We need to be able to count bits in BitmapPtr containers. This only
comes up if you have a non-container-aligned range count, which we
never do in real production yet, but the API allows it so it should
work. In order to do this, we need to provide the tx to countRange
so it can grab pages as needed. Arguably, we should be able to avoid
actually creating/copying that page since we're only using it
internally, never returning it, but this is a pretty rare case
and probably not performance-critical.
This test was supposed to check against all the container types,
but especially bitmaps, but turns out not to work because the
containers turn into RLE containers. Oops. Now, we start with
every-other-bit for the first 8k, then start filling in the holes,
so we get some bitmap containers and then start generating
RLE containers.
When a run started and ended within a single word, the entirety of the word would be checked.
This would cause small runs to be processed incorrectly, and caused Distinct-on-sets to select rows that did not match the specified filter.
We want to distinguish different *kinds* of GroupCounts, so we're
making the GroupCounts parent object track its type so we can keep that
correct.
Adding this to protobuf, etc, then creates some weird behaviors
because sometimes we expect []GroupCount, and sometimes we expect
*GroupCounts. This implies changes to test cases. Also, the
changes to test cases imply that some test cases are probably now
wrong; for instance, they're expecting a "sum" column, equal to zero,
when no sum was requested.
We try to make the encoder handle a []*GroupCount gotten from another
node without panicing, and avoid breaking the semantics of the existing
messages, renumbering messages or components, etc.
Since a previous version, the `.Groups` member has been privatized,
and the `.Get()` convenience accessor has been renamed `.Groups()`
and is now used consistently in a way that should reduce the risk
of nil pointers causing crashes. Also, NewGroupCounts is used in
a couple more places.
