Bug 1456565 - Fetch fallback locale eagerly in Fluent. r=stas

MozReview-Commit-ID: A9wBGxzdD2m

--HG--
extra : rebase_source : 5b8cd54faff389e9a94412b3ec928f1c36bdd4a2

intl/l10n/Localization.jsm

@@ -27,17 +27,17 @@ const { Services } = ChromeUtils.import("resource://gre/modules/Services.jsm", {
 const { AppConstants } = ChromeUtils.import("resource://gre/modules/AppConstants.jsm", {});
 
 /*
- * CachedIterable caches the elements yielded by an iterable.
+ * CachedAsyncIterable caches the elements yielded by an iterable.
  *
  * It can be used to iterate over an iterable many times without depleting the
  * iterable.
  */
-class CachedIterable {
+class CachedAsyncIterable {
   /**
-   * Create an `CachedIterable` instance.
+   * Create an `CachedAsyncIterable` instance.
    *
    * @param {Iterable} iterable
-   * @returns {CachedIterable}
+   * @returns {CachedAsyncIterable}
    */
   constructor(iterable) {
     if (Symbol.asyncIterator in Object(iterable)) {
@@ -82,11 +82,16 @@ class CachedIterable {
   /**
    * This method allows user to consume the next element from the iterator
    * into the cache.
+   *
+   * @param {number} count - number of elements to consume
    */
-  touchNext() {
+  async touchNext(count = 1) {
     const { seen, iterator } = this;
+    let idx = 0;
+    while (idx++ < count) {
       if (seen.length === 0 || seen[seen.length - 1].done === false) {
-      seen.push(iterator.next());
+        seen.push(await iterator.next());
+      }
     }
   }
 }
@@ -122,7 +127,7 @@ class Localization {
   constructor(resourceIds, generateMessages = defaultGenerateMessages) {
     this.resourceIds = resourceIds;
     this.generateMessages = generateMessages;
-    this.ctxs = new CachedIterable(this.generateMessages(this.resourceIds));
+    this.ctxs = new CachedAsyncIterable(this.generateMessages(this.resourceIds));
   }
 
   /**
@@ -268,7 +273,7 @@ class Localization {
    * that language negotiation or available resources changed.
    */
   onLanguageChange() {
-    this.ctxs = new CachedIterable(this.generateMessages(this.resourceIds));
+    this.ctxs = new CachedAsyncIterable(this.generateMessages(this.resourceIds));
   }
 }
 

intl/l10n/l10n.js

@@ -46,8 +46,8 @@
 
   document.l10n = new DOMLocalization(window, resourceIds);
 
-  // trigger first context to be fetched eagerly
+  // Trigger the first two contexts to be loaded eagerly.
-  document.l10n.ctxs.touchNext();
+  document.l10n.ctxs.touchNext(2);
 
   document.l10n.ready = documentReady().then(() => {
     document.l10n.registerObservers();