New makeChildrenAppender function and Node factory refactoring

The makeChildAppender function is used for adding a node of a
type with maxOccurs=1. For adding nodes of a type with
maxOccurs>1, the new makeChildrenAppender function was added.

With this new function, it turned out that more convenience for
creating node factories is required. The makeChildNodeFactory
function was renamed to makeSimpleNodeFactory, and it now can
create node factories where not only the namespace, but also the
node name can be fixed.

src/ol/xml.js

@@ -11,7 +11,7 @@ goog.require('goog.userAgent');
 
 
 /**
- * @typedef {{node:Node, context}}
+ * @typedef {{node:Node}}
  */
 ol.xml.NodeStackItem;
 
@@ -358,6 +358,9 @@ ol.xml.makeParsersNS = function(namespaceURIs, parsers, opt_parsersNS) {
 
 
 /**
+ * Creates a serializer that appends its `nodeWriter`'s to its designated
+ * parent. The parent node is the `node` of the {@link ol.xml.NodeStackItem} at
+ * the top of the `objectStack`.
  * @param {function(this: T, Node, V, Array.<*>)}
  *     nodeWriter Node writer.
  * @param {T=} opt_this The object to use as `this` in `nodeWriter`.
@@ -378,20 +381,75 @@ ol.xml.makeChildAppender = function(nodeWriter, opt_this) {
 
 
 /**
- * @param {string=} opt_namespaceURI Namespace URI which will be used
+ * Creates a serializer that creates multiple nodes of the same name and appends
- *     for all created nodes. If not provided, the namespace of the parent node
+ * them to the designated parent. The parent node is the `node` of the
- *     will be used.
+ * {@link ol.xml.NodeStackItem} at the top of the `objectStack`.
- * @return {function(*, Array.<*>, (string|undefined)): Node} Node factory.
+ * @param {function(this: T, Node, V, Array.<*>)}
+ *     nodeWriter Node writer.
+ * @param {T=} opt_this The object to use as `this` in `nodeWriter`.
+ * @return {ol.xml.Serializer} Serializer.
+ * @template T, V
  */
-ol.xml.makeChildNodeFactory = function(opt_namespaceURI) {
+ol.xml.makeChildrenAppender = function(nodeWriter, opt_this) {
-  var namespaceURI = /** @type {string} */
+  var writer = ol.xml.makeChildAppender(nodeWriter);
-      (goog.isDef(opt_namespaceURI) ? opt_namespaceURI : null);
+  var serializersNS, nodeFactory;
-  return function(value, objectStack, nodeName) {
+  return function(node, value, objectStack) {
+    if (!goog.isDef(serializersNS)) {
+      serializersNS = {};
+      var serializers = {};
+      goog.object.set(serializers, node.localName, writer);
+      goog.object.set(serializersNS, node.namespaceURI, serializers);
+      nodeFactory = ol.xml.makeSimpleNodeFactory(node.localName);
+    }
+    ol.xml.pushSerializeAndPop(/** @type {ol.xml.NodeStackItem} */
+        (objectStack[objectStack.length - 1]), serializersNS, nodeFactory,
+        value, objectStack);
+  };
+};
+
+
+/**
+ * @param {string=} opt_nodeName Fixed node name which will be used for all
+ *     created nodes. If not provided, the nodeName will be the 3rd argument to
+ *     the resulting node factory.
+ * @param {string=} opt_namespaceURI Fixed namespace URI which will be used for
+ *     all created nodes. If not provided, the namespace of the parent node will
+ *     be used.
+ * @return {function(*, Array.<*>, string=): Node} Node factory.
+ */
+ol.xml.makeSimpleNodeFactory = function(opt_nodeName, opt_namespaceURI) {
+  var fixedNodeName = opt_nodeName;
+  /**
+   * @param {*} value Value.
+   * @param {Array.<*>} objectStack Object stack.
+   * @param {string=} opt_nodeName Node name.
+   * @return {Node} Node.
+   */
+  return function(value, objectStack, opt_nodeName) {
+    var context = objectStack[objectStack.length - 1];
+    var node = context.node;
+    goog.asserts.assert(ol.xml.isNode(node) || ol.xml.isDocument(node));
+    var nodeName = fixedNodeName;
+    if (!goog.isDef(nodeName)) {
+      nodeName = opt_nodeName;
+    }
+    var namespaceURI = opt_namespaceURI;
+    if (!goog.isDef(opt_namespaceURI)) {
+      namespaceURI = node.namespaceURI;
+    }
+    goog.asserts.assert(goog.isDef(nodeName));
     return ol.xml.createElementNS(namespaceURI, nodeName);
   };
 };
 
 
+/**
+ * @const
+ * @type {function(*, Array.<*>, string=): Node}
+ */
+ol.xml.OBJECT_PROPERTY_NODE_FACTORY = ol.xml.makeSimpleNodeFactory();
+
+
 /**
  * @param {Object.<string, V>} object Key-value pairs for the sequence.
  * @param {Array.<string>} orderedKeys Keys in the order of the sequence.