Merge #14291: if a header has non-ascii unicode, default to CTE using utf-8

In Python2, if a unicode string was assigned as the value of a header,
email would automatically CTE encode it using the UTF8 charset.
This capability was lost in the Python3 translation, and this patch
restores it.

Patch by Ali Ikinci, assisted by R. David Murray.

I also added a fix for the mailbox test that was depending (with a comment
that it was a bad idea to so depend) on non-ASCII causing message_from_string
to raise an error.  It now uses support.patch to induce an error during
message serialization.

1 files changed, 4 insertions, 4 deletions

diff --git a/Lib/test/test_mailbox.py b/Lib/test/test_mailbox.py
index 212ceb9..54963a9 100644
--- a/Lib/test/test_mailbox.py
+++ b/Lib/test/test_mailbox.py
@@ -111,10 +111,10 @@ class TestMailbox(TestBase):
         self.assertMailboxEmpty()
 
     def test_add_that_raises_leaves_mailbox_empty(self):
-        # XXX This test will start failing when Message learns to handle
-        # non-ASCII string headers, and a different internal failure will
-        # need to be found or manufactured.
-        with self.assertRaises(ValueError):
+        def raiser(*args, **kw):
+            raise Exception("a fake error")
+        support.patch(self, email.generator.BytesGenerator, 'flatten', raiser)
+        with self.assertRaises(Exception):
             self._box.add(email.message_from_string("From: Alphöso"))
         self.assertEqual(len(self._box), 0)
         self._box.close()