Score value is 0 in _explanation with random_score query

[marevol]

Sending random_score function query with explain=true to Elasticsearch 1.5.1, the value is always 0 in _explanation as below.

...
              {
                 "value": 0,
                 "description": "Math.min of",
                 "details": [
                    {
                       "value": 0,
                       "description": "product of:",
                       "details": [
                          {
                             "value": 0,
                             "description": "random score function (seed: 49)"
                          },
                          {
                             "value": 1,
                             "description": "weight"
                          }
                       ]
                    },
                    {
                       "value": 3.4028235e+38,
                       "description": "maxBoost"
                    }
                 ]
              },
...

I looked into RandomScoreFunction class.
I think that exp.setValue(CombineFunction.toFloat(score(docId, subQueryScore.getValue()))) needs to be call in explainScore method.

[rjernst]

I think this was actually fixed today as part of upgrading our lucene snapshot in master:
https://github.com/elastic/elasticsearch/pull/10727/files#diff-8

So this is already fixed in 2.0. I will backport the fix 1.x.