Is your feature request related to a problem or challenge?

It seems the design of Arrow extension types is nearing consensus and will arrive soon

• Add ExtensionType trait and CanonicalExtensionType enum arrow-rs#5822
• Related to Extension Types / User Defined Types #12644

The extension type information is encoded in an Arrow Field (doclink link) (which has both a DataType and the metadata information)

In this world, supporting a user function for a user defined type (e.g. a geometry type) I think would look like

1. Creating a user defined function and declaring in the signature that it takes DataType::Binary
2. Implementing the return_type_from_args function which would then try to get the user defined type information from the Binary column and verify it was correct

However, since the ReturnTypeInfo only provides DataType the the Field information will not be present and thus UDF writers will not be able to access extension type information

Describe the solution you'd like

Since we have not released return_type_from_args yet (it will be released in DataFusion 45) I would like to try and change the API before release to support user defined types

Describe alternatives you've considered

Specifically, I would like to pass in Field instead of DataType in ReturnTypeArgs

So instead of

pub struct ReturnTypeArgs<'a> {
    /// The data types of the arguments to the function
    pub arg_types: &'a [DataType],
    /// ...
    pub scalar_arguments: &'a [Option<&'a ScalarValue>],
    /// Can argument `i` (ever) null?
    pub nullables: &'a [bool],
}

I think it would be better to be

pub struct ReturnTypeArgs<'a> {
    /// The schema fields of the arguments. Fields include DataType, nullability and other information.
    pub arg_fields: &'a [Field],
    /// ...
    pub scalar_arguments: &'a [Option<&'a ScalarValue>],
}

Additional context

This was inspired by a comment from @milenkovicm on the DataFusion sync up call yesterday