Fixed bare raise and exception chaining when a handler raises an ex…

…ception (#71)

CHANGES.rst

@@ -7,6 +7,10 @@ This library adheres to `Semantic Versioning 2.0 <http://semver.org/>`_.
 - `catch()` now raises a `TypeError` if passed an async exception handler instead of
   just giving a `RuntimeWarning` about the coroutine never being awaited. (#66, PR by
   John Litborn)
+- Fixed plain ``raise`` statement in an exception handler callback to work like a
+  ``raise`` in an ``except*`` block
+- Fixed new exception group not being chained to the original exception when raising an
+  exception group from exceptions raised in handler callbacks
 
 **1.1.2**
 

src/exceptiongroup/_catch.py

@@ -34,7 +34,16 @@ def __exit__(
             elif unhandled is None:
                 return True
             else:
-                raise unhandled from None
+                if isinstance(exc, BaseExceptionGroup):
+                    try:
+                        raise unhandled from exc.__cause__
+                    except BaseExceptionGroup:
+                        # Change __context__ to __cause__ because Python 3.11 does this
+                        # too
+                        unhandled.__context__ = exc.__cause__
+                        raise
+
+                raise unhandled from exc
 
         return False
 
@@ -50,7 +59,12 @@ def handle_exception(self, exc: BaseException) -> BaseException | None:
             matched, excgroup = excgroup.split(exc_types)
             if matched:
                 try:
-                    result = handler(matched)
+                    try:
+                        raise matched
+                    except BaseExceptionGroup:
+                        result = handler(matched)
+                except BaseExceptionGroup as new_exc:
+                    new_exceptions.extend(new_exc.exceptions)
                 except BaseException as new_exc:
                     new_exceptions.append(new_exc)
                 else:
@@ -67,9 +81,6 @@ def handle_exception(self, exc: BaseException) -> BaseException | None:
             if len(new_exceptions) == 1:
                 return new_exceptions[0]
 
-            if excgroup:
-                new_exceptions.append(excgroup)
-
             return BaseExceptionGroup("", new_exceptions)
         elif (
             excgroup and len(excgroup.exceptions) == 1 and excgroup.exceptions[0] is exc

tests/test_catch.py

@@ -148,9 +148,41 @@ def test_catch_handler_raises():
     def handler(exc):
         raise RuntimeError("new")
 
-    with pytest.raises(RuntimeError, match="new"):
+    with pytest.raises(RuntimeError, match="new") as exc:
         with catch({(ValueError, ValueError): handler}):
-            raise ExceptionGroup("booboo", [ValueError("bar")])
+            excgrp = ExceptionGroup("booboo", [ValueError("bar")])
+            raise excgrp
+
+    context = exc.value.__context__
+    assert isinstance(context, ExceptionGroup)
+    assert str(context) == "booboo (1 sub-exception)"
+    assert len(context.exceptions) == 1
+    assert isinstance(context.exceptions[0], ValueError)
+    assert exc.value.__cause__ is None
+
+
+def test_bare_raise_in_handler():
+    """Test that a bare "raise"  "middle" ecxeption group gets discarded."""
+
+    def handler(exc):
+        raise
+
+    with pytest.raises(ExceptionGroup) as excgrp:
+        with catch({(ValueError,): handler, (RuntimeError,): lambda eg: None}):
+            try:
+                first_exc = RuntimeError("first")
+                raise first_exc
+            except RuntimeError as exc:
+                middle_exc = ExceptionGroup(
+                    "bad", [ValueError(), ValueError(), TypeError()]
+                )
+                raise middle_exc from exc
+
+    assert len(excgrp.value.exceptions) == 2
+    assert all(isinstance(exc, ValueError) for exc in excgrp.value.exceptions)
+    assert excgrp.value is not middle_exc
+    assert excgrp.value.__cause__ is first_exc
+    assert excgrp.value.__context__ is first_exc
 
 
 def test_catch_subclass():

tests/test_catch_py311.py

@@ -128,12 +128,20 @@ def test_catch_full_match():
     reason="Behavior was changed in 3.11.4",
 )
 def test_catch_handler_raises():
-    with pytest.raises(RuntimeError, match="new"):
+    with pytest.raises(RuntimeError, match="new") as exc:
         try:
-            raise ExceptionGroup("booboo", [ValueError("bar")])
+            excgrp = ExceptionGroup("booboo", [ValueError("bar")])
+            raise excgrp
         except* ValueError:
             raise RuntimeError("new")
 
+    context = exc.value.__context__
+    assert isinstance(context, ExceptionGroup)
+    assert str(context) == "booboo (1 sub-exception)"
+    assert len(context.exceptions) == 1
+    assert isinstance(context.exceptions[0], ValueError)
+    assert exc.value.__cause__ is None
+
 
 def test_catch_subclass():
     lookup_errors = []
@@ -146,3 +154,25 @@ def test_catch_subclass():
     assert isinstance(lookup_errors[0], ExceptionGroup)
     exceptions = lookup_errors[0].exceptions
     assert isinstance(exceptions[0], KeyError)
+
+
+def test_bare_raise_in_handler():
+    """Test that the "middle" ecxeption group gets discarded."""
+    with pytest.raises(ExceptionGroup) as excgrp:
+        try:
+            try:
+                first_exc = RuntimeError("first")
+                raise first_exc
+            except RuntimeError as exc:
+                middle_exc = ExceptionGroup(
+                    "bad", [ValueError(), ValueError(), TypeError()]
+                )
+                raise middle_exc from exc
+        except* ValueError:
+            raise
+        except* TypeError:
+            pass
+
+    assert excgrp.value is not middle_exc
+    assert excgrp.value.__cause__ is first_exc
+    assert excgrp.value.__context__ is first_exc