Cross-output focus focus floating exception

Focusing across outputs with `focus [direction]` should focus an
existing floating con when no tiling con exists on the output in
[direction].

src/tree.c

@@ -582,6 +582,13 @@ static bool _tree_next(Con *con, char way, orientation_t orientation, bool wrap)
             return true;
 
         Con *focus = con_descend_direction(workspace, direction);
+
+        /* special case: if there was no tiling con to focus and the workspace
+         * has a floating con in the focus stack, focus the top of the focus
+         * stack (which may be floating) */
+        if (focus == workspace)
+            focus = con_descend_focused(workspace);
+
         if (focus) {
             con_focus(focus);
             x_set_warp_to(&(focus->rect));

testcases/t/520-regress-focus-direction-floating.t

@@ -0,0 +1,48 @@
+#!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)
+#
+# Ensure that `focus [direction]` will focus an existing floating con when no
+# tiling con exists on the output in [direction] when focusing across outputs
+# Bug still in: 4.7.2-204-g893dbae
+use i3test i3_autostart => 0;
+
+my $config = <<EOT;
+# i3 config file (v4)
+font -misc-fixed-medium-r-normal--13-120-75-75-C-70-iso10646-1
+
+workspace ws_left output fake-0
+workspace ws_right output fake-1
+
+mouse_warping none
+
+fake-outputs 1024x768+0+0,1024x768+1024+0
+EOT
+
+my $pid = launch_with_config($config);
+
+cmd 'workspace ws_left';
+my $win = open_window();
+
+cmd 'floating enable';
+cmd 'focus output right';
+cmd 'focus left';
+
+is($x->input_focus, $win->id,
+    'Focusing across outputs with `focus [direction]` should focus an existing floating con when no tiling con exists on the output in [direction].');
+
+exit_gracefully($pid);
+
+done_testing;