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From "Steven Rowe (JIRA)" <j...@apache.org>
Subject [jira] Issue Comment Edited: (LUCENE-1683) RegexQuery matches terms the input regex doesn't actually match
Date Thu, 16 Jul 2009 18:14:14 GMT

    [ https://issues.apache.org/jira/browse/LUCENE-1683?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12732060#action_12732060
] 

Steven Rowe edited comment on LUCENE-1683 at 7/16/09 11:12 AM:
---------------------------------------------------------------

bq. ... why is RegexQuery treating the trailing "." as a ".*" instead? 

JavaUtilRegexCapabilities.match() is implemented as j.u.regex.Matcher.lookingAt(), which is
equivalent to adding a trailing ".*", unless you explicity append a "$" to the pattern.

By contrast, JakartaRegexpCapabilities.match() is implemented as RE.match(), which does not
imply the trailing ".*".

The difference in the two implementations implies this is a kind of bug, especially since
the javadoc "contract" on RegexCapabilities.match() just says "@return true if string matches
the pattern last passed to compile".

The fix is to switch JavaUtilRegexCapabilities.match to use Matcher.match() instead of lookingAt().

      was (Author: steve_rowe):
    bq. ... why is RegexQuery treating the trailing "." as a ".*" instead? 

JavaUtilRegexCapabilities.match() is implemented as j.u.Matcher.lookingAt(), which is equivalent
to adding a trailing ".*", unless you explicity append a "$" to the pattern.

By contrast, JakartaRegexpCapabilities.match() is implemented as RE.match(), which does not
imply the trailing ".*".

The difference in the two implementations implies this is a kind of bug, especially since
the javadoc "contract" on RegexCapabilities.match() just says "@return true if string matches
the pattern last passed to compile".

The fix is to switch JavaUtilRegexCapabilities.match to use j.u.Matcher.match() instead of
lookingAt().
  
> RegexQuery matches terms the input regex doesn't actually match
> ---------------------------------------------------------------
>
>                 Key: LUCENE-1683
>                 URL: https://issues.apache.org/jira/browse/LUCENE-1683
>             Project: Lucene - Java
>          Issue Type: Improvement
>          Components: contrib/*
>    Affects Versions: 2.3.2
>            Reporter: Trejkaz
>
> I was writing some unit tests for our own wrapper around the Lucene regex classes, and
got tripped up by something interesting.
> The regex "cat." will match "cats" but also anything with "cat" and 1+ following letters
(e.g. "cathy", "catcher", ...)  It is as if there is an implicit .* always added to the end
of the regex.
> Here's a unit test for the behaviour I would expect myself:
>     @Test
>     public void testNecessity() throws Exception {
>         File dir = new File(new File(System.getProperty("java.io.tmpdir")), "index");
>         IndexWriter writer = new IndexWriter(dir, new StandardAnalyzer(), true);
>         try {
>             Document doc = new Document();
>             doc.add(new Field("field", "cat cats cathy", Field.Store.YES, Field.Index.TOKENIZED));
>             writer.addDocument(doc);
>         } finally {
>             writer.close();
>         }
>         IndexReader reader = IndexReader.open(dir);
>         try {
>             TermEnum terms = new RegexQuery(new Term("field", "cat.")).getEnum(reader);
>             assertEquals("Wrong term", "cats", terms.term());
>             assertFalse("Should have only been one term", terms.next());
>         } finally {
>             reader.close();
>         }
>     }
> This test fails on the term check with terms.term() equal to "cathy".
> Our workaround is to mangle the query like this:
>     String fixed = String.format("(?:%s)$", original);

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