This patch adds a "guix gc" button to the low disk space notification
that 'gsd-housekeeping' emits.

diff --git a/plugins/housekeeping/gsd-disk-space.c b/plugins/housekeeping/gsd-disk-space.c
index bd3437e..89027d8 100644
--- a/plugins/housekeeping/gsd-disk-space.c
+++ b/plugins/housekeeping/gsd-disk-space.c
@@ -546,6 +546,21 @@ empty_trash_callback (NotifyNotification *n,
         notify_notification_close (n, NULL);
 }
 
+static void
+guix_gc_callback (NotifyNotification *n,
+                  const char         *action)
+{
+        const gchar *argv[] = { "guix", "gc", NULL };
+
+        g_assert (action != NULL);
+        g_assert (strcmp (action, "run-guix-gc") == 0);
+
+        g_spawn_async (NULL, (gchar **) argv, NULL, G_SPAWN_SEARCH_PATH,
+                       NULL, NULL, NULL, NULL);
+
+        notify_notification_close (n, NULL);
+}
+
 static void
 on_notification_closed (NotifyNotification *n)
 {
@@ -591,6 +606,13 @@ ldsm_notify (const char *summary,
                                                 g_free);
         }
 
+        notify_notification_add_action (notification,
+                                        "run-guix-gc",
+                                        _("Collect Unused Guix Items"),
+                                        (NotifyActionCallback) guix_gc_callback,
+                                        NULL,
+                                        NULL);
+
         has_trash = ldsm_mount_has_trash (mount_path);
 
         if (has_trash) {
idden' name='id' value='d588cc8fa96e4a4bce56fac2ba3bbaaeaaed0047'/><select name='qt'>
<option value='grep'>log msg</option>
<option value='author'>author</option>
<option value='committer'>committer</option>
<option value='range'>range</option>
</select>
<input class='txt' type='search' size='10' name='q' value=''/>
<input type='submit' value='search'/>
</form>
</td></tr></table>
<div class='path'>path: <a href='/guix/log/?id=d588cc8fa96e4a4bce56fac2ba3bbaaeaaed0047'>root</a>/<a href='/guix/log/TODO?id=d588cc8fa96e4a4bce56fac2ba3bbaaeaaed0047'>TODO</a></div><div class='content'><table class='list nowrap'><tr class='nohover'><th class='left'>Age</th><th class='left'>Commit message (<a href='/guix/log/TODO?id=d588cc8fa96e4a4bce56fac2ba3bbaaeaaed0047&amp;showmsg=1'>Expand</a>)</th><th class='left'>Author</th></tr>
<tr><td><span title='2019-01-21 09:59:41 +0100'>2019-01-21</span></td><td><a href='/guix/commit/TODO?id=b93d2602f72dbbd9334a4f5c75b8721e1f2fa35a'>Update 'TODO'</a><span class='msg-avail'>...<span class='msg-tooltip'>* TODO (Installer): Add Pierre Neidhardt suggestions described here:
  https://lists.gnu.org/archive/html/guix-devel/2019-01/msg00305.html
</span></span></td><td>Mathieu Othacehe</td></tr>
<tr><td><span title='2019-01-17 14:11:15 +0100'>2019-01-17</span></td><td><a href='/guix/commit/TODO?id=11b68c90cd89288906c595d5c31a0413ed8a496f'>Update 'TODO'.</a><span class='msg-avail'>...<span class='msg-tooltip'>* TODO (Installer): New section.
</span></span></td><td>Mathieu Othacehe</td></tr>