Also chain codec exceptions that allow weakrefs

The zlib and hex codecs throw custom exception types with
weakref support if the input type is valid, but the data
fails validation. Make sure the exception chaining in the
codec infrastructure can wrap those as well.

1 files changed, 14 insertions, 3 deletions

diff --git a/Objects/exceptions.c b/Objects/exceptions.c
index 3476db02df..af40bc8fea 100644
--- a/Objects/exceptions.c
+++ b/Objects/exceptions.c
@@ -2630,16 +2630,27 @@ _PyErr_TrySetFromCause(const char *format, ...)
     PyTypeObject *caught_type;
     PyObject **dictptr;
     PyObject *instance_args;
-    Py_ssize_t num_args;
+    Py_ssize_t num_args, caught_type_size, base_exc_size;
     PyObject *new_exc, *new_val, *new_tb;
     va_list vargs;
+    int same_basic_size;
 
     PyErr_Fetch(&exc, &val, &tb);
     caught_type = (PyTypeObject *)exc;
-    /* Ensure type info indicates no extra state is stored at the C level */
+    /* Ensure type info indicates no extra state is stored at the C level
+     * and that the type can be reinstantiated using PyErr_Format
+     */
+    caught_type_size = caught_type->tp_basicsize;
+    base_exc_size = _PyExc_BaseException.tp_basicsize;
+    same_basic_size = (
+        caught_type_size == base_exc_size ||
+        (PyType_SUPPORTS_WEAKREFS(caught_type) &&
+            (caught_type_size == base_exc_size + sizeof(PyObject *))
+        )
+    );
     if (caught_type->tp_init != (initproc)BaseException_init ||
         caught_type->tp_new != BaseException_new ||
-        caught_type->tp_basicsize != _PyExc_BaseException.tp_basicsize ||
+        !same_basic_size ||
         caught_type->tp_itemsize != _PyExc_BaseException.tp_itemsize) {
         /* We can't be sure we can wrap this safely, since it may contain
          * more state than just the exception type. Accordingly, we just