pack: Singularity environemt sources the profile's 'etc/profile'.

Fixes #419 where the same search path is used multiple times, leading to the
last one overriding the previous one.

The solution relies on the #$profile/etc/profile file that is already verified
and in case of errors, it is just one place to repair instead of repairing at
multiple places, like in singularity-environment-file

* guix/pack.scm (singularity-environment-file): Source #$profile/etc/profile

Reported-by: Alexis Simon <alexis.simon@runbox.com>
Change-Id: Ic304fef99ad34d83e4e10cdd2b26d3b1802b5251
Signed-off-by: Ludovic Courtès <ludo@gnu.org>

guix/scripts/pack.scm

@@ -312,25 +312,12 @@ added to the pack."
   "Return a shell script that defines the environment variables corresponding
 to the search paths of PROFILE."
   (define build
-    (with-extensions (list guile-gcrypt)
-      (with-imported-modules `(((guix config) => ,(make-config.scm))
-                               ,@(source-module-closure
-                                  `((guix profiles)
-                                    (guix search-paths))
-                                  #:select? not-config?))
-        #~(begin
-            (use-modules (guix profiles) (guix search-paths)
-                         (ice-9 match))
+    #~(begin
+        (use-modules (ice-9 match))
 
-            (call-with-output-file #$output
-              (lambda (port)
-                (for-each (match-lambda
-                            ((spec . value)
-                             (format port "~a=~a~%export ~a~%"
-                                     (search-path-specification-variable spec)
-                                     value
-                                     (search-path-specification-variable spec))))
-                          (profile-search-paths #$profile))))))))
+        (call-with-output-file #$output
+          (lambda (port)
+            (format port ". ~a/etc/profile~%" #$profile)))))
 
   (computed-file "singularity-environment.sh" build))