Unwrap Proxy objects when scanning declared_attr

Fixed bug where the declarative scan for attributes would receive the
expression proxy delivered by a hybrid attribute at the class level, and
not the hybrid attribute itself, when receiving the descriptor via the
``@declared_attr`` callable on a subclass of an already-mapped class. This
would lead to an attribute that did not report itself as a hybrid when
viewed within :attr:`.Mapper.all_orm_descriptors`.

Fixes: #4326
Change-Id: I582d03f05c3768b3344f93e3791240e9e69b9d1e

3 files changed, 10 insertions, 0 deletions

diff --git a/lib/sqlalchemy/orm/attributes.py b/lib/sqlalchemy/orm/attributes.py
index 0bbe70655..745032e44 100644
--- a/lib/sqlalchemy/orm/attributes.py
+++ b/lib/sqlalchemy/orm/attributes.py
@@ -271,6 +271,8 @@ def create_proxied_attribute(descriptor):
             self._adapt_to_entity = adapt_to_entity
             self.__doc__ = doc
 
+        _is_internal_proxy = True
+
         @property
         def property(self):
             return self.comparator.property
diff --git a/lib/sqlalchemy/orm/base.py b/lib/sqlalchemy/orm/base.py
index 8c9d56269..e06e1fc78 100644
--- a/lib/sqlalchemy/orm/base.py
+++ b/lib/sqlalchemy/orm/base.py
@@ -475,6 +475,13 @@ class InspectionAttr(object):
 
     """
 
+    _is_internal_proxy = False
+    """True if this object is an internal proxy object.
+
+    .. versionadded:: 1.2.12
+
+    """
+
     is_clause_element = False
     """True if this object is an instance of :class:`.ClauseElement`."""
 
diff --git a/lib/sqlalchemy/orm/descriptor_props.py b/lib/sqlalchemy/orm/descriptor_props.py
index a8db3fe1c..aaf53b698 100644
--- a/lib/sqlalchemy/orm/descriptor_props.py
+++ b/lib/sqlalchemy/orm/descriptor_props.py
@@ -500,6 +500,7 @@ class ConcreteInheritedProperty(DescriptorProperty):
                                  (self.parent, self.key, self.parent))
 
         class NoninheritedConcreteProp(object):
+
             def __set__(s, obj, value):
                 warn()