fix this, we can simply create a sorting key that mirrors our desired order and sort that normally. This way, it's guaranteed to have all the necessary properties. By *always* sorting uppercase identifiers first, we ensure that `A > _`.
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Added the tests |
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The sorting tries to create a lowercase>Capital>SCREAMING relation, but does this in a way that causes non-transitive behavior for identifiers starting with
_. These identifiers are neither Capital nor SCREAMING so they are always compared via lexicographic ASCII matching.This causes a problem, because
A < _ < alexicographically in ASCII. ButA > awith our special case rules!When doing these manual comparisons, hitting these issues is very easy. To fix this, we can simply create a sorting key that mirrors our desired order and sort that normally. This way, it's guaranteed to have all the necessary properties.
By always sorting uppercase identifiers first, we ensure that
A > _.fixes #6668
This may cause formatting changes if there are identifiers starting with
_in use items, but that breakage is necessary as the previous formatting was completely arbitrary and subject to change by the standard library (and prone to crash rustfmt alltogether).