Fix bugs and make replace(all) operations SMT-LIB compliant #75
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matthewhague
commented
Jul 19, 2023
matthewhague
commented
- Add a bunch of tests for ReplacePreOp that should have been there long ago
- Fix old bugs with string replacement (I still wasn't building the right transducer from the string..)
- Original fix 69c2ae8 wasn't quite right, and should have been done for ReplacePreOp too.
- Add ReplaceAllShortestPreOp, rename existing pre-op to ReplaceAllLongestPreOp
- For regex, longest and shortest both only look for non-empty matches, which is ok by SMT-LIB
- Add ReplaceShortestPreOp, rename existing pre-op to ReplaceLongestPreOp
- Implement correct prepend semantics for shortest if regex accepts the empty word
- When replace_all s t t' when t is empty, then return s unchanged (via a new NOPPreOp)
- When replace s t t' when t is empty, return t's as per SMT-LIB
The bug found was the same bug as fixed in 69c2ae8, except in the analogous ReplacePreOp (rather than ReplaceAllPreOp) code. It occurred in the case where a failed word match has a suffix that could have been the start of another match attempt.
When matching e.g. abc, if an a is read instead of a b, then that a could be the start of the new match. This was the old bug that was fixed. I didn't account for the fact that a could alternatively be the last character read, and so there should be an accepting transition for that case (you can't accept part way through a match, so existing transitions didn't work).
That is, in replace(x, "", y), y is prepended to x.
If the string to replace is empty, then the defined SMT-LIB semantics for shortest match is to return the string unchanged. Support this with a new NOPPreOp object.
That is, allow an empty match in the regex, but expect the result not to use it. (SMT-LIB semantics)
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