Detect recursion by tracking widget tree depth

The old recursion marker approach was very slow, and didn't catch test cases like editions/test/tiddlers/tests/data/transclude/Recursion.tid

core/modules/widgets/error.js

@@ -0,0 +1,63 @@
+/*\
+title: $:/core/modules/widgets/error.js
+type: application/javascript
+module-type: widget
+
+Error widget
+
+\*/
+(function(){
+
+/*jslint node: true, browser: true */
+/*global $tw: false */
+"use strict";
+
+var Widget = require("$:/core/modules/widgets/widget.js").widget;
+
+var ErrorWidget = function(parseTreeNode,options) {
+	this.initialise(parseTreeNode,options);
+};
+
+/*
+Inherit from the base widget class
+*/
+ErrorWidget.prototype = new Widget();
+
+/*
+Render this widget into the DOM
+*/
+ErrorWidget.prototype.render = function(parent,nextSibling) {
+	this.parentDomNode = parent;
+	this.computeAttributes();
+	this.execute();
+	var message = this.getAttribute("$message","Unknown error"),
+		domNode = this.document.createElement("span");
+	domNode.appendChild(this.document.createTextNode(message));
+	domNode.className = "tc-error";
+	parent.insertBefore(domNode,nextSibling);
+	this.domNodes.push(domNode);
+};
+
+/*
+Compute the internal state of the widget
+*/
+ErrorWidget.prototype.execute = function() {
+	// Nothing to do for a text node
+};
+
+/*
+Selectively refreshes the widget if needed. Returns true if the widget or any of its children needed re-rendering
+*/
+ErrorWidget.prototype.refresh = function(changedTiddlers) {
+	var changedAttributes = this.computeAttributes();
+	if(changedAttributes["$message"]) {
+		this.refreshSelf();
+		return true;
+	} else {
+		return false;
+	}
+};
+
+exports.error = ErrorWidget;
+
+})();