fix(region): Decorative images ignored by region rule (#4412)

Issue was around [decorative
images](https://www.w3.org/WAI/tutorials/images/decorative/),
specifically 1 pixel wide/tall marketing tracking images, that get added
outside of regions failing the region rule. An easy and fairly robust
solution [the issue opener agreed
with](#4145 (comment))
was ignoring images with `alt=''` and so that's what this PR implements.

Dev notes:

- Added `isPresentationGraphic/1` check which currently only handles
`alt=''` and ignores them for the region rule
- role='presentation' test added as well, but this already worked
previously prior to this code change
- svg I believe is handled differently already, there's a test called
`treats svg elements as regions` so the new function doesn't check for
svg's

fix: #4145

lib/checks/navigation/region-evaluate.js

@@ -1,4 +1,5 @@
 import * as dom from '../../commons/dom';
+import { hasChildTextNodes } from '../../commons/dom/has-content-virtual';
 import { getRole } from '../../commons/aria';
 import * as standards from '../../commons/standards';
 import matches from '../../commons/matches';
@@ -45,7 +46,10 @@ function getRegionlessNodes(options) {
  */
 function findRegionlessElms(virtualNode, options) {
   const node = virtualNode.actualNode;
-  // End recursion if the element is a landmark, skiplink, or hidden content
+  // End recursion if the element is...
+  // - a landmark
+  // - a skiplink
+  // - hidden content
   if (
     getRole(virtualNode) === 'button' ||
     isRegion(virtualNode, options) ||
@@ -73,7 +77,8 @@ function findRegionlessElms(virtualNode, options) {
     // @see https://github.com/dequelabs/axe-core/issues/2049
   } else if (
     node !== document.body &&
-    dom.hasContent(node, /* noRecursion: */ true)
+    dom.hasContent(node, /* noRecursion: */ true) &&
+    !isShallowlyHidden(virtualNode)
   ) {
     return [virtualNode];
 
@@ -86,6 +91,14 @@ function findRegionlessElms(virtualNode, options) {
   }
 }
 
+function isShallowlyHidden(virtualNode) {
+  // The element itself is not visible to screen readers, but its descendants might be
+  return (
+    ['none', 'presentation'].includes(getRole(virtualNode)) &&
+    !hasChildTextNodes(virtualNode)
+  );
+}
+
 // Check if the current element is a landmark
 function isRegion(virtualNode, options) {
   const node = virtualNode.actualNode;

test/checks/navigation/region.js

@@ -46,14 +46,87 @@ describe('region', function () {
     assert.isTrue(checkEvaluate.apply(checkContext, checkArgs));
   });
 
-  it('should return false when img content is outside the region', function () {
-    var checkArgs = checkSetup(
-      '<img id="target" src="data:image/gif;base64,R0lGODlhEAAQAMQAAORHHOVSKudfOulrSOp3WOyDZu6QdvCchPGolfO0o/XBs/fNwfjZ0frl3/zy7////wAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAACH5BAkAABAALAAAAAAQABAAAAVVICSOZGlCQAosJ6mu7fiyZeKqNKToQGDsM8hBADgUXoGAiqhSvp5QAnQKGIgUhwFUYLCVDFCrKUE1lBavAViFIDlTImbKC5Gm2hB0SlBCBMQiB0UjIQA7"><div role="main"><h1 id="mainheader" tabindex="0">Introduction</h1></div>'
-    );
+  it('should return false when img content is outside the region, no alt attribute at all', function () {
+    const checkArgs = checkSetup(`
+      <img id="target" src="data:image/gif;base64,R0lGODlhEAAQAMQAAORHHOVSKudfOulrSOp3WOyDZu6QdvCchPGolfO0o/XBs/fNwfjZ0frl3/zy7////wAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAACH5BAkAABAALAAAAAAQABAAAAVVICSOZGlCQAosJ6mu7fiyZeKqNKToQGDsM8hBADgUXoGAiqhSvp5QAnQKGIgUhwFUYLCVDFCrKUE1lBavAViFIDlTImbKC5Gm2hB0SlBCBMQiB0UjIQA7">
+      <div role="main">Content</div>
+    `);
+
+    assert.isFalse(checkEvaluate.apply(checkContext, checkArgs));
+  });
+
+  it('should return true when img content outside of the region is decorative, via an empty alt attr', function () {
+    const checkArgs = checkSetup(`
+      <img id="target" src="#" alt="" />
+      <div role="main">Content</div>
+    `);
+
+    assert.isTrue(checkEvaluate.apply(checkContext, checkArgs));
+  });
+
+  it('should return true when img content outside of the region is explicitly decorative, via a presentation role', function () {
+    const checkArgs = checkSetup(`
+      <img id="target" src="#" role="presentation" />
+      <div role="main">Content</div>
+    `);
+
+    assert.isTrue(checkEvaluate.apply(checkContext, checkArgs));
+  });
+
+  it('should return false when img content outside of the region is focusable (implicit role=img)', function () {
+    const checkArgs = checkSetup(`
+      <img id="target" src="#" tabindex="0" alt="" />
+      <div role="main">Content</div>
+    `);
+
+    assert.isFalse(checkEvaluate.apply(checkContext, checkArgs));
+  });
+
+  it('should return false when img content outside of the region has a global aria attribute (implicit role=img)', function () {
+    const checkArgs = checkSetup(`
+      <img id="target" src="#" aria-atomic="true" alt="" />
+      <div role="main">Content</div>
+    `);
+
+    assert.isFalse(checkEvaluate.apply(checkContext, checkArgs));
+  });
+
+  it('should return true when canvas role=none', function () {
+    const checkArgs = checkSetup(`
+      <canvas id="target" role="none" />
+      <div role="main">Content</div>
+    `);
+
+    assert.isTrue(checkEvaluate.apply(checkContext, checkArgs));
+  });
+
+  it('should return false when object has an aria-label', function () {
+    const checkArgs = checkSetup(`
+      <object id="target" aria-label="bar"></object>
+      <div role="main">Content</div>
+    `);
 
     assert.isFalse(checkEvaluate.apply(checkContext, checkArgs));
   });
 
+  it('should return false when a non-landmark has text content but a role=none', function () {
+    const checkArgs = checkSetup(`
+      <div id="target" role="none">apples</div>
+      <div role="main">Content</div>
+    `);
+
+    assert.isFalse(checkEvaluate.apply(checkContext, checkArgs));
+  });
+
+  it('should return true when a non-landmark does NOT have text content and a role=none', function () {
+    const checkArgs = checkSetup(`
+      <div id="target" role="none"></div>
+      <div role="main">Content</div>
+    `);
+
+    assert.isTrue(checkEvaluate.apply(checkContext, checkArgs));
+  });
+
   it('should return true when textless text content is outside the region', function () {
     var checkArgs = checkSetup(
       '<p id="target"></p><div role="main"><h1 id="mainheader" tabindex="0">Introduction</h1></div>'
@@ -166,6 +239,15 @@ describe('region', function () {
     assert.isFalse(checkEvaluate.apply(checkContext, checkArgs));
   });
 
+  it('ignores native landmark elements with an overwriting role with a nested child', function () {
+    var checkArgs = checkSetup(`
+      <main id="target" role="none"><p>Content</p></main>
+			<div role="main">Content</div>
+    `);
+
+    assert.isFalse(checkEvaluate.apply(checkContext, checkArgs));
+  });
+
   it('returns false for content outside of form tags with accessible names', function () {
     var checkArgs = checkSetup(
       '<p id="target">Text</p><form aria-label="form"></form>'

test/integration/full/region/region-fail.html

@@ -40,6 +40,22 @@ <h1 id="mainheader" tabindex="0">This is a header.</h1>
       </section>
     </div>
 
+    <div id="img-no-alt">
+      <img src="#" />
+    </div>
+    <div id="img-focusable">
+      <img src="#" tabindex="0" alt="" />
+    </div>
+    <div id="img-aria-global">
+      <img src="#" aria-atomic="true" alt="" />
+    </div>
+    <div id="labeled-object">
+      <object aria-label="bar"></object>
+    </div>
+    <div id="none-role-div">
+      <div id="target" role="none">apples</div>
+    </div>
+
     This should be ignored
 
     <main id="mocha"></main>

test/integration/full/region/region-fail.js

@@ -15,12 +15,40 @@ describe('region fail test', function () {
   });
 
   describe('violations', function () {
-    it('should find one', function () {
-      assert.lengthOf(results.violations[0].nodes, 1);
+    it('should find all violations', function () {
+      assert.lengthOf(results.violations[0].nodes, 6);
     });
 
     it('should find wrapper', function () {
       assert.deepEqual(results.violations[0].nodes[0].target, ['#wrapper']);
     });
+
+    it('should find image without an alt tag', function () {
+      assert.deepEqual(results.violations[0].nodes[1].target, ['#img-no-alt']);
+    });
+
+    it('should find focusable image', function () {
+      assert.deepEqual(results.violations[0].nodes[2].target, [
+        '#img-focusable'
+      ]);
+    });
+
+    it('should find image with global aria attr', function () {
+      assert.deepEqual(results.violations[0].nodes[3].target, [
+        '#img-aria-global'
+      ]);
+    });
+
+    it('should find object with a label', function () {
+      assert.deepEqual(results.violations[0].nodes[4].target, [
+        '#labeled-object'
+      ]);
+    });
+
+    it('should find div with an role of none', function () {
+      assert.deepEqual(results.violations[0].nodes[5].target, [
+        '#none-role-div'
+      ]);
+    });
   });
 });

test/integration/full/region/region-pass.html

@@ -20,6 +20,16 @@
   </head>
   <body>
     <a href="#mainheader" id="skiplink">This is a skip link.</a>
+    <!-- Decorative image -->
+    <img src="#" alt="" />
+    <!-- Decorative image -->
+    <img src="#" role="presentation" />
+    <!-- SVG's may be outside of a landmark -->
+    <svg role="none" aria-label="foo"></svg>
+    <!-- Div with a role of none may be outside a landmark -->
+    <div role="none"></div>
+    <!-- Canvas with a role of none may be outside a landmark -->
+    <canvas role="none" />
     <div id="wrapper">
       <div role="main">
         <h1 id="mainheader" tabindex="0">This is a header.</h1>