add recursion guard in split

Author: iritkatriel

Lib/test/test_exception_group.py

@@ -337,6 +337,24 @@ def test_basics_split_by_predicate__match(self):
                     rest, ExceptionGroup, rest_template)
 
 
+class DeepRecursionInSplitAndSubgroup(unittest.TestCase):
+    def make_deep_eg(self):
+        e = TypeError(1)
+        for i in range(2000):
+            e = ExceptionGroup('eg', [e])
+        return e
+
+    def test_deep_split(self):
+        e = self.make_deep_eg()
+        with self.assertRaises(RecursionError):
+            e.split(TypeError)
+
+    def test_deep_subgroup(self):
+        e = self.make_deep_eg()
+        with self.assertRaises(RecursionError):
+            e.subgroup(TypeError)
+
+
 def leaf_generator(exc, tbs=None):
     if tbs is None:
         tbs = []

Objects/exceptions.c

@@ -982,13 +982,18 @@ exceptiongroup_split_recursive(PyObject *exc,
     for (Py_ssize_t i = 0; i < num_excs; i++) {
         PyObject *e = PyTuple_GET_ITEM(eg->excs, i);
         _exceptiongroup_split_result rec_result;
+        if (Py_EnterRecursiveCall(" in exceptiongroup_split_recursive")) {
+            goto done;
+        }
         if (exceptiongroup_split_recursive(
                 e, matcher_type, matcher_value,
                 construct_rest, &rec_result) == -1) {
             assert(!rec_result.match);
             assert(!rec_result.rest);
+            Py_LeaveRecursiveCall();
             goto done;
         }
+        Py_LeaveRecursiveCall();
         if (rec_result.match) {
             assert(PyList_CheckExact(match_list));
             if (PyList_Append(match_list, rec_result.match) == -1) {