guix gc: Add '--derivers'.

* guix/scripts/gc.scm (show-help, %options): Add '--derivers'.
(guix-gc): Handle 'list-derivers'.
* tests/guix-gc.sh: Add test.
* doc/guix.texi (Invoking guix gc): Document it.

1 files changed, 4 insertions, 1 deletions

diff --git a/tests/guix-gc.sh b/tests/guix-gc.sh
index efbc7e759cc..ef2d9543b72 100644
--- a/tests/guix-gc.sh
+++ b/tests/guix-gc.sh
@@ -1,5 +1,5 @@
 # GNU Guix --- Functional package management for GNU
-# Copyright © 2013, 2015, 2017 Ludovic Courtès <ludo@gnu.org>
+# Copyright © 2013, 2015, 2017, 2018 Ludovic Courtès <ludo@gnu.org>
 #
 # This file is part of GNU Guix.
 #
@@ -54,6 +54,9 @@ guix gc --references "$out/bin/guile"
 if guix gc --references /dev/null;
 then false; else true; fi
 
+# Check derivers.
+guix gc --derivers "$out" | grep "$drv"
+
 # Add then reclaim a .drv file.
 drv="`guix build idutils -d`"
 test -f "$drv"