As discussed in SOLR-8396, we should use SortedNumericDocValues. There are already some (ignored) tests in TestPointFields for this feature, once it's available.

Here is a first patch. Some nocommits and some tests are failing. This requires LUCENE-7673

Here is another patch, with some more tests and support for multivalued stats (same feature support as single value). I think this is ready to commit

Wow you did a lot of work for this! Thanks for doing this work.

As I skimmed through with curiosity, one thing caught my eye:

+//            We should do this, but mincount=0 is currently the default
+//            if (ft.isPointField() && mincount <= 0) {
+//              throw new SolrException(ErrorCode.BAD_REQUEST, FacetParams.FACET_MINCOUNT + " <= 0 is not supported on point types");
+//            }

Judging from this and nearby code changes, if minCount is 0 then you make it 1 instead (for PointFields only); is this right? This seems wrong to me. I suspect we all agree that the default of 0 is unfortunate but ignoring it and pretending it's not in certain cases but not others seems wrong. Instead, I propose that we make the default '1' for 7.0. Obviously such a change would be in another issue.

Thanks for reviewing David. The issue is that facet.mincount=0 doesn't work currently (SOLR-10033), and it's not easy, since we don't have TermsEnum for PointFields. So yes, if the user sets facet.mincount=0 in the request I'm currently blindly changing it to 1, which is the same thing that happens today with TrieFields that have indexed="false" and docValues="true" (since SOLR-5260, before that we would throw an exception).
An extra issue is that currently by default in distributed facet requests, shard requests are always set to facet.mincount=0 (see SOLR-8988 and SOLR-9152). I don't want to put this exception back until the defaults change.

Ugh; ok. I was a watcher on SOLR-5260 but missed the implication.

+1 to commit then.

Commit 7dcf9de41f6435a741910a6367ef9fece11a588b in lucene-solr's branch refs/heads/master from Tomas Fernandez Lobbe
[ https://git-wip-us.apache.org/repos/asf?p=lucene-solr.git;h=7dcf9de ]

SOLR-9987: Implement support for multi-valued DocValues in PointFields
CC SOLR-8396

Commit bc10fa67b641d0cfb9bd1954378019d4fc343ae8 in lucene-solr's branch refs/heads/branch_6x from Tomas Fernandez Lobbe
[ https://git-wip-us.apache.org/repos/asf?p=lucene-solr.git;h=bc10fa6 ]

SOLR-9987: Implement support for multi-valued DocValues in PointFields
CC SOLR-8396

Commit 81b4288a2133dce87e0ac92da5f6e37dc28176f6 in lucene-solr's branch refs/heads/branch_6x from Tomas Fernandez Lobbe
[ https://git-wip-us.apache.org/repos/asf?p=lucene-solr.git;h=81b4288 ]

SOLR-8396, SOLR-9987, SOLR-10011: Move CHANGES entries from 7.0 to 6.5