Fixed #7048 -- Added ClearableFileInput widget to clear file fields. Thanks for report and patch, jarrow and Carl Meyer.

git-svn-id: http://code.djangoproject.com/svn/django/trunk@13968 bcc190cf-cafb-0310-a4f2-bffc1f526a37

django/forms/widgets.py

@@ -7,7 +7,7 @@ from itertools import chain
 from django.conf import settings
 from django.utils.datastructures import MultiValueDict, MergeDict
 from django.utils.html import escape, conditional_escape
-from django.utils.translation import ugettext
+from django.utils.translation import ugettext, ugettext_lazy
 from django.utils.encoding import StrAndUnicode, force_unicode
 from django.utils.safestring import mark_safe
 from django.utils import datetime_safe, formats
@@ -18,7 +18,7 @@ from urlparse import urljoin
 
 __all__ = (
     'Media', 'MediaDefiningClass', 'Widget', 'TextInput', 'PasswordInput',
-    'HiddenInput', 'MultipleHiddenInput',
+    'HiddenInput', 'MultipleHiddenInput', 'ClearableFileInput',
     'FileInput', 'DateInput', 'DateTimeInput', 'TimeInput', 'Textarea', 'CheckboxInput',
     'Select', 'NullBooleanSelect', 'SelectMultiple', 'RadioSelect',
     'CheckboxSelectMultiple', 'MultiWidget',
@@ -134,6 +134,7 @@ class Widget(object):
     is_hidden = False          # Determines whether this corresponds to an <input type="hidden">.
     needs_multipart_form = False # Determines does this widget need multipart-encrypted form
     is_localized = False
+    is_required = False
 
     def __init__(self, attrs=None):
         if attrs is not None:
@@ -286,6 +287,67 @@ class FileInput(Input):
             return False
         return True
 
+FILE_INPUT_CONTRADICTION = object()
+
+class ClearableFileInput(FileInput):
+    initial_text = ugettext_lazy('Currently')
+    input_text = ugettext_lazy('Change')
+    clear_checkbox_label = ugettext_lazy('Clear')
+
+    template_with_initial = u'%(initial_text)s: %(initial)s %(clear_template)s<br />%(input_text)s: %(input)s'
+
+    template_with_clear = u'%(clear)s <label for="%(clear_checkbox_id)s">%(clear_checkbox_label)s</label>'
+
+    def clear_checkbox_name(self, name):
+        """
+        Given the name of the file input, return the name of the clear checkbox
+        input.
+        """
+        return name + '-clear'
+
+    def clear_checkbox_id(self, name):
+        """
+        Given the name of the clear checkbox input, return the HTML id for it.
+        """
+        return name + '_id'
+
+    def render(self, name, value, attrs=None):
+        substitutions = {
+            'initial_text': self.initial_text,
+            'input_text': self.input_text,
+            'clear_template': '',
+            'clear_checkbox_label': self.clear_checkbox_label,
+        }
+        template = u'%(input)s'
+        substitutions['input'] = super(ClearableFileInput, self).render(name, value, attrs)
+
+        if value and hasattr(value, "url"):
+            template = self.template_with_initial
+            substitutions['initial'] = (u'<a target="_blank" href="%s">%s</a>'
+                                        % (value.url, value))
+            if not self.is_required:
+                checkbox_name = self.clear_checkbox_name(name)
+                checkbox_id = self.clear_checkbox_id(checkbox_name)
+                substitutions['clear_checkbox_name'] = checkbox_name
+                substitutions['clear_checkbox_id'] = checkbox_id
+                substitutions['clear'] = CheckboxInput().render(checkbox_name, False, attrs={'id': checkbox_id})
+                substitutions['clear_template'] = self.template_with_clear % substitutions
+
+        return mark_safe(template % substitutions)
+
+    def value_from_datadict(self, data, files, name):
+        upload = super(ClearableFileInput, self).value_from_datadict(data, files, name)
+        if not self.is_required and CheckboxInput().value_from_datadict(
+            data, files, self.clear_checkbox_name(name)):
+            if upload:
+                # If the user contradicts themselves (uploads a new file AND
+                # checks the "clear" checkbox), we return a unique marker
+                # object that FileField will turn into a ValidationError.
+                return FILE_INPUT_CONTRADICTION
+            # False signals to clear any existing value, as opposed to just None
+            return False
+        return upload
+
 class Textarea(Widget):
     def __init__(self, attrs=None):
         # The 'rows' and 'cols' attributes are required for HTML correctness.