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https://issues.apache.org/jira/browse/LUCENE-8776?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16827208#comment-16827208
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Ram Venkat edited comment on LUCENE-8776 at 4/27/19 3:37 PM:
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Adrien,
There was no trade-off required here. Postings and negative offsets could have
peacefully coexisted, with different implementations using one or the other. A
choice was made knowingly or unknowingly to break some implementations, to the
benefit of a new feature.
Michael G,
I like the PositionLengthAttribute. But, like I said earlier, that still means
that all the relevant query parsers have to make use of the positionLength,
before it can replace the negative offsets feature. Till that happens, this
check cannot be forced on the users.
was (Author: venkat11):
Adrien,
There was no trade-off required here. Postings and negative offsets could have
peacefully coexisted, with two different implementations. A choice was made
knowingly or unknowingly to break some implementations, to the benefit of a new
feature.
Michael G,
I like the PositionLengthAttribute. But, like I said earlier, that still means
that all the relevant query parsers have to make use of the positionLength,
before it can replace the negative offsets feature. Till that happens, this
check cannot be forced on the users.
> 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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