Function data_types 

pub fn data_types(
    function_name: impl AsRef<str>,
    current_types: &[DataType],
    signature: &Signature,
) -> Result<Vec<DataType>>

Performs type coercion for function arguments.

Returns the data types to which each argument must be coerced to match signature.

For more details on coercion in general, please see the type_coercion module.