store: Change 'export-paths' to always export in topological order.

* guix/store.scm (export-paths): Pass PATHS through
  'topologically-sorted' before iterating.
* tests/store.scm ("export/import paths, ensure topological order"): New
  test.

1 files changed, 3 insertions, 3 deletions

diff --git a/guix/store.scm b/guix/store.scm
index eca0de7d97..b9b9d9e55a 100644
--- a/guix/store.scm
+++ b/guix/store.scm
@@ -732,10 +732,10 @@ is raised if the set of paths read from PORT is not signed (as per
     (= 1 (read-int s))))
 
 (define* (export-paths server paths port #:key (sign? #t))
-  "Export the store paths listed in PATHS to PORT, signing them if SIGN?
-is true."
+  "Export the store paths listed in PATHS to PORT, in topological order,
+signing them if SIGN? is true."
   (let ((s (nix-server-socket server)))
-    (let loop ((paths paths))
+    (let loop ((paths (topologically-sorted server paths)))
       (match paths
         (()
          (write-int 0 port))