Bug 1373061 - Fallback on en-US in sdk/l10n.get. r=Pike

Users of getPreferedLocales method expect to always have `en-US` as a last resort.
This patch brings back the behavior which regressed with the landing of bug 1346616.

MozReview-Commit-ID: 8bgm7PJnSRJ

--HG--
extra : rebase_source : c63ba6e4508117a6d4bd9d2a18a2c8665dd52bbe

addon-sdk/source/lib/sdk/l10n/locale.js

@@ -12,7 +12,15 @@ const { Cu, Cc, Ci } = require("chrome");
 const { Services } = Cu.import("resource://gre/modules/Services.jsm");
 
 function getPreferedLocales(caseSensitve) {
-  return Services.locale.getRequestedLocales();
+  const locales = Services.locale.getRequestedLocales();
+
+  // This API expects to always append en-US fallback, so for compatibility
+  // reasons, we're going to inject it here.
+  // See bug 1373061 for details.
+  if (!locales.includes('en-US')) {
+    locales.push('en-US');
+  }
+  return locales;
 }
 exports.getPreferedLocales = getPreferedLocales;
 

addon-sdk/source/test/test-l10n-locale.js

@@ -2,7 +2,10 @@
  * 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/. */
 
-const { findClosestLocale } = require("sdk/l10n/locale");
+const { Cu, Cc, Ci } = require("chrome");
+const { Services } = Cu.import('resource://gre/modules/Services.jsm');
+const { findClosestLocale,
+        getPreferedLocales } = require("sdk/l10n/locale");
 
 exports.testFindClosestLocale = function(assert) {
   // Second param of findClosestLocale (aMatchLocales) have to be in lowercase
@@ -44,4 +47,14 @@ exports.testFindClosestLocale = function(assert) {
                    "ja", "We accept locale with 1 part from locale with 3 parts");
 };
 
+exports.testGetPreferedLocales = function(assert) {
+  let currentLocales = Services.locale.getRequestedLocales();
+
+  Services.locale.setRequestedLocales(['pl']);
+
+  assert.equal(getPreferedLocales().includes('en-US'), true, "en-US should always be in the list");
+
+  Services.locale.setRequestedLocales(currentLocales);
+};
+
 require('sdk/test').run(exports);