==================
from dockerfile command
==================

foo:
  FROM DOCKERFILE ./

---

    (source_file
      (target
        name: (identifier)
        (block
          (from_dockerfile_command
            context: (string
              (unquoted_string))))))


==================
from dockerfile with targets
==================

foo:
  FROM DOCKERFILE -f +sometarget/Dockerfile +someothertarget/*


---

    (source_file
      (target
        (identifier)
        (block
          (from_dockerfile_command
            (options
              (docker_file
                (target_artifact
                  (target_ref
                    (identifier))
                  (unquoted_string))))
            (target_artifact
              (target_ref
                (identifier))
              (unquoted_string))))))

==================
from dockerfile command with options
==================

foo:
  FROM DOCKERFILE \
    -f Dockerfile.backend \
    --build-arg version=1.2.3 \
    --target prod \
    ./

---

    (source_file
      (target
        name: (identifier)
        (block
          (from_dockerfile_command
            (line_continuation)
            options: (options
              (docker_file
                value: (string
                  (unquoted_string)))
              (line_continuation)
              (docker_build_arg
                key: (identifier)
                value: (string
                  (unquoted_string)))
              (line_continuation)
              (docker_target
                value: (identifier)))
            (line_continuation)
            context: (string
              (unquoted_string))))))
