Changed handling of a single exception raised in exception group hand…

…lers to match Python 3.11.4

Fixes #64.

CHANGES.rst

@@ -3,6 +3,12 @@ Version history
 
 This library adheres to `Semantic Versioning 2.0 <http://semver.org/>`_.
 
+**UNRELEASED**
+
+- Changed handling of exceptions in exception group handler callbacks to not wrap a
+  single exception in an exception group, as per
+  `CPython issue 103590 <https://github.com/python/cpython/issues/103590>`_
+
 **1.1.1**
 
 - Worked around

src/exceptiongroup/_catch.py

@@ -37,7 +37,7 @@ def __exit__(
 
         return False
 
-    def handle_exception(self, exc: BaseException) -> BaseExceptionGroup | None:
+    def handle_exception(self, exc: BaseException) -> BaseException | None:
         excgroup: BaseExceptionGroup | None
         if isinstance(exc, BaseExceptionGroup):
             excgroup = exc
@@ -57,6 +57,9 @@ def handle_exception(self, exc: BaseException) -> BaseExceptionGroup | None:
                 break
 
         if new_exceptions:
+            if len(new_exceptions) == 1:
+                return new_exceptions[0]
+
             if excgroup:
                 new_exceptions.append(excgroup)
 

tests/test_catch.py

@@ -148,15 +148,9 @@ def test_catch_handler_raises():
     def handler(exc):
         raise RuntimeError("new")
 
-    try:
+    with pytest.raises(RuntimeError, match="new"):
         with catch({(ValueError, ValueError): handler}):
             raise ExceptionGroup("booboo", [ValueError("bar")])
-    except ExceptionGroup as exc:
-        assert exc.message == ""
-        assert len(exc.exceptions) == 1
-        assert isinstance(exc.exceptions[0], RuntimeError)
-    else:
-        pytest.fail("Did not raise an ExceptionGroup")
 
 
 def test_catch_subclass():

tests/test_catch_py311.py

@@ -122,17 +122,11 @@ def test_catch_full_match():
 
 
 def test_catch_handler_raises():
-    try:
+    with pytest.raises(RuntimeError, match="new"):
         try:
             raise ExceptionGroup("booboo", [ValueError("bar")])
         except* ValueError:
             raise RuntimeError("new")
-    except ExceptionGroup as exc:
-        assert exc.message == ""
-        assert len(exc.exceptions) == 1
-        assert isinstance(exc.exceptions[0], RuntimeError)
-    else:
-        pytest.fail("Did not raise an ExceptionGroup")
 
 
 def test_catch_subclass():