Fixed #6106 -- Prevented makemessages from changing .po files when up to date.

Co-authored-by: Daniyal Abbasi <abbasi.daniyal98@gmail.com>

django/core/management/commands/makemessages.py

@@ -4,6 +4,7 @@ import re
 import sys
 from functools import total_ordering
 from itertools import dropwhile
+from pathlib import Path
 
 import django
 from django.conf import settings
@@ -208,7 +209,7 @@ class Command(BaseCommand):
 
     requires_system_checks = []
 
-    msgmerge_options = ['-q', '--previous']
+    msgmerge_options = ['-q', '--backup=none', '--previous', '--update']
     msguniq_options = ['--to-code=utf-8']
     msgattrib_options = ['--no-obsolete']
     xgettext_options = ['--from-code=UTF-8', '--add-comments=Translators']
@@ -615,13 +616,14 @@ class Command(BaseCommand):
 
         if os.path.exists(pofile):
             args = ['msgmerge'] + self.msgmerge_options + [pofile, potfile]
-            msgs, errors, status = popen_wrapper(args)
+            _, errors, status = popen_wrapper(args)
             if errors:
                 if status != STATUS_OK:
                     raise CommandError(
                         "errors happened while running msgmerge\n%s" % errors)
                 elif self.verbosity > 0:
                     self.stdout.write(errors)
+            msgs = Path(pofile).read_text(encoding='utf-8')
         else:
             with open(potfile, encoding='utf-8') as fp:
                 msgs = fp.read()

tests/i18n/test_extraction.py

@@ -804,3 +804,37 @@ class NoSettingsExtractionTests(AdminScriptTestCase):
         out, err = self.run_django_admin(['makemessages', '-l', 'en', '-v', '0'])
         self.assertNoOutput(err)
         self.assertNoOutput(out)
+
+
+class UnchangedPoExtractionTests(ExtractorTests):
+    work_subdir = 'unchanged'
+
+    def setUp(self):
+        super().setUp()
+        po_file = Path(self.PO_FILE)
+        po_file_tmp = Path(self.PO_FILE + '.tmp')
+        if os.name == 'nt':
+            # msgmerge outputs Windows style paths on Windows.
+            po_contents = po_file_tmp.read_text().replace(
+                '#: __init__.py',
+                '#: .\\__init__.py',
+            )
+            po_file.write_text(po_contents)
+        else:
+            po_file_tmp.rename(po_file)
+        self.original_po_contents = po_file.read_text()
+
+    def test_po_remains_unchanged(self):
+        """PO files are unchanged unless there are new changes."""
+        _, po_contents = self._run_makemessages()
+        self.assertEqual(po_contents, self.original_po_contents)
+
+    def test_po_changed_with_new_strings(self):
+        """PO files are updated when new changes are detected."""
+        Path('models.py.tmp').rename('models.py')
+        _, po_contents = self._run_makemessages()
+        self.assertNotEqual(po_contents, self.original_po_contents)
+        self.assertMsgId(
+            'This is a hitherto undiscovered translatable string.',
+            po_contents,
+        )

tests/i18n/unchanged/__init__.py

@@ -0,0 +1,4 @@
+from django.utils.translation import gettext as _
+
+string1 = _('This is a translatable string.')
+string2 = _('This is another translatable string.')

tests/i18n/unchanged/locale/de/LC_MESSAGES/django.po.tmp

@@ -0,0 +1,26 @@
+# SOME DESCRIPTIVE TITLE.
+# Copyright (C) YEAR THE PACKAGE'S COPYRIGHT HOLDER
+# This file is distributed under the same license as the PACKAGE package.
+# FIRST AUTHOR <EMAIL@ADDRESS>, YEAR.
+#
+#, fuzzy
+msgid ""
+msgstr ""
+"Project-Id-Version: PACKAGE VERSION\n"
+"Report-Msgid-Bugs-To: \n"
+"POT-Creation-Date: 2014-04-25 15:39-0500\n"
+"PO-Revision-Date: 2014-05-25 15:39-0500\n"
+"Last-Translator: FULL NAME <EMAIL@ADDRESS>\n"
+"Language-Team: LANGUAGE <LL@li.org>\n"
+"Language: \n"
+"MIME-Version: 1.0\n"
+"Content-Type: text/plain; charset=UTF-8\n"
+"Content-Transfer-Encoding: 8bit\n"
+
+#: __init__.py:3
+msgid "This is a translatable string."
+msgstr "And this has been translated."
+
+#: __init__.py:4
+msgid "This is another translatable string."
+msgstr "And this also has been translated."

tests/i18n/unchanged/models.py.tmp

@@ -0,0 +1,3 @@
+from django.utils.translation import gettext as _
+
+string3 = _('This is a hitherto undiscovered translatable string.')