gnu: hplip: Actually wrap binaries.

* gnu/packages/cups.scm (hplip)[arguments]: Reduce indentation.
Replace ‘wrap-binaries’ phase with a custom implementation.

gnu/packages/cups.scm

@@ -491,7 +491,8 @@ (define-public hplip
                   (guix build utils)
                   ((guix build python-build-system) #:prefix python:))
 
-       #:phases (modify-phases %standard-phases
+       #:phases
+       (modify-phases %standard-phases
          (add-after 'unpack 'fix-hard-coded-file-names
            (lambda* (#:key inputs outputs #:allow-other-keys)
              (let ((out (assoc-ref outputs "out"))
@@ -535,10 +536,38 @@ (define-public hplip
                                  "/lib/systemd/system"))
                  (("/etc/sane.d")
                   (string-append out "/etc/sane.d"))))))
-
-                  ;; Wrap bin/* so that the Python libraries are found.
          (add-after 'install 'wrap-binaries
-                    (assoc-ref python:%standard-phases 'wrap)))))
+           ;; Scripts in /bin are all symlinks to .py files in /share/hplip.
+           ;; Symlinks are immune to the Python build system's 'WRAP phase,
+           ;; and the .py files can't be wrapped because they are reused as
+           ;; modules.  Replacing the symlinks in /bin with copies and
+           ;; wrapping them also doesn't work (“ModuleNotFoundError:
+           ;; No module named 'base'”).  Behold: a custom WRAP-PROGRAM.
+           (lambda* (#:key inputs outputs #:allow-other-keys)
+             (let* ((out (assoc-ref outputs "out"))
+                    (bin (string-append out "/bin"))
+                    (python (assoc-ref inputs "python")))
+               (with-directory-excursion bin
+                 (for-each (lambda (file)
+                             (let ((target (readlink file)))
+                               (delete-file file)
+                               (with-output-to-file file
+                                 (lambda _
+                                   (format #t
+                                           "#!~a~@
+                                           export PYTHONPATH=\"~a:~a\"~@
+                                           exec -a \"$0\" \"~a/~a\" \"$@\"~%"
+                                           (which "bash")
+                                           (string-append
+                                            out "/lib/python"
+                                            (python:python-version python)
+                                            "/site-packages")
+                                           (getenv "PYTHONPATH")
+                                           bin target)))
+                               (chmod file #o755)))
+                  (find-files "." (lambda (file stat)
+                                    (eq? 'symlink (stat:type stat)))))
+                 #t)))))))
 
     ;; Note that the error messages printed by the tools in the case of
     ;; missing dependencies are often downright misleading.