Moved has_changed logic from widget to form field

Refs #16612. Thanks Aymeric Augustin for the suggestion.

5 files changed, 88 insertions, 106 deletions

diff --git a/django/forms/extras/widgets.py b/django/forms/extras/widgets.py
index c5ca1424c8..e939a8f665 100644
--- a/django/forms/extras/widgets.py
+++ b/django/forms/extras/widgets.py
@@ -135,11 +135,3 @@ class SelectDateWidget(Widget):
         s = Select(choices=choices)
         select_html = s.render(field % name, val, local_attrs)
         return select_html
-
-    def _has_changed(self, initial, data):
-        try:
-            input_format = get_format('DATE_INPUT_FORMATS')[0]
-            data = datetime_safe.datetime.strptime(data, input_format).date()
-        except (TypeError, ValueError):
-            pass
-        return super(SelectDateWidget, self)._has_changed(initial, data)
diff --git a/django/forms/fields.py b/django/forms/fields.py
index 4438812a37..1e9cbcb4d9 100644
--- a/django/forms/fields.py
+++ b/django/forms/fields.py
@@ -175,6 +175,25 @@ class Field(object):
         """
         return {}
 
+    def _has_changed(self, initial, data):
+        """
+        Return True if data differs from initial.
+        """
+        # For purposes of seeing whether something has changed, None is
+        # the same as an empty string, if the data or inital value we get
+        # is None, replace it w/ ''.
+        if data is None:
+            data_value = ''
+        else:
+            data_value = data
+        if initial is None:
+            initial_value = ''
+        else:
+            initial_value = initial
+        if force_text(initial_value) != force_text(data_value):
+            return True
+        return False
+
     def __deepcopy__(self, memo):
         result = copy.copy(self)
         memo[id(self)] = result
@@ -348,6 +367,13 @@ class BaseTemporalField(Field):
     def strptime(self, value, format):
         raise NotImplementedError('Subclasses must define this method.')
 
+    def _has_changed(self, initial, data):
+        try:
+            data = self.to_python(data)
+        except ValidationError:
+            return True
+        return self.to_python(initial) != data
+
 class DateField(BaseTemporalField):
     widget = DateInput
     input_formats = formats.get_format_lazy('DATE_INPUT_FORMATS')
@@ -371,6 +397,7 @@ class DateField(BaseTemporalField):
     def strptime(self, value, format):
         return datetime.datetime.strptime(value, format).date()
 
+
 class TimeField(BaseTemporalField):
     widget = TimeInput
     input_formats = formats.get_format_lazy('TIME_INPUT_FORMATS')
@@ -529,6 +556,12 @@ class FileField(Field):
             return initial
         return data
 
+    def _has_changed(self, initial, data):
+        if data is None:
+            return False
+        return True
+
+
 class ImageField(FileField):
     default_error_messages = {
         'invalid_image': _("Upload a valid image. The file you uploaded was either not an image or a corrupted image."),
@@ -618,6 +651,7 @@ class URLField(CharField):
             value = urlunsplit(url_fields)
         return value
 
+
 class BooleanField(Field):
     widget = CheckboxInput
 
@@ -636,6 +670,15 @@ class BooleanField(Field):
             raise ValidationError(self.error_messages['required'])
         return value
 
+    def _has_changed(self, initial, data):
+        # Sometimes data or initial could be None or '' which should be the
+        # same thing as False.
+        if initial == 'False':
+            # show_hidden_initial may have transformed False to 'False'
+            initial = False
+        return bool(initial) != bool(data)
+
+
 class NullBooleanField(BooleanField):
     """
     A field whose valid values are None, True and False. Invalid values are
@@ -660,6 +703,15 @@ class NullBooleanField(BooleanField):
     def validate(self, value):
         pass
 
+    def _has_changed(self, initial, data):
+        # None (unknown) and False (No) are not the same
+        if initial is not None:
+            initial = bool(initial)
+        if data is not None:
+            data = bool(data)
+        return initial != data
+
+
 class ChoiceField(Field):
     widget = Select
     default_error_messages = {
@@ -739,6 +791,7 @@ class TypedChoiceField(ChoiceField):
     def validate(self, value):
         pass
 
+
 class MultipleChoiceField(ChoiceField):
     hidden_widget = MultipleHiddenInput
     widget = SelectMultiple
@@ -765,6 +818,18 @@ class MultipleChoiceField(ChoiceField):
             if not self.valid_value(val):
                 raise ValidationError(self.error_messages['invalid_choice'] % {'value': val})
 
+    def _has_changed(self, initial, data):
+        if initial is None:
+            initial = []
+        if data is None:
+            data = []
+        if len(initial) != len(data):
+            return True
+        initial_set = set([force_text(value) for value in initial])
+        data_set = set([force_text(value) for value in data])
+        return data_set != initial_set
+
+
 class TypedMultipleChoiceField(MultipleChoiceField):
     def __init__(self, *args, **kwargs):
         self.coerce = kwargs.pop('coerce', lambda val: val)
@@ -899,6 +964,18 @@ class MultiValueField(Field):
         """
         raise NotImplementedError('Subclasses must implement this method.')
 
+    def _has_changed(self, initial, data):
+        if initial is None:
+            initial = ['' for x in range(0, len(data))]
+        else:
+            if not isinstance(initial, list):
+                initial = self.widget.decompress(initial)
+        for field, initial, data in zip(self.fields, initial, data):
+            if field._has_changed(initial, data):
+                return True
+        return False
+
+
 class FilePathField(ChoiceField):
     def __init__(self, path, match=None, recursive=False, allow_files=True,
                  allow_folders=False, required=True, widget=None, label=None,
diff --git a/django/forms/forms.py b/django/forms/forms.py
index 3299c2becc..f532391296 100644
--- a/django/forms/forms.py
+++ b/django/forms/forms.py
@@ -341,7 +341,13 @@ class BaseForm(object):
                     hidden_widget = field.hidden_widget()
                     initial_value = hidden_widget.value_from_datadict(
                         self.data, self.files, initial_prefixed_name)
-                if field.widget._has_changed(initial_value, data_value):
+                if hasattr(field.widget, '_has_changed'):
+                    warnings.warn("The _has_changed method on widgets is deprecated,"
+                        " define it at field level instead.",
+                        PendingDeprecationWarning, stacklevel=2)
+                    if field.widget._has_changed(initial_value, data_value):
+                        self._changed_data.append(name)
+                elif field._has_changed(initial_value, data_value):
                     self._changed_data.append(name)
         return self._changed_data
     changed_data = property(_get_changed_data)
diff --git a/django/forms/models.py b/django/forms/models.py
index 03a14dc9ff..837da74814 100644
--- a/django/forms/models.py
+++ b/django/forms/models.py
@@ -858,15 +858,12 @@ def inlineformset_factory(parent_model, model, form=ModelForm,
 
 # Fields #####################################################################
 
-class InlineForeignKeyHiddenInput(HiddenInput):
-    def _has_changed(self, initial, data):
-        return False
-
 class InlineForeignKeyField(Field):
     """
     A basic integer field that deals with validating the given value to a
     given parent instance in an inline.
     """
+    widget = HiddenInput
     default_error_messages = {
         'invalid_choice': _('The inline foreign key did not match the parent instance primary key.'),
     }
@@ -881,7 +878,6 @@ class InlineForeignKeyField(Field):
             else:
                 kwargs["initial"] = self.parent_instance.pk
         kwargs["required"] = False
-        kwargs["widget"] = InlineForeignKeyHiddenInput
         super(InlineForeignKeyField, self).__init__(*args, **kwargs)
 
     def clean(self, value):
@@ -899,6 +895,9 @@ class InlineForeignKeyField(Field):
             raise ValidationError(self.error_messages['invalid_choice'])
         return self.parent_instance
 
+    def _has_changed(self, initial, data):
+        return False
+
 class ModelChoiceIterator(object):
     def __init__(self, field):
         self.field = field
diff --git a/django/forms/widgets.py b/django/forms/widgets.py
index d6ea56f0c8..303844d44b 100644
--- a/django/forms/widgets.py
+++ b/django/forms/widgets.py
@@ -208,25 +208,6 @@ class Widget(six.with_metaclass(MediaDefiningClass)):
         """
         return data.get(name, None)
 
-    def _has_changed(self, initial, data):
-        """
-        Return True if data differs from initial.
-        """
-        # For purposes of seeing whether something has changed, None is
-        # the same as an empty string, if the data or inital value we get
-        # is None, replace it w/ ''.
-        if data is None:
-            data_value = ''
-        else:
-            data_value = data
-        if initial is None:
-            initial_value = ''
-        else:
-            initial_value = initial
-        if force_text(initial_value) != force_text(data_value):
-            return True
-        return False
-
     def id_for_label(self, id_):
         """
         Returns the HTML ID attribute of this Widget for use by a <label>,
@@ -325,10 +306,6 @@ class FileInput(Input):
         "File widgets take data from FILES, not POST"
         return files.get(name, None)
 
-    def _has_changed(self, initial, data):
-        if data is None:
-            return False
-        return True
 
 FILE_INPUT_CONTRADICTION = object()
 
@@ -426,17 +403,6 @@ class DateInput(TextInput):
             return value.strftime(self.format)
         return value
 
-    def _has_changed(self, initial, data):
-        # If our field has show_hidden_initial=True, initial will be a string
-        # formatted by HiddenInput using formats.localize_input, which is not
-        # necessarily the format used for this widget. Attempt to convert it.
-        try:
-            input_format = formats.get_format('DATE_INPUT_FORMATS')[0]
-            initial = datetime.datetime.strptime(initial, input_format).date()
-        except (TypeError, ValueError):
-            pass
-        return super(DateInput, self)._has_changed(self._format_value(initial), data)
-
 
 class DateTimeInput(TextInput):
     def __init__(self, attrs=None, format=None):
@@ -456,17 +422,6 @@ class DateTimeInput(TextInput):
             return value.strftime(self.format)
         return value
 
-    def _has_changed(self, initial, data):
-        # If our field has show_hidden_initial=True, initial will be a string
-        # formatted by HiddenInput using formats.localize_input, which is not
-        # necessarily the format used for this widget. Attempt to convert it.
-        try:
-            input_format = formats.get_format('DATETIME_INPUT_FORMATS')[0]
-            initial = datetime.datetime.strptime(initial, input_format)
-        except (TypeError, ValueError):
-            pass
-        return super(DateTimeInput, self)._has_changed(self._format_value(initial), data)
-
 
 class TimeInput(TextInput):
     def __init__(self, attrs=None, format=None):
@@ -485,17 +440,6 @@ class TimeInput(TextInput):
             return value.strftime(self.format)
         return value
 
-    def _has_changed(self, initial, data):
-        # If our field has show_hidden_initial=True, initial will be a string
-        # formatted by HiddenInput using formats.localize_input, which is not
-        # necessarily the format used for this  widget. Attempt to convert it.
-        try:
-            input_format = formats.get_format('TIME_INPUT_FORMATS')[0]
-            initial = datetime.datetime.strptime(initial, input_format).time()
-        except (TypeError, ValueError):
-            pass
-        return super(TimeInput, self)._has_changed(self._format_value(initial), data)
-
 
 # Defined at module level so that CheckboxInput is picklable (#17976)
 def boolean_check(v):
@@ -530,13 +474,6 @@ class CheckboxInput(Widget):
             value = values.get(value.lower(), value)
         return bool(value)
 
-    def _has_changed(self, initial, data):
-        # Sometimes data or initial could be None or '' which should be the
-        # same thing as False.
-        if initial == 'False':
-            # show_hidden_initial may have transformed False to 'False'
-            initial = False
-        return bool(initial) != bool(data)
 
 class Select(Widget):
     allow_multiple_selected = False
@@ -612,14 +549,6 @@ class NullBooleanSelect(Select):
                 'False': False,
                 False: False}.get(value, None)
 
-    def _has_changed(self, initial, data):
-        # For a NullBooleanSelect, None (unknown) and False (No)
-        # are not the same
-        if initial is not None:
-            initial = bool(initial)
-        if data is not None:
-            data = bool(data)
-        return initial != data
 
 class SelectMultiple(Select):
     allow_multiple_selected = True
@@ -639,16 +568,6 @@ class SelectMultiple(Select):
             return data.getlist(name)
         return data.get(name, None)
 
-    def _has_changed(self, initial, data):
-        if initial is None:
-            initial = []
-        if data is None:
-            data = []
-        if len(initial) != len(data):
-            return True
-        initial_set = set([force_text(value) for value in initial])
-        data_set = set([force_text(value) for value in data])
-        return data_set != initial_set
 
 @python_2_unicode_compatible
 class RadioInput(SubWidget):
@@ -844,17 +763,6 @@ class MultiWidget(Widget):
     def value_from_datadict(self, data, files, name):
         return [widget.value_from_datadict(data, files, name + '_%s' % i) for i, widget in enumerate(self.widgets)]
 
-    def _has_changed(self, initial, data):
-        if initial is None:
-            initial = ['' for x in range(0, len(data))]
-        else:
-            if not isinstance(initial, list):
-                initial = self.decompress(initial)
-        for widget, initial, data in zip(self.widgets, initial, data):
-            if widget._has_changed(initial, data):
-                return True
-        return False
-
     def format_output(self, rendered_widgets):
         """
         Given a list of rendered widgets (as strings), returns a Unicode string