Fill-out dataclass-related attr resolution

Fixed issue where mixin attribute rules were not taking
effect correctly for attributes pulled from dataclasses
using the approach added in #5745.

Fixes: #5876
Change-Id: I45099a42de1d9611791e72250fe0edc69bed684c

2 files changed, 21 insertions, 0 deletions

diff --git a/lib/sqlalchemy/util/__init__.py b/lib/sqlalchemy/util/__init__.py
index 5f8788a6e..2d86b8b63 100644
--- a/lib/sqlalchemy/util/__init__.py
+++ b/lib/sqlalchemy/util/__init__.py
@@ -66,6 +66,7 @@ from .compat import int_types  # noqa
 from .compat import iterbytes  # noqa
 from .compat import itertools_filter  # noqa
 from .compat import itertools_filterfalse  # noqa
+from .compat import local_dataclass_fields  # noqa
 from .compat import namedtuple  # noqa
 from .compat import next  # noqa
 from .compat import nullcontext  # noqa
diff --git a/lib/sqlalchemy/util/compat.py b/lib/sqlalchemy/util/compat.py
index 1eed2c3af..5b7a3eb9f 100644
--- a/lib/sqlalchemy/util/compat.py
+++ b/lib/sqlalchemy/util/compat.py
@@ -425,17 +425,37 @@ if py37:
     import dataclasses
 
     def dataclass_fields(cls):
+        """Return a sequence of all dataclasses.Field objects associated
+        with a class."""
+
         if dataclasses.is_dataclass(cls):
             return dataclasses.fields(cls)
         else:
             return []
 
+    def local_dataclass_fields(cls):
+        """Return a sequence of all dataclasses.Field objects associated with
+        a class, excluding those that originate from a superclass."""
+
+        if dataclasses.is_dataclass(cls):
+            super_fields = set()
+            for sup in cls.__bases__:
+                super_fields.update(dataclass_fields(sup))
+            return [
+                f for f in dataclasses.fields(cls) if f not in super_fields
+            ]
+        else:
+            return []
+
 
 else:
 
     def dataclass_fields(cls):
         return []
 
+    def local_dataclass_fields(cls):
+        return []
+
 
 def raise_from_cause(exception, exc_info=None):
     r"""legacy.  use raise\_()"""