Don't warn for mixin-based __table_args__, __mapper_args__ declared_attr

Removed a warning that would be emitted when calling upon
``__table_args__``, ``__mapper_args__`` as named with a ``@declared_attr``
method, when called from a non-mapped declarative mixin.  Calling these
directly is documented as the approach to use when one is overidding one
of these methods on a mapped class.  The warning still emits for regular
attribute names.

Change-Id: Iae7ed0bd625a2c163c910aa777cef4779128580a
Fixes: #4221

1 files changed, 13 insertions, 0 deletions

diff --git a/test/ext/declarative/test_mixin.py b/test/ext/declarative/test_mixin.py
index 0b1b117fb..07c790dc4 100644
--- a/test/ext/declarative/test_mixin.py
+++ b/test/ext/declarative/test_mixin.py
@@ -1540,6 +1540,19 @@ class DeclaredAttrTest(DeclarativeTestBase, testing.AssertsCompiledSQL):
             getattr, Mixin, "my_prop"
         )
 
+    def test_can_we_access_the_mixin_straight_special_names(self):
+        class Mixin(object):
+            @declared_attr
+            def __table_args__(cls):
+                return (1, 2, 3)
+
+            @declared_attr
+            def __arbitrary__(cls):
+                return (4, 5, 6)
+
+        eq_(Mixin.__table_args__, (1, 2, 3))
+        eq_(Mixin.__arbitrary__, (4, 5, 6))
+
     def test_non_decl_access(self):
         counter = mock.Mock()