Fixed #19915 - Made blocktrans tag honor TEMPLATE_STRING_IF_INVALID.

Thanks Natalia Bidart for the report and Matías Bordese for the fix.

django/templatetags/i18n.py

 from __future__ import unicode_literals
 import re
 
+from django.conf import settings
 from django.template import (Node, Variable, TemplateSyntaxError,
     TokenParser, Library, TOKEN_TEXT, TOKEN_VAR)
 from django.template.base import render_value_in_context
@@ -17,7 +18,6 @@ class GetAvailableLanguagesNode(Node):
         self.variable = variable
 
     def render(self, context):
-        from django.conf import settings
         context[self.variable] = [(k, translation.ugettext(v)) for k, v in settings.LANGUAGES]
         return ''
 
@@ -143,7 +143,10 @@ class BlockTranslateNode(Node):
                 result = translation.pgettext(message_context, singular)
             else:
                 result = translation.ugettext(singular)
-        data = dict([(v, render_value_in_context(context.get(v, ''), context)) for v in vars])
+        default_value = settings.TEMPLATE_STRING_IF_INVALID
+        render_value = lambda v: render_value_in_context(
+            context.get(v, default_value), context)
+        data = dict([(v, render_value(v)) for v in vars])
         context.pop()
         try:
             result = result % data

tests/template_tests/tests.py

@@ -1392,7 +1392,10 @@ class Templates(TestCase):
             'i18n33': ('{% load i18n %}{{ langcode|language_name }} {{ langcode|language_name_local }} {{ langcode|language_bidi }}', {'langcode': 'nl'}, 'Dutch Nederlands False'),
 
             # blocktrans handling of variables which are not in the context.
-            'i18n34': ('{% load i18n %}{% blocktrans %}{{ missing }}{% endblocktrans %}', {}, ''),
+            # this should work as if blocktrans was not there (bug #19915)
+            'i18n34': ('{% load i18n %}{% blocktrans %}{{ missing }}{% endblocktrans %}', {}, ('', 'INVALID')),
+            'i18n34_2': ("{% load i18n %}{% blocktrans with a='α' %}{{ missing }}{% endblocktrans %}", {}, ('', 'INVALID')),
+            'i18n34_3': ('{% load i18n %}{% blocktrans with a=anton %}{{ missing }}{% endblocktrans %}', {'anton': 'α'}, ('', 'INVALID')),
 
             # trans tag with as var
             'i18n35': ('{% load i18n %}{% trans "Page not found" as page_not_found %}{{ page_not_found }}', {'LANGUAGE_CODE': 'de'}, "Seite nicht gefunden"),