Fixed #23151 -- Deprecated RegexField.error_message.

Thanks Baptiste Mispelon for the suggestion.

django/contrib/flatpages/forms.py

@@ -8,8 +8,11 @@ class FlatpageForm(forms.ModelForm):
     url = forms.RegexField(label=_("URL"), max_length=100, regex=r'^[-\w/\.~]+$',
         help_text=_("Example: '/about/contact/'. Make sure to have leading"
                     " and trailing slashes."),
-        error_message=_("This value must contain only letters, numbers,"
-                        " dots, underscores, dashes, slashes or tildes."))
+        error_messages={
+            "invalid": _("This value must contain only letters, numbers,"
+                         " dots, underscores, dashes, slashes or tildes."),
+        },
+    )
 
     class Meta:
         model = FlatPage

django/forms/fields.py

@@ -25,7 +25,7 @@ from django.forms.widgets import (
 from django.utils import formats
 from django.utils.encoding import smart_text, force_str, force_text
 from django.utils.ipv6 import clean_ipv6_address
-from django.utils.deprecation import RemovedInDjango19Warning
+from django.utils.deprecation import RemovedInDjango19Warning, RemovedInDjango20Warning
 from django.utils import six
 from django.utils.six.moves.urllib.parse import urlsplit, urlunsplit
 from django.utils.translation import ugettext_lazy as _, ungettext_lazy
@@ -531,6 +531,11 @@ class RegexField(CharField):
         """
         # error_message is just kept for backwards compatibility:
         if error_message is not None:
+            warnings.warn(
+                "The 'error_message' argument is deprecated. Use "
+                "Field.error_messages['invalid'] instead.",
+                RemovedInDjango20Warning, stacklevel=2
+            )
             error_messages = kwargs.get('error_messages') or {}
             error_messages['invalid'] = error_message
             kwargs['error_messages'] = error_messages

docs/internals/deprecation.txt

@@ -40,6 +40,8 @@ about each item can often be found in the release notes of two versions prior.
 
 * ``django.template.resolve_variable`` will be removed.
 
+* The ``error_message`` argument of ``django.forms.RegexField`` will be removed.
+
 .. _deprecation-removed-in-1.9:
 
 1.9

docs/ref/forms/fields.txt

@@ -805,10 +805,13 @@ For each field, we describe the default widget used if you don't specify
     Also takes ``max_length`` and ``min_length``, which work just as they do for
     ``CharField``.
 
-    The optional argument ``error_message`` is also accepted for backwards
-    compatibility. The preferred way to provide an error message is to use the
-    ``error_messages`` argument, passing a dictionary with ``'invalid'`` as a key
-    and the error message as the value.
+    .. deprecated:: 1.8
+
+        The optional argument ``error_message`` is also accepted for backwards
+        compatibility but will be removed in Django 2.0. The preferred way to
+        provide an error message is to use the :attr:`~Field.error_messages`
+        argument, passing a dictionary with ``'invalid'`` as a key and the error
+        message as the value.
 
 ``SlugField``
 ~~~~~~~~~~~~~

docs/releases/1.8.txt

@@ -625,3 +625,9 @@ The function has been informally marked as "Deprecated" for some time. Replace
 It provided the :ttag:`lorem` template tag which is now included in the
 built-in tags. Simply remove ``'django.contrib.webdesign'`` from
 :setting:`INSTALLED_APPS` and ``{% load webdesign %}`` from your templates.
+
+``error_message`` argument to ``django.forms.RegexField``
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+
+It provided backwards compatibility for pre-1.0 code, but its functionality is
+redundant. Use ``Field.error_messages['invalid']`` instead.

tests/forms_tests/tests/test_fields.py

@@ -32,6 +32,7 @@ import re
 import os
 from decimal import Decimal
 from unittest import skipIf
+import warnings
 
 try:
     from PIL import Image
@@ -630,7 +631,10 @@ class FieldsTests(SimpleTestCase):
         self.assertRaisesMessage(ValidationError, "'Enter a valid value.'", f.clean, '2A2 ')
 
     def test_regexfield_4(self):
-        f = RegexField('^[0-9][0-9][0-9][0-9]$', error_message='Enter a four-digit number.')
+        # deprecated error_message argument; remove in Django 2.0
+        with warnings.catch_warnings(record=True) as w:
+            warnings.simplefilter("always")
+            f = RegexField('^[0-9][0-9][0-9][0-9]$', error_message='Enter a four-digit number.')
         self.assertEqual('1234', f.clean('1234'))
         self.assertRaisesMessage(ValidationError, "'Enter a four-digit number.'", f.clean, '123')
         self.assertRaisesMessage(ValidationError, "'Enter a four-digit number.'", f.clean, 'abcd')