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https://issues.apache.org/jira/browse/LUCENE-4078?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13284113#comment-13284113
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Hoss Man commented on LUCENE-4078:
----------------------------------
bq. It doesn't match an empty string. It matches an empty string in between
characters...
Well, it's more complicated then that. it *does* match the empty string (in
the sense of "does this regex match this entire string which happens to be
empty) but in the context of "find" or "replace" on a larger string you are
correct that it matches nothing, which means it matches the emptiness between
characters.
bq. I'd be convinced '|' is a consistent way of saying 'match empty string or
empty string' if "+" pattern worked ("match empty string one or more times"),
but it doesn't -- this will fail with an error. So '|' is kind of special here.
I think that's just a fluke of syntax/precedence ... if you use parens
(capturing or otherwise) you can say "match the empty pattern 1 or more
times)...
{code}
$ perl -MData::Dumper -le 'print Dumper split /(?:)+/, "ABCD";'
$VAR1 = 'A';
$VAR2 = 'B';
$VAR3 = 'C';
$VAR4 = 'D';
{code}
Bottom Line: these patterns are all valid and meaningful, and everything we've
discussed is tangential to the problem -- which seems to be that the JVM lets
the empty pattern split in between chars instead of codepoints, which seems
like a bug.
> PatternReplaceCharFilter assertion error
> ----------------------------------------
>
> Key: LUCENE-4078
> URL: https://issues.apache.org/jira/browse/LUCENE-4078
> Project: Lucene - Java
> Issue Type: Bug
> Reporter: Dawid Weiss
> Assignee: Dawid Weiss
> Priority: Minor
> Fix For: 4.0
>
>
> Build: https://builds.apache.org/job/Lucene-trunk/1942/
> 1 tests failed.
> REGRESSION:
> org.apache.lucene.analysis.pattern.TestPatternReplaceCharFilter.testRandomStrings
> Error Message:
> Stack Trace:
> java.lang.AssertionError
> at
> __randomizedtesting.SeedInfo.seed([8E91A6AC395FEED9:618A6129A5BB9EC]:0)
> at
> org.apache.lucene.analysis.MockTokenizer.readCodePoint(MockTokenizer.java:153)
> at
> org.apache.lucene.analysis.MockTokenizer.incrementToken(MockTokenizer.java:123)
> at
> org.apache.lucene.analysis.BaseTokenStreamTestCase.checkAnalysisConsistency(BaseTokenStreamTestCase.java:558)
> at
> org.apache.lucene.analysis.BaseTokenStreamTestCase.checkRandomData(BaseTokenStreamTestCase.java:488)
> at
> org.apache.lucene.analysis.BaseTokenStreamTestCase.checkRandomData(BaseTokenStreamTestCase.java:430)
> at
> org.apache.lucene.analysis.BaseTokenStreamTestCase.checkRandomData(BaseTokenStreamTestCase.java:424)
> at
> org.apache.lucene.analysis.pattern.TestPatternReplaceCharFilter.testRandomStrings(TestPatternReplaceCharFilter.java:323)
> at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
> at
> sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:57)
> at
> sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
> at java.lang.reflect.Method.invoke(Method.java:616)
> at
> com.carrotsearch.randomizedtesting.RandomizedRunner.invoke(RandomizedRunner.java:1969)
> at
> com.carrotsearch.randomizedtesting.RandomizedRunner.access$1100(RandomizedRunner.java:132)
> at
> com.carrotsearch.randomizedtesting.RandomizedRunner$6.evaluate(RandomizedRunner.java:814)
> at
> com.carrotsearch.randomizedtesting.RandomizedRunner$7.evaluate(RandomizedRunner.java:875)
> at
> com.carrotsearch.randomizedtesting.RandomizedRunner$8.evaluate(RandomizedRunner.java:889)
> at
> org.apache.lucene.util.TestRuleSetupTeardownChained$1.evaluate(TestRuleSetupTeardownChained.java:50)
> at
> org.apache.lucene.util.TestRuleFieldCacheSanity$1.evaluate(TestRuleFieldCacheSanity.java:32)
> at
> org.apache.lucene.util.AbstractBeforeAfterRule$1.evaluate(AbstractBeforeAfterRule.java:45)
> at
> com.carrotsearch.randomizedtesting.rules.SystemPropertiesInvariantRule$1.evaluate(SystemPropertiesInvariantRule.java:55)
> at
> org.apache.lucene.util.TestRuleReportUncaughtExceptions$1.evaluate(TestRuleReportUncaughtExceptions.java:68)
> at
> org.apache.lucene.util.TestRuleThreadAndTestName$1.evaluate(TestRuleThreadAndTestName.java:48)
> at
> org.apache.lucene.util.TestRuleMarkFailure$1.evaluate(TestRuleMarkFailure.java:48)
> at
> com.carrotsearch.randomizedtesting.RandomizedRunner.runSingleTest(Randomized
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