Bugfix: Don’t attach tiling containers to floating containers

This bug happened when there were only floating containers on a workspace and a
new tiling window was to be opened.

testcases/t/38-floating-attach.t

@@ -0,0 +1,63 @@
+#!perl
+# vim:ts=4:sw=4:expandtab
+# Regression test: New windows were attached to the container of a floating window
+# if only a floating window is present on the workspace.
+
+use i3test tests => 7;
+use X11::XCB qw(:all);
+use Time::HiRes qw(sleep);
+
+BEGIN {
+    use_ok('X11::XCB::Window');
+}
+
+my $i3 = i3("/tmp/nestedcons");
+
+my $tmp = get_unused_workspace();
+$i3->command("workspace $tmp")->recv;
+
+#############################################################################
+# 1: open a floating window, get it mapped
+#############################################################################
+
+my $x = X11::XCB::Connection->new;
+
+# Create a floating window
+my $window = $x->root->create_child(
+    class => WINDOW_CLASS_INPUT_OUTPUT,
+    rect => [ 0, 0, 30, 30],
+    background_color => '#C0C0C0',
+    # replace the type with 'utility' as soon as the coercion works again in X11::XCB
+    window_type => $x->atom(name => '_NET_WM_WINDOW_TYPE_UTILITY'),
+);
+
+isa_ok($window, 'X11::XCB::Window');
+
+$window->map;
+
+sleep 0.25;
+
+ok($window->mapped, 'Window is mapped');
+
+my $ws = get_ws($tmp);
+my ($nodes, $focus) = get_ws_content($tmp);
+
+is(@{$ws->{floating_nodes}}, 1, 'one floating node');
+is(@{$nodes}, 0, 'no tiling nodes');
+
+# Create a tiling window
+my $twindow = $x->root->create_child(
+    class => WINDOW_CLASS_INPUT_OUTPUT,
+    rect => [ 0, 0, 30, 30],
+    background_color => '#C0C0C0',
+);
+
+isa_ok($twindow, 'X11::XCB::Window');
+
+$twindow->map;
+
+sleep 0.25;
+
+($nodes, $focus) = get_ws_content($tmp);
+
+is(@{$nodes}, 1, 'one tiling node');