Github user kl0u commented on the issue:
https://github.com/apache/flink/pull/2361
Hi @mushketyk ! Thanks a lot!
The problem is in the `NFACompiler` and more specifically the way the
pattern is compiled. I have not come up with a concrete solution yet but I
would say that:
i) there should be another `StateType` as well, sth like `PotentialFinal`
(or a better name) and in the case that the final pattern is optional, then it
gets assigned this `StateType`. This also propagates backwards in the pattern
graph in the case that the final pattern is optional (0 to sth times).
ii) the `addTransitions()` should also be extended to account for
quantifiers at the end and at the start of the pattern when "unrolling" or
expanding the original pattern, e.g. the `expandRepeatingPattern()` should not
always assign `State.StateType.Normal` to the unrolled patterns as they may be
at the end or the start.
iii) the `NFA` should also be modified to account for the new
`PotentialFinal` state. In this case, when we see such a pattern, a flag should
be set, and for example in the one-to-many case the pattern should be matched
when the next non-matching element comes.
Again these are some initial thoughts. We can discuss more on the design if
you want, as this seems to be a bigger change than expected ;)
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