This breezy backstager is memorable for its Burton Lane-Ira Gershwin score and for the once-in-a-lifetime collaboration of three legendary musical-world directors: Stanley Donen (Singin’ in the Rain) behind the camera and Gower Champion and Bob Fosse (future directors of, respectively, Broadway’s Hello, Dolly and Chicago) bringing dazzling dance grace and physicality to the other side of the lens.