bpo-42500: Fix recursion in or after except (GH-23568) (#24501)

* Use counter, rather boolean state when handling soft overflows.

(cherry picked from commit 4e7a69bdb63a104587759d7784124492dcdd496e)

1 files changed, 50 insertions, 2 deletions

diff --git a/Lib/test/test_exceptions.py b/Lib/test/test_exceptions.py
index 8d125b5..9c09bdc 100644
--- a/Lib/test/test_exceptions.py
+++ b/Lib/test/test_exceptions.py
@@ -1043,7 +1043,7 @@ class ExceptionTests(unittest.TestCase):
                 # tstate->recursion_depth is equal to (recursion_limit - 1)
                 # and is equal to recursion_limit when _gen_throw() calls
                 # PyErr_NormalizeException().
-                recurse(setrecursionlimit(depth + 2) - depth - 1)
+                recurse(setrecursionlimit(depth + 2) - depth)
             finally:
                 sys.setrecursionlimit(recursionlimit)
                 print('Done.')
@@ -1073,6 +1073,54 @@ class ExceptionTests(unittest.TestCase):
                       b'while normalizing an exception', err)
         self.assertIn(b'Done.', out)
 
+
+    def test_recursion_in_except_handler(self):
+
+        def set_relative_recursion_limit(n):
+            depth = 1
+            while True:
+                try:
+                    sys.setrecursionlimit(depth)
+                except RecursionError:
+                    depth += 1
+                else:
+                    break
+            sys.setrecursionlimit(depth+n)
+
+        def recurse_in_except():
+            try:
+                1/0
+            except:
+                recurse_in_except()
+
+        def recurse_after_except():
+            try:
+                1/0
+            except:
+                pass
+            recurse_after_except()
+
+        def recurse_in_body_and_except():
+            try:
+                recurse_in_body_and_except()
+            except:
+                recurse_in_body_and_except()
+
+        recursionlimit = sys.getrecursionlimit()
+        try:
+            set_relative_recursion_limit(10)
+            for func in (recurse_in_except, recurse_after_except, recurse_in_body_and_except):
+                with self.subTest(func=func):
+                    try:
+                        func()
+                    except RecursionError:
+                        pass
+                    else:
+                        self.fail("Should have raised a RecursionError")
+        finally:
+            sys.setrecursionlimit(recursionlimit)
+
+
     @cpython_only
     def test_recursion_normalizing_with_no_memory(self):
         # Issue #30697. Test that in the abort that occurs when there is no
@@ -1109,7 +1157,7 @@ class ExceptionTests(unittest.TestCase):
             except MemoryError as e:
                 tb = e.__traceback__
             else:
-                self.fail("Should have raises a MemoryError")
+                self.fail("Should have raised a MemoryError")
             return traceback.format_tb(tb)
 
         tb1 = raiseMemError()