Move container to marked workspace: refine corner case

This commit should fix "move con to parent" trick (see below) in the
case when con->parent->parent is a workspace.

The trick:

    mark _a, focus parent, focus parent, mark _b,
    [con_mark=_a] move window to mark _b, [con_mark=_a] focus

The trick got broken in commit 626af81232
in order to fix an i3 crash (#2003).  Reverting said commit fixes the
trick.  The crash is caused by the fact that empty workspace isn't
considered a split (checked in src/con.c:1324), so the moved window ends
up as a sibling of the target workspace, not as its child.

src/con.c

@@ -1312,8 +1312,8 @@ bool con_move_to_mark(Con *con, const char *mark) {
         return true;
     }
 
-    if (target->type == CT_WORKSPACE) {
+    if (target->type == CT_WORKSPACE && con_is_leaf(target)) {
-        DLOG("target container is a workspace, simply moving the container there.\n");
+        DLOG("target container is an empty workspace, simply moving the container there.\n");
         con_move_to_workspace(con, target, true, false, false);
         return true;
     }

testcases/lib/i3test.pm.in

@@ -1230,7 +1230,7 @@ sub create_layout {
 
             $r = $r . '{"swallows": [{';
             $r = $r . '"class": "^' . "$char" . '$"';
-            $r = $r . '}]},';
+            $r = $r . '}]}' . ($depth == 0 ? "\n" : ',');
         } else {
             die "Could not understand $char";
         }

testcases/t/243-move-to-mark.t

@@ -361,6 +361,7 @@ does_i3_live;
 ###############################################################################
 # Given 'S' and 'M' where 'M' is a workspace and 'S' is on a different
 # workspace, then 'S' ends up as a tiling container on 'M'.
+# See issue: #2003
 ###############################################################################
 
 fresh_workspace;

testcases/t/306-move-to-parent.t

@@ -0,0 +1,37 @@
+#!perl
+# vim:ts=4:sw=4:expandtab
+#
+# Please read the following documents before working on tests:
+# • https://build.i3wm.org/docs/testsuite.html
+#   (or docs/testsuite)
+#
+# • https://build.i3wm.org/docs/lib-i3test.html
+#   (alternatively: perldoc ./testcases/lib/i3test.pm)
+#
+# • https://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)
+#
+# Make sure the trick used to move the container to its parent works.
+# https://github.com/i3/i3/issues/1326#issuecomment-349082811
+use i3test;
+
+cmp_tree(
+    msg => 'Move to parent when the parent is a workspace',
+    layout_before => 'a H[b*] c',
+    layout_after => 'a b* c',
+    cb => sub {
+        cmd 'mark _a, focus parent, focus parent, mark _b, [con_mark=_a] move window to mark _b, [con_mark=_a] focus';
+    });
+
+cmp_tree(
+    msg => 'Move to parent when the parent is a split',
+    layout_before => 'V[a H[b*] c]',
+    layout_after => 'V[a b* c]',
+    cb => sub {
+        cmd 'mark _a, focus parent, focus parent, mark _b, [con_mark=_a] move window to mark _b, [con_mark=_a] focus';
+    });
+
+done_testing;