Huh, I'm not familiar with \K. Another bit we need to get into Joni.

@headius, I must admit, I had never encountered \K either. I found this problem (and the one regarding \X) by testing diffs between Java and Ruby on Regular-Expressions.info. Most headings in that TOC links to a page where the compared flavors can be selected at the top. I found it to be quite helpful.

Done in jruby/joni@59dbb27

AFAICT, this isn't completely fixed. When running my example I get a warning Unknown escape \K is ignored. I'm using joni-2.1.27 and the subsequent match fails.

unknownEscWarn:145, ScanEnvironment (org.joni)
convertBackslashValue:129, ScanEnvironment (org.joni)
fetchEscapedValueBackSlash:184, Lexer (org.joni)
fetchEscapedValue:179, Lexer (org.joni)
fetchToken:1166, Lexer (org.joni)
parseStringLoop:1090, Parser (org.joni)
parseExpTkByte:1085, Parser (org.joni)
parseExp:801, Parser (org.joni)
parseBranch:1342, Parser (org.joni)
parseSubExp:1368, Parser (org.joni)
parseRegexp:1401, Parser (org.joni)
compile:78, Analyser (org.joni)
<init>:155, Regex (org.joni)
<init>:134, Regex (org.joni)
<init>:120, Regex (org.joni)
<init>:100, Regex (org.joni)

There was indeed a break missing for \K in the lexer. Fixed in jruby/joni@ee4bafb

joni-2.1.28 is released

Thanks. Works like a charm!

@thallgren, can you show the case that was not matching (or a reduced form of it), se we can plug it into our test suite ?
For now, we're running all of Onigmo's suite for \K at https://github.com/jruby/joni/blob/master/test/org/joni/test/TestU8.java#L102

My test is for an evaluator for the Puppet type system, written in Java. It has its own Regexp and Matcher classes to wrap the Onigmo ones so the test will need to be rewritten to suit your style. This is the test that failed: https://github.com/puppetlabs/pcore-java/blob/b234d044d41b3db73aefa478c7ede779b073d27f/src/test/java/com/puppet/pcore/regex/RegexpTest.java#L189