Set EWMH desktop properties on startup.

Calls ewmh_update_current_desktop on startup to set the
_NET_CURRENT_DESKTOP property. Without this change the property only
gets set after the workspaces have been manipulated. Also exclude
hidden workspaces (i.e. those starting with "__" from the workspace
index.

Adds tests for startup and workspace switching.

src/ewmh.c

@@ -27,6 +27,9 @@ void ewmh_update_current_desktop(void) {
     TAILQ_FOREACH(output, &(croot->nodes_head), nodes) {
         Con *ws;
         TAILQ_FOREACH(ws, &(output_get_content(output)->nodes_head), nodes) {
+            if (STARTS_WITH(ws->name, "__"))
+                continue;
+
             if (ws == focused_ws) {
                 xcb_change_property(conn, XCB_PROP_MODE_REPLACE, root,
                         A__NET_CURRENT_DESKTOP, XCB_ATOM_CARDINAL, 32, 1, &idx);

src/main.c

@@ -761,6 +761,9 @@ int main(int argc, char *argv[]) {
     x_set_i3_atoms();
     ewmh_update_workarea();
 
+    /* Set the _NET_CURRENT_DESKTOP property. */
+    ewmh_update_current_desktop();
+
     struct ev_io *xcb_watcher = scalloc(sizeof(struct ev_io));
     struct ev_io *xkb = scalloc(sizeof(struct ev_io));
     xcb_check = scalloc(sizeof(struct ev_check));

testcases/t/217-NET_CURRENT_DESKTOP.t

@@ -0,0 +1,75 @@
+#!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)
+#
+# Verifies the _NET_CURRENT_DESKTOP property correctly tracks the currently
+# active workspace. Specifically checks that the property is 0 on startup with
+# an empty config, tracks changes when switching workspaces and when
+# workspaces are created and deleted.
+#
+# The property not being set on startup was last present in commit
+# 6578976b6159437c16187cf8d1ea38aa9fec9fc8.
+
+use i3test i3_autostart => 0;
+use X11::XCB qw(PROP_MODE_REPLACE);
+
+my $config = <<EOT;
+# i3 config file (v4)
+font font -misc-fixed-medium-r-normal--13-120-75-75-C-70-iso10646-1
+EOT
+
+my $root = $x->get_root_window;
+# Manually intern _NET_CURRENT_DESKTOP as $x->atom will not create atoms if
+# they are not yet interned.
+my $atom_cookie = $x->intern_atom(0, length("_NET_CURRENT_DESKTOP"), "_NET_CURRENT_DESKTOP");
+my $_NET_CURRENT_DESKTOP = $x->intern_atom_reply($atom_cookie->{sequence})->{atom};
+my $CARDINAL = $x->atom(name => 'CARDINAL')->id;
+
+$x->delete_property($root, $_NET_CURRENT_DESKTOP);
+
+$x->flush();
+
+sub current_desktop_index {
+    # Returns the _NET_CURRENT_DESKTOP property from the root window. This is
+    # the 0 based index of the current desktop.
+
+    my $cookie = $x->get_property(0, $root, $_NET_CURRENT_DESKTOP,
+                                  $CARDINAL, 0, 1);
+    my $reply = $x->get_property_reply($cookie->{sequence});
+
+    return undef if $reply->{value_len} != 1;
+    return undef if $reply->{format} != 32;
+    return undef if $reply->{type} != $CARDINAL;
+
+    return unpack 'L', $reply->{value};
+}
+
+my $pid = launch_with_config($config);
+
+is(current_desktop_index, 0, "Starting on desktop 0");
+cmd 'workspace 1';
+is(current_desktop_index, 0, "Change from empty to empty");
+open_window;
+cmd 'workspace 0';
+is(current_desktop_index, 0, "Open on 1 and view 0");
+open_window;
+cmd 'workspace 1';
+is(current_desktop_index, 1, "Open on 0 and view 1");
+cmd 'workspace 2';
+is(current_desktop_index, 2, "Open and view empty");
+
+exit_gracefully($pid);
+
+done_testing;