Code in RangeMapFloatFunction:

  @Override
  public String description() {
    return "map(" + source.description() + "," + min + "," + max + "," + target.description() + ")";
  }

Hmm, should this be a Lucene jira perhaps?

Attaching patch which prints default value in explain and description.

defaultVal is allowed to be null, and in that case it defaults to the x (source) value. In this patch I explicitly print the source value in that case. An alternative could be to omit default value and print only map(x,min,max,target) as today.

Shalin Shekhar Mangar, you have been involved in this class before, what is your opinion?

Jan, maybe we should display null instead of source.description() when defaultVal is null? I think the output could be a bit confusing otherwise as it would look like default values were provided even though they were not?

Agree, it more precisely shows what the user-function looks like. Attached is new patch.

+1

Commit 1713729 from janhoy@apache.org in branch 'dev/trunk'
[ https://svn.apache.org/r1713729 ]

LUCENE-6888: Explain output of map() function now also prints default value

Commit 1713738 from janhoy@apache.org in branch 'dev/branches/branch_5x'
[ https://svn.apache.org/r1713738 ]

LUCENE-6888: Explain output of map() function now also prints default value (backport)