update for ES7.0.0

[umeshdangat]

Still some work to be done to get it completely working:

• Scorer must now implement getMaxScore. This is the upstream lucene PR. For now I return a default value for all Scorer implementations, not sure how this method affects some of the custom Scorers.
• Got to fix some failing tests in particular
  • lucene does not allow negative scores anymore

[umeshdangat]

Updated to use Elasticsearch 7.0.0
Fixed some tests and relevant code

• Lucene:7996 - Scorers cant generate negative scores. Removed test which is not relevant anymore and the check for Float.isNan
• Lucene:8020
  indexSearch.termStatistics can now return null

[umeshdangat]

Fixed the remaining tests

• LambdaMART generated negative values, used RankNet instead for those tests. Changed LambaMART output to be positive in one test.
• Fixed integration tests since es now returns hits.total as an object.

@nomoa @softwaredoug @worleydl I think this PR should be ready for review now.

[nomoa]

great!

left some comments (mostly minor).

As for the situation about the new restriction of having positive scores I'd be for the following solution while we fix rankers:
Add new param to the ltr/sltr query that would indicate the failure mode in case of negative score returned by some rankers:

• fail (throw IOException() from the score method)
• log a warning and clamp min to 0

I'd be for opening a dedicated ticket to discuss this.

[nomoa]

we should keep this test perhaps just expect that IllegalArgumentException is thrown?

[umeshdangat]

The issue is we cant even build a BoostQuery object anymore since that is the one that throws IllegalArgumentException so essentially we never even get to the code we want to test.

[nomoa]

and the circleci config will have to be updated to pull java 12 I suppose.

[jettro]

Curious about the status of the PR. I have used the plugin with my basic sample, everything still seems to work.

[umeshdangat]

@jettro I need to address the comments mentioned by @nomoa. Should get to them sometime later this week. Been somewhat busy with https://haystackconf.com/2019/evolution/.
In case anyone of you want to go ahead and address some issues please feel free to go ahead or I will get to them most likely post haystack.

[umeshdangat]

and the circleci config will have to be updated to pull java 12 I suppose.

I dont see openjdk-12 image available on circleci. https://circleci.com/docs/2.0/circleci-images/#openjdk

[nomoa]

LGTM!