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https://issues.apache.org/jira/browse/LUCENE-10059?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=17406501#comment-17406501
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Anh Dung Bui commented on LUCENE-10059:
---------------------------------------

Thanks [~mikemccand], we already backported to Lucene 8.x. I'll resolve this 
and create follow-up JIRA.

> Assertion error in JapaneseTokenizer backtrace
> ----------------------------------------------
>
>                 Key: LUCENE-10059
>                 URL: https://issues.apache.org/jira/browse/LUCENE-10059
>             Project: Lucene - Core
>          Issue Type: Bug
>    Affects Versions: 8.8
>            Reporter: Anh Dung Bui
>            Priority: Major
>          Time Spent: 1h 20m
>  Remaining Estimate: 0h
>
> There is a rare case which causes an AssertionError in the backtrace step of 
> JapaneseTokenizer that we (Amazon Product Search) found in our tests.
> If there is a text span of length 1024 (determined by 
> [MAX_BACKTRACE_GAP|https://github.com/apache/lucene/blob/main/lucene/analysis/kuromoji/src/java/org/apache/lucene/analysis/ja/JapaneseTokenizer.java#L116])
>  where the regular backtrace is not called, a [forced 
> backtrace|https://github.com/apache/lucene/blob/main/lucene/analysis/kuromoji/src/java/org/apache/lucene/analysis/ja/JapaneseTokenizer.java#L781]
>  will be applied. If the partially best path at this point happens to end at 
> the last pos, and since there is always a [final 
> backtrace|https://github.com/apache/lucene/blob/main/lucene/analysis/kuromoji/src/java/org/apache/lucene/analysis/ja/JapaneseTokenizer.java#L1044]
>  applied at the end, the final backtrace will try to backtrace from and to 
> the same position, causing an AssertionError in RollingCharBuffer.get() when 
> it tries to generate an empty buffer.
> We are fixing it by returning prematurely in the backtrace() method when the 
> from and to pos are the same:
> {code:java}
>     if (endPos == lastBackTracePos) {
>       return;
>     }
> {code}
> The backtrace() method is essentially no-op when this condition happens, thus 
> when _-ea_ is not enabled, it can still output the correct tokens.
> We will open a PR for this issue.



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