[3.12] pythongh-119821: Support non-dict globals in LOAD_FROM_DICT_OR_GLOBALS (python#119822) (python#119890)

The implementation basically copies LOAD_GLOBAL. Possibly it could be deduplicated,
but that seems like it may get hairy since the two operations have different operands.

This is important to fix in 3.14 for PEP 649, but it's a bug in earlier versions too,
and we should backport to 3.13 and 3.12 if possible.

(cherry picked from commit 80a4e38)

Author: JelleZijlstra

Lib/test/test_type_aliases.py

@@ -1,4 +1,5 @@
 import pickle
+import textwrap
 import types
 import unittest
 from test.support import check_syntax_error, run_code
@@ -328,3 +329,22 @@ def test_pickling_local(self):
                 with self.subTest(thing=thing, proto=proto):
                     with self.assertRaises(pickle.PickleError):
                         pickle.dumps(thing, protocol=proto)
+
+
+class TypeParamsExoticGlobalsTest(unittest.TestCase):
+    def test_exec_with_unusual_globals(self):
+        class customdict(dict):
+            def __missing__(self, key):
+                return key
+
+        code = compile("type Alias = undefined", "test", "exec")
+        ns = customdict()
+        exec(code, ns)
+        Alias = ns["Alias"]
+        self.assertEqual(Alias.__value__, "undefined")
+
+        code = compile("class A: type Alias = undefined", "test", "exec")
+        ns = customdict()
+        exec(code, ns)
+        Alias = ns["A"].Alias
+        self.assertEqual(Alias.__value__, "undefined")

Misc/NEWS.d/next/Core and Builtins/2024-05-30-23-01-00.gh-issue-119821.jPGfvt.rst

@@ -0,0 +1,2 @@
+Fix execution of :ref:`annotation scopes <annotation-scopes>` within classes
+when ``globals`` is set to a non-dict. Patch by Jelle Zijlstra.

Python/bytecodes.c

@@ -1196,35 +1196,41 @@ dummy_func(
                 }
             }
             if (v == NULL) {
-                v = PyDict_GetItemWithError(GLOBALS(), name);
-                if (v != NULL) {
+                if (PyDict_CheckExact(GLOBALS())
+                    && PyDict_CheckExact(BUILTINS()))
+                {
+                    v = _PyDict_LoadGlobal((PyDictObject *)GLOBALS(),
+                                        (PyDictObject *)BUILTINS(),
+                                        name);
+                    if (v == NULL) {
+                        if (!_PyErr_Occurred(tstate)) {
+                            /* _PyDict_LoadGlobal() returns NULL without raising
+                            * an exception if the key doesn't exist */
+                            format_exc_check_arg(tstate, PyExc_NameError,
+                                                NAME_ERROR_MSG, name);
+                        }
+                        ERROR_IF(true, error);
+                    }
                     Py_INCREF(v);
                 }
-                else if (_PyErr_Occurred(tstate)) {
-                    goto error;
-                }
                 else {
-                    if (PyDict_CheckExact(BUILTINS())) {
-                        v = PyDict_GetItemWithError(BUILTINS(), name);
-                        if (v == NULL) {
-                            if (!_PyErr_Occurred(tstate)) {
-                                format_exc_check_arg(
-                                        tstate, PyExc_NameError,
-                                        NAME_ERROR_MSG, name);
-                            }
-                            goto error;
-                        }
-                        Py_INCREF(v);
-                    }
-                    else {
+                    /* Slow-path if globals or builtins is not a dict */
+
+                    /* namespace 1: globals */
+                    v = PyObject_GetItem(GLOBALS(), name);
+                    if (v == NULL) {
+                        ERROR_IF(!_PyErr_ExceptionMatches(tstate, PyExc_KeyError), error);
+                        _PyErr_Clear(tstate);
+
+                        /* namespace 2: builtins */
                         v = PyObject_GetItem(BUILTINS(), name);
                         if (v == NULL) {
                             if (_PyErr_ExceptionMatches(tstate, PyExc_KeyError)) {
                                 format_exc_check_arg(
                                             tstate, PyExc_NameError,
                                             NAME_ERROR_MSG, name);
                             }
-                            goto error;
+                            ERROR_IF(true, error);
                         }
                     }
                 }