[2.1.x] Fixed #29452 -- Fixed makemessages setting charset of .pot files.

Backport of 2bc014750a from master

AUTHORS

@@ -97,6 +97,7 @@ answer newbie questions, and generally made Django that much better:
     Baptiste Mispelon <bmispelon@gmail.com>
     Barry Pederson <bp@barryp.org>
     Bartolome Sanchez Salado <i42sasab@uco.es>
+    Bartosz Grabski <bartosz.grabski@gmail.com>
     Bashar Al-Abdulhadi
     Bastian Kleineidam <calvin@debian.org>
     Batiste Bieler <batiste.bieler@gmail.com>

django/core/management/commands/makemessages.py

@@ -182,6 +182,7 @@ def write_pot_file(potfile, msgs):
         found, header_read = False, False
         for line in pot_lines:
             if not found and not header_read:
+                if 'charset=CHARSET' in line:
                     found = True
                     line = line.replace('charset=CHARSET', 'charset=UTF-8')
             if not line and not found:

tests/i18n/test_extraction.py

@@ -1,6 +1,7 @@
 import os
 import re
 import shutil
+import tempfile
 import time
 import warnings
 from io import StringIO
@@ -12,7 +13,7 @@ from django.core import management
 from django.core.management import execute_from_command_line
 from django.core.management.base import CommandError
 from django.core.management.commands.makemessages import (
-    Command as MakeMessagesCommand,
+    Command as MakeMessagesCommand, write_pot_file,
 )
 from django.core.management.utils import find_command
 from django.test import SimpleTestCase, override_settings
@@ -394,6 +395,26 @@ class BasicExtractorTests(ExtractorTests):
             po_contents = fp.read()
             self.assertMsgStr("Größe", po_contents)
 
+    def test_pot_charset_header_is_utf8(self):
+        """Content-Type: ... charset=CHARSET is replaced with charset=UTF-8"""
+        msgs = (
+            '# SOME DESCRIPTIVE TITLE.\n'
+            '# (some lines truncated as they are not relevant)\n'
+            '"Content-Type: text/plain; charset=CHARSET\\n"\n'
+            '"Content-Transfer-Encoding: 8bit\\n"\n'
+            '\n'
+            '#: somefile.py:8\n'
+            'msgid "mañana; charset=CHARSET"\n'
+            'msgstr ""\n'
+        )
+        with tempfile.NamedTemporaryFile() as pot_file:
+            pot_filename = pot_file.name
+        write_pot_file(pot_filename, msgs)
+        with open(pot_filename, 'r', encoding='utf-8') as fp:
+            pot_contents = fp.read()
+            self.assertIn('Content-Type: text/plain; charset=UTF-8', pot_contents)
+            self.assertIn('mañana; charset=CHARSET', pot_contents)
+
 
 class JavascriptExtractorTests(ExtractorTests):