gh-111375: Use `NULL` rather than `None` in the exception stack to indicate that an exception was handled (#113302)

Misc/NEWS.d/next/Core and Builtins/2023-12-19-22-03-43.gh-issue-111375.M9vuA6.rst

@@ -0,0 +1,2 @@
+Only use ``NULL`` in the exception stack to indicate an exception was
+handled. Patch by Carey Metcalfe.

Objects/frameobject.c

@@ -811,7 +811,7 @@ frame_setlineno(PyFrameObject *f, PyObject* p_new_lineno, void *Py_UNUSED(ignore
             PyObject *exc = _PyFrame_StackPop(f->f_frame);
             assert(PyExceptionInstance_Check(exc) || exc == Py_None);
             PyThreadState *tstate = _PyThreadState_GET();
-            Py_XSETREF(tstate->exc_info->exc_value, exc);
+            Py_XSETREF(tstate->exc_info->exc_value, exc == Py_None ? NULL : exc);
         }
         else {
             PyObject *v = _PyFrame_StackPop(f->f_frame);

Python/bytecodes.c

@@ -1100,7 +1100,7 @@ dummy_func(
 
         inst(POP_EXCEPT, (exc_value -- )) {
             _PyErr_StackItem *exc_info = tstate->exc_info;
-            Py_XSETREF(exc_info->exc_value, exc_value);
+            Py_XSETREF(exc_info->exc_value, exc_value == Py_None ? NULL : exc_value);
         }
 
         inst(RERAISE, (values[oparg], exc -- values[oparg])) {

Python/errors.c

@@ -121,11 +121,11 @@ _PyErr_GetTopmostException(PyThreadState *tstate)
     _PyErr_StackItem *exc_info = tstate->exc_info;
     assert(exc_info);
 
-    while ((exc_info->exc_value == NULL || exc_info->exc_value == Py_None) &&
-           exc_info->previous_item != NULL)
+    while (exc_info->exc_value == NULL && exc_info->previous_item != NULL)
     {
         exc_info = exc_info->previous_item;
     }
+    assert(!Py_IsNone(exc_info->exc_value));
     return exc_info;
 }
 
@@ -592,7 +592,7 @@ PyErr_GetHandledException(void)
 void
 _PyErr_SetHandledException(PyThreadState *tstate, PyObject *exc)
 {
-    Py_XSETREF(tstate->exc_info->exc_value, Py_XNewRef(exc));
+    Py_XSETREF(tstate->exc_info->exc_value, Py_XNewRef(exc == Py_None ? NULL : exc));
 }
 
 void

Python/executor_cases.c.h

@@ -806,7 +806,7 @@
             PyObject *exc_value;
             exc_value = stack_pointer[-1];
             _PyErr_StackItem *exc_info = tstate->exc_info;
-            Py_XSETREF(exc_info->exc_value, exc_value);
+            Py_XSETREF(exc_info->exc_value, exc_value == Py_None ? NULL : exc_value);
             stack_pointer += -1;
             break;
         }

Python/generated_cases.c.h

@@ -4567,7 +4567,7 @@
             PyObject *exc_value;
             exc_value = stack_pointer[-1];
             _PyErr_StackItem *exc_info = tstate->exc_info;
-            Py_XSETREF(exc_info->exc_value, exc_value);
+            Py_XSETREF(exc_info->exc_value, exc_value == Py_None ? NULL : exc_value);
             stack_pointer += -1;
             DISPATCH();
         }