Guix package for simple script with "literal" source provided as `(plain-file ...)`

manifest.scm

(use-modules
  (gnu packages python)
  (guix build-system copy)
  (guix channels)
  (guix download)
  (guix inferior)
  (guix gexp)
  ((guix licenses) #:select (wtfpl2 license-uri))
  (guix packages)
  (guix profiles)
  (srfi srfi-1))

(define license
  (package
    (name "license")
    (version "0")
    (source (program-file
              "license.scm"
              (with-imported-modules
                '((ice-9 popen)
                  (ice-9 format)
                  (ice-9 textual-ports)
                  (srfi srfi-19))
                #~(begin
                    (use-modules
                      (ice-9 popen)
                      (ice-9 format)
                      (ice-9 textual-ports)
                      (srfi srfi-19))  ; date/time

                    (define (license)
                      (copy-file "/usr/src/COPYING.WTFPL" "LICENSE"))

                    (define (copying)
                      (with-output-to-file "COPYING"
                        (lambda ()
                          (format #t "\
Copyright © ~a ~a ~a

This work is free. You can redistribute it and/or modify it under the
terms of the Do What The Fuck You Want To Public License, Version 2,
as published by Sam Hocevar. See the LICENSE file for more details.
"
                            (date-year (current-date))
                            (string-trim-both (get-string-all (open-input-pipe "git config user.name")))
                            (string-trim-both (get-string-all (open-input-pipe "git config user.email")))))))

                    (define (main _)
                      (license)
                      (copying))))))
    (build-system copy-build-system) ; gnu-build-system?
    (arguments
      `(#:install-plan
        `(("license.scm" "bin/")
          #~`((string-append #$(this-package-input "wtfpl") "/copying") "/usr/src/COPYING.WTFPL"))
        #:phases
        (modify-phases %standard-phases
          ; (replace 'install
          ;   (lambda* (#:key inputs outputs #:allow-other-keys)
          ;     (let ((wtfpl (assoc-ref inputs "wtfpl"))
          ;           (out (assoc-ref outputs "out")))
          ;       (mkdir-p (string-append out "/usr/src"))
          ;       (copy-file (string-append wtfpl "/copying")
          ;                  (string-append out "/usr/src/COPYING.WTFPL")))))
          (add-after 'install 'make-script-executable
            (lambda* (#:key outputs #:allow-other-keys)
              (let ((out (assoc-ref outputs "out")))
                (chmod (string-append out "/bin/license.scm") #o755)))))))
    (inputs
      `(
        ; `("guile" ,guile)))
        ("wtfpl" ,(origin
                    (method url-fetch)
                    (uri (string-append (license-uri wtfpl2) "/txt/copying"))
                    (sha256
                      (base32 "1r93nakq692clnh97mns4x7f8zv2zrf5c0ga8hfxr471j61jamh3"))))))
    (synopsis "Produces LICENSE and COPYING files under working directory")
    (description #f)
    (license wtfpl2)
    (home-page #f)))