Allow None to be passed into arguments annotated as type "object" (GH-4669)

Cython/Compiler/Nodes.py

@@ -973,6 +973,9 @@ class CArgDeclNode(Node):
                 error(annotation.pos, "Only Python type arguments can use typing.Optional[...]")
             else:
                 self.or_none = True
+        elif arg_type is py_object_type:
+            # exclude ": object" from the None check - None is a generic object.
+            self.or_none = True
         elif arg_type and arg_type.is_pyobject and self.default and self.default.is_none:
             # "x: ... = None"  =>  implicitly allow 'None', but warn about it.
             if not self.or_none:

tests/run/ext_type_none_arg.pyx

@@ -205,6 +205,30 @@ def object_default(object o): # always behaves like 'or None'
     """
     return type(o).__name__
 
+@cython.allow_none_for_extension_args(False)
+def object_default_annotation(o : object):
+    """
+    >>> object_default_annotation(object())
+    'object'
+    >>> object_default_annotation([])
+    'list'
+    >>> object_default_annotation(None)
+    'NoneType'
+    """
+    return type(o).__name__
+
+# no decorator
+def object_default_annotation2(o : object):
+    """
+    >>> object_default_annotation2(object())
+    'object'
+    >>> object_default_annotation2([])
+    'list'
+    >>> object_default_annotation2(None)
+    'NoneType'
+    """
+    return type(o).__name__
+
 @cython.allow_none_for_extension_args(False)
 def object_default_none(object o=None): # behaves like 'or None'
     """