build/python-build-system: Fix easy-install.pth collisions.

* guix/build/python-build-system.scm (rename-pth-file): New rename-pth-file
  phase and corresponding function.

guix/build/python-build-system.scm

@@ -105,9 +105,26 @@ (define bindirs
                             files)))
               bindirs)))
 
+(define* (rename-pth-file #:key name inputs outputs #:allow-other-keys)
+  "Rename easy-install.pth to NAME.pth to avoid conflicts between packages
+installed with setuptools."
+  (let* ((out (assoc-ref outputs "out"))
+         (python (assoc-ref inputs "python"))
+         (site-packages (string-append out "/lib/python"
+                                       (get-python-version python)
+                                       "/site-packages"))
+         (easy-install-pth (string-append site-packages "/easy-install.pth"))
+         (new-pth (string-append site-packages "/" name ".pth")))
+    (when (file-exists? easy-install-pth)
+      (rename-file easy-install-pth new-pth))
+    #t))
+
 (define %standard-phases
   ;; 'configure' and 'build' phases are not needed.  Everything is done during
   ;; 'install'.
+  (alist-cons-before
+   'strip 'rename-pth-file
+   rename-pth-file
    (alist-cons-after
     'install 'wrap
     wrap
@@ -117,7 +134,7 @@ (define %standard-phases
       'check check
       (alist-replace 'install install
                      (alist-delete 'configure
-                                               gnu:%standard-phases))))))
+                                   gnu:%standard-phases)))))))
 
 (define* (python-build #:key inputs (phases %standard-phases)
                        #:allow-other-keys #:rest args)