How to add variable product info to variations?

During feed setting, you may want your variations products information to come from their variable (parent) product.

There are three Output Type to add variable product info to variations:

parent: Variable product info if the variable value is not empty else variation info.

parent_if_empty: Add variable product info if the variation info is empty.

only_parent: Only add variable product info either its have value or empty.

How to add variable product info to variations?
Get variable product description if variation description is empty.