Return new lists on calls to getValues.

[jpountz]

Scripts currently share the same list across invocations to getValues. This
caused a bug in script fields where all documents coming from the same segment
would get the same values (basically, for the next document for which script
values have been requested). Scripts now return a fresh new list on every
invocation to getValues.

Close #8576

[s1monw]

I wonder if we should fix this Interface and return Iterable<T> instead such that folks need to make copies of it if they really need and we can just lazily fetch the values?

[jpountz]

I am not sure it would fix the issue? Someone could still keep references to the Iterable instance?

I think it is the right trade-off to have these interfaces potentially slow but easy to use. It avoids surprises, and if someone needs better performance it is still possible to access directly the fielddata interfaces (via the getInternalValues method).

[s1monw]

I am not sure it would fix the issue? Someone could still keep references to the Iterable instance?

yes they should becuse each call to getValues would return a new iterable. but it would produce the values each time. The common case here is that stuff iterated once if you need it more often you should copy it?

[jpountz]

@s1monw I updated the patch with your suggestion. So now we have doc['field'] which implements java.util.List and its scope is limited to the current document. And we also have doc['field'].values which returns a copy so that it can survive changes of scope. So for instance doc['field'].values is required in script fields for things to work correctly but it is perfectly fine to use doc['field'] in the context of an aggregation since we don't keep references to the produced list. Is it what you had in mind?

[s1monw]

awesome - LGTM