Readjustments to the way we cope with exceptions from subclasses'

mro() methods.  Now any exception aborts the whole __bases__ change.

And more tests.

Lib/test/test_descr.py

@@ -3434,7 +3434,7 @@ def do_this_first():
     # (before PyType_Ready(tuple) is called)
     type.mro(tuple)
 
-def mutable_bases():
+def test_mutable_bases():
     # stuff that should work:
     class C(object):
         pass
@@ -3523,6 +3523,80 @@ def mutable_bases():
     else:
         raise TestFailed, "new-style class must have a new-style base"
 
+def test_mutable_bases_with_failing_mro():
+    class WorkOnce(type):
+        def __new__(self, name, bases, ns):
+            self.flag = 0
+            return super(WorkOnce, self).__new__(WorkOnce, name, bases, ns)
+        def mro(self):
+            if self.flag > 0:
+                raise RuntimeError, "bozo"
+            else:
+                self.flag += 1
+                return type.mro(self)
+
+    class WorkAlways(type):
+        def mro(self):
+            # this is here to make sure that .mro()s aren't called
+            # with an exception set (which was possible at one point).
+            # An error message will be printed in a debug build.
+            # What's a good way to test for this?
+            return type.mro(self)
+
+    class C(object):
+        pass
+
+    class C2(object):
+        pass
+
+    class D(C):
+        pass
+
+    class E(D):
+        pass
+
+    class F(D):
+        __metaclass__ = WorkOnce
+
+    class G(D):
+        __metaclass__ = WorkAlways
+
+    # Immediate subclasses have their mro's adjusted in alphabetical
+    # order, so E's will get adjusted before adjusting F's fails.  We
+    # check here that E's gets restored.
+    
+    E_mro_before = E.__mro__
+
+    try:
+        D.__bases__ = (C2,)
+    except RuntimeError:
+        vereq(E.__mro__, E_mro_before)
+    else:
+        raise TestFailed, "exception not propagated"
+
+def test_mutable_bases_catch_mro_conflict():
+    class A(object):
+        pass
+
+    class B(object):
+        pass
+
+    class C(A, B):
+        pass
+
+    class D(A, B):
+        pass
+
+    class E(C, D):
+        pass
+
+    try:
+        C.__bases__ = (B, A)
+    except TypeError:
+        pass
+    else:
+        raise TestFailed, "didn't catch MRO conflict"
+    
 def mutable_names():
     class C(object):
         pass
@@ -3608,8 +3682,11 @@ def test_main():
     slotmultipleinheritance()
     testrmul()
     testipow()
-    mutable_bases()
+    test_mutable_bases()
+    test_mutable_bases_with_failing_mro()
+    test_mutable_bases_catch_mro_conflict()
     mutable_names()
+
     if verbose: print "All OK"
 
 if __name__ == "__main__":

Objects/typeobject.c

@@ -142,11 +142,11 @@ static void remove_subclass(PyTypeObject *, PyTypeObject *);
 static void update_all_slots(PyTypeObject *);
 
 static int
-mro_subclasses(PyTypeObject *type)
+mro_subclasses(PyTypeObject *type, PyObject* temp)
 {
 	PyTypeObject *subclass;
 	PyObject *ref, *subclasses, *old_mro;
-	int i, n, r = 0;
+	int i, n;
 
 	subclasses = type->tp_subclasses;
 	if (subclasses == NULL)
@@ -164,22 +164,27 @@ mro_subclasses(PyTypeObject *type)
 		old_mro = subclass->tp_mro;
 		if (mro_internal(subclass) < 0) {
 			subclass->tp_mro = old_mro;
-			r = -1;
+			return -1;
 		}
 		else {
-			Py_DECREF(old_mro);
+			PyObject* tuple;
+			tuple = Py_BuildValue("OO", subclass, old_mro);
+			if (!tuple)
+				return -1;
+			if (PyList_Append(temp, tuple) < 0)
+				return -1;
 		}
-		if (mro_subclasses(subclass) < 0)
-			r = -1;
+		if (mro_subclasses(subclass, temp) < 0)
+			return -1;
 	}
-	return r;
+	return 0;
 }
 
 static int
 type_set_bases(PyTypeObject *type, PyObject *value, void *context)
 {
 	int i, r = 0;
-	PyObject* ob;
+	PyObject *ob, *temp;
 	PyTypeObject *new_base, *old_base;
 	PyObject *old_bases, *old_mro;
 
@@ -247,8 +252,25 @@ type_set_bases(PyTypeObject *type, PyObject *value, void *context)
 		return -1;
 	}
 
-	if (mro_subclasses(type) < 0)
-		r = -1;
+	temp = PyList_New(0);
+
+	r = mro_subclasses(type, temp);
+
+	if (r < 0) {
+		for (i = 0; i < PyList_Size(temp); i++) {
+			PyTypeObject* cls;
+			PyObject* mro;
+			PyArg_ParseTuple(PyList_GetItem(temp, i),
+					 "OO", &cls, &mro);
+			Py_DECREF(cls->tp_mro);
+			cls->tp_mro = mro;
+			Py_INCREF(cls->tp_mro);
+		}
+		Py_DECREF(temp);
+		return r;
+	}
+
+	Py_DECREF(temp);
 
 	/* any base that was in __bases__ but now isn't, we
 	   need to remove |type| from it's tp_subclasses.