Find the system locale from the browser or OS

pkg/intl/intl.dart

 // Copyright (c) 2012, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
 /**
  * Internationalization object providing access to message formatting objects,
  * date formatting, parsing, bidirectional text relative to a specific locale.
  */
 #library('intl');
 
@@ skipping 88 matching lines @@
    * Note that null is interpreted as meaning the default locale, so if
    * [newLocale] is null it will be returned.
    */
   static String verifiedLocale(String newLocale) {
     // TODO(alanknight): This is specific to DateFormat, and only used there
     // now. This should be moved, renamed, or generalized.
     if (newLocale == null) return _getDefaultLocale();
     if (_localeExists(newLocale)) {
       return newLocale;
     }
-    for (var each in [_canonicalized(newLocale), _shortLocale(newLocale)]) {
+    for (var each in [canonicalizedLocale(newLocale), _shortLocale(newLocale)]) {
       if (_localeExists(each)) {
         return each;
       }
     }
     throw new IllegalArgumentException("Invalid locale '$newLocale'");
   }
 
   /** Return the short version of a locale name, e.g. 'en_US' => 'en' */
   static String _shortLocale(String aLocale) {
     if (aLocale.length < 2) return aLocale;
     return aLocale.substring(0, 2).toLowerCase();
   }
 
   /**
    * Return a locale name turned into xx_YY where it might possibly be
    * in the wrong case or with a hyphen instead of an underscore.
    */
-  static String _canonicalized(String aLocale) {
+  static String canonicalizedLocale(String aLocale) {
     // Locales of length < 5 are presumably two-letter forms, or else malformed.
     // Locales of length > 6 are likely to be malformed. In either case we
     // return them unmodified and if correct they will be found.
     if ((aLocale.length < 5) || (aLocale.length > 6)) return aLocale;
     if (aLocale[2] != '-' && (aLocale[2] != '_')) return aLocale;
     return '${aLocale[0]}${aLocale[1]}_${aLocale[3].toUpperCase()}'
            '${aLocale[4].toUpperCase()}';
   }
 
   /**
    * Support method for message formatting. Select the correct plural form from
    * [cases] given [howMany].
    */
   static String plural(var howMany, Map cases, [num offset=0]) {
     // TODO(efortuna): Deal with "few" and "many" cases, offset, and others!
     return select(howMany.toString(), cases);
   }
 
   /**
    * Format the given function with a specific [locale], given a
    * [msg_function] that takes no parameters and returns a String. We
    * basically delay calling the message function proper until after the proper
    * locale has been set.
    */
   static String withLocale(String locale, Function msg_function) {
     // We have to do this silliness because Locale is not known at compile time,
     // but must be a static variable.
-    if (_defaultLocale == null) _defaultLocale = _getDefaultLocale();
+    if (_defaultLocale == null) _defaultLocale = systemLocale;
     var oldLocale = _defaultLocale;
     _defaultLocale = locale;
     var result = msg_function();
     _defaultLocale = oldLocale;
     return result;
   }
 
   /**
    * Support method for message formatting. Select the correct exact (gender,
    * usually) form from [cases] given the user [choice].
    */
   static String select(String choice, Map cases) {
     if (cases.containsKey(choice)) {
       return cases[choice];
     } else if (cases.containsKey('other')){
       return cases['other'];
     } else {
       return '';
     }
   }
 
   /**
+   * The system's locale, as obtained from the window.navigator.language
+   * or other operating system mechanism. Note that due to system limitations
+   * this is not automatically set, and must be set by importing one of
+   * intl_browser.dart or intl_standalone.dart and calling findSystemLocale().
+   */
+  // TODO(alanknight): Detect this without forcing the jump through hoops.
+  // Issue 5171.
+  static String systemLocale = 'en_US';

[Emily Fortuna, 2012/09/17 21:26:38]

in that case, should by default we make systemLocale = '' or null, to ensure
that the user ends up with the locale they want?

Also, if we're making another class field, let's move it up with the other
fields at the top of this file

[Alan Knight, 2012/09/17 22:16:18]

Default: The user may not call either of these mechanisms, so I wanted to give
it a default that would at least do something rather than just failing. If we
can make this happen transparently, then we wouldn't need a default value.

Moving up: Done.

+
+  /**
    * Helper to detect the locale as defined at runtime.
    */
   static String _getDefaultLocale() {
-    // TODO(efortuna): Detect the default locale given the user preferences.
-    // That would mean using window.navigator.language in a browser or
-    // an environment variable or other OS mechanism for the standalone VM.
-    // Yay, hard-coding for now!
-    return 'en_US';
+    return systemLocale;
   }
 
   /**
    * Accessor for the current locale. This should always == the default locale,
    * unless for some reason this gets called inside a message that resets the
    * locale.
    */
   static String getCurrentLocale() {
-    if (_defaultLocale == null) _defaultLocale = _getDefaultLocale();
+    if (_defaultLocale == null) _defaultLocale = systemLocale;

[Emily Fortuna, 2012/09/17 21:26:38]

if you add this systemLocale variable, the necessity for the _getDefaultLocale()
function goes away. Can we just get rid of it?

[Alan Knight, 2012/09/17 22:16:18]

Yes. I think I'd thought that but then forgot. Done.

     return _defaultLocale;
   }
 }
 
 /**
  * The internal mechanism for looking up messages. We expect this to be set
  * by the implementing package so that we're not dependent on its
  * implementation.
  */
 var _messageLookup = const
     UninitializedLocaleData('initializeMessages(<locale>)');
 
 /**
  * Initialize the message lookup mechanism. This is for internal use only.
  * User applications should import message_lookup_local.dart and call
  * initializeMessages
  */
 void initializeInternalMessageLookup(Function lookupFunction) {
   if (_messageLookup is UninitializedLocaleData) {
     _messageLookup = lookupFunction();
   }
 }