Allow the tree parameter and the xpath parameter to be used together in the REST API.

Previously, the presence of the xpath parameter suppressed the tree
parameter processing. This change fixes that so that the tree parameter
can be used for building small DOM, then XPath to manipulate the data
further.

core/src/main/java/hudson/model/Api.java

@@ -35,6 +35,7 @@ import org.kohsuke.stapler.QueryParameter;
 import org.kohsuke.stapler.StaplerRequest;
 import org.kohsuke.stapler.StaplerResponse;
 import org.kohsuke.stapler.export.*;
+import org.kohsuke.stapler.export.TreePruner.ByDepth;
 
 import javax.servlet.ServletException;
 import javax.servlet.http.HttpServletResponse;
@@ -79,6 +80,7 @@ public class Api extends AbstractModelObject {
     public void doXml(StaplerRequest req, StaplerResponse rsp,
                       @QueryParameter String xpath,
                       @QueryParameter String wrapper,
+                      @QueryParameter String tree,
                       @QueryParameter int depth) throws IOException, ServletException {
         String[] excludes = req.getParameterValues("exclude");
 
@@ -92,7 +94,8 @@ public class Api extends AbstractModelObject {
 
         // first write to String
         Model p = MODEL_BUILDER.get(bean.getClass());
-        p.writeTo(bean,depth,Flavor.XML.createDataWriter(bean,sw));
+        TreePruner pruner = (tree!=null) ? new NamedPathPruner(tree) : new ByDepth(1 - depth);
+        p.writeTo(bean,pruner,Flavor.XML.createDataWriter(bean,sw));
 
         // apply XPath
         Object result;