Introduced preliminary idea for infinite recurse exception

core/modules/utils/errors.js

@@ -0,0 +1,17 @@
+/*\
+title: $:/core/modules/utils/errors.js
+type: application/javascript
+module-type: utils
+
+Custom errors for TiddlyWiki.
+
+\*/
+(function(){
+
+function TranscludeRecursionError(transcludeMarker) {
+	this.marker = transcludeMarker;
+};
+
+exports.TranscludeRecursionError = TranscludeRecursionError;
+
+})();

core/modules/widgets/transclude.js

@@ -30,7 +30,24 @@ TranscludeWidget.prototype.render = function(parent,nextSibling) {
 	this.parentDomNode = parent;
 	this.computeAttributes();
 	this.execute();
-	this.renderChildren(parent,nextSibling);
+	try {
+		this.renderChildren(parent,nextSibling);
+	} catch(error) {
+		if(error instanceof $tw.utils.TranscludeRecursionError) {
+			// We were infinite looping.
+			// We need to try and abort as much of the loop as we can, so we will keep "throwing" upward until we find a transclusion that has a different signature.
+			// Hopefully that will land us just outside where the loop began. That's where we want to issue an error.
+			// Rendering widgets beneath this point may result in a freezing browser if they explode exponentially.
+			if(error.marker !== this.getVariable("transclusion")) {
+				this.children = [this.makeChildWidget({type: "error", attributes: {
+					"$message": {type: "string", value: $tw.language.getString("Error/RecursiveTransclusion")}
+				}})];
+				this.renderChildren(parent,nextSibling);
+				return;
+			}
+		}
+		throw error;
+	}
 };
 
 /*

core/modules/widgets/widget.js

@@ -495,9 +495,7 @@ Widget.prototype.makeChildWidgets = function(parseTreeNodes,options) {
 	var self = this;
 	// Check for too much recursion
 	if(this.getAncestorCount() > MAX_WIDGET_TREE_DEPTH) {
-		this.children.push(this.makeChildWidget({type: "error", attributes: {
-			"$message": {type: "string", value: $tw.language.getString("Error/RecursiveTransclusion")}
-		}}));
+		throw new $tw.utils.TranscludeRecursionError(this.getVariable("transclusion"));
 	} else {
 		// Create set variable widgets for each variable
 		$tw.utils.each(options.variables,function(value,name) {

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

@@ -160,6 +160,26 @@ 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() {
+		var wiki = new $tw.Wiki();
+		// Add a tiddler
+		wiki.addTiddlers([
+			{title: "TiddlerOne", text: "<$tiddler tiddler='TiddlerOne'><$transclude /> <$transclude /></$tiddler>"},
+		]);
+		// 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> <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