Adding an absolute path to an OpenAPI YAML file

I'm trying to put the getBaseDir function from PHP in my OpenAPI YAML file to get the absolute path, but I don't know how to do it.

   responses:
     '200':
       description: successful Operation
       content:
         application/json:
           schema:
             $ref: 'var/www/docroot/www/app/code/local/Project/Myproject/OpenAPI/components/schemas/test.yaml'