bug#20765: Python .egg files must not be compressed

[Ludovic Courtès]

The other day on IRC Ricardo and 宋文武 noted that python-pillow
currently comes with a compressed egg.  Because it is compressed, the
daemon’s conservative scanning fails to see what store items it refers
to; in particular Ricardo noted that on his machine, python-pillow
refers to a non-existent store item for OpenJPEG.

To fix that, python-build-system must be tweaked to ask for uncompressed
eggs.  I tried the attached patch, which uses the ‘--always-unzip’
option of easyinstall.

Unfortunately, that option is unsupported by some setup.py, such as that
of setuptools itself.

What would be the right way to do that?

TIA.  :-)

Ludo’.

--- a/guix/build/python-build-system.scm
+++ b/guix/build/python-build-system.scm
@@ -60,14 +60,20 @@
                   #:allow-other-keys)
   "Install a given Python package."
   (let* ((out (assoc-ref outputs "out"))
-         (params (append (list (string-append "--prefix=" out))
+         (params (cons* (string-append "--prefix=" out)
+
+                        ;; Make sure the .egg files are kept unzipped,
+                        ;; otherwise the daemon's conservative scanning may
+                        ;; not find store references embedded in it.
+                        "--always-unzip"
+
                         configure-flags))
          (python-version (get-python-version (assoc-ref inputs "python")))
          (old-path (getenv "PYTHONPATH"))
          (add-path (string-append out "/lib/python" python-version
                                   "/site-packages/")))
-        ;; create the module installation directory and add it to PYTHONPATH
-        ;; to make setuptools happy
+    ;; Create the module installation directory and add it to PYTHONPATH
+    ;; to make setuptools happy.
     (mkdir-p add-path)
     (setenv "PYTHONPATH"
             (string-append (if old-path