Don't override unknown inherited __reduce__.

Cython/Compiler/ModuleNode.py

@@ -2807,6 +2807,15 @@ class ModuleNode(Nodes.Node, Nodes.BlockNode):
                             weakref_entry.cname))
                     else:
                         error(weakref_entry.pos, "__weakref__ slot must be of type 'object'")
+                if scope.lookup_here("__reduce_cython__"):
+                    # Unfortunately, we cannot reliably detect whether a
+                    # superclass defined __reduce__ at compile time, so we must
+                    # do so at runtime.
+                    code.globalstate.use_utility_code(
+                        UtilityCode.load_cached('SetupReduce', 'ExtensionTypes.c'))
+                    code.putln('if (__Pyx_setup_reduce((PyObject*)&%s) < 0) %s' % (
+                                  typeobj_cname,
+                                  code.error_goto(entry.pos)))
 
     def generate_exttype_vtable_init_code(self, entry, code):
         # Generate code to initialise the C method table of an

Cython/Compiler/ParseTreeTransforms.py

@@ -1579,12 +1579,18 @@ if VALUE is not None:
         all_members = []
         cls = node.entry.type
         cinit = None
+        inherited_reduce = None
         while cls is not None:
             all_members.extend(e for e in cls.scope.var_entries if e.name not in ('__weakref__', '__dict__'))
             cinit = cinit or cls.scope.lookup('__cinit__')
+            inherited_reduce = inherited_reduce or cls.scope.lookup('__reduce__') or cls.scope.lookup('__reduce_ex__')
             cls = cls.base_type
         all_members.sort(key=lambda e: e.name)
 
+        if inherited_reduce:
+            # This is not failsafe, as we may not know whether a cimported class defines a __reduce__.
+            return
+
         non_py = [
             e for e in all_members
             if not e.type.is_pyobject and (not e.type.create_from_py_utility_code(env)
@@ -1601,7 +1607,7 @@ if VALUE is not None:
                 error(node.pos, msg)
 
             pickle_func = TreeFragment(u"""
-                def __reduce__(self):
+                def __reduce_cython__(self):
                     raise TypeError("%s")
                 """ % msg,
                 level='c_class', pipeline=[NormalizeTree(None)]).substitute({})
@@ -1643,7 +1649,7 @@ if VALUE is not None:
             self.extra_module_declarations.append(unpickle_func)
 
             pickle_func = TreeFragment(u"""
-                def __reduce__(self):
+                def __reduce_cython__(self):
                     if hasattr(self, '__getstate__'):
                         state = self.__getstate__()
                     elif hasattr(self, '__dict__'):

Cython/Utility/ExtensionTypes.c

@@ -51,3 +51,57 @@ static void __Pyx_call_next_tp_clear(PyObject* obj, inquiry current_tp_clear) {
     if (type && type->tp_clear)
         type->tp_clear(obj);
 }
+
+/////////////// SetupReduce.proto ///////////////
+
+static int __Pyx_setup_reduce(PyObject* type_obj);
+
+/////////////// SetupReduce ///////////////
+
+#define __Pyx_setup_reduce_GET_ATTR_OR_BAD(res, obj, name) res = PyObject_GetAttrString(obj, name); if (res == NULL) goto BAD;
+
+static int __Pyx_setup_reduce(PyObject* type_obj) {
+    int ret = 0;
+    PyObject* builtin_object = NULL;
+    static PyObject *object_reduce = NULL;
+    static PyObject *object_reduce_ex = NULL;
+    PyObject *reduce = NULL;
+    PyObject *reduce_ex = NULL;
+    PyObject *reduce_cython = NULL;
+    PyObject *reduce_name = NULL;
+    PyObject *reduce_cython_name = NULL;
+    PyObject *same_name = NULL;
+
+    if (object_reduce_ex == NULL) {
+        __Pyx_setup_reduce_GET_ATTR_OR_BAD(builtin_object, __pyx_b, "object");
+        __Pyx_setup_reduce_GET_ATTR_OR_BAD(object_reduce, builtin_object, "__reduce__");
+        __Pyx_setup_reduce_GET_ATTR_OR_BAD(object_reduce_ex, builtin_object, "__reduce_ex__");
+    }
+
+    __Pyx_setup_reduce_GET_ATTR_OR_BAD(reduce_ex, type_obj, "__reduce_ex__");
+    if (reduce_ex == object_reduce_ex) {
+        __Pyx_setup_reduce_GET_ATTR_OR_BAD(reduce, type_obj, "__reduce__");
+        __Pyx_setup_reduce_GET_ATTR_OR_BAD(reduce_cython, type_obj, "__reduce_cython__");
+        __Pyx_setup_reduce_GET_ATTR_OR_BAD(reduce_name, reduce, "__name__");
+        __Pyx_setup_reduce_GET_ATTR_OR_BAD(reduce_cython_name, reduce_cython, "__name__");
+        same_name = PyObject_RichCompare(reduce_name, reduce_cython_name, Py_EQ); if (same_name == NULL) goto BAD;
+        if (object_reduce == reduce || PyObject_IsTrue(same_name)) {
+            ret = PyDict_SetItemString(((PyTypeObject*)type_obj)->tp_dict, "__reduce__", reduce_cython); if (ret < 0) goto BAD;
+            ret = PyDict_DelItemString(((PyTypeObject*)type_obj)->tp_dict, "__reduce_cython__");
+            PyType_Modified((PyTypeObject*)type_obj);
+        }
+    }
+    goto GOOD;
+
+BAD:
+    ret = -1;
+GOOD:
+    Py_XDECREF(builtin_object);
+    Py_XDECREF(reduce);
+    Py_XDECREF(reduce_ex);
+    Py_XDECREF(reduce_cython);
+    Py_XDECREF(reduce_name);
+    Py_XDECREF(reduce_cython_name);
+    Py_XDECREF(same_name);
+    return ret;
+}

tests/run/reduce_pickle.pyx

@@ -46,18 +46,30 @@ cdef class B:
 
     cdef int x, y
 
+    def __cinit__(self):
+        self.x = self.y = -1
+
     def __init__(self, x=0, y=0):
         self.x = x
         self.y = y
 
     def __repr__(self):
-        return "B(x=%s, y=%s)" % (self.x, self.y)
+        return "%s(x=%s, y=%s)" % (self.__class__.__name__, self.x, self.y)
 
     def __reduce__(self):
-        return makeB, ({'x': self.x, 'y': self.y},)
+        return makeObj, (type(self), {'x': self.x, 'y': self.y})
+
+def makeObj(obj_type, kwds):
+    return obj_type(**kwds)
 
-def makeB(kwds):
-    return B(**kwds)
+
+cdef class C(B):
+    """
+    >>> import pickle
+    >>> pickle.loads(pickle.dumps(C(x=37, y=389)))
+    C(x=37, y=389)
+    """
+    pass
 
 
 @cython.auto_pickle(True)  # Not needed, just to test the directive.