Bug 1945994 - Explicitly block the load event until the cached script is executed. r=nbp,emilio

Differential Revision: https://phabricator.services.mozilla.com/D236980

dom/script/ScriptLoader.cpp

@@ -1335,6 +1335,45 @@ bool ScriptLoader::ProcessExternalScript(nsIScriptElement* aElement,
         }
         return false;
       }
+    } else {
+      // https://html.spec.whatwg.org/#prepare-the-script-element
+      //
+      // Step 33. If el's type is "classic" and el has a src attribute, or el's
+      //          type is "module":
+      // ...
+      // Step 33.2. If el has an async attribute or el's force async is true:
+      // Step 33.2.1. Let scripts be el's preparation-time document's set of
+      //              scripts that will execute as soon as possible.
+      // Step 33.2.2. Append el to scripts.
+      // ...
+      // Step 33.3. Otherwise, if el is not parser-inserted:
+      // Step 33.3.1. Let scripts be el's preparation-time document's list of
+      //              scripts that will execute in order as soon as possible.
+      // Step 33.3.2. Append el to scripts.
+      // ...
+      //
+      // https://html.spec.whatwg.org/#the-end
+      //
+      // Step 7. Spin the event loop until the set of scripts that will execute
+      //         as soon as possible and the list of scripts that will execute
+      //         in order as soon as possible are empty.
+      //
+      // For scripts that creates the actual necko channel, the request is
+      // associated with the document's load group, and the load group manages
+      // the script set and the script list above implicitly, and the above
+      // "spin the event loop" is handled by IsBusy() check inside
+      // nsDocLoader::DocLoaderIsEmpty.
+      //
+      // https://searchfox.org/mozilla-central/rev/e85232b4b28ecc970240d39203e417d1c320623c/uriloader/base/nsDocLoader.cpp#704
+      //
+      // For in-memory-cached scripts, no channel is created, and those scripts
+      // should explicitly block the step 7 above.
+      //
+      // NOTE: IsAsyncScript represents both "async" and "force async".
+      if (request->GetScriptLoadContext()->IsAsyncScript() ||
+          parserMetadata == ParserMetadata::NotParserInserted) {
+        request->GetScriptLoadContext()->BlockOnload(mDocument);
+      }
     }
   }
 

dom/tests/browser/browser.toml

@@ -149,6 +149,13 @@ support-files = [
   "counter_server.sjs",
 ]
 
+["browser_scriptCache_load_events.js"]
+skip-if = ["!nightly_build"]
+support-files = [
+  "file_scriptCache_load_events.js",
+  "page_scriptCache_load_events.html",
+]
+
 ["browser_scriptCache_perf_timeline.js"]
 skip-if = ["!nightly_build"]
 support-files = [

dom/tests/browser/browser_scriptCache_load_events.js

@@ -0,0 +1,56 @@
+const TEST_URL =
+  "https://example.com/browser/dom/tests/browser/page_scriptCache_load_events.html";
+
+function clearAllCache() {
+  return new Promise(function (resolve) {
+    Services.clearData.deleteData(
+      Ci.nsIClearDataService.CLEAR_ALL_CACHES,
+      resolve
+    );
+  });
+}
+
+async function testOrder() {
+  await clearAllCache();
+
+  const tab = await BrowserTestUtils.openNewForegroundTab({
+    gBrowser,
+    url: TEST_URL,
+  });
+
+  // The script should be executed in between DOMContentLoaded and load events.
+
+  // Uncached cache.
+  let result = await SpecialPowers.spawn(tab.linkedBrowser, [], () => {
+    return content.document.getElementById("result").textContent;
+  });
+  is(result, "DOMContentLoaded+script+load");
+
+  await BrowserTestUtils.reloadTab(tab);
+
+  // Cached cache.
+  result = await SpecialPowers.spawn(tab.linkedBrowser, [], () => {
+    return content.document.getElementById("result").textContent;
+  });
+  is(result, "DOMContentLoaded+script+load");
+
+  BrowserTestUtils.removeTab(tab);
+}
+
+add_task(async function test_withoutNavigationCache() {
+  await SpecialPowers.pushPrefEnv({
+    set: [["dom.script_loader.navigation_cache", false]],
+  });
+  registerCleanupFunction(() => SpecialPowers.popPrefEnv());
+
+  await testOrder();
+});
+
+add_task(async function test_withNavigationCache() {
+  await SpecialPowers.pushPrefEnv({
+    set: [["dom.script_loader.navigation_cache", true]],
+  });
+  registerCleanupFunction(() => SpecialPowers.popPrefEnv());
+
+  await testOrder();
+});

dom/tests/browser/file_scriptCache_load_events.js

@@ -0,0 +1 @@
+document.getElementById("result").textContent += "+script";

dom/tests/browser/page_scriptCache_load_events.html

@@ -0,0 +1,20 @@
+<!DOCTYPE html>
+<head>
+  <meta charset="utf-8">
+  <title>load events order test</title>
+  <script>
+window.addEventListener("DOMContentLoaded", () => {
+  document.getElementById("result").textContent += "DOMContentLoaded";
+
+  const script = document.createElement("script");
+  script.src = "file_scriptCache_load_events.js";
+  document.getElementsByTagName("head")[0].appendChild(script);
+});
+function onLoad() {
+  document.getElementById("result").textContent += "+load";
+}
+  </script>
+</head>
+<body onload="onLoad()">
+  <span id="result"></span>
+</body>