Optimize redundant calls to UDFs producing `StructArray`

[liningpan]

Is your feature request related to a problem or challenge?

Since UDF can only return a single column as output, returning a StructArray is desired in many cases. However, accessing fields of the returned struct results in redundant calls to the UDF.

SELECT
    example_struct(c)['a'],
    example_struct(c)['b']
FROM (SELECT unnest(range(1,100)) as c)

Datafusion produces the following projection step for the query, resulting in calling the UDF with the same column twice.

ProjectionExec: expr=[get_field(example_struct(c@0), a) as example_struct(c)[a], get_field(example_struct(c@0), b) as example_struct(c)[b]]

Note that calling the UDF in a CTE or view does not change the execution plan.

Here is a minimal example https://github.com/liningpan/udf-get-field-optimization.

Describe the solution you'd like

@adriangb mentioned that CSE (Common Sub-expression Elimination) optimizer might be able to handle this.

Describe alternatives you've considered

No response

Additional context

No response

[tohuya6]

take