Bug 1627809 - Make the DocumentL10n translate the document when initialized lazily. r=smaug

Differential Revision: https://phabricator.services.mozilla.com/D71224

dom/base/Document.cpp

@@ -3865,8 +3865,6 @@ void Document::LocalizationLinkAdded(Element* aLinkElement) {
     return;
   }
 
-  bool mWasDocumentL10nSet = mDocumentL10n;
-
   EnsureL10n();
 
   nsAutoString href;
@@ -3875,15 +3873,15 @@ void Document::LocalizationLinkAdded(Element* aLinkElement) {
   mDocumentL10n->AddResourceId(href);
 
   if (mReadyState >= READYSTATE_INTERACTIVE) {
-    // We're past the initial translation. No need to block layout, let's go
-    // directly to activate DocumentL10n.
     mDocumentL10n->Activate(true);
+    mDocumentL10n->TriggerInitialTranslation();
   } else {
-    if (!mWasDocumentL10nSet) {
+    if (!mDocumentL10n->mBlockingLayout) {
       // Our initial translation is going to block layout start.  Make sure
       // we don't fire the load event until after that stops happening and
       // layout has a chance to start.
       BlockOnload();
+      mDocumentL10n->mBlockingLayout = true;
     }
   }
 }
@@ -3933,13 +3931,14 @@ void Document::OnParsingCompleted() {
 }
 
 void Document::InitialTranslationCompleted() {
-  MOZ_ASSERT(mDocumentL10n,
-             "DocumentL10n must be initialized before this point.");
-  // This means we blocked the load event in LocalizationLinkAdded.  It's
-  // important that the load blocker removal here be async, because our caller
-  // will notify the content sink after us, and we want the content sync's
-  // work to happen before the load event fires.
-  UnblockOnload(/* aFireSync = */ false);
+  if (mDocumentL10n->mBlockingLayout) {
+    // This means we blocked the load event in LocalizationLinkAdded.  It's
+    // important that the load blocker removal here be async, because our caller
+    // will notify the content sink after us, and we want the content sync's
+    // work to happen before the load event fires.
+    UnblockOnload(/* aFireSync = */ false);
+    mDocumentL10n->mBlockingLayout = false;
+  }
 
   mL10nProtoElements.Clear();
 

dom/l10n/DocumentL10n.cpp

@@ -60,20 +60,23 @@ void DocumentL10n::Activate(const bool aLazy) {
     return;
   }
 
-  if (aLazy) {
-    DOMLocalization::Activate(false, true, {});
-    mReady->MaybeResolveWithUndefined();
-    mState = DocumentL10nState::Ready;
-  } else {
-    Element* elem = mDocument->GetDocumentElement();
-    if (NS_WARN_IF(!elem)) {
-      return;
-    }
-    bool isSync = elem->HasAttr(kNameSpaceID_None, nsGkAtoms::datal10nsync);
-
-    DOMLocalization::Activate(isSync, true, {});
-    mState = DocumentL10nState::Activated;
+  Element* elem = mDocument->GetDocumentElement();
+  if (NS_WARN_IF(!elem)) {
+    return;
   }
+  bool isSync = elem->HasAttr(kNameSpaceID_None, nsGkAtoms::datal10nsync);
+
+  if (aLazy) {
+    if (isSync) {
+      NS_WARNING(
+          "Document localization initialized lazy, data-l10n-sync attribute "
+          "has no effect.");
+    }
+    DOMLocalization::Activate(false, true, {});
+  } else {
+    DOMLocalization::Activate(isSync, true, {});
+  }
+  mState = DocumentL10nState::Activated;
 }
 
 JSObject* DocumentL10n::WrapObject(JSContext* aCx,

dom/l10n/DocumentL10n.h

@@ -79,6 +79,8 @@ class DocumentL10n final : public DOMLocalization {
   void ConnectRoot(nsINode& aNode, bool aTranslate, ErrorResult& aRv);
 
   DocumentL10nState GetState() { return mState; };
+
+  bool mBlockingLayout = false;
 };
 
 }  // namespace dom

dom/l10n/tests/mochitest/document_l10n/test_docl10n_lazy.html

@@ -22,10 +22,10 @@
     link.setAttribute("href", "crashreporter/aboutcrashes.ftl");
     document.head.appendChild(link);
 
+    // Verify now that `l10n.ready` exists and is fulfilled.
     await document.l10n.ready;
 
-    await document.l10n.translateElements([desc]);
-
+    // Lazy initialized localization should translate the document.
     is(desc.textContent.length > 0, true, "main-desc is translated");
 
     document.head.removeChild(link);