bpo-39960: Allow heap types in the "Carlo Verre" hack check that override "tp_setattro()" (GH-21092)

Automerge-Triggered-By: @gvanrossum

1 files changed, 30 insertions, 11 deletions

diff --git a/Objects/typeobject.c b/Objects/typeobject.c
index f0e349e..16f95f0 100644
--- a/Objects/typeobject.c
+++ b/Objects/typeobject.c
@@ -97,6 +97,9 @@ clear_slotdefs(void);
 static PyObject *
 lookup_maybe_method(PyObject *self, _Py_Identifier *attrid, int *unbound);
 
+static int
+slot_tp_setattro(PyObject *self, PyObject *name, PyObject *value);
+
 /*
  * finds the beginning of the docstring's introspection signature.
  * if present, returns a pointer pointing to the first '('.
@@ -5945,22 +5948,38 @@ wrap_delitem(PyObject *self, PyObject *args, void *wrapped)
 }
 
 /* Helper to check for object.__setattr__ or __delattr__ applied to a type.
-   This is called the Carlo Verre hack after its discoverer. */
+   This is called the Carlo Verre hack after its discoverer.  See
+   https://mail.python.org/pipermail/python-dev/2003-April/034535.html
+   */
 static int
 hackcheck(PyObject *self, setattrofunc func, const char *what)
 {
     PyTypeObject *type = Py_TYPE(self);
-    while (type && type->tp_flags & Py_TPFLAGS_HEAPTYPE)
-        type = type->tp_base;
-    /* If type is NULL now, this is a really weird type.
-       In the spirit of backwards compatibility (?), just shut up. */
-    if (type && type->tp_setattro != func) {
-        PyErr_Format(PyExc_TypeError,
-                     "can't apply this %s to %s object",
-                     what,
-                     type->tp_name);
-        return 0;
+    PyObject *mro = type->tp_mro;
+    if (!mro) {
+        /* Probably ok not to check the call in this case. */
+        return 1;
+    }
+    assert(PyTuple_Check(mro));
+    Py_ssize_t i, n;
+    n = PyTuple_GET_SIZE(mro);
+    for (i = 0; i < n; i++) {
+        PyTypeObject *base = (PyTypeObject*) PyTuple_GET_ITEM(mro, i);
+        if (base->tp_setattro == func) {
+            /* 'func' is the earliest non-Python implementation in the MRO. */
+            break;
+        } else if (base->tp_setattro != slot_tp_setattro) {
+            /* 'base' is not a Python class and overrides 'func'.
+               Its tp_setattro should be called instead. */
+            PyErr_Format(PyExc_TypeError,
+                         "can't apply this %s to %s object",
+                         what,
+                         type->tp_name);
+            return 0;
+        }
     }
+    /* Either 'func' is not in the mro (which should fail when checking 'self'),
+       or it's the right slot function to call. */
     return 1;
 }