It's still pretty early days with it at the moment so things are liable to change, but I have elastic set up right now. I'm completely new to search though, so I don't really know the ins and outs of different solutions. Plenty of time to learn though, as I'm still working on the crawler part right now.
Google wrote a regex code search engine based on trigrams, and you can download it[1]. I don't think Lucene supports regexes, but it can do some somewhat simpler pattern matches, and I don't necessarily see why regexes are necessary for searching code. Lucene does a lot more for search than match strings, and I don't necessarily see why searching code is fundamentally unlike searching other kinds of documents, so a lot of those features might help you get much better results.
