Better handling of infinite recursion

But it could be better still...

core/modules/utils/errors.js

@@ -8,8 +8,9 @@ Custom errors for TiddlyWiki.
 \*/
 (function(){
 
-function TranscludeRecursionError(transcludeMarker) {
-	this.marker = transcludeMarker;
+function TranscludeRecursionError(depth) {
+	this.depth = depth;
+	this.signatures = Object.create(null);
 };
 
 exports.TranscludeRecursionError = TranscludeRecursionError;

core/modules/widgets/transclude.js

@@ -38,7 +38,13 @@ TranscludeWidget.prototype.render = function(parent,nextSibling) {
 			// We need to try and abort as much of the loop as we can, so we will keep "throwing" upward until we find a transclusion that has a different signature.
 			// Hopefully that will land us just outside where the loop began. That's where we want to issue an error.
 			// Rendering widgets beneath this point may result in a freezing browser if they explode exponentially.
-			if(error.marker !== this.getVariable("transclusion")) {
+			var transcludeSignature = this.getVariable("transclusion");
+			if(this.getAncestorCount() > error.depth - 50) {
+				// For the first fifty transcludes we climb up, we simply collect signatures.
+				// We're assuming that those first 50 will likely include all transcludes involved in the loop.
+				error.signatures[transcludeSignature] = true;
+			} else if(!error.signatures[transcludeSignature]) {
+				// Now that we're past the first 50, let's look for the first signature that wasn't in the loop. That'll be where we print the error and resume rendering.
 				this.children = [this.makeChildWidget({type: "error", attributes: {
 					"$message": {type: "string", value: $tw.language.getString("Error/RecursiveTransclusion")}
 				}})];

core/modules/widgets/widget.js

@@ -495,7 +495,7 @@ Widget.prototype.makeChildWidgets = function(parseTreeNodes,options) {
 	var self = this;
 	// Check for too much recursion
 	if(this.getAncestorCount() > MAX_WIDGET_TREE_DEPTH) {
-		throw new $tw.utils.TranscludeRecursionError(this.getVariable("transclusion"));
+		throw new $tw.utils.TranscludeRecursionError(MAX_WIDGET_TREE_DEPTH);
 	} else {
 		// Create set variable widgets for each variable
 		$tw.utils.each(options.variables,function(value,name) {

editions/test/tiddlers/tests/test-widget.js

@@ -160,7 +160,7 @@ describe("Widget module", function() {
 		expect(wrapper.innerHTML).toBe("<span class=\"tc-error\">Recursive transclusion error in transclude widget</span>");
 	});
 
-	it("should handle recursion with branching nodes", function() {
+	it("should handle single-tiddler recursion with branching nodes", function() {
 		var wiki = new $tw.Wiki();
 		// Add a tiddler
 		wiki.addTiddlers([
@@ -180,6 +180,27 @@ describe("Widget module", function() {
 		expect(wrapper.innerHTML).toBe("<span class=\"tc-error\">Recursive transclusion error in transclude widget</span> <span class=\"tc-error\">Recursive transclusion error in transclude widget</span>");
 	});
 
+	fit("should handle many-tiddler recursion with branching nodes", function() {
+		var wiki = new $tw.Wiki();
+		// Add a tiddler
+		wiki.addTiddlers([
+			{title: "TiddlerOne", text: "<$transclude tiddler='TiddlerTwo'/> <$transclude tiddler='TiddlerTwo'/>"},
+			{title: "TiddlerTwo", text: "<$transclude tiddler='TiddlerOne'/>"}
+		]);
+		// Test parse tree
+		var parseTreeNode = {type: "widget", children: [
+								{type: "transclude", attributes: {
+										"tiddler": {type: "string", value: "TiddlerOne"}
+									}}
+							]};
+		// Construct the widget node
+		var widgetNode = createWidgetNode(parseTreeNode,wiki);
+		// Render the widget node to the DOM
+		var wrapper = renderWidgetNode(widgetNode);
+		// Test the rendering
+		expect(wrapper.innerHTML).toBe("<span class=\"tc-error\">Recursive transclusion error in transclude widget</span>");
+	});
+
 	it("should deal with SVG elements", function() {
 		var wiki = new $tw.Wiki();
 		// Construct the widget node