ModelAdmin.fields wasn't able to refer to fields only on a custom form

Regressed in r11737 which used get_field instead of opts.get_field and ignoring
fields not found.

git-svn-id: http://code.djangoproject.com/svn/django/trunk@12279 bcc190cf-cafb-0310-a4f2-bffc1f526a37

django/contrib/admin/validation.py

@@ -211,7 +211,12 @@ def validate_base(cls, model):
                 # validation of such things.
                 continue
             check_formfield(cls, model, opts, 'fields', field)
-            f = get_field(cls, model, opts, 'fields', field)
+            try:
+                f = opts.get_field(field)
+            except models.FieldDoesNotExist:
+                # If we can't find a field on the model that matches,
+                # it could be an extra field on the form.
+                continue
             if isinstance(f, models.ManyToManyField) and not f.rel.through._meta.auto_created:
                 raise ImproperlyConfigured("'%s.fields' can't include the ManyToManyField "
                     "field '%s' because '%s' manually specifies "

tests/regressiontests/admin_validation/models.py

@@ -215,4 +215,18 @@ ImproperlyConfigured: 'FieldsetBookAdmin.fieldsets[1][1]['fields']' can't includ
 # the validation will fail.
 >>> validate(BookAdmin, Book)
 
+# Regression for ensuring ModelAdmin.fields can contain non-model fields
+# that broke with r11737
+
+>>> class SongForm(forms.ModelForm):
+...     extra_data = forms.CharField()
+...     class Meta:
+...         model = Song
+
+>>> class FieldsOnFormOnlyAdmin(admin.ModelAdmin):
+...     form = SongForm
+...     fields = ['title', 'extra_data']
+
+>>> validate(FieldsOnFormOnlyAdmin, Song)
+
 """}