Percent signs escaping in templatetags

Closes python-babel#43

In Django >= 1.9, `%` signs are escaped to `%%` during extraction
then replaced by `%` during the rendering. [1]
Before Django 1.9, only single percent signs were escaped.

The extraction now behaves in the same way.

[1] django/django@b750889

django_babel/extract.py

@@ -11,6 +11,12 @@
     from django.utils.translation.template import (
         inline_re, block_re, endblock_re, plural_re, constant_re)
 
+try:
+    from django.utils.translation.trans_real import one_percent_re
+except ImportError:
+    # Django 1.9+
+    one_percent_re = None
+
 
 def join_tokens(tokens, trim=False):
     message = ''.join(tokens)
@@ -112,10 +118,14 @@ def extract_django(fileobj, keywords, comment_tags, options):
                 else:
                     singular.append('%%(%s)s' % t.contents)
             elif t.token_type == TOKEN_TEXT:
+                if one_percent_re:
+                    contents = one_percent_re.sub('%%', t.contents)
+                else:
+                    contents = t.contents.replace('%', '%%')
                 if inplural:
-                    plural.append(t.contents)
+                    plural.append(contents)
                 else:
-                    singular.append(t.contents)
+                    singular.append(contents)
         else:
             if t.token_type == TOKEN_BLOCK:
                 imatch = inline_re.match(t.contents)
@@ -124,6 +134,10 @@ def extract_django(fileobj, keywords, comment_tags, options):
                 if imatch:
                     g = imatch.group(1)
                     g = strip_quotes(g)
+                    if one_percent_re:
+                        g = one_percent_re.sub('%%', g)
+                    else:
+                        g = g.replace('%', '%%')
                     message_context = imatch.group(3)
                     if message_context:
                         # strip quotes

tests/test_extract.py

@@ -218,3 +218,33 @@ def test_blocktrans_with_whitespace_trimmed(self):
         buf = BytesIO(test_tmpl)
         messages = list(extract_django(buf, default_keys, [], {}))
         self.assertEqual([(4, None, u'foo bar', [])], messages)
+
+    @pytest.mark.skipif(django.VERSION >= (1, 9),
+                        reason='%-sign escaping changed in django 1.9')
+    def test_extract_trans_percents_old_way(self):
+        """Before Django 1.9, only a signle %-sign was escaped to %%"""
+        buf = BytesIO(b'{% trans "1 %, 2 %%, 3 %%%" %}')
+        messages = list(extract_django(buf, default_keys, [], {}))
+        self.assertEqual([(1, None, u'1 %%, 2 %%, 3 %%%', [])], messages)
+
+    @pytest.mark.skipif(django.VERSION >= (1, 9),
+                        reason='%-sign escaping changed in django 1.9')
+    def test_extract_blocktrans_percents_old_way(self):
+        """Before Django 1.9, only a signle %-sign was escaped to %%"""
+        buf = BytesIO(b'{% blocktrans %}1 %, 2 %%, 3 %%%{% endblocktrans %}')
+        messages = list(extract_django(buf, default_keys, [], {}))
+        self.assertEqual([(1, None, u'1 %%, 2 %%, 3 %%%', [])], messages)
+
+    @pytest.mark.skipif(django.VERSION < (1, 9),
+                        reason='%-sign escaping changed in django 1.9')
+    def test_extract_trans_percents(self):
+        buf = BytesIO(b'{% trans "1 %, 2 %%, 3 %%%" %}')
+        messages = list(extract_django(buf, default_keys, [], {}))
+        self.assertEqual([(1, None, u'1 %%, 2 %%%%, 3 %%%%%%', [])], messages)
+
+    @pytest.mark.skipif(django.VERSION < (1, 9),
+                        reason='%-sign escaping changed in django 1.9')
+    def test_extract_blocktrans_percents(self):
+        buf = BytesIO(b'{% blocktrans %}1 %, 2 %%, 3 %%%{% endblocktrans %}')
+        messages = list(extract_django(buf, default_keys, [], {}))
+        self.assertEqual([(1, None, u'1 %%, 2 %%%%, 3 %%%%%%', [])], messages)