Fixed #20311 -- Make sure makemessages doesn't create duplicate Plural-Forms .po file headers.

Thanks naktinis for the report and initial patch.

django/core/management/commands/makemessages.py

@@ -402,11 +402,11 @@ class Command(NoArgsCommand):
                     if self.verbosity > 1:
                         self.stdout.write("copying plural forms: %s\n" % m.group('value'))
                     lines = []
-                    seen = False
+                    found = False
                     for line in msgs.split('\n'):
-                        if not line and not seen:
+                        if not found and (not line or plural_forms_re.search(line)):
                             line = '%s\n' % m.group('value')
-                            seen = True
+                            found = True
                         lines.append(line)
                     msgs = '\n'.join(lines)
                     break

tests/i18n/commands/__init__.py

@@ -1,4 +1,4 @@
-from django.utils.translation import ugettext as _
+from django.utils.translation import ugettext as _, ungettext
 
 # Translators: This comment should be extracted
 dummy1 = _("This is a translatable string.")
@@ -6,3 +6,7 @@ dummy1 = _("This is a translatable string.")
 # This comment should not be extracted
 dummy2 = _("This is another translatable string.")
 
+# This file has a literal with plural forms. When processed first, makemessages
+# shouldn't create a .po file with duplicate `Plural-Forms` headers
+number = 3
+dummuy3 = ungettext("%(number)s Foo", "%(number)s Foos", number) % {'number': number}

tests/i18n/commands/extraction.py

@@ -329,6 +329,15 @@ class SymlinkExtractorTests(ExtractorTests):
 
 
 class CopyPluralFormsExtractorTests(ExtractorTests):
+    PO_FILE_ES = 'locale/es/LC_MESSAGES/django.po'
+
+    def tearDown(self):
+        os.chdir(self.test_dir)
+        try:
+            self._rmrf('locale/es')
+        except OSError:
+            pass
+        os.chdir(self._cwd)
 
     def test_copy_plural_forms(self):
         os.chdir(self.test_dir)
@@ -338,6 +347,16 @@ class CopyPluralFormsExtractorTests(ExtractorTests):
             po_contents = force_text(fp.read())
             self.assertTrue('Plural-Forms: nplurals=2; plural=(n != 1)' in po_contents)
 
+    def test_override_plural_forms(self):
+        """Ticket #20311."""
+        os.chdir(self.test_dir)
+        management.call_command('makemessages', locale='es', extensions=['djtpl'], verbosity=0)
+        self.assertTrue(os.path.exists(self.PO_FILE_ES))
+        with open(self.PO_FILE_ES, 'r') as fp:
+            po_contents = force_text(fp.read())
+            found = re.findall(r'^(?P<value>"Plural-Forms.+?\\n")\s*$', po_contents, re.MULTILINE | re.DOTALL)
+            self.assertEqual(1, len(found))
+
 
 class NoWrapExtractorTests(ExtractorTests):
 

tests/i18n/commands/templates/plural.djtpl

@@ -0,0 +1,6 @@
+{% load i18n %}
+{% comment %}
+This file has a literal with plural forms. When processed first, makemessages
+shouldn't create a .po file with duplicate `Plural-Forms` headers
+{% endcomment %}
+{% blocktrans count number=3 %}{{ number }} Bar{% plural %}{{ number }} Bars{% endblocktrans %}