Bug 1558602 - Allow DocumentL10n to use LocalizationSync. r=smaug,Pike

Differential Revision: https://phabricator.services.mozilla.com/D34584

--HG--
extra : moz-landing-system : lando

browser/components/aboutlogins/AboutLoginsParent.jsm

@@ -9,8 +9,6 @@ var EXPORTED_SYMBOLS = ["AboutLoginsParent"];
 const {XPCOMUtils} = ChromeUtils.import("resource://gre/modules/XPCOMUtils.jsm");
 ChromeUtils.defineModuleGetter(this, "E10SUtils",
                                "resource://gre/modules/E10SUtils.jsm");
-ChromeUtils.defineModuleGetter(this, "Localization",
-                               "resource://gre/modules/Localization.jsm");
 ChromeUtils.defineModuleGetter(this, "LoginHelper",
                                "resource://gre/modules/LoginHelper.jsm");
 ChromeUtils.defineModuleGetter(this, "MigrationUtils",

browser/components/newtab/lib/OnboardingMessageProvider.jsm

@@ -2,7 +2,6 @@
  * 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 {Localization} = ChromeUtils.import("resource://gre/modules/Localization.jsm");
 const {FxAccountsConfig} = ChromeUtils.import("resource://gre/modules/FxAccountsConfig.jsm");
 const {AttributionCode} = ChromeUtils.import("resource:///modules/AttributionCode.jsm");
 const {AddonRepository} = ChromeUtils.import("resource://gre/modules/addons/AddonRepository.jsm");

browser/components/preferences/in-content/main.js

@@ -13,7 +13,6 @@ var {FileUtils} = ChromeUtils.import("resource://gre/modules/FileUtils.jsm");
 var {TransientPrefs} = ChromeUtils.import("resource:///modules/TransientPrefs.jsm");
 var {AppConstants} = ChromeUtils.import("resource://gre/modules/AppConstants.jsm");
 var {L10nRegistry} = ChromeUtils.import("resource://gre/modules/L10nRegistry.jsm");
-var {Localization} = ChromeUtils.import("resource://gre/modules/Localization.jsm");
 var {HomePage} = ChromeUtils.import("resource:///modules/HomePage.jsm");
 ChromeUtils.defineModuleGetter(this, "CloudStorage",
   "resource://gre/modules/CloudStorage.jsm");

browser/components/touchbar/MacTouchBar.js

@@ -9,7 +9,6 @@ XPCOMUtils.defineLazyModuleGetters(this, {
   PrivateBrowsingUtils: "resource://gre/modules/PrivateBrowsingUtils.jsm",
   Services: "resource://gre/modules/Services.jsm",
   AppConstants: "resource://gre/modules/AppConstants.jsm",
-  Localization: "resource://gre/modules/Localization.jsm",
 });
 
 /**

dom/l10n/DOMLocalization.cpp

@@ -309,13 +309,54 @@ already_AddRefed<Promise> DOMLocalization::TranslateElements(
     return nullptr;
   }
 
-  RefPtr<Promise> callbackResult = FormatMessages(cx, l10nKeys, aRv);
+  if (mIsSync) {
-  if (NS_WARN_IF(aRv.Failed())) {
+    nsTArray<JS::Value> jsKeys;
-    return nullptr;
+    SequenceRooter<JS::Value> keysRooter(cx, &jsKeys);
-  }
+    for (auto& key : l10nKeys) {
+      JS::RootedValue jsKey(cx);
+      if (!ToJSValue(cx, key, &jsKey)) {
+        aRv.NoteJSContextException(cx);
+        return nullptr;
+      }
+      jsKeys.AppendElement(jsKey);
+    }
 
-  nativeHandler->SetReturnValuePromise(promise);
+    nsTArray<JS::Value> messages;
-  callbackResult->AppendNativeHandler(nativeHandler);
+    SequenceRooter<JS::Value> messagesRooter(cx, &messages);
+    mLocalization->FormatMessagesSync(jsKeys, messages);
+    nsTArray<L10nMessage> l10nData;
+    SequenceRooter<L10nMessage> l10nDataRooter(cx, &l10nData);
+
+    for (auto& msg : messages) {
+      JS::Rooted<JS::Value> rootedMsg(cx);
+      rootedMsg.set(msg);
+      L10nMessage* slotPtr = l10nData.AppendElement(mozilla::fallible);
+      if (!slotPtr) {
+        promise->MaybeRejectWithUndefined();
+        return MaybeWrapPromise(promise);
+      }
+
+      if (!slotPtr->Init(cx, rootedMsg)) {
+        promise->MaybeRejectWithUndefined();
+        return MaybeWrapPromise(promise);
+      }
+    }
+
+    ApplyTranslations(domElements, l10nData, aRv);
+    if (NS_WARN_IF(aRv.Failed())) {
+      promise->MaybeRejectWithUndefined();
+      return MaybeWrapPromise(promise);
+    }
+
+    promise->MaybeResolveWithUndefined();
+  } else {
+    RefPtr<Promise> callbackResult = FormatMessages(cx, l10nKeys, aRv);
+    if (NS_WARN_IF(aRv.Failed())) {
+      return nullptr;
+    }
+    nativeHandler->SetReturnValuePromise(promise);
+    callbackResult->AppendNativeHandler(nativeHandler);
+  }
 
   return MaybeWrapPromise(promise);
 }

dom/l10n/DocumentL10n.cpp

@@ -34,6 +34,11 @@ DocumentL10n::DocumentL10n(Document* aDocument)
       mDocument(aDocument),
       mState(DocumentL10nState::Initialized) {
   mContentSink = do_QueryInterface(aDocument->GetCurrentContentSink());
+
+  Element* elem = mDocument->GetDocumentElement();
+  if (elem) {
+    mIsSync = elem->HasAttr(kNameSpaceID_None, nsGkAtoms::datal10nsync);
+  }
 }
 
 void DocumentL10n::Init(nsTArray<nsString>& aResourceIds, ErrorResult& aRv) {
@@ -133,6 +138,14 @@ void DocumentL10n::InitialDocumentTranslationCompleted() {
   if (mContentSink) {
     mContentSink->InitialDocumentTranslationCompleted();
   }
+
+  // If sync was true, we want to change the state of
+  // mozILocalization to async now.
+  if (mIsSync) {
+    mIsSync = false;
+
+    mLocalization->SetIsSync(mIsSync);
+  }
 }
 
 Promise* DocumentL10n::Ready() { return mReady; }

dom/l10n/tests/mochitest/chrome.ini

@@ -36,5 +36,6 @@
 [document_l10n/test_docl10n_initialize_after_parse.xul]
 [document_l10n/test_docl10n.xhtml]
 [document_l10n/test_docl10n.html]
+[document_l10n/test_docl10n_sync.html]
 [document_l10n/test_docl10n_ready_rejected.html]
 [document_l10n/test_docl10n_removeResourceIds.html]

dom/l10n/tests/mochitest/document_l10n/test_docl10n_sync.html

@@ -0,0 +1,54 @@
+<!DOCTYPE HTML>
+<html data-l10n-sync>
+<head>
+  <meta charset="utf-8">
+  <title>Test DocumentL10n in HTML environment</title>
+  <script src="chrome://mochikit/content/tests/SimpleTest/SimpleTest.js"></script>
+  <link rel="stylesheet" type="text/css" href="chrome://mochikit/content/tests/SimpleTest/test.css">
+  <link rel="localization" href="crashreporter/aboutcrashes.ftl"/>
+  <script type="application/javascript">
+  "use strict";
+  SimpleTest.waitForExplicitFinish();
+
+  document.addEventListener("DOMContentLoaded", async function() {
+    await document.l10n.ready;
+
+    // Test for initial localization applied.
+    let desc = document.getElementById("main-desc");
+    is(desc.textContent.length > 0, true);
+
+    // Test for manual value formatting.
+    let msg = await document.l10n.formatValue("id-heading");
+    is(msg.length > 0, true);
+
+    // Test for mutations applied.
+    let verifyL10n = () => {
+      if (label.textContent.length > 0) {
+        window.removeEventListener("MozAfterPaint", verifyL10n);
+        SimpleTest.finish();
+      }
+    };
+    window.addEventListener("MozAfterPaint", verifyL10n);
+
+    let label = document.getElementById("label1");
+    document.l10n.setAttributes(
+      label,
+      "date-crashed-heading",
+      {
+        name: "John",
+      }
+    );
+
+    // Test for l10n.getAttributes
+    let l10nArgs = document.l10n.getAttributes(label);
+    is(l10nArgs.id, "date-crashed-heading");
+    is(l10nArgs.args.name, "John");
+  }, { once: true});
+  </script>
+</head>
+<body>
+  <h1 id="main-desc" data-l10n-id="crash-reports-title"></h1>
+
+  <p id="label1"></p>
+</body>
+</html>

intl/l10n/L10nRegistry.jsm

@@ -81,7 +81,7 @@ const isParentProcess = appinfo.processType === appinfo.PROCESS_TYPE_DEFAULT;
  *
  * Notice: L10nRegistry is primarily an asynchronous API, but
  * it does provide a synchronous version of it's main method
- * for use by the `LocalizationSync` class.
+ * for use  by the `Localization` class when in `sync` state.
  * This API should be only used in very specialized cases and
  * the uses should be reviewed by the toolkit owner/peer.
  */

intl/l10n/Localization.cpp

@@ -34,14 +34,16 @@ NS_INTERFACE_MAP_BEGIN_CYCLE_COLLECTION(Localization)
   NS_INTERFACE_MAP_ENTRY(nsISupportsWeakReference)
 NS_INTERFACE_MAP_END
 
-Localization::Localization(nsIGlobalObject* aGlobal) : mGlobal(aGlobal) {}
+Localization::Localization(nsIGlobalObject* aGlobal)
+    : mGlobal(aGlobal), mIsSync(false) {}
 
 void Localization::Init(nsTArray<nsString>& aResourceIds, ErrorResult& aRv) {
   nsCOMPtr<mozILocalizationJSM> jsm =
       do_ImportModule("resource://gre/modules/Localization.jsm");
   MOZ_RELEASE_ASSERT(jsm);
 
-  Unused << jsm->GetLocalization(aResourceIds, getter_AddRefs(mLocalization));
+  Unused << jsm->GetLocalization(aResourceIds, mIsSync,
+                                 getter_AddRefs(mLocalization));
   MOZ_RELEASE_ASSERT(mLocalization);
 
   RegisterObservers();

intl/l10n/Localization.h

@@ -74,6 +74,7 @@ class Localization : public nsIObserver,
 
   nsCOMPtr<nsIGlobalObject> mGlobal;
   nsCOMPtr<mozILocalization> mLocalization;
+  bool mIsSync;
 };
 
 }  // namespace intl

intl/l10n/Localization.jsm

@@ -211,20 +211,28 @@ function maybeReportErrorToGecko(error) {
  */
 class Localization {
   /**
-   * @param {Array<String>} resourceIds     - List of resource IDs
+   * @param {Array<String>} resourceIds         - List of resource IDs
-   * @param {Function}      generateBundles - Function that returns a
+   * @param {Function}      generateBundles     - Function that returns an async
-   *                                          generator over FluentBundles
+   *                                              generator over FluentBundles
+   * @param {Function}      generateBundlesSync - Function that returns a sync
+   *                                              generator over FluentBundles
    *
    * @returns {Localization}
    */
-  constructor(resourceIds = [], generateBundles = defaultGenerateBundles) {
+  constructor(resourceIds = [], sync = false, generateBundles = defaultGenerateBundles, generateBundlesSync = defaultGenerateBundlesSync) {
+    this.isSync = sync;
     this.resourceIds = resourceIds;
     this.generateBundles = generateBundles;
+    this.generateBundlesSync = generateBundlesSync;
     this.onChange(true);
   }
 
   cached(iterable) {
-    return CachedAsyncIterable.from(iterable);
+    if (this.isSync) {
+      return CachedSyncIterable.from(iterable);
+    } else {
+      return CachedAsyncIterable.from(iterable);
+    }
   }
 
   /**
@@ -280,6 +288,46 @@ class Localization {
     return translations;
   }
 
+  /**
+   * Format translations and handle fallback if needed.
+   *
+   * Format translations for `keys` from `FluentBundle` instances on this
+   * Localization. In case of errors, fetch the next context in the
+   * fallback chain.
+   *
+   * @param   {Array<Object>}         keys    - Translation keys to format.
+   * @param   {Function}              method  - Formatting function.
+   * @returns {Array<string|Object>}
+   * @private
+   */
+  formatWithFallbackSync(keys, method) {
+    if (!this.isSync) {
+      throw new Error("Can't use sync formatWithFallback when state is async.");
+    }
+    const translations = new Array(keys.length);
+    let hasAtLeastOneBundle = false;
+
+    for (const bundle of this.bundles) {
+      hasAtLeastOneBundle = true;
+      const missingIds = keysFromBundle(method, bundle, keys, translations);
+
+      if (missingIds.size === 0) {
+        break;
+      }
+
+      const locale = bundle.locales[0];
+      const ids = Array.from(missingIds).join(", ");
+      maybeReportErrorToGecko(`[fluent] Missing translations in ${locale}: ${ids}.`);
+    }
+
+    if (!hasAtLeastOneBundle) {
+      maybeReportErrorToGecko(`[fluent] Request for keys failed because no resource bundles got generated.\n keys: ${JSON.stringify(keys)}.\n resourceIds: ${JSON.stringify(this.resourceIds)}.`);
+    }
+
+    return translations;
+  }
+
+
   /**
    * Format translations into {value, attributes} objects.
    *
@@ -300,7 +348,7 @@ class Localization {
    *     //   }
    *     // ]
    *
-   * Returns a Promise resolving to an array of the translation strings.
+   * Returns a Promise resolving to an array of the translation messages.
    *
    * @param   {Array<Object>} keys
    * @returns {Promise<Array<{value: string, attributes: Object}>>}
@@ -310,6 +358,19 @@ class Localization {
     return this.formatWithFallback(keys, messageFromBundle);
   }
 
+  /**
+   * Sync version of `formatMessages`.
+   *
+   * Returns an array of the translation messages.
+   *
+   * @param   {Array<Object>} keys
+   * @returns {Array<{value: string, attributes: Object}>}
+   * @private
+   */
+  formatMessagesSync(keys) {
+    return this.formatWithFallbackSync(keys, messageFromBundle);
+  }
+
   /**
    * Retrieve translations corresponding to the passed keys.
    *
@@ -333,6 +394,19 @@ class Localization {
     return this.formatWithFallback(keys, valueFromBundle);
   }
 
+  /**
+   * Sync version of `formatValues`.
+   *
+   * Returns an array of the translation strings.
+   *
+   * @param   {Array<Object>} keys
+   * @returns {Array<string>}
+   * @private
+   */
+  formatValuesSync(keys) {
+    return this.formatWithFallbackSync(keys, valueFromBundle);
+  }
+
   /**
    * Retrieve the translation corresponding to the `id` identifier.
    *
@@ -345,7 +419,7 @@ class Localization {
    *
    *     // 'Hello, world!'
    *
-   * Returns a Promise resolving to the translation string.
+   * Returns a Promise resolving to a translation string.
    *
    * Use this sparingly for one-off messages which don't need to be
    * retranslated when the user changes their language preferences, e.g. in
@@ -360,6 +434,20 @@ class Localization {
     return val;
   }
 
+  /**
+   * Sync version of `formatValue`.
+   *
+   * Returns a translation string.
+   *
+   * @param   {Array<Object>} keys
+   * @returns {string>}
+   * @private
+   */
+  formatValueSync(id, args) {
+    const [val] = this.formatValuesSync([{id, args}]);
+    return val;
+  }
+
   /**
    * Register weak observers on events that will trigger cache invalidation
    */
@@ -398,8 +486,8 @@ class Localization {
    * @param {bool} eager - whether the I/O for new context should begin eagerly
    */
   onChange(eager = false) {
-    this.bundles = this.cached(
+    let generateMessages = this.isSync ? this.generateBundlesSync : this.generateBundles;
-      this.generateBundles(this.resourceIds));
+    this.bundles = this.cached(generateMessages(this.resourceIds));
     if (eager) {
       // If the first app locale is the same as last fallback
       // it means that we have all resources in this locale, and
@@ -412,51 +500,17 @@ class Localization {
       this.bundles.touchNext(prefetchCount);
     }
   }
+
+  setIsSync(isSync) {
+    this.isSync = isSync;
+    this.onChange();
+  }
 }
 
 Localization.prototype.QueryInterface = ChromeUtils.generateQI([
   Ci.nsISupportsWeakReference,
 ]);
 
-class LocalizationSync extends Localization {
-  constructor(resourceIds = [], generateBundles = defaultGenerateBundlesSync) {
-    super(resourceIds, generateBundles);
-  }
-
-  cached(iterable) {
-    return CachedSyncIterable.from(iterable);
-  }
-
-  formatWithFallback(keys, method) {
-    const translations = new Array(keys.length);
-    let hasAtLeastOneBundle = false;
-
-    for (const bundle of this.bundles) {
-      hasAtLeastOneBundle = true;
-      const missingIds = keysFromBundle(method, bundle, keys, translations);
-
-      if (missingIds.size === 0) {
-        break;
-      }
-
-      const locale = bundle.locales[0];
-      const ids = Array.from(missingIds).join(", ");
-      maybeReportErrorToGecko(`[fluent] Missing translations in ${locale}: ${ids}.`);
-    }
-
-    if (!hasAtLeastOneBundle) {
-      maybeReportErrorToGecko(`[fluent] Request for keys failed because no resource bundles got generated.\n keys: ${JSON.stringify(keys)}.\n resourceIds: ${JSON.stringify(this.resourceIds)}.`);
-    }
-
-    return translations;
-  }
-
-  formatValue(id, args) {
-    const [val] = this.formatValues([{id, args}]);
-    return val;
-  }
-}
-
 /**
  * Format the value of a message into a string.
  *
@@ -577,7 +631,6 @@ function keysFromBundle(method, bundle, keys, translations) {
     }
   });
 
-
   return missingIds;
 }
 
@@ -585,14 +638,13 @@ function keysFromBundle(method, bundle, keys, translations) {
  * Helper function which allows us to construct a new
  * Localization from Localization.
  */
-var getLocalization = (resourceIds) => {
+var getLocalization = (resourceIds, sync = false) => {
-  return new Localization(resourceIds);
+  return new Localization(resourceIds, sync);
 };
 
 var getLocalizationWithCustomGenerateMessages = (resourceIds, generateMessages) => {
-  return new Localization(resourceIds, generateMessages);
+  return new Localization(resourceIds, false, generateMessages);
 };
 
 this.Localization = Localization;
-this.LocalizationSync = LocalizationSync;
+var EXPORTED_SYMBOLS = ["Localization", "getLocalization", "getLocalizationWithCustomGenerateMessages"];
-var EXPORTED_SYMBOLS = ["Localization", "LocalizationSync", "getLocalization", "getLocalizationWithCustomGenerateMessages"];

intl/l10n/docs/fluent_tutorial.rst

@@ -540,16 +540,16 @@ contexts manually using the `Localization` class:
 
   const { Localization } =
     ChromeUtils.import("resource://gre/modules/Localization.jsm", {});
-  
+
-  
+
   const myL10n = new Localization([
     "branding/brand.ftl",
     "browser/preferences/preferences.ftl"
   ]);
-  
+
-  
+
   let [isDefaultMsg, isNotDefaultMsg] =
-    myL10n.formatValues({id: "is-default"}, {id: "is-not-default"});
+    await myL10n.formatValues({id: "is-default"}, {id: "is-not-default"});
 
 
 .. admonition:: Example
@@ -563,6 +563,32 @@ contexts manually using the `Localization` class:
   A developer may create manually a new context with the same resources as the main one,
   but hardcode it to `en-US` and then build the search index using both contexts.
 
+
+By default, all `Localization` contexts are asynchronous. It is possible to create a synchronous
+one by passing an `sync = false` argument to the constructor, or calling the `SetIsSync(bool)` method
+on the class.
+
+
+.. code-block:: javascript
+
+  const { Localization } =
+    ChromeUtils.import("resource://gre/modules/Localization.jsm", {});
+
+
+  const myL10n = new Localization([
+    "branding/brand.ftl",
+    "browser/preferences/preferences.ftl"
+  ], false);
+
+
+  let [isDefaultMsg, isNotDefaultMsg] =
+    myL10n.formatValuesSync({id: "is-default"}, {id: "is-not-default"});
+
+
+Synchronous contexts should be always avoided as they require synchronous I/O. If you think your use case
+requires a synchronous localization context, please consult Gecko, Performance and L10n Drivers teams.
+
+
 Designing Localizable APIs
 ==========================
 

intl/l10n/mozILocalization.idl

@@ -3,6 +3,12 @@
  * 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/. */
 
+/**
+ * This is an internal XPIDL used to expose a JS based Localization class to be used
+ * by its C++ wrapper.
+ *
+ * Consumers should use the WebIDL Localization API instead of this one.
+ */
 #include "nsISupports.idl"
 
 [scriptable, uuid(7d468600-551f-4fe0-98c9-92a53b63ec8d)]
@@ -15,11 +21,14 @@ interface mozILocalization : nsISupports
   Promise formatMessages(in Array<jsval> aKeys);
   Promise formatValues(in Array<jsval> aKeys);
   Promise formatValue(in AString aId, [optional] in jsval aArgs);
+
+  Array<jsval> formatMessagesSync(in Array<jsval> aKeys);
+  void setIsSync(in boolean isSync);
 };
 
 [scriptable, uuid(96632d26-1422-12e9-b1ce-9bb586acd241)]
 interface mozILocalizationJSM : nsISupports
 {
-  mozILocalization getLocalization(in Array<AString> resourceIds);
+  mozILocalization getLocalization(in Array<AString> resourceIds, in bool sync);
   mozILocalization getLocalizationWithCustomGenerateMessages(in Array<AString> resourceIds, in jsval generateMessages);
 };

intl/l10n/test/test_localization.js

@@ -35,7 +35,7 @@ add_task(async function test_methods_calling() {
 
   const l10n = new Localization([
     "/browser/menu.ftl",
-  ], generateMessages);
+  ], false, generateMessages);
 
   let values = await l10n.formatValues([{id: "key"}, {id: "key2"}]);
 
@@ -81,7 +81,7 @@ key = { PLATFORM() ->
 
   const l10n = new Localization([
     "/test.ftl",
-  ], generateMessages);
+  ], false, generateMessages);
 
   let values = await l10n.formatValues([{id: "key"}]);
 
@@ -114,7 +114,7 @@ add_task(async function test_add_remove_resourceIds() {
     yield * await L10nRegistry.generateBundles(["en-US"], resIds);
   }
 
-  const l10n = new Localization(["/browser/menu.ftl"], generateMessages);
+  const l10n = new Localization(["/browser/menu.ftl"], false, generateMessages);
 
   let values = await l10n.formatValues([{id: "key1"}, {id: "key2"}]);
 
@@ -139,3 +139,81 @@ add_task(async function test_add_remove_resourceIds() {
   L10nRegistry.load = originalLoad;
   Services.locale.requestedLocales = originalRequested;
 });
+
+add_task(async function test_switch_to_async() {
+  const { L10nRegistry, FileSource } =
+    ChromeUtils.import("resource://gre/modules/L10nRegistry.jsm");
+
+  const fs = {
+    "/localization/en-US/browser/menu.ftl": "key1 = Value1",
+    "/localization/en-US/toolkit/menu.ftl": "key2 = Value2",
+  };
+  const originalLoad = L10nRegistry.load;
+  const originalLoadSync = L10nRegistry.loadSync;
+  const originalRequested = Services.locale.requestedLocales;
+
+  let syncLoads = 0;
+  let asyncLoads = 0;
+
+  L10nRegistry.load = async function(url) {
+    asyncLoads += 1;
+    return fs[url];
+  };
+
+  L10nRegistry.loadSync = function(url) {
+    syncLoads += 1;
+    return fs[url];
+  };
+
+  const source = new FileSource("test", ["en-US"], "/localization/{locale}");
+  L10nRegistry.registerSource(source);
+
+  async function* generateMessages(resIds) {
+    yield * await L10nRegistry.generateBundles(["en-US"], resIds);
+  }
+
+  function* generateMessagesSync(resIds) {
+    yield * L10nRegistry.generateBundlesSync(["en-US"], resIds);
+  }
+
+  const l10n = new Localization(["/browser/menu.ftl"], false, generateMessages, generateMessagesSync);
+
+  let values = await l10n.formatValues([{id: "key1"}, {id: "key2"}]);
+
+  equal(values[0], "Value1");
+  equal(values[1], undefined);
+  equal(syncLoads, 0);
+  equal(asyncLoads, 1);
+
+  l10n.setIsSync(true);
+
+  l10n.addResourceIds(["/toolkit/menu.ftl"]);
+
+  // Nothing happens when we switch, because
+  // the next load is lazy.
+  equal(syncLoads, 0);
+  equal(asyncLoads, 1);
+
+  values = l10n.formatValuesSync([{id: "key1"}, {id: "key2"}]);
+  let values2 = await l10n.formatValues([{id: "key1"}, {id: "key2"}]);
+
+  deepEqual(values, values2);
+  equal(values[0], "Value1");
+  equal(values[1], "Value2");
+  equal(syncLoads, 1);
+  equal(asyncLoads, 1);
+
+  l10n.removeResourceIds(["/browser/menu.ftl"]);
+
+  values = await l10n.formatValues([{id: "key1"}, {id: "key2"}]);
+
+  equal(values[0], undefined);
+  equal(values[1], "Value2");
+  equal(syncLoads, 1);
+  equal(asyncLoads, 1);
+
+  L10nRegistry.sources.clear();
+  L10nRegistry.load = originalLoad;
+  L10nRegistry.loadSync = originalLoadSync;
+  Services.locale.requestedLocales = originalRequested;
+});

intl/l10n/test/test_localization_sync.js

@@ -0,0 +1,151 @@
+/* Any copyright is dedicated to the Public Domain.
+   http://creativecommons.org/publicdomain/zero/1.0/ */
+
+const { AppConstants } = ChromeUtils.import("resource://gre/modules/AppConstants.jsm");
+const { Localization } = ChromeUtils.import("resource://gre/modules/Localization.jsm");
+const { Services } = ChromeUtils.import("resource://gre/modules/Services.jsm");
+
+add_task(function test_methods_calling() {
+  const { L10nRegistry, FileSource } =
+    ChromeUtils.import("resource://gre/modules/L10nRegistry.jsm");
+
+  const fs = {
+    "/localization/de/browser/menu.ftl": "key = [de] Value2",
+    "/localization/en-US/browser/menu.ftl": "key = [en] Value2\nkey2 = [en] Value3",
+  };
+  const originalLoadSync = L10nRegistry.loadSync;
+  const originalRequested = Services.locale.requestedLocales;
+
+  L10nRegistry.loadSync = function(url) {
+    return fs[url];
+  };
+
+  const source = new FileSource("test", ["de", "en-US"], "/localization/{locale}");
+  L10nRegistry.registerSource(source);
+
+  function* generateMessagesSync(resIds) {
+    yield * L10nRegistry.generateBundlesSync(["de", "en-US"], resIds);
+  }
+
+  const l10n = new Localization([
+    "/browser/menu.ftl",
+  ], true, null, generateMessagesSync);
+
+  let values = l10n.formatValuesSync([{id: "key"}, {id: "key2"}]);
+
+  equal(values[0], "[de] Value2");
+  equal(values[1], "[en] Value3");
+
+  L10nRegistry.sources.clear();
+  L10nRegistry.loadSync = originalLoadSync;
+  Services.locale.requestedLocales = originalRequested;
+});
+
+add_task(function test_builtins() {
+  const { L10nRegistry, FileSource } =
+    ChromeUtils.import("resource://gre/modules/L10nRegistry.jsm");
+
+  const known_platforms = {
+    "linux": "linux",
+    "win": "windows",
+    "macosx": "macos",
+    "android": "android",
+  };
+
+  const fs = {
+    "/localization/en-US/test.ftl": `
+key = { PLATFORM() ->
+        ${ Object.values(known_platforms).map(
+              name => `      [${ name }] ${ name.toUpperCase() } Value\n`).join("") }
+       *[other] OTHER Value
+    }`,
+  };
+  const originalLoadSync = L10nRegistry.loadSync;
+
+  L10nRegistry.loadSync = function(url) {
+    return fs[url];
+  };
+
+  const source = new FileSource("test", ["en-US"], "/localization/{locale}");
+  L10nRegistry.registerSource(source);
+
+  function* generateMessagesSync(resIds) {
+    yield * L10nRegistry.generateBundlesSync(["en-US"], resIds);
+  }
+
+  const l10n = new Localization([
+    "/test.ftl",
+  ], true, null, generateMessagesSync);
+
+  let values = l10n.formatValuesSync([{id: "key"}]);
+
+  ok(values[0].includes(
+    `${ known_platforms[AppConstants.platform].toUpperCase() } Value`));
+
+  L10nRegistry.sources.clear();
+  L10nRegistry.loadSync = originalLoadSync;
+});
+
+add_task(function test_add_remove_resourceIds() {
+  const { L10nRegistry, FileSource } =
+    ChromeUtils.import("resource://gre/modules/L10nRegistry.jsm");
+
+  const fs = {
+    "/localization/en-US/browser/menu.ftl": "key1 = Value1",
+    "/localization/en-US/toolkit/menu.ftl": "key2 = Value2",
+  };
+  const originalLoadSync = L10nRegistry.loadSYnc;
+  const originalRequested = Services.locale.requestedLocales;
+
+  L10nRegistry.loadSync = function(url) {
+    return fs[url];
+  };
+
+  const source = new FileSource("test", ["en-US"], "/localization/{locale}");
+  L10nRegistry.registerSource(source);
+
+  function* generateMessagesSync(resIds) {
+    yield * L10nRegistry.generateBundlesSync(["en-US"], resIds);
+  }
+
+  const l10n = new Localization(["/browser/menu.ftl"], true, null, generateMessagesSync);
+
+  let values = l10n.formatValuesSync([{id: "key1"}, {id: "key2"}]);
+
+  equal(values[0], "Value1");
+  equal(values[1], undefined);
+
+  l10n.addResourceIds(["/toolkit/menu.ftl"]);
+
+  values = l10n.formatValuesSync([{id: "key1"}, {id: "key2"}]);
+
+  equal(values[0], "Value1");
+  equal(values[1], "Value2");
+
+  l10n.removeResourceIds(["/browser/menu.ftl"]);
+
+  values = l10n.formatValuesSync([{id: "key1"}, {id: "key2"}]);
+
+  equal(values[0], undefined);
+  equal(values[1], "Value2");
+
+  L10nRegistry.sources.clear();
+  L10nRegistry.loadSync = originalLoadSync;
+  Services.locale.requestedLocales = originalRequested;
+});
+
+add_task(function test_calling_sync_methods_in_async_mode_fails() {
+  const l10n = new Localization(["/browser/menu.ftl"], false);
+
+  Assert.throws(() => {
+    l10n.formatValuesSync([{ id: "key1" }, { id: "key2" }]);
+  }, /Can't use sync formatWithFallback when state is async./);
+
+  Assert.throws(() => {
+    l10n.formatValueSync("key1");
+  }, /Can't use sync formatWithFallback when state is async./);
+
+  Assert.throws(() => {
+    l10n.formatMessagesSync([{ id: "key1"}]);
+  }, /Can't use sync formatWithFallback when state is async./);
+});

intl/l10n/test/test_pseudo.js

@@ -46,7 +46,7 @@ add_task(async function test_accented_works() {
 
   const l10n = new Localization([
     "/browser/menu.ftl",
-  ], generateMessages);
+  ], false, generateMessages);
   l10n.registerObservers();
 
   {
@@ -108,7 +108,7 @@ add_task(async function test_unavailable_strategy_works() {
 
   const l10n = new Localization([
     "/browser/menu.ftl",
-  ], generateMessages);
+  ], false, generateMessages);
   l10n.registerObservers();
 
   {

intl/l10n/test/xpcshell.ini

@@ -4,5 +4,6 @@ head =
 [test_l10nregistry.js]
 [test_l10nregistry_sync.js]
 [test_localization.js]
+[test_localization_sync.js]
 [test_messagecontext.js]
 [test_pseudo.js]

toolkit/components/mozintl/mozIntl.jsm

@@ -3,7 +3,7 @@
  * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
 
 const {Services} = ChromeUtils.import("resource://gre/modules/Services.jsm");
-const { LocalizationSync } = ChromeUtils.import("resource://gre/modules/Localization.jsm", null);
+const { Localization } = ChromeUtils.import("resource://gre/modules/Localization.jsm", null);
 
 const mozIntlHelper =
   Cc["@mozilla.org/mozintlhelper;1"].getService(Ci.mozIMozIntlHelper);
@@ -269,7 +269,7 @@ class MozIntl {
     }
 
     if (!this._cache.hasOwnProperty("languageLocalization")) {
-      const loc = new LocalizationSync(["toolkit/intl/languageNames.ftl"]);
+      const loc = new Localization(["toolkit/intl/languageNames.ftl"], true);
       this._cache.languageLocalization = loc;
     }
 
@@ -281,7 +281,7 @@ class MozIntl {
       }
       let lcLangCode = langCode.toLowerCase();
       if (availableLocaleDisplayNames.language.has(lcLangCode)) {
-        const value = loc.formatValue(`language-name-${lcLangCode}`);
+        const value = loc.formatValueSync(`language-name-${lcLangCode}`);
         if (value !== undefined) {
           return value;
         }
@@ -296,7 +296,7 @@ class MozIntl {
     }
 
     if (!this._cache.hasOwnProperty("regionLocalization")) {
-      const loc = new LocalizationSync(["toolkit/intl/regionNames.ftl"]);
+      const loc = new Localization(["toolkit/intl/regionNames.ftl"], true);
       this._cache.regionLocalization = loc;
     }
 
@@ -308,7 +308,7 @@ class MozIntl {
       }
       let lcRegionCode = regionCode.toLowerCase();
       if (availableLocaleDisplayNames.region.has(lcRegionCode)) {
-        const value = loc.formatValue(`region-name-${lcRegionCode}`);
+        const value = loc.formatValueSync(`region-name-${lcRegionCode}`);
         if (value !== undefined) {
           return value;
         }

tools/lint/eslint/eslint-plugin-mozilla/lib/environments/privileged.js

@@ -312,6 +312,7 @@ module.exports = {
     "KeyEvent": false,
     "KeyboardEvent": false,
     "KeyframeEffect": false,
+    "Localization": false,
     "Location": false,
     "MIDIAccess": false,
     "MIDIConnectionEvent": false,

xpcom/ds/StaticAtoms.py

@@ -289,6 +289,7 @@ STATIC_ATOMS = [
     Atom("datal10nargs", "data-l10n-args"),
     Atom("datal10nattrs", "data-l10n-attrs"),
     Atom("datal10nname", "data-l10n-name"),
+    Atom("datal10nsync", "data-l10n-sync"),
     Atom("dataType", "data-type"),
     Atom("dateTime", "date-time"),
     Atom("date", "date"),