(native-inputs `(
         ("foobar"
          ,(origin
             (method git-fetch)
             (uri (git-reference
                   (url "https://foo/bar")
                   (commit (string-append "v" version))))
             (file-name (git-file-name "foo" version))
             (sha256
              (base32 "0i7gh99w4mi0hdv16261jcdiqyv1nkjdcwy9prw32s0lvplx8fdy")))))

then in a phase:

  (copy-recursively (assoc-ref native-inputs "foobar") target)

  (if it's from git)