feat(rule): Require unique aria labels in checkboxgroup & radiogroup

lib/checks/forms/group-labelledby-after.js

@@ -1,5 +1,8 @@
 var seen = {};
 
+// Filter out nodes that have the same type and name.
+// If you have two `<input type="radio" name="foo" />` elements
+// only the first one can pass / fail the rule.
 return results.filter(function(result) {
 	var data = result.data;
 	if (data) {

lib/checks/forms/group-labelledby.js

@@ -1,34 +1,61 @@
-this.data({
-	name: node.getAttribute('name'),
-	type: node.getAttribute('type')
-});
+const { dom, text, utils } = axe.commons;
+
+const type = utils.escapeSelector(node.type);
+const name = utils.escapeSelector(node.name);
+const doc = dom.getRootNode(node);
+const data = {
+	name: node.name,
+	type: node.type
+};
 
-var doc = axe.commons.dom.getRootNode(node);
-var matchingNodes = doc.querySelectorAll(
-	'input[type="' +
-		axe.commons.utils.escapeSelector(node.type) +
-		'"][name="' +
-		axe.commons.utils.escapeSelector(node.name) +
-		'"]'
+const matchingNodes = Array.from(
+	doc.querySelectorAll(`input[type="${type}"][name="${name}"]`)
 );
+// There is only one node with this name & type, so there's no need for a group
 if (matchingNodes.length <= 1) {
+	this.data(data);
 	return true;
 }
 
-// Check to see if there's an aria-labelledby value that all nodes have in common
-return (
-	[].map
-		.call(matchingNodes, function(m) {
-			var l = m.getAttribute('aria-labelledby');
-			return l ? l.split(/\s+/) : [];
-		})
-		.reduce(function(prev, curr) {
-			return prev.filter(function(n) {
-				return curr.includes(n);
-			});
-		})
-		.filter(function(n) {
-			var labelNode = doc.getElementById(n);
-			return labelNode && axe.commons.text.accessibleText(labelNode, true);
-		}).length !== 0
+let sharedLabels = dom.idrefs(node, 'aria-labelledby').filter(label => !!label); // Filter for "null" labels
+let uniqueLabels = sharedLabels.slice();
+
+// Figure out which labels are unique, which are shared by all items, or neither
+matchingNodes.forEach(groupItem => {
+	if (groupItem === node) {
+		return;
+	}
+	// Find new labels associated with current groupItem
+	const labels = dom
+		.idrefs(groupItem, 'aria-labelledby')
+		.filter(newLabel => newLabel);
+
+	sharedLabels = sharedLabels.filter(sharedLabel =>
+		labels.includes(sharedLabel)
+	);
+	uniqueLabels = uniqueLabels.filter(
+		uniqueLabel => !labels.includes(uniqueLabel)
+	);
+});
+
+// filter items with no accessible name, do this last for performance reasons
+uniqueLabels = uniqueLabels.filter(labelNode =>
+	text.accessibleText(labelNode, true)
+);
+sharedLabels = sharedLabels.filter(labelNode =>
+	text.accessibleText(labelNode, true)
 );
+
+if (uniqueLabels.length > 0 && sharedLabels.length > 0) {
+	this.data(data);
+	return true;
+}
+
+if (uniqueLabels.length > 0 && sharedLabels.length === 0) {
+	data.failureCode = 'no-shared-label';
+} else if (uniqueLabels.length === 0 && sharedLabels.length > 0) {
+	data.failureCode = 'no-unique-label';
+}
+
+this.data(data);
+return false;

lib/checks/forms/group-labelledby.json

@@ -5,8 +5,8 @@
 	"metadata": {
 		"impact": "critical",
 		"messages": {
-			"pass": "All elements with the name \"{{=it.data.name}}\" reference the same element with aria-labelledby",
-			"fail": "All elements with the name \"{{=it.data.name}}\" do not reference the same element with aria-labelledby"
+			"pass": "Elements with the name \"{{=it.data.name}}\" have both a shared label, and a unique label, referenced through aria-labelledby",
+			"fail": "{{var code = it.data && it.data.failureCode;}}Elements with the name \"{{=it.data.name}}\" do not all have {{? code === 'no-shared-label' }}a shared label{{?? code === 'no-unique-label' }}a unique label{{??}}both a shared label, and a unique label{{?}}, referenced through aria-labelledby"
 		}
 	}
 }