Expose user defined functions in the FFI #14562
Description
Is your feature request related to a problem or challenge?
By adding the foreign function interface to this project, we exposed a host of features to end users. It allows for easy integration of DataFusion libraries across projects, specifically impacting datafusion-python.
I recommend that we work to expose scalar, aggregate, and window user defined functions via FFI. This is to support the issue apache/datafusion-python#1017
Describe the solution you'd like
Follow the existing pattern within the datafusion repository and expose these types of user defined functions.
- scalar
- aggregate
- window
- table
Note: The table functions are not currently in use in datafusion-python, but it would be a good addition.
Describe alternatives you've considered
For the datafusion-python project, we can work around via python calls but this would be a far more elegant approach in my opinion.
Additional context
Once we have these exposed, we could expose the function registry, which would get us very close to a FFI SessionContext. That would have impacts on the ballista and datafusion-ray projects.