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) {
ef='/guix/diff/gnu/packages/busybox.scm?id=b114aba2840a878ba64e5f9cd8056636885ba457'>diff</a></td><td class='form'><form class='right' method='get' action='/guix/log/gnu/packages/busybox.scm'>
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<div class='path'>path: <a href='/guix/log/?id=b114aba2840a878ba64e5f9cd8056636885ba457&amp;showmsg=1'>root</a>/<a href='/guix/log/gnu?id=b114aba2840a878ba64e5f9cd8056636885ba457&amp;showmsg=1'>gnu</a>/<a href='/guix/log/gnu/packages?id=b114aba2840a878ba64e5f9cd8056636885ba457&amp;showmsg=1'>packages</a>/<a href='/guix/log/gnu/packages/busybox.scm?id=b114aba2840a878ba64e5f9cd8056636885ba457&amp;showmsg=1'>busybox.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/gnu/packages/busybox.scm?id=b114aba2840a878ba64e5f9cd8056636885ba457'>Collapse</a>)</th><th class='left'>Author</th></tr>
<tr class='logheader'><td><span title='2018-12-12 09:27:17 +0200'>2018-12-12</span></td><td class='logsubject'><a href='/guix/commit/gnu/packages/busybox.scm?id=42140fd434a333d0565617471b51323d6815ee13'>gnu: Add toybox.</a></td><td>Efraim Flashner</td></tr>
<tr class='nohover-highlight'><td/><td colspan='3' class='logmsg'>
* gnu/packages/busybox.com (toybox): New variable.


</td></tr>
<tr class='logheader'><td><span title='2018-09-18 14:18:43 +0200'>2018-09-18</span></td><td class='logsubject'><a href='/guix/commit/gnu/packages/busybox.scm?id=56c180750c8b7aca5ae82d133caac7c398c688b7'>gnu: busybox: Update to 1.29.3.</a></td><td>Tobias Geerinckx-Rice</td></tr>
<tr class='nohover-highlight'><td/><td colspan='3' class='logmsg'>
* gnu/packages/busybox.scm (busybox): Update to 1.29.3.


</td></tr>
<tr class='logheader'><td><span title='2018-07-19 21:29:14 +0300'>2018-07-19</span></td><td class='logsubject'><a href='/guix/commit/gnu/packages/busybox.scm?id=e9ab4b40a8bf6ddf7242bc0d67b61148a4078419'>gnu: busybox: Update to 1.29.1.</a></td><td>Efraim Flashner</td></tr>
<tr class='nohover-highlight'><td/><td colspan='3' class='logmsg'>
* gnu/packages/busybox.scm (busybox): Update to 1.29.1.
[arguments]: Add custom phase to change the default value of TASKSET.


</td></tr>
<tr class='logheader'><td><span title='2018-06-22 22:00:23 +0200'>2018-06-22</span></td><td class='logsubject'><a href='/guix/commit/gnu/packages/busybox.scm?id=f7705d4cb891b262a8b5247ff251dfc409cdeb6a'>gnu: busybox: Return #t from all phases.</a></td><td>Tobias Geerinckx-Rice</td></tr>
<tr class='nohover-highlight'><td/><td colspan='3' class='logmsg'>
* gnu/packages/busybox.scm (busybox)[arguments]: Substitute INVOKE for
SYSTEM*.


</td></tr>
<tr class='logheader'><td><span title='2017-06-21 10:13:39 +0300'>2017-06-21</span></td><td class='logsubject'><a href='/guix/commit/gnu/packages/busybox.scm?id=6d96af5eaade0d873c5e5c1a2cc60df13cd590df'>gnu: busybox: Fix indentation.</a></td><td>Efraim Flashner</td></tr>
<tr class='nohover-highlight'><td/><td colspan='3' class='logmsg'>
* gnu/packages/busybox.scm (busybox)[arguments]: Whitespace changes.


</td></tr>
<tr class='logheader'><td><span title='2017-06-21 10:10:39 +0300'>2017-06-21</span></td><td class='logsubject'><a href='/guix/commit/gnu/packages/busybox.scm?id=5897428f1c6fe4033c5b143e4dddc5040ed6827b'>gnu: busybox: Update to 1.26.2.</a></td><td>Efraim Flashner</td></tr>
<tr class='nohover-highlight'><td/><td colspan='3' class='logmsg'>
* gnu/packages/busybox.scm (busybox): Update to 1.26.2.


</td></tr>
<tr class='logheader'><td><span title='2017-06-20 18:10:35 +0530'>2017-06-20</span></td><td class='logsubject'><a href='/guix/commit/gnu/packages/busybox.scm?id=148585c240f848ad08f6541ede7db3fca3411007'>gnu: Move contents of zip module into compression module.</a></td><td>Arun Isaac</td></tr>
<tr class='nohover-highlight'><td/><td colspan='3' class='logmsg'>
* gnu/packages/zip.scm (zip, unzip, zziplib, perl-zip): Move to...
* gnu/packages/compression.scm: ...here.
* gnu/packages/zip.scm: Delete file.
* gnu/local.mk (GNU_SYSTEM_MODULES): Unregister deleted file.
* po/packages/POTFILES.in: Unregister deleted file.
* gnu/packages/{audio, avr, bioinformatics, busybox, cdrom, ci, compression,
docbook, documentation, fonts, fpga, game-development, games, gl, gnome,
gnuzilla, graphics, guile, haskell, image, java, kodi, ldc, libreoffice,
markup, maths, mc, monitoring, music, php, pretty-print, python, scheme,
smalltalk, statistics, synergy, tex, textutils, video, web-browsers, xml,
zip}.scm, guix/build-system/{ant, font}.scm, guix/{download, packages}.scm:
Adapt module import.


</td></tr>