innerHits highlight issue with _source disabled

[rgoene]

*Elasticsearch version : 7.10.1

Plugins installed: none

JVM version : embedded jvm

*OS version: Darwin Kernel Version 19.6.0, 8.04.1-Ubuntu SMP

Description of the problem including expected versus actual behavior:

A text field with indexed offsets in a nested document produces an error when querying with highlights. We use stored fields and not the _source.

• This worked properly with 7.9.3.
• This issue does not occur with non-nested fields.
• Disabling the _source field in the mapping is relevant for the issue.

The following error occurs:
"type": "illegal_state_exception",
"reason": "extracted source isn't an object or an array"

There is only one place in the src where this message is thrown:
https://github.com/elastic/elasticsearch/blob/master/server/src/main/java/org/elasticsearch/search/fetch/FetchPhase.java

This recent work seems to be relevant: #65292

Steps to reproduce:

curl -X DELETE "http://localhost:9200/bugtest"

curl -X PUT "http://localhost:9200/bugtest/" -d '{ "mappings": { "_source": { "enabled": false }, "properties": { "text": { "type": "text", "store": true, "index_options": "offsets" }, "page": { "type": "nested", "properties": { "text": { "type": "text", "store": true, "index_options": "offsets" } } } } } }' -H 'Content-Type: application/json'

curl -X PUT "http://localhost:9200/bugtest/_doc/testdoc" -d '{ "text": "test text with nothing else than a simple test", "page": [ {"text": "test text with nothing else than a simple test"}, {"text": "test two"} ] }' -H 'Content-Type: application/json'

curl -X POST "http://localhost:9200/bugtest/_search" -d '{ "query": { "nested": { "path": "page", "query": { "match": {"page.text" : "test"} }, "inner_hits": { "stored_fields": ["page.text"], "highlight" : { "fields" : { "page.text": {"type": "unified"} } } } } } } ' -H 'Content-Type: application/json'

[elasticmachine]

Pinging @elastic/es-search (Team:Search)

[jtibshirani]

Thanks a lot @rgoene for reporting this, we had some unfortunate regressions around nested hits in 7.10. The fix will be available in the upcoming 7.10.2 and 7.11 releases.

[rgoene]

Thanks for the quick response @jtibshirani !