[ARROW-17239] [C++] Calculate output type from aggregate to convert arrow aggregate to substrait

• Type: Improvement
• Status: Open
• Priority: Major
• Resolution: Unresolved
• Fix Version/s: 11.0.0
• Component/s: C++
• Labels: substrait
• External issue URL: https://github.com/apache/arrow/issues/32524
• Assignee: Vibhatha Lakmal Abeykoon
• Reporter: Weston Pace
• Created: 28/Jul/22 13:55
• Updated: 11/Jan/23 11:49

Description

I am adding support for mapping to/from Arrow aggregates and Substrait aggregates in ARROW-15582. However, the Arrow-Substrait direction is currently blocked because the Substrait plan needs to know the output type of an aggregate and there is no easy way to determine that from the Arrow information we have.

We should be able to get this information from the function registry but the conversion routines do not have access to the function registry that I can tell. I'm not sure if the best solution is to pass the function registry into ToProto or to add the output type to the aggregate in Arrow.