Defer translated string evaluation on validators. (#5452)

* Customize validators to defer error string evaluation.

* Add docstring for `CustomValidatorMessage`

rest_framework/compat.py

@@ -11,13 +11,18 @@
 import django
 from django.apps import apps
 from django.conf import settings
-from django.core.exceptions import ImproperlyConfigured
+from django.core.exceptions import ImproperlyConfigured, ValidationError
+from django.core.validators import \
+    MaxLengthValidator as DjangoMaxLengthValidator
+from django.core.validators import MaxValueValidator as DjangoMaxValueValidator
+from django.core.validators import \
+    MinLengthValidator as DjangoMinLengthValidator
+from django.core.validators import MinValueValidator as DjangoMinValueValidator
 from django.db import connection, models, transaction
 from django.template import Context, RequestContext, Template
 from django.utils import six
 from django.views.generic import View
 
-
 try:
     from django.urls import (
         NoReverseMatch, RegexURLPattern, RegexURLResolver, ResolverMatch, Resolver404, get_script_prefix, reverse, reverse_lazy, resolve
@@ -293,6 +298,28 @@ def pygments_css(style):
 except ImportError:
     DecimalValidator = None
 
+class CustomValidatorMessage(object):
+    """
+    We need to avoid evaluation of `lazy` translated `message` in `django.core.validators.BaseValidator.__init__`.
+    https://github.com/django/django/blob/75ed5900321d170debef4ac452b8b3cf8a1c2384/django/core/validators.py#L297
+    
+    Ref: https://github.com/encode/django-rest-framework/pull/5452
+    """
+    def __init__(self, *args, **kwargs):
+        self.message = kwargs.pop('message', self.message)
+        super(CustomValidatorMessage, self).__init__(*args, **kwargs)
+
+class MinValueValidator(CustomValidatorMessage, DjangoMinValueValidator):
+    pass
+
+class MaxValueValidator(CustomValidatorMessage, DjangoMaxValueValidator):
+    pass
+
+class MinLengthValidator(CustomValidatorMessage, DjangoMinLengthValidator):
+    pass
+
+class MaxLengthValidator(CustomValidatorMessage, DjangoMaxLengthValidator):
+    pass
 
 def set_rollback():
     if hasattr(transaction, 'set_rollback'):

rest_framework/fields.py

@@ -13,8 +13,7 @@
 from django.core.exceptions import ValidationError as DjangoValidationError
 from django.core.exceptions import ObjectDoesNotExist
 from django.core.validators import (
-    EmailValidator, MaxLengthValidator, MaxValueValidator, MinLengthValidator,
-    MinValueValidator, RegexValidator, URLValidator, ip_address_validators
+    EmailValidator, RegexValidator, URLValidator, ip_address_validators
 )
 from django.forms import FilePathField as DjangoFilePathField
 from django.forms import ImageField as DjangoImageField
@@ -25,14 +24,16 @@
 from django.utils.duration import duration_string
 from django.utils.encoding import is_protected_type, smart_text
 from django.utils.formats import localize_input, sanitize_separators
+from django.utils.functional import lazy
 from django.utils.ipv6 import clean_ipv6_address
 from django.utils.timezone import utc
 from django.utils.translation import ugettext_lazy as _
 
 from rest_framework import ISO_8601
 from rest_framework.compat import (
-    InvalidTimeError, get_remote_field, unicode_repr, unicode_to_repr,
-    value_from_object
+    InvalidTimeError, MaxLengthValidator, MaxValueValidator,
+    MinLengthValidator, MinValueValidator, get_remote_field, unicode_repr,
+    unicode_to_repr, value_from_object
 )
 from rest_framework.exceptions import ErrorDetail, ValidationError
 from rest_framework.settings import api_settings
@@ -750,11 +751,17 @@ def __init__(self, **kwargs):
         self.min_length = kwargs.pop('min_length', None)
         super(CharField, self).__init__(**kwargs)
         if self.max_length is not None:
-            message = self.error_messages['max_length'].format(max_length=self.max_length)
-            self.validators.append(MaxLengthValidator(self.max_length, message=message))
+            message = lazy(
+                self.error_messages['max_length'].format,
+                six.text_type)(max_length=self.max_length)
+            self.validators.append(
+                MaxLengthValidator(self.max_length, message=message))
         if self.min_length is not None:
-            message = self.error_messages['min_length'].format(min_length=self.min_length)
-            self.validators.append(MinLengthValidator(self.min_length, message=message))
+            message = lazy(
+                self.error_messages['min_length'].format,
+                six.text_type)(min_length=self.min_length)
+            self.validators.append(
+                MinLengthValidator(self.min_length, message=message))
 
     def run_validation(self, data=empty):
         # Test for the empty string here so that it does not get validated,
@@ -909,11 +916,17 @@ def __init__(self, **kwargs):
         self.min_value = kwargs.pop('min_value', None)
         super(IntegerField, self).__init__(**kwargs)
         if self.max_value is not None:
-            message = self.error_messages['max_value'].format(max_value=self.max_value)
-            self.validators.append(MaxValueValidator(self.max_value, message=message))
+            message = lazy(
+                self.error_messages['max_value'].format,
+                six.text_type)(max_value=self.max_value)
+            self.validators.append(
+                MaxValueValidator(self.max_value, message=message))
         if self.min_value is not None:
-            message = self.error_messages['min_value'].format(min_value=self.min_value)
-            self.validators.append(MinValueValidator(self.min_value, message=message))
+            message = lazy(
+                self.error_messages['min_value'].format,
+                six.text_type)(min_value=self.min_value)
+            self.validators.append(
+                MinValueValidator(self.min_value, message=message))
 
     def to_internal_value(self, data):
         if isinstance(data, six.text_type) and len(data) > self.MAX_STRING_LENGTH:
@@ -943,11 +956,17 @@ def __init__(self, **kwargs):
         self.min_value = kwargs.pop('min_value', None)
         super(FloatField, self).__init__(**kwargs)
         if self.max_value is not None:
-            message = self.error_messages['max_value'].format(max_value=self.max_value)
-            self.validators.append(MaxValueValidator(self.max_value, message=message))
+            message = lazy(
+                self.error_messages['max_value'].format,
+                six.text_type)(max_value=self.max_value)
+            self.validators.append(
+                MaxValueValidator(self.max_value, message=message))
         if self.min_value is not None:
-            message = self.error_messages['min_value'].format(min_value=self.min_value)
-            self.validators.append(MinValueValidator(self.min_value, message=message))
+            message = lazy(
+                self.error_messages['min_value'].format,
+                six.text_type)(min_value=self.min_value)
+            self.validators.append(
+                MinValueValidator(self.min_value, message=message))
 
     def to_internal_value(self, data):
 
@@ -996,11 +1015,17 @@ def __init__(self, max_digits, decimal_places, coerce_to_string=None, max_value=
         super(DecimalField, self).__init__(**kwargs)
 
         if self.max_value is not None:
-            message = self.error_messages['max_value'].format(max_value=self.max_value)
-            self.validators.append(MaxValueValidator(self.max_value, message=message))
+            message = lazy(
+                self.error_messages['max_value'].format,
+                six.text_type)(max_value=self.max_value)
+            self.validators.append(
+                MaxValueValidator(self.max_value, message=message))
         if self.min_value is not None:
-            message = self.error_messages['min_value'].format(min_value=self.min_value)
-            self.validators.append(MinValueValidator(self.min_value, message=message))
+            message = lazy(
+                self.error_messages['min_value'].format,
+                six.text_type)(min_value=self.min_value)
+            self.validators.append(
+                MinValueValidator(self.min_value, message=message))
 
     def to_internal_value(self, data):
         """
@@ -1797,8 +1822,11 @@ def __init__(self, model_field, **kwargs):
         max_length = kwargs.pop('max_length', None)
         super(ModelField, self).__init__(**kwargs)
         if max_length is not None:
-            message = self.error_messages['max_length'].format(max_length=max_length)
-            self.validators.append(MaxLengthValidator(max_length, message=message))
+            message = lazy(
+                self.error_messages['max_length'].format,
+                six.text_type)(max_length=self.max_length)
+            self.validators.append(
+                MaxLengthValidator(self.max_length, message=message))
 
     def to_internal_value(self, data):
         rel = get_remote_field(self.model_field, default=None)