Fixed #27334 -- Allowed FileField to move rather than copy a file.

When a FileField is set to an instance of File that is not also an
instance of FieldFile, pre_save() passes that object as the contents to
Storage.save(). This allows the file to be moved rather than copied
to the upload destination.

tests/model_fields/test_filefield.py

@@ -1,4 +1,10 @@
-from django.test import TestCase
+import os
+import sys
+import unittest
+
+from django.core.files import temp
+from django.core.files.uploadedfile import TemporaryUploadedFile
+from django.test import TestCase, override_settings
 
 from .models import Document
 
@@ -54,3 +60,16 @@ class FileFieldTests(TestCase):
     def test_defer(self):
         Document.objects.create(myfile='something.txt')
         self.assertEqual(Document.objects.defer('myfile')[0].myfile, 'something.txt')
+
+    @unittest.skipIf(sys.platform.startswith('win'), "Windows doesn't support moving open files.")
+    # The file's source and destination must be on the same filesystem.
+    @override_settings(MEDIA_ROOT=temp.gettempdir())
+    def test_move_temporary_file(self):
+        """
+        The temporary uploaded file is moved rather than copied to the
+        destination.
+        """
+        with TemporaryUploadedFile('something.txt', 'text/plain', 0, 'UTF-8') as tmp_file:
+            tmp_file_path = tmp_file.temporary_file_path()
+            Document.objects.create(myfile=tmp_file)
+            self.assertFalse(os.path.exists(tmp_file_path), 'Temporary file still exists')