Merge "read from cls.__dict__ so init_subclass works" into main

3 files changed, 20 insertions, 6 deletions

diff --git a/lib/sqlalchemy/orm/decl_api.py b/lib/sqlalchemy/orm/decl_api.py
index 4a699f63b..70507015b 100644
--- a/lib/sqlalchemy/orm/decl_api.py
+++ b/lib/sqlalchemy/orm/decl_api.py
@@ -109,6 +109,10 @@ class DeclarativeMeta(
     def __init__(
         cls, classname: Any, bases: Any, dict_: Any, **kw: Any
     ) -> None:
+        # use cls.__dict__, which can be modified by an
+        # __init_subclass__() method (#7900)
+        dict_ = cls.__dict__
+
         # early-consume registry from the initial declarative base,
         # assign privately to not conflict with subclass attributes named
         # "registry"
@@ -293,7 +297,8 @@ class declared_attr(interfaces._MappedAttribute[_T]):
 
         # here, we are inside of the declarative scan.  use the registry
         # that is tracking the values of these attributes.
-        declarative_scan = manager.declarative_scan
+        declarative_scan = manager.declarative_scan()
+        assert declarative_scan is not None
         reg = declarative_scan.declared_attr_reg
 
         if self in reg:
diff --git a/lib/sqlalchemy/orm/decl_base.py b/lib/sqlalchemy/orm/decl_base.py
index 3fb8af80c..804d05ce1 100644
--- a/lib/sqlalchemy/orm/decl_base.py
+++ b/lib/sqlalchemy/orm/decl_base.py
@@ -161,7 +161,13 @@ def _check_declared_props_nocascade(obj, name, cls):
 
 
 class _MapperConfig:
-    __slots__ = ("cls", "classname", "properties", "declared_attr_reg")
+    __slots__ = (
+        "cls",
+        "classname",
+        "properties",
+        "declared_attr_reg",
+        "__weakref__",
+    )
 
     @classmethod
     def setup_mapping(cls, registry, cls_, dict_, table, mapper_kw):
@@ -311,13 +317,15 @@ class _ClassScanMapperConfig(_MapperConfig):
         mapper_kw,
     ):
 
+        # grab class dict before the instrumentation manager has been added.
+        # reduces cycles
+        self.clsdict_view = (
+            util.immutabledict(dict_) if dict_ else util.EMPTY_DICT
+        )
         super(_ClassScanMapperConfig, self).__init__(registry, cls_, mapper_kw)
         self.registry = registry
         self.persist_selectable = None
 
-        self.clsdict_view = (
-            util.immutabledict(dict_) if dict_ else util.EMPTY_DICT
-        )
         self.collected_attributes = {}
         self.collected_annotations: Dict[str, Tuple[Any, bool]] = {}
         self.declared_columns = util.OrderedSet()
diff --git a/lib/sqlalchemy/orm/instrumentation.py b/lib/sqlalchemy/orm/instrumentation.py
index a5dc305d2..0d4b630da 100644
--- a/lib/sqlalchemy/orm/instrumentation.py
+++ b/lib/sqlalchemy/orm/instrumentation.py
@@ -39,6 +39,7 @@ from typing import Optional
 from typing import Set
 from typing import TYPE_CHECKING
 from typing import TypeVar
+import weakref
 
 from . import base
 from . import collections
@@ -167,7 +168,7 @@ class ClassManager(
         if registry:
             registry._add_manager(self)
         if declarative_scan:
-            self.declarative_scan = declarative_scan
+            self.declarative_scan = weakref.ref(declarative_scan)
         if expired_attribute_loader:
             self.expired_attribute_loader = expired_attribute_loader