fix factoring of common prefixes in alternations #107
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In the past, `a.*?c|a.*?b` was factored to `a.*?[bc]`. Thus, given "abc" as its input string, the automaton would consume "ab" and then stop (when unanchored) whereas it should consume all of "abc" as per leftmost semantics. This fix is ported from Go's regex impl, https://go-review.googlesource.com/c/go/+/18357/. Fixes google#93.
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In the past,
a.*?c|a.*?bwas factored toa.*?[bc]. Thus, given"abc" as its input string, the automaton would consume "ab" and
then stop (when unanchored) whereas it should consume all of "abc"
as per leftmost semantics.
This fix is ported from Go's regex impl,
https://go-review.googlesource.com/c/go/+/18357/.
Fixes #93.