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From "Robert Muir (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (LUCENE-8776) Start offset going backwards has a legitimate purpose
Date Fri, 03 May 2019 12:03:00 GMT

    [ https://issues.apache.org/jira/browse/LUCENE-8776?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16832449#comment-16832449
] 

Robert Muir commented on LUCENE-8776:
-------------------------------------

I don't think we should change the exception message at all.
Please remember: the code is open source, you can modify the source code for whatever purpose.

So I think such a message comes out wrong, I don't even buy the argument that it "broke" anything:
we're not putting a gun to your head and forcing you to upgrade or anything. You can stay
on an older version of the code, you can fork the code and modify it, all kinds of solutions.

> Start offset going backwards has a legitimate purpose
> -----------------------------------------------------
>
>                 Key: LUCENE-8776
>                 URL: https://issues.apache.org/jira/browse/LUCENE-8776
>             Project: Lucene - Core
>          Issue Type: Bug
>          Components: core/search
>    Affects Versions: 7.6
>            Reporter: Ram Venkat
>            Priority: Major
>
> Here is the use case where startOffset can go backwards:
> Say there is a line "Organic light-emitting-diode glows", and I want to run span queries
and highlight them properly. 
> During index time, light-emitting-diode is split into three words, which allows me to
search for 'light', 'emitting' and 'diode' individually. The three words occupy adjacent positions
in the index, as 'light' adjacent to 'emitting' and 'light' at a distance of two words from
'diode' need to match this word. So, the order of words after splitting are: Organic, light,
emitting, diode, glows. 
> But, I also want to search for 'organic' being adjacent to 'light-emitting-diode' or
'light-emitting-diode' being adjacent to 'glows'. 
> The way I solved this was to also generate 'light-emitting-diode' at two positions: (a)
In the same position as 'light' and (b) in the same position as 'glows', like below:
> ||organic||light||emitting||diode||glows||
> | |light-emitting-diode| |light-emitting-diode| |
> |0|1|2|3|4|
> The positions of the two 'light-emitting-diode' are 1 and 3, but the offsets are obviously
the same. This works beautifully in Lucene 5.x in both searching and highlighting with span
queries. 
> But when I try this in Lucene 7.6, it hits the condition "Offsets must not go backwards"
at DefaultIndexingChain:818. This IllegalArgumentException is being thrown without any comments
on why this check is needed. As I explained above, startOffset going backwards is perfectly
valid, to deal with word splitting and span operations on these specialized use cases. On
the other hand, it is not clear what value is added by this check and which highlighter code
is affected by offsets going backwards. This same check is done at BaseTokenStreamTestCase:245. 
> I see others talk about how this check found bugs in WordDelimiter etc. but it also prevents
legitimate use cases. Can this check be removed?  



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