guix package: Register non-default profiles as GC roots.

* guix/scripts/package.scm (maybe-register-gc-root): New procedure.
* tests/guix-package.sh (profile): Grep the output of "guix gc
  --list-live" in a couple of places.

guix/scripts/package.scm

@@ -723,6 +723,11 @@ (define (options->removable options manifest)
                (_ #f))
               options))
 
+(define (maybe-register-gc-root store profile)
+  "Register PROFILE as a GC root, unless it doesn't need it."
+  (unless (string=? profile %current-profile)
+    (add-indirect-root store (canonicalize-path profile))))
+
 
 ;;;
 ;;; Entry point.
@@ -915,6 +920,7 @@ (define (delete-generation number)
                               (let ((count (length entries)))
                                 (switch-symlinks name prof)
                                 (switch-symlinks profile name)
+                                (maybe-register-gc-root (%store) profile)
                                 (format #t (N_ "~a package in profile~%"
                                                "~a packages in profile~%"
                                                count)

tests/guix-package.sh

@@ -41,6 +41,9 @@ guix package --bootstrap -p "$profile" -i guile-bootstrap
 test -L "$profile" && test -L "$profile-1-link"
 test -f "$profile/bin/guile"
 
+# Make sure the profile is a GC root.
+guix gc --list-live | grep "`readlink "$profile-1-link"`"
+
 # Installing the same package a second time does nothing.
 guix package --bootstrap -p "$profile" -i guile-bootstrap
 test -L "$profile" && test -L "$profile-1-link"
@@ -209,6 +212,10 @@ fi
 default_profile="`readlink "$HOME/.guix-profile"`"
 for i in `seq 1 3`
 do
+    # Make sure the current generation is a GC root.
+    profile_link="`readlink "$default_profile"`"
+    guix gc --list-live | grep "`readlink "$profile_link"`"
+
     guix package --bootstrap --roll-back
     ! test -f "$HOME/.guix-profile/bin"
     ! test -f "$HOME/.guix-profile/lib"