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) {
><td class='form'><form class='right' method='get' action='/guix/log/tests/discovery.scm'>
<input type='hidden' name='id' value='e8da79ab6ff8a725e20863ef5d36ff350d5f2791'/><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=e8da79ab6ff8a725e20863ef5d36ff350d5f2791'>root</a>/<a href='/guix/log/tests?id=e8da79ab6ff8a725e20863ef5d36ff350d5f2791'>tests</a>/<a href='/guix/log/tests/discovery.scm?id=e8da79ab6ff8a725e20863ef5d36ff350d5f2791'>discovery.scm</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/tests/discovery.scm?id=e8da79ab6ff8a725e20863ef5d36ff350d5f2791&amp;showmsg=1'>Expand</a>)</th><th class='left'>Author</th></tr>
<tr><td><span title='2017-07-03 23:51:23 +0200'>2017-07-03</span></td><td><a href='/guix/commit/tests/discovery.scm?id=960c6ce96d746cf19829ad26e092ec5dad2a5c62'>discovery: Recurse into directories pointed to by a symlink.</a><span class='msg-avail'>...<span class='msg-tooltip'>Reported by Christopher Baines &lt;mail@cbaines.net&gt;
and Alex Kost &lt;alezost@gmail.com&gt;
at &lt;https://lists.gnu.org/archive/html/guix-devel/2017-06/msg00290.html&gt;.

* guix/discovery.scm (scheme-files): When ENTRY is a symlink that
doesn't end in '.scm', call 'stat' and recurse if it points to a
directory.
* tests/discovery.scm ("scheme-modules recurses in symlinks to
directories"): New test.
</span></span></td><td>Ludovic Courtès</td></tr>
<tr><td><span title='2017-06-18 00:14:07 +0200'>2017-06-18</span></td><td><a href='/guix/commit/tests/discovery.scm?id=d46c4423f46278bd2f96770ceb0667431414349e'>discovery: 'scheme-files' returns '() for a non-accessible directory.</a><span class='msg-avail'>...<span class='msg-tooltip'>Fixes a regression introduced in
d27cc3bfaafe6b5b0831e88afb1c46311d382a0b.

Reported by Ricardo Wurmus &lt;rekado@elephly.net&gt;.

* guix/discovery.scm (scheme-files): Catch 'scandir*' system errors.
Return '() and optionally raise a warning upon 'system-error'.
* tests/discovery.scm ("scheme-modules, non-existent directory"): New
test.
</span></span></td><td>Ludovic Courtès</td></tr>
<tr><td><span title='2017-05-03 23:50:15 +0200'>2017-05-03</span></td><td><a href='/guix/commit/tests/discovery.scm?id=cd903ef7871170d3c4eced45418459d293ef48a7'>Add (guix discovery).</a><span class='msg-avail'>...<span class='msg-tooltip'>* guix/discovery.scm, tests/discovery.scm: New files.
* gnu/packages.scm (scheme-files, file-name-&gt;module-name)
(scheme-modules, all-package-modules): Remove.
(fold-packages): Rewrite in terms of 'fold-module-public-variables'.
* gnu/tests.scm: Use (guix discovery).
* Makefile.am (MODULES): Add guix/discovery.scm.
(SCM_TESTS): Add tests/discovery.scm.
</span></span></td><td>Ludovic Courtès</td></tr>