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https://issues.apache.org/jira/browse/LUCENE-5977?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14151584#comment-14151584
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Dawid Weiss commented on LUCENE-5977:
-------------------------------------
I looked a bit more closely at the logic of updating offsets in the
DefaultIndexingChain and I see offsets *are* propagated for multiple fields,
here:
{code}
// trigger streams to perform end-of-stream operations
stream.end();
// TODO: maybe add some safety? then again, its already checked
// when we come back around to the field...
invertState.position +=
invertState.posIncrAttribute.getPositionIncrement();
invertState.offset += invertState.offsetAttribute.endOffset();
{code}
So the problem with my implementation was that it should have set offsets
properly in end(). I still feel this should be verified / asserted cleaner
somehow, so I'll leave this issue open looking for suggestions.
> IW should safeguard against token streams returning invalid offsets for
> multi-valued fields
> -------------------------------------------------------------------------------------------
>
> Key: LUCENE-5977
> URL: https://issues.apache.org/jira/browse/LUCENE-5977
> Project: Lucene - Core
> Issue Type: Improvement
> Affects Versions: 4.9, 4.9.1, 4.10, 4.10.1
> Reporter: Dawid Weiss
> Priority: Minor
>
> We have a custom token stream that emits information about offsets of each
> token. My (wrong) assumption was that for multi-valued fields a token
> stream's offset information is magically shifted, much like this is the case
> with positions. It's not the case -- offsets should be increasing and
> monotonic across all instances of a field, even if it has custom token
> streams. So, something like this:
> {code}
> doc.add(new Field("field-foo", new CannedTokenStream(token("bar", 1,
> 150, 160)), ftype));
> doc.add(new Field("field-foo", new CannedTokenStream(token("bar", 1,
> 50, 60)), ftype));
> {code}
> where the token function is defined as:
> {code}
> token(String image, int positionIncrement, int startOffset, int endOffset)
> {code}
> will result in either a cryptic assertion thrown from IW:
> {code}
> Exception in thread "main" java.lang.AssertionError
> at
> org.apache.lucene.index.FreqProxTermsWriterPerField.writeOffsets(FreqProxTermsWriterPerField.java:99)
> {code}
> or nothing (or a codec error) if run without assertions.
> Obviously returning non-shifted offsets from subsequent token streams makes
> little sense but I wonder if it could be made more explicit (or asserted)
> that offsets need to be increasing between multiple-values. The minimum is to
> add some documentation to OffsetAttribute. I don't know if offsets should be
> shifted automatically, as it's the case with positions -- this would change
> the semantics of existing tokenizers and filters which implement such
> shifting internally already.
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