Implement the window::fullscreen_mode event

The fullscreen_mode event is a window with the "change" property set to
"fullscreen_mode". This event should be emitted whenever a window enters
or exits fullscreen mode.

This event can be used to turn off dpms off when a window is fullscreen
or display the fullscreen container name in the status line for
instance.

docs/ipc

@@ -634,7 +634,7 @@ mode (2)::
 window (3)::
 	Sent when a client's window is successfully reparented (that is when i3
 	has finished fitting it into a container), when a window received input
-	focus or when a window title has been updated.
+	focus or when certain properties of the window have changed.
 barconfig_update (4)::
     Sent when the hidden_state or mode field in the barconfig of any bar
     instance was updated and when the config is reloaded.
@@ -714,8 +714,12 @@ mode is simply named default.
 === window event
 
 This event consists of a single serialized map containing a property
-+change (string)+ which indicates the type of the change ("focus", "new",
++change (string)+ which indicates the type of the change
-"title").
+
+* +new+ - the window has become managed by i3
+* +focus+ - the window has received input focus
+* +title+ - the window's title has changed
+* +fullscreen_mode+ - the window has entered or exited fullscreen mode
 
 Additionally a +container (object)+ field will be present, which consists
 of the window's parent container. Be aware that for the "new" event, the

src/con.c

@@ -609,6 +609,9 @@ void con_toggle_fullscreen(Con *con, int fullscreen_mode) {
 
     DLOG("mode now: %d\n", con->fullscreen_mode);
 
+    /* Send an ipc window "fullscreen_mode" event */
+    ipc_send_window_event("fullscreen_mode", con);
+
     /* update _NET_WM_STATE if this container has a window */
     /* TODO: when a window is assigned to a container which is already
      * fullscreened, this state needs to be pushed to the client, too */

testcases/t/225-ipc-window-fullscreen.t

@@ -0,0 +1,59 @@
+#!perl
+# vim:ts=4:sw=4:expandtab
+#
+# Please read the following documents before working on tests:
+# • http://build.i3wm.org/docs/testsuite.html
+#   (or docs/testsuite)
+#
+# • http://build.i3wm.org/docs/lib-i3test.html
+#   (alternatively: perldoc ./testcases/lib/i3test.pm)
+#
+# • http://build.i3wm.org/docs/ipc.html
+#   (or docs/ipc)
+#
+# • http://onyxneon.com/books/modern_perl/modern_perl_a4.pdf
+#   (unless you are already familiar with Perl)
+#
+# Tests that the ipc window::fullscreen_mode event works properly
+#
+# Bug still in: 4.7.2-135-g7deb23c
+use i3test;
+
+my $i3 = i3(get_socket_path());
+$i3->connect()->recv;
+
+my $cv;
+my $t;
+
+sub reset_test {
+    $cv = AE::cv;
+    $t = AE::timer(0.5, 0, sub { $cv->send(0); });
+}
+
+reset_test;
+
+$i3->subscribe({
+        window => sub {
+            my ($e) = @_;
+            if ($e->{change} eq 'fullscreen_mode') {
+                $cv->send($e->{container});
+            }
+        },
+    })->recv;
+
+my $window = open_window;
+
+cmd 'fullscreen';
+my $con = $cv->recv;
+
+ok($con, 'got fullscreen window event (on)');
+is($con->{fullscreen_mode}, 1, 'window is fullscreen');
+
+reset_test;
+cmd 'fullscreen';
+$con = $cv->recv;
+
+ok($con, 'got fullscreen window event (off)');
+is($con->{fullscreen_mode}, 0, 'window is not fullscreen');
+
+done_testing;