fix #544: Correctly pass StopIteration trough wrappers

Raising a StopIteration in a generator triggers a RuntimeError.
If the RuntimeError of a generator has the passed in StopIteration as cause
resume with that StopIteration as normal exception instead of failing with the RuntimeError.

changelog/544.bugfix.rst

@@ -0,0 +1,5 @@
+Correctly pass StopIteration trough wrappers.
+
+Raising a StopIteration in a generator triggers a RuntimeError.
+If the RuntimeError of a generator has the passed in StopIteration as cause
+resume with that StopIteration as normal exception instead of failing with the RuntimeError.

src/pluggy/_callers.py

@@ -119,7 +119,17 @@ def _multicall(
             for teardown in reversed(teardowns):
                 try:
                     if exception is not None:
-                        teardown.throw(exception)  # type: ignore[union-attr]
+                        try:
+                            teardown.throw(exception)  # type: ignore[union-attr]
+                        except RuntimeError as re:
+                            if (
+                                isinstance(exception, StopIteration)
+                                and re.__cause__ is exception
+                            ):
+                                teardown.close()  # type: ignore[union-attr]
+                                continue
+                            else:
+                                raise
                     else:
                         teardown.send(result)  # type: ignore[union-attr]
                     # Following is unreachable for a well behaved hook wrapper.

testing/test_multicall.py

@@ -416,6 +416,31 @@ def m2():
     ]
 
 
+def test_wrapper_stopiteration_passtrough():
+    out = []
+
+    @hookimpl(wrapper=True)
+    def wrap():
+        out.append("wrap")
+        try:
+            yield
+        finally:
+            out.append("wrap done")
+
+    @hookimpl
+    def stop():
+        out.append("stop")
+        raise StopIteration
+
+    with pytest.raises(StopIteration):
+        try:
+            MC([stop, wrap], {})
+        finally:
+            out.append("finally")
+
+    assert out == ["wrap", "stop", "wrap done", "finally"]
+
+
 def test_suppress_inner_wrapper_teardown_exc() -> None:
     out = []