Merge pull request #584 from dangra/581-deprecated-subclass-fix

Fix wrong checks on subclassing of deprecated classes

scrapy/tests/test_utils_deprecate.py

@@ -145,6 +145,9 @@ class WarnWhenSubclassedTest(unittest.TestCase):
             class OutdatedUserClass1(DeprecatedName):
                 pass
 
+            class OutdatedUserClass1a(DeprecatedName):
+                pass
+
             class UnrelatedClass(object):
                 pass
 
@@ -159,6 +162,8 @@ class WarnWhenSubclassedTest(unittest.TestCase):
         assert not issubclass(UnrelatedClass, DeprecatedName)
         assert not issubclass(OldStyleClass, DeprecatedName)
         assert not issubclass(OldStyleClass, DeprecatedName)
+        assert not issubclass(OutdatedUserClass1, OutdatedUserClass1a)
+        assert not issubclass(OutdatedUserClass1a, OutdatedUserClass1)
 
         self.assertRaises(TypeError, issubclass, object(), DeprecatedName)
 
@@ -175,6 +180,9 @@ class WarnWhenSubclassedTest(unittest.TestCase):
             class OutdatedUserClass2(DeprecatedName):
                 pass
 
+            class OutdatedUserClass2a(DeprecatedName):
+                pass
+
             class UnrelatedClass(object):
                 pass
 
@@ -186,6 +194,9 @@ class WarnWhenSubclassedTest(unittest.TestCase):
         assert isinstance(UpdatedUserClass2(), DeprecatedName)
         assert isinstance(UpdatedUserClass2a(), DeprecatedName)
         assert isinstance(OutdatedUserClass2(), DeprecatedName)
+        assert isinstance(OutdatedUserClass2a(), DeprecatedName)
+        assert not isinstance(OutdatedUserClass2a(), OutdatedUserClass2)
+        assert not isinstance(OutdatedUserClass2(), OutdatedUserClass2a)
         assert not isinstance(UnrelatedClass(), DeprecatedName)
         assert not isinstance(OldStyleClass(), DeprecatedName)
 

scrapy/utils/deprecate.py

@@ -79,12 +79,18 @@ def create_deprecated_class(name, new_class, clsdict=None,
                        for c in {type(inst), inst.__class__})
 
         def __subclasscheck__(cls, sub):
+            if cls is not DeprecatedClass.deprecated_class:
+                # we should do the magic only if second `issubclass` argument
+                # is the deprecated class itself - subclasses of the
+                # deprecated class should not use custom `__subclasscheck__`
+                # method.
+                return super(DeprecatedClass, cls).__subclasscheck__(sub)
+
             if not inspect.isclass(sub):
                 raise TypeError("issubclass() arg 1 must be a class")
 
             mro = getattr(sub, '__mro__', ())
-            candidates = {cls, new_class}
-            return any(c in candidates for c in mro)
+            return any(c in {cls, new_class} for c in mro)
 
         def __call__(cls, *args, **kwargs):
             old = DeprecatedClass.deprecated_class