[renderblocking] Don't cancel implicit render-blocking when blocking …

…attribute is removed 1. This patch adds tests for whatwg/html#7857. When `blocking=render` is removed, if the element is implicitly render-blocking, we shouldn't unblock rendering for it. 2. This patch fixes how <link> element respond to `blocking` attribute changes. Previously, the element simply reprocesses (cancel and then restart) on every `blocking` attribute change, causing unnecessary work and also some bugs on stylesheets. This patch changes that into unblock rendering if needed to match the spec. Bug: 1271296 Change-Id: I54a2f33dc1ed9971eaeceeb677a165d598d5d4d1
web-platform-tests · Apr 27, 2022 · ccb8ffa · ccb8ffa
1 parent 71f67d1
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diff --git a/html/dom/render-blocking/remove-attr-script-keeps-blocking.tentative.html b/html/dom/render-blocking/remove-attr-script-keeps-blocking.tentative.html
@@ -0,0 +1,25 @@
+<!DOCTYPE html>
+<title>Synchronous script element still blocks rendering after removing `blocking=render`</title>
+<script src="/resources/testharness.js"></script>
+<script src="/resources/testharnessreport.js"></script>
+<script src="support/test-render-blocking.js"></script>
+
+<script>
+// Test script must be added before the synchronous script because the
+// synchronous script is parser-blocking.
+
+promise_setup(async () => {
+  let script = await nodeInserted(document.head, node => node.id === 'script');
+  script.blocking = '';
+
+  // Also inserts some contents for non-compliant UA to render
+  document.body = document.createElement('body');
+  document.body.appendChild(document.createTextNode('Some text'));
+});
+
+test_render_blocking(
+    () => assert_equals(window.dummy, 1),
+    'Render-blocking script is loaded and evaluated');
+</script>
+
+<script id="script" blocking="render" src="support/dummy-1.js?pipe=trickle(d1)"></script>
diff --git a/html/dom/render-blocking/remove-attr-style-keeps-blocking.tentative.html b/html/dom/render-blocking/remove-attr-style-keeps-blocking.tentative.html
@@ -0,0 +1,28 @@
+<!DOCTYPE html>
+<title>Parser-inserted style element still blocks rendering after removing `blocking=render`</title>
+<script src="/resources/testharness.js"></script>
+<script src="/resources/testharnessreport.js"></script>
+<script src="support/test-render-blocking.js"></script>
+
+<script>
+// Test script must be added before the style element because the style
+// element is script-blocking.
+
+promise_setup(async () => {
+  let sheet = await nodeInserted(document.head, node => node.id === 'sheet');
+  sheet.blocking = '';
+});
+
+test_render_blocking(
+    () => {
+      let color = getComputedStyle(document.querySelector('.target')).color;
+      assert_equals(color, 'rgb(255, 0, 0)');
+    },
+    'Render-blocking stylesheet is applied');
+</script>
+
+<style id="sheet" blocking="render">
+@import url("support/target-red.css?pipe=trickle(d1)");
+</style>
+
+<div class="target">Some text</div>
diff --git a/html/dom/render-blocking/remove-attr-stylesheet-link-keeps-blocking.tentative.html b/html/dom/render-blocking/remove-attr-stylesheet-link-keeps-blocking.tentative.html
@@ -0,0 +1,27 @@
+<!DOCTYPE html>
+<title>Parser-inserted stylesheet link still blocks rendering after removing `blocking=render`</title>
+<script src="/resources/testharness.js"></script>
+<script src="/resources/testharnessreport.js"></script>
+<script src="support/test-render-blocking.js"></script>
+
+<script>
+// Test script must be added before the stylesheet link because the stylesheet
+// link is script-blocking.
+
+promise_setup(async () => {
+  let sheet = await nodeInserted(document.head, node => node.id === 'sheet');
+  sheet.blocking = '';
+});
+
+test_render_blocking(
+    () => {
+      let color = getComputedStyle(document.querySelector('.target')).color;
+      assert_equals(color, 'rgb(255, 0, 0)');
+    },
+    'Render-blocking stylesheet is applied');
+</script>
+
+<link id="sheet" rel="stylesheet" blocking="render"
+      href="support/target-red.css?pipe=trickle(d1)">
+
+<div class="target">Some text</div>
diff --git a/html/dom/render-blocking/support/test-render-blocking.js b/html/dom/render-blocking/support/test-render-blocking.js
@@ -30,6 +30,22 @@ class LoadObserver {
   }
 }
 
+// Observes the insertion of a script/parser-blocking element into DOM via
+// MutationObserver, so that we can access the element before it's loaded.
+function nodeInserted(parentNode, predicate) {
+  return new Promise(resolve => {
+    function callback(mutationList) {
+      for (let mutation of mutationList) {
+        for (let node of mutation.addedNodes) {
+          if (predicate(node))
+            resolve(node);
+        }
+      }
+    }
+    new MutationObserver(callback).observe(parentNode, {childList: true});
+  });
+}
+
 function createAutofocusTarget() {
   const autofocusTarget = document.createElement('textarea');
   autofocusTarget.setAttribute('autofocus', '');