Bug 1686194 - Fire pagetitlechanged when initialized with an empty string r=smaug

Differential Revision: https://phabricator.services.mozilla.com/D102054

dom/ipc/WindowGlobalParent.cpp

@@ -364,11 +364,11 @@ IPCResult WindowGlobalParent::RecvUpdateDocumentPrincipal(
 }
 mozilla::ipc::IPCResult WindowGlobalParent::RecvUpdateDocumentTitle(
     const nsString& aTitle) {
-  if (mDocumentTitle == aTitle) {
+  if (mDocumentTitle.isSome() && mDocumentTitle.value() == aTitle) {
     return IPC_OK();
   }
 
-  mDocumentTitle = aTitle;
+  mDocumentTitle = Some(aTitle);
 
   // Send a pagetitlechanged event only for changes to the title
   // for top-level frames.

dom/ipc/WindowGlobalParent.h

@@ -119,7 +119,9 @@ class WindowGlobalParent final : public WindowContext,
   // The current URI which loaded in the document.
   nsIURI* GetDocumentURI() override { return mDocumentURI; }
 
-  void GetDocumentTitle(nsAString& aTitle) const { aTitle = mDocumentTitle; }
+  void GetDocumentTitle(nsAString& aTitle) const {
+    aTitle = mDocumentTitle.valueOr(nsString());
+  }
 
   nsIPrincipal* GetContentBlockingAllowListPrincipal() const {
     return mDocContentBlockingAllowListPrincipal;
@@ -284,7 +286,7 @@ class WindowGlobalParent final : public WindowContext,
   // The principal to use for the content blocking allow list.
   nsCOMPtr<nsIPrincipal> mDocContentBlockingAllowListPrincipal;
   nsCOMPtr<nsIURI> mDocumentURI;
-  nsString mDocumentTitle;
+  Maybe<nsString> mDocumentTitle;
 
   bool mIsInitialDocument;
 

dom/ipc/tests/browser.ini

@@ -20,3 +20,5 @@ skip-if = !e10s
 [browser_bug1646088.js]
 support-files = file_dummy.html
 skip-if = !e10s
+[browser_bug1686194.js]
+support-files = file_dummy.html

dom/ipc/tests/browser_bug1686194.js

@@ -0,0 +1,47 @@
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+"use strict";
+
+const TEST_PAGE =
+  "http://mochi.test:8888/browser/dom/ipc/tests/file_dummy.html";
+
+function untilPageTitleChanged() {
+  return new Promise(resolve =>
+    gBrowser.addEventListener("pagetitlechanged", resolve, { once: true })
+  );
+}
+
+add_task(async () => {
+  const tab = await BrowserTestUtils.openNewForegroundTab({
+    gBrowser,
+    opening: TEST_PAGE,
+  });
+
+  const { linkedBrowser } = tab;
+  ok(
+    tab.getAttribute("label").includes("file_dummy.html"),
+    "The title should be the raw path"
+  );
+
+  await Promise.all([
+    SpecialPowers.spawn(linkedBrowser, [], function() {
+      content.document.title = "Title";
+    }),
+    untilPageTitleChanged(),
+  ]);
+
+  is(tab.getAttribute("label"), "Title", "The title should change");
+
+  linkedBrowser.reload();
+
+  await untilPageTitleChanged();
+
+  ok(
+    tab.getAttribute("label").includes("file_dummy.html"),
+    "The title should be the raw path again"
+  );
+
+  BrowserTestUtils.removeTab(tab);
+});