Use the incoming node's parent if outgoing has already been removed

Fixes #2212

This won't work for all scenarios - when an element is removed it is de-parented, and so if the order of calls had lead to both elements already being detached, there won't be a parent to re-attach to.

Author: jhy

CHANGES.md

@@ -15,6 +15,8 @@
 * In the `TreeBuilder`, the `onNodeInserted()` and `onNodeClosed()` events are now also fired for the outermost /
   root `Document` node. This enables source position tracking on the Document node (which was previously unset). And
   it also enables the node traversor to see the outer Document node. [2182](https://github.com/jhy/jsoup/pull/2182)
+* Selected Elements can now be position swapped inline using
+  `Elements#set()`. [2212](https://github.com/jhy/jsoup/issues/2212)
 
 ### Bug Fixes
 

src/main/java/org/jsoup/nodes/Node.java

@@ -509,6 +509,7 @@ void nodelistChanged() {
      */
     public void replaceWith(Node in) {
         Validate.notNull(in);
+        if (parentNode == null) parentNode = in.parentNode; // allows old to have been temp removed before replacing
         Validate.notNull(parentNode);
         parentNode.replaceChild(this, in);
     }

src/test/java/org/jsoup/nodes/NodeTest.java

@@ -176,11 +176,8 @@ public void handlesAbsOnProtocolessAbsoluteUris() {
         assertEquals("One <em>foo</em> three", p.html());
     }
 
-    /**
-     * test case for
-     * <a href="https://github.com/jhy/jsoup/issues/2212">Issue #2212</a>
-     */
     @Test public void testReplaceTwice() {
+        // https://github.com/jhy/jsoup/issues/2212
         Document doc = Jsoup.parse("<p><span>Child One</span><span>Child Two</span><span>Child Three</span><span>Child Four</span></p>");
         Elements children = doc.select("p").first().children();
         // first swap 0 and 1