From 80449f243b13311d660eab3a751648029bcdd833 Mon Sep 17 00:00:00 2001
From: Pablo Galindo <Pablogsal@gmail.com>
Date: Thu, 5 Nov 2020 09:23:15 +0000
Subject: [PATCH] bpo-42266: Handle monkey-patching descriptors in LOAD_ATTR
 cache (GH-23157)

---
 Lib/test/test_opcache.py                      | 23 +++++++++++++++++++
 .../2020-11-04-23-03-25.bpo-42266.G4hGDe.rst  |  3 +++
 PCbuild/lib.pyproj                            |  1 +
 Python/ceval.c                                |  8 +------
 4 files changed, 28 insertions(+), 7 deletions(-)
 create mode 100644 Lib/test/test_opcache.py
 create mode 100644 Misc/NEWS.d/next/Core and Builtins/2020-11-04-23-03-25.bpo-42266.G4hGDe.rst

diff --git a/Lib/test/test_opcache.py b/Lib/test/test_opcache.py
new file mode 100644
index 00000000000..61f337d70ea
--- /dev/null
+++ b/Lib/test/test_opcache.py
@@ -0,0 +1,23 @@
+import unittest
+
+class TestLoadAttrCache(unittest.TestCase):
+    def test_descriptor_added_after_optimization(self):
+        class Descriptor:
+            pass
+
+        class C:
+            def __init__(self):
+                self.x = 1
+            x = Descriptor()
+
+        def f(o):
+            return o.x
+
+        o = C()
+        for i in range(1025):
+            assert f(o) == 1
+
+        Descriptor.__get__ = lambda self, instance, value: 2
+        Descriptor.__set__ = lambda *args: None
+
+        self.assertEqual(f(o), 2)
diff --git a/Misc/NEWS.d/next/Core and Builtins/2020-11-04-23-03-25.bpo-42266.G4hGDe.rst b/Misc/NEWS.d/next/Core and Builtins/2020-11-04-23-03-25.bpo-42266.G4hGDe.rst
new file mode 100644
index 00000000000..a8598cfde04
--- /dev/null
+++ b/Misc/NEWS.d/next/Core and Builtins/2020-11-04-23-03-25.bpo-42266.G4hGDe.rst	
@@ -0,0 +1,3 @@
+Fixed a bug with the LOAD_ATTR opcode cache that was not respecting
+monkey-patching a class-level attribute to make it a descriptor. Patch by
+Pablo Galindo.
diff --git a/PCbuild/lib.pyproj b/PCbuild/lib.pyproj
index a15165d92ef..1be60b1a11b 100644
--- a/PCbuild/lib.pyproj
+++ b/PCbuild/lib.pyproj
@@ -1196,6 +1196,7 @@
     <Compile Include="test\test_nntplib.py" />
     <Compile Include="test\test_ntpath.py" />
     <Compile Include="test\test_numeric_tower.py" />
+    <Compile Include="test\test_opcache.py" />
     <Compile Include="test\test_opcodes.py" />
     <Compile Include="test\test_openpty.py" />
     <Compile Include="test\test_operator.py" />
diff --git a/Python/ceval.c b/Python/ceval.c
index 13b209fc706..32e3019682f 100644
--- a/Python/ceval.c
+++ b/Python/ceval.c
@@ -3179,7 +3179,6 @@ main_loop:
                 if (co_opcache != NULL && /* co_opcache can be NULL after a DEOPT() call. */
                     type->tp_getattro == PyObject_GenericGetAttr)
                 {
-                    PyObject *descr;
                     Py_ssize_t ret;
 
                     if (type->tp_dictoffset > 0) {
@@ -3190,12 +3189,7 @@ main_loop:
                                 goto error;
                             }
                         }
-
-                        descr = _PyType_Lookup(type, name);
-                        if (descr == NULL ||
-                            Py_TYPE(descr)->tp_descr_get == NULL ||
-                            !PyDescr_IsData(descr))
-                        {
+                        if (_PyType_Lookup(type, name) == NULL) {
                             dictptr = (PyObject **) ((char *)owner + type->tp_dictoffset);
                             dict = *dictptr;