fix ascii class bug and 'Hir::is_match_empty' bug#860
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This fixes a bug in how ASCII class unioning was implemented. Namely, it previously and erroneously unioned together two classes and then applied negation/case-folding based on the most recently added class, even if the class added previously wasn't negated. So for example, given the regex '[[:alnum:][:^ascii:]]', this would initialize the class with '[:alnum:]', then add all '[:^ascii:]' codepoints and then negate the entire thing because of the negation in '[:^ascii:]'. Negating the entire thing is clearly wrong and not the intended semantics. We fix this by applying negation/case-folding only to the class we're dealing with, and then we union it with whatever existing class we're building. Fixes #680
This was incorrectly defined for \b. Previously, I had erroneously made it return true only for \B since \B matches '' and \b does not match ''. However, \b does match the empty string. Like \B, it only matches a subset of empty strings, depending on what the surrounding context is. The important bit is that it can match *an* empty string, not that it matches *the* empty string. We were not yet using this predicate anywhere in the regex crate, so we just fix the implementation and update the tests. This does present a compatibility hazard for anyone who was using this function, but as of this time, I'm considering this a bug fix since \b clearly matches an empty string. Fixes #859
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The commit messages should explain a bit, but this picks off a couple low hanging bug fruits.
Fixes #680, Fixes #859