More robust infinite recursion handling with custom exception (#7882)

* Introduced preliminary idea for infinite recurse exception

* Better handling of infinite recursion

But it could be better still...

* the TransclusionError is a proper error

Moved the magic number to be on the error's class. Not sure if that's
a great idea.

* Fixed minor minor issue that came up in conflict

The minor fix to the jasmine regexp that escaped a '+' somehow
broke some random test.

core/modules/utils/errors.js

@@ -0,0 +1,23 @@
+/*\
+title: $:/core/modules/utils/errors.js
+type: application/javascript
+module-type: utils
+
+Custom errors for TiddlyWiki.
+
+\*/
+(function(){
+
+function TranscludeRecursionError() {
+	Error.apply(this,arguments);
+	this.signatures = Object.create(null);
+};
+
+/* Maximum permitted depth of the widget tree for recursion detection */
+TranscludeRecursionError.MAX_WIDGET_TREE_DEPTH = 1000;
+
+TranscludeRecursionError.prototype = Object.create(Error);
+
+exports.TranscludeRecursionError = TranscludeRecursionError;
+
+})();

core/modules/widgets/transclude.js

@@ -30,7 +30,30 @@ 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.
+			var transcludeSignature = this.getVariable("transclusion");
+			if(this.getAncestorCount() > $tw.utils.TranscludeRecursionError.MAX_WIDGET_TREE_DEPTH - 50) {
+				// For the first fifty transcludes we climb up, we simply collect signatures.
+				// We're assuming that those first 50 will likely include all transcludes involved in the loop.
+				error.signatures[transcludeSignature] = true;
+			} else if(!error.signatures[transcludeSignature]) {
+				// Now that we're past the first 50, let's look for the first signature that wasn't in the loop. That'll be where we print the error and resume rendering.
+				this.children = [this.makeChildWidget({type: "error", attributes: {
+					"$message": {type: "string", value: $tw.language.getString("Error/RecursiveTransclusion")}
+				}})];
+				this.renderChildren(parent,nextSibling);
+				return;
+			}
+		}
+		throw error;
+	}
 };
 
 /*

core/modules/widgets/widget.js

@@ -12,9 +12,6 @@ Widget base class
 /*global $tw: false */
 "use strict";
 
-/* Maximum permitted depth of the widget tree for recursion detection */
-var MAX_WIDGET_TREE_DEPTH = 1000;
-
 /*
 Create a widget object for a parse tree node
 	parseTreeNode: reference to the parse tree node to be rendered
@@ -494,10 +491,8 @@ Widget.prototype.makeChildWidgets = function(parseTreeNodes,options) {
 	this.children = [];
 	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")}
-		}}));
+	if(this.getAncestorCount() > $tw.utils.TranscludeRecursionError.MAX_WIDGET_TREE_DEPTH) {
+		throw new $tw.utils.TranscludeRecursionError();
 	} else {
 		// Create set variable widgets for each variable
 		$tw.utils.each(options.variables,function(value,name) {

editions/test/tiddlers/tests/data/transclude/Recursion.tid

@@ -7,7 +7,8 @@ title: Output
 
 \whitespace trim
 <$transclude $tiddler="Output"/>
+
 +
 title: ExpectedResult
 
-<p><span class="tc-error">Recursive transclusion error in transclude widget</span></p>
+<span class="tc-error">Recursive transclusion error in transclude widget</span>

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

@@ -160,6 +160,47 @@ describe("Widget module", function() {
 		expect(wrapper.innerHTML).toBe("<span class=\"tc-error\">Recursive transclusion error in transclude widget</span>");
 	});
 
+	it("should handle single-tiddler 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 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