Fixed #16192 -- Made unique error messages in ModelForm customizable.

Overriding the error messages now works for both unique fields, unique_together
and unique_for_date.

This patch changed the overriding logic to allow customizing NON_FIELD_ERRORS
since previously only fields' errors were customizable.

Refs #20199.

Thanks leahculver for the suggestion.

1 files changed, 1 insertions, 3 deletions

diff --git a/django/forms/forms.py b/django/forms/forms.py
index bcc0d6dfa4..e34e089878 100644
--- a/django/forms/forms.py
+++ b/django/forms/forms.py
@@ -8,7 +8,7 @@ from collections import OrderedDict
 import copy
 import warnings
 
-from django.core.exceptions import ValidationError
+from django.core.exceptions import ValidationError, NON_FIELD_ERRORS
 from django.forms.fields import Field, FileField
 from django.forms.utils import flatatt, ErrorDict, ErrorList
 from django.forms.widgets import Media, MediaDefiningClass, TextInput, Textarea
@@ -21,8 +21,6 @@ from django.utils import six
 
 __all__ = ('BaseForm', 'Form')
 
-NON_FIELD_ERRORS = '__all__'
-
 
 def pretty_name(name):
     """Converts 'first_name' to 'First name'"""