ModelAdmin ignores dynamic fields of ModelForm

I've solved this in the meantime by updating contrib/admin/options.py in:

    def get_fieldsets(self, request, obj=None):
        "Hook for specifying fieldsets for the add form."
        if self.declared_fieldsets:
            return self.declared_fieldsets
        #form = self.get_form(request, obj)
        #return [(None, {'fields': form.base_fields.keys()})]
        form = self.get_form(request, obj)(instance=obj)
        return [(None, {'fields': form.fields.keys()})]

Seems to be a harmless fix, possible to get this applied upstream?

(reformat description, also it hasn't a patch until it has a patch)

I think the declared_fieldsets too satic too. Why not using a callable that people can override?

I can provide a patch if needed.

Attempt to use dynamic fieldsets generation

The patch I sent seems to work quite oki, but if I add a field dynamicaly, even if it's in the form object, the new value is not saved:

    def dynamic_fieldsets(self, request, obj=None, **kwargs):

        general_fields = list(self.general_fields)
        perms = PagePermission(request.user)

        if perms.check('freeze'):
            general_fields.append('freeze_date')

        return [
            [_('General'), {
                'fields': general_fields,
                'classes': ('module-general',),
            }],
            (_('Options'), {
                'fields': self.normal_fields,
                'classes': ('module-options',),
            }),
        ]

My freeze field is added properly in the admin interface, but the value is not saved. But in the other hand if I do things like that:

    def get_fieldsets(self, request, obj=None):
        """
        Add fieldsets of placeholders to the list of already
        existing fieldsets.
        """
        general_fields = list(self.general_fields)
        perms = PagePermission(request.user)

        # some ugly business to remove freeze_date
        # from the field list
        general_module = {
            'fields': list(self.general_fields),
            'classes': ('module-general',),
        }

        default_fieldsets = list(self.fieldsets)
        if not perms.check('freeze'):
            general_module['fields'].remove('freeze_date')

        default_fieldsets[0][1] = general_module

The latest version works, but it feels like a very hackish way to do things.

Can somebody explain me what's wrong here? Does Django have a more elegant way to do this?