fix: Ignore shadowRoots on elements that don't allow them

lib/core/utils/flattened-tree.js

@@ -51,6 +51,20 @@ function getSlotChildren(node) {
 	return retVal;
 }
 
+const possibleShadowRoots = ['article', 'aside', 'blockquote', 
+		'body', 'div', 'footer', 'h1', 'h2', 'h3', 'h4', 'h5', 'h6', 
+		'header', 'main', 'nav', 'p', 'section', 'span'];
+axe.utils.isShadowRoot = function isShadowRoot (node) {
+	const nodeName = node.nodeName.toLowerCase();
+	if (node.shadowRoot) {
+		if (/^[a-z][a-z0-9_.-]*-[a-z0-9_.-]*$/.test(nodeName) ||
+				possibleShadowRoots.includes(nodeName)) {
+			return true;
+		}
+	}
+	return false;
+};
+
 /**
  * Recursvely returns an array of the virtual DOM nodes at this level
  * excluding comment nodes and the shadow DOM nodes <content> and <slot>
@@ -75,8 +89,8 @@ axe.utils.getFlattenedTree = function (node, shadowId) {
 		node = node.documentElement;
 	}
 	nodeName = node.nodeName.toLowerCase();
-	// for some reason Chrome's marquee element has an open shadow DOM
-	if (node.shadowRoot && nodeName !== 'marquee') {
+
+	if (axe.utils.isShadowRoot(node)) {
 		// generate an ID for this shadow root and overwrite the current
 		// closure shadowId with this value so that it cascades down the tree
 		retVal = virtualDOMfromNode(node, shadowId);

test/core/utils/flattened-tree.js

@@ -66,6 +66,32 @@ function shadowIdAssertions () {
 
 }
 
+describe('isShadowRoot', function () {
+	'use strict';
+	var isShadowRoot = axe.utils.isShadowRoot;
+
+	it('returns false if the node has no shadowRoot', function () {
+		assert.isFalse(isShadowRoot({ nodeName: 'DIV', shadowRoot: undefined }));
+	});
+	it('returns true if the native element allows shadow DOM', function () {
+		assert.isTrue(isShadowRoot({ nodeName: 'DIV', shadowRoot: {} }));
+		assert.isTrue(isShadowRoot({ nodeName: 'H1', shadowRoot: {} }));
+		assert.isTrue(isShadowRoot({ nodeName: 'ASIDE', shadowRoot: {} }));
+	});
+	it('returns true if a custom element with shadowRoot', function () {
+		assert.isTrue(isShadowRoot({ nodeName: 'X-BUTTON', shadowRoot: {} }));
+		assert.isTrue(isShadowRoot({ nodeName: 'T1000-SCHWARZENEGGER', shadowRoot: {} }));
+	});
+	it('returns true if an invalid custom element with shadowRoot', function () {
+		assert.isFalse(isShadowRoot({ nodeName: '0-BUZZ', shadowRoot: {} }));
+		assert.isFalse(isShadowRoot({ nodeName: '--ELM--', shadowRoot: {} }));
+	});
+	it('returns false if the native element does not allow shadow DOM', function () {
+		assert.isFalse(isShadowRoot({ nodeName: 'IFRAME', shadowRoot: {} }));
+		assert.isFalse(isShadowRoot({ nodeName: 'STRONG', shadowRoot: {} }));
+	});
+});
+
 if (shadowSupport.v0) {
 	describe('flattened-tree shadow DOM v0', function () {
 		'use strict';
@@ -154,6 +180,26 @@ if (shadowSupport.v1) {
 			assert.isTrue(virtualDOM[0].children[2].children[1].children[0].children[0].actualNode.textContent === 'fallback content');
 			assert.isTrue(virtualDOM[0].children[2].children[1].children[0].children[1].actualNode.nodeName === 'LI');
 		});
+		it('calls isShadowRoot to identify a shadow root', function () {
+			var isShadowRoot = axe.utils.isShadowRoot;
+			fixture.innerHTML = '<div></div>';
+			var div = fixture.querySelector('div');
+			var shadowRoot = div.attachShadow({ mode: 'open' });
+			shadowRoot.innerHTML = '<h1>Just a man in the back</h1>';
+
+			// Test without isShqdowRoot overwritten
+			assert.equal(axe.utils.getFlattenedTree(div)[0].children.length, 1);
+
+			var called = false;
+			axe.utils.isShadowRoot = function () {
+				called = true;
+				return false;
+			};
+			// Test with isShadowRoot overwritten
+			assert.equal(axe.utils.getFlattenedTree(div)[0].children.length, 0);
+			assert.isTrue(called);
+			axe.utils.isShadowRoot = isShadowRoot;
+		});
 	});
 	describe('flattened-tree shadow DOM v1: boxed slots', function () {
 		'use strict';