Function cast_struct_column 

fn cast_struct_column(
    source_col: &ArrayRef,
    target_fields: &[Arc<Field>],
    cast_options: &CastOptions<'_>,
) -> Result<ArrayRef>

Cast a struct column to match target struct fields, handling nested structs recursively.

This function implements struct-to-struct casting with the assumption that structs should always be allowed to cast to other structs. However, the source column must already be a struct type - non-struct sources will result in an error.

Field Matching Strategy

• By Name: Source struct fields are matched to target fields by name (case-sensitive)
• Type Adaptation: When a matching field is found, it is recursively cast to the target field’s type
• Missing Fields: Target fields not present in the source are filled with null values
• Extra Fields: Source fields not present in the target are ignored

Nested Struct Handling

• Nested structs are handled recursively using the same casting rules
• Each level of nesting follows the same field matching and null-filling strategy
• This allows for complex struct transformations while maintaining data integrity

Arguments

• source_col - The source array to cast (must be a struct array)
• target_fields - The target struct field definitions to cast to

Returns

A Result<ArrayRef> containing the cast struct array

Errors

Returns a DataFusionError::Plan if the source column is not a struct type