css/css-layout-api/fallback-layout-invalid-fragment.https.html

<!DOCTYPE html>
<html class=reftest-wait>
<link rel="help" href="https://drafts.css-houdini.org/css-layout-api/#invoke-a-layout-callback">
<link rel="match" href="fallback-ref.html">
<meta name="assert" content="This test checks that a layout() class returning an invalid fragment will fallback to block layout." />
<style>
.test {
  background: red;
  border: solid 2px;
  width: 100px;
}

.test > div {
  height: 100px;
}

@supports (display: layout(bad-request)) {
  .test {
    display: layout(bad-request);
    background: green;
  }
}
</style>
<script src="/common/reftest-wait.js"></script>
<script src="/common/worklet-reftest.js"></script>

<div class="test">
  <div></div>
</div>

<script id="code" type="text/worklet">
registerLayout('bad-request', class {
  static get inputProperties() { return ['--fail']; }

  *intrinsicSizes() {}
  *layout(children, _, __, styleMap) {
    if (styleMap.get('--fail').toString() !== 'true') {
      this.fragment = yield children[0].layoutNextFragment({});
    }

    // Return, if the fragment is invalid (we skipped the if statement above)
    // we should fallback to block layout.
    return {autoBlockSize: 0, childFragments: [this.fragment]};
  }
});
</script>

<script>
function raf() {
  return new Promise((resolve) => {
    requestAnimationFrame(() => {
      resolve();
    });
  });
}

(async function() {
  if (typeof CSS.layoutWorklet === 'undefined') {
    takeScreenshot();
    return;
  }

  await importWorklet(CSS.layoutWorklet, document.getElementById('code').textContent);

  // Ensure that all instances have a child to perform an invalid layout upon.
  const test = document.getElementsByClassName('test')[0];
  for (let i = 0; i < 100; i++) {
    test.innerHTML = '<div><div>';
    await raf();
  }

  // The next layout should mean that we will fallback to block.
  test.innerHTML = '<div></div>';
  test.style.setProperty('--fail', 'true');

  // Finish up the test.
  await raf();
  await raf();
  takeScreenshot();
})();
</script>
</html>