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https://issues.apache.org/jira/browse/LUCENE-2039?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12776502#action_12776502
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Yonik Seeley commented on LUCENE-2039:
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bq. I think one problem lucene has today, is that the queryparser code in very
tightly integrated with the javacc code.
This almost seems more of an issue for core lucene developers - it's an
annoyance that one needs to recompile the javacc grammar when just tweaking
what one of the methods does. Seems like this could easily be solved by just
separating into two files... the javacc grammar would have a base class that
left things like getFieldQuery() unimplemented, and then the standard
QueryParser (in a different java file) would override and implement those
methods.
bq. We should decouple the user extensions from the JAVACC generated code.
It already is today via subclassing QueryParser and overriding methods like
getFieldQuery... that's very simple for users to understand and to leverage.
bq. Just like in the new queryparser framework does, the queryparser should
allow for the user to register these extensions at run time, and have Interface
that extensions should implement.
I don't understand the motivation for this - it's complex and harder for a user
to understand. Java's own extension mechanism (overriding) has worked
perfectly fine in the past.
> Regex support and beyond in JavaCC QueryParser
> ----------------------------------------------
>
> Key: LUCENE-2039
> URL: https://issues.apache.org/jira/browse/LUCENE-2039
> Project: Lucene - Java
> Issue Type: Improvement
> Components: QueryParser
> Reporter: Simon Willnauer
> Assignee: Grant Ingersoll
> Priority: Minor
> Fix For: 3.1
>
> Attachments: LUCENE-2039.patch
>
>
> Since the early days the standard query parser was limited to the queries
> living in core, adding other queries or extending the parser in any way
> always forced people to change the grammar file and regenerate. Even if you
> change the grammar you have to be extremely careful how you modify the parser
> so that other parts of the standard parser are affected by customisation
> changes. Eventually you had to live with all the limitation the current
> parser has like tokenizing on whitespaces before a tokenizer / analyzer has
> the chance to look at the tokens.
> I was thinking about how to overcome the limitation and add regex support to
> the query parser without introducing any dependency to core. I added a new
> special character that basically prevents the parser from interpreting any of
> the characters enclosed in the new special characters. I choose the forward
> slash '/' as the delimiter so that everything in between two forward slashes
> is basically escaped and ignored by the parser. All chars embedded within
> forward slashes are treated as one token even if it contains other special
> chars like * []?{} or whitespaces. This token is subsequently passed to a
> pluggable "parser extension" with builds a query from the embedded string. I
> do not interpret the embedded string in any way but leave all the subsequent
> work to the parser extension. Such an extension could be another full
> featured query parser itself or simply a ctor call for regex query. The
> interface remains quiet simple but makes the parser extendible in an easy way
> compared to modifying the javaCC sources.
> The downsides of this patch is clearly that I introduce a new special char
> into the syntax but I guess that would not be that much of a deal as it is
> reflected in the escape method though. It would truly be nice to have more
> than once extension an have this even more flexible so treat this patch as a
> kickoff though.
> Another way of solving the problem with RegexQuery would be to move the JDK
> version of regex into the core and simply have another method like:
> {code}
> protected Query newRegexQuery(Term t) {
> ...
> }
> {code}
> which I would like better as it would be more consistent with the idea of the
> query parser to be a very strict and defined parser.
> I will upload a patch in a second which implements the extension based
> approach I guess I will add a second patch with regex in core soon too.
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