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https://issues.apache.org/jira/browse/LUCENE-3940?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13243782#comment-13243782
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Michael McCandless commented on LUCENE-3940:
--------------------------------------------
Here's an example where we create a compound token with punctuation.
I got this from the Japanese Wikipedia export, with our MockCharFilter
sometimes doubling characters: we are at a position that the
characters 〇〇'''、''' after it... that 〇 is this Unicode character
http://www.fileformat.info/info/unicode/char/3007/index.htm
When Kuromoji extends from this position, both 〇 and 〇〇 are KNOWN,
but then we also extend by unknown 〇〇'''、''' (ie, 〇〇 plus only
punctuation):
Note that 〇 is not considered punctuation by Kuromoji's isPunctuation
method...
{noformat}
+ UNKNOWN word 〇〇'''、''' toPos=41 cost=21223 penalty=3400 toPos.idx=0
+ KNOWN word 〇〇 toPos=34 cost=9895 penalty=0 toPos.idx=0
+ KNOWN word 〇 toPos=33 cost=2766 penalty=0 toPos.idx=0
+ KNOWN word 〇 toPos=33 cost=5256 penalty=0 toPos.idx=1
{noformat}
And then on backtrace we make a compound token (UNKNOWN) for all of
"〇〇'''、'''", while the decompounded path keeps two separate "〇"
tokens but drops the '''、''' since it's all punctuation, thus
creating inconsistent offsets.
> When Japanese (Kuromoji) tokenizer removes a punctuation token it should
> leave a hole
> -------------------------------------------------------------------------------------
>
> Key: LUCENE-3940
> URL: https://issues.apache.org/jira/browse/LUCENE-3940
> Project: Lucene - Java
> Issue Type: Bug
> Reporter: Michael McCandless
> Assignee: Michael McCandless
> Priority: Minor
> Fix For: 4.0
>
> Attachments: LUCENE-3940.patch, LUCENE-3940.patch, LUCENE-3940.patch
>
>
> I modified BaseTokenStreamTestCase to assert that the start/end
> offsets match for graph (posLen > 1) tokens, and this caught a bug in
> Kuromoji when the decompounding of a compound token has a punctuation
> token that's dropped.
> In this case we should leave hole(s) so that the graph is intact, ie,
> the graph should look the same as if the punctuation tokens were not
> initially removed, but then a StopFilter had removed them.
> This also affects tokens that have no compound over them, ie we fail
> to leave a hole today when we remove the punctuation tokens.
> I'm not sure this is serious enough to warrant fixing in 3.6 at the
> last minute...
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