Merge pull request #1382 from loic/ticket19617

Fixed #19617 -- Refactored form metaclasses to support more inheritance scenarios.

4 files changed, 42 insertions, 4 deletions

diff --git a/docs/internals/deprecation.txt b/docs/internals/deprecation.txt
index a965627a1c..b584a28ba1 100644
--- a/docs/internals/deprecation.txt
+++ b/docs/internals/deprecation.txt
@@ -467,6 +467,8 @@ these changes.
 * The ``use_natural_keys`` argument for ``serializers.serialize()`` will be
   removed. Use ``use_natural_foreign_keys`` instead.
 
+* ``django.forms.get_declared_fields`` will be removed.
+
 2.0
 ---
 
diff --git a/docs/ref/forms/api.txt b/docs/ref/forms/api.txt
index 14092512dc..c15f748308 100644
--- a/docs/ref/forms/api.txt
+++ b/docs/ref/forms/api.txt
@@ -854,6 +854,13 @@ classes::
     <li>Instrument: <input type="text" name="instrument" /></li>
     <li>Haircut type: <input type="text" name="haircut_type" /></li>
 
+.. versionadded:: 1.7
+
+* It's possible to opt-out from a ``Field`` inherited from a parent class by
+  shadowing it. While any non-``Field`` value works for this purpose, it's
+  recommended to use ``None`` to make it explicit that a field is being
+  nullified.
+
 .. _form-prefix:
 
 Prefixes for forms
diff --git a/docs/releases/1.7.txt b/docs/releases/1.7.txt
index 7a49f13327..5c208e22ac 100644
--- a/docs/releases/1.7.txt
+++ b/docs/releases/1.7.txt
@@ -288,6 +288,14 @@ Forms
   :func:`~django.forms.formsets.formset_factory` to allow validating
   a minimum number of submitted forms.
 
+* The metaclasses used by ``Form`` and ``ModelForm`` have been reworked to
+  support more inheritance scenarios. The previous limitation that prevented
+  inheriting from both ``Form`` and ``ModelForm`` simultaneously have been
+  removed as long as ``ModelForm`` appears first in the MRO.
+
+* It's now possible to opt-out from a ``Form`` field declared in a parent class
+  by shadowing it with a non-``Field`` value.
+
 Internationalization
 ^^^^^^^^^^^^^^^^^^^^
 
@@ -513,6 +521,12 @@ Miscellaneous
   still worked, even though it was not documented or officially supported. If
   you're still using it, please update to the current :setting:`CACHES` syntax.
 
+* The default ordering of ``Form`` fields in case of inheritance has changed to
+  follow normal Python MRO. Fields are now discovered by iterating through the
+  MRO in reverse with the topmost class coming last. This only affects you if
+  you relied on the default field ordering while having fields defined on both
+  the current class *and* on a parent ``Form``.
+
 Features deprecated in 1.7
 ==========================
 
diff --git a/docs/topics/forms/modelforms.txt b/docs/topics/forms/modelforms.txt
index c65c705a58..2a48aa75dc 100644
--- a/docs/topics/forms/modelforms.txt
+++ b/docs/topics/forms/modelforms.txt
@@ -644,11 +644,24 @@ There are a couple of things to note, however.
   used. This means the child's ``Meta``, if it exists, otherwise the
   ``Meta`` of the first parent, etc.
 
-* For technical reasons, a subclass cannot inherit from both a ``ModelForm``
-  and a ``Form`` simultaneously.
+.. versionchanged:: 1.7
 
-Chances are these notes won't affect you unless you're trying to do something
-tricky with subclassing.
+* It's possible to inherit from both ``Form`` and ``ModelForm`` simultaneuosly,
+  however, you must ensure that ``ModelForm`` appears first in the MRO. This is
+  because these classes rely on different metaclasses and a class can only have
+  one metaclass.
+
+.. versionadded:: 1.7
+
+* It's possible to opt-out from a ``Field`` inherited from a parent class by
+  shadowing it. While any non-``Field`` value works for this purpose, it's
+  recommended to use ``None`` to make it explicit that a field is being
+  nullified.
+
+  You can only use this technique to opt out from a field defined declaratively
+  by a parent class; it won't prevent the ``ModelForm`` metaclass from generating
+  a default field. To opt-out from default fields, see
+  :ref:`controlling-fields-with-fields-and-exclude`.
 
 .. _modelforms-factory:
 
@@ -748,6 +761,8 @@ instances of the model, you can specify an empty QuerySet::
    >>> AuthorFormSet(queryset=Author.objects.none())
 
 
+.. _controlling-fields-with-fields-and-exclude:
+
 Controlling which fields are used with ``fields`` and ``exclude``
 -----------------------------------------------------------------