Merge.

1 files changed, 34 insertions, 0 deletions

diff --git a/Lib/test/test_contextlib.py b/Lib/test/test_contextlib.py
index 30a6377..516403e 100644
--- a/Lib/test/test_contextlib.py
+++ b/Lib/test/test_contextlib.py
@@ -762,6 +762,40 @@ class TestExitStack(unittest.TestCase):
         stack.push(cm)
         self.assertIs(stack._exit_callbacks[-1], cm)
 
+    def test_dont_reraise_RuntimeError(self):
+        # https://bugs.python.org/issue27122
+        class UniqueException(Exception): pass
+        class UniqueRuntimeError(RuntimeError): pass
+
+        @contextmanager
+        def second():
+            try:
+                yield 1
+            except Exception as exc:
+                raise UniqueException("new exception") from exc
+
+        @contextmanager
+        def first():
+            try:
+                yield 1
+            except Exception as exc:
+                raise exc
+
+        # The UniqueRuntimeError should be caught by second()'s exception
+        # handler which chain raised a new UniqueException.
+        with self.assertRaises(UniqueException) as err_ctx:
+            with ExitStack() as es_ctx:
+                es_ctx.enter_context(second())
+                es_ctx.enter_context(first())
+                raise UniqueRuntimeError("please no infinite loop.")
+
+        exc = err_ctx.exception
+        self.assertIsInstance(exc, UniqueException)
+        self.assertIsInstance(exc.__context__, UniqueRuntimeError)
+        self.assertIsNone(exc.__context__.__context__)
+        self.assertIsNone(exc.__context__.__cause__)
+        self.assertIs(exc.__cause__, exc.__context__)
+
 
 class TestRedirectStream: