added a trans filter (closes #85)

CHANGELOG

@@ -5,6 +5,7 @@ Backward incompatibilities:
  * the odd and even filters are now tests:
      {{ foo|odd }} must now be written {{ foo is(odd) }}
 
+ * added a "trans" filter
  * added "test" feature (accessible via the "is" operator)
  * removed the debug tag (should be done in an extension)
  * fixed trans tag when no vars are used in plural form

doc/02-Twig-for-Template-Designers.markdown

@@ -881,6 +881,12 @@ The `plural` tag should provide the `count` used to select the right string.
 Within the translatable string, the special `count` variable always contain
 the count value (here the value of `apple_count`).
 
+Within an expression or in a tag, you can use the `trans` filter to translate
+simple strings or variables:
+
+    [twig]
+    {{ var|default(default_value|trans) }}
+
 Expressions
 -----------
 

doc/06-Recipes.markdown

@@ -243,3 +243,23 @@ Use the standard `xgettext` utility as you would have done with plain PHP
 code:
 
     xgettext --default-domain=messages -p ./locale --from-code=UTF-8 -n --omit-header -L PHP /tmp/cache/*.php
+
+Complex Translations within an Expression or Tag
+------------------------------------------------
+
+Translations can be done with both the `trans` tag and the `trans` filter. The
+filter is less powerful as it only works for simple variables or strings. For
+more complex scenario, like pluralization, you can use a two-step strategy:
+
+    [twig]
+    {# assign the translation to a temporary variable #}
+    {% set default_value %}
+        {% trans %}
+          Hey {{ name }}, I have one apple.
+        {% plural apple_count %}
+          Hey {{ name }}, I have {{ count }} apples.
+        {% endtrans %}
+    {% endset %}
+
+    {# use the temporary variable within an expression #}
+    {{ var|default(default_value|trans) }}

lib/Twig/Extension/I18n.php

@@ -20,6 +20,18 @@ class Twig_Extension_I18n extends Twig_Extension
         return array(new Twig_TokenParser_Trans());
     }
 
+    /**
+     * Returns a list of filters to add to the existing list.
+     *
+     * @return array An array of filters
+     */
+    public function getFilters()
+    {
+        return array(
+            'trans' => new Twig_Filter_Function('gettext'),
+        );
+    }
+
     /**
      * Returns the name of the extension.
      *