fix: Prevent set_output_types from being called when the `output_ty…

…pes` decorator is used

haystack/core/component/component.py

@@ -449,6 +449,13 @@ def run(self, value: int):
                 return {"output_1": 1, "output_2": "2"}
         ```
         """
+        has_decorator = hasattr(instance.run, "_output_types_cache")
+        if has_decorator:
+            raise ComponentError(
+                "Cannot call `set_output_types` on a component that already has "
+                "the 'output_types' decorator on its `run` method"
+            )
+
         instance.__haystack_output__ = Sockets(
             instance, {name: OutputSocket(name=name, type=type_) for name, type_ in types.items()}, OutputSocket
         )

releasenotes/notes/component-set-output-type-override-852a19b3f0621fb0.yaml

@@ -0,0 +1,4 @@
+---
+fixes:
+  - |
+    Prevent `set_output_types`` from being called when the `output_types`` decorator is used.

test/core/component/test_component.py

@@ -315,6 +315,20 @@ def from_dict(cls, data):
                 return cls()
 
 
+def test_output_types_decorator_and_set_output_types():
+    @component
+    class MockComponent:
+        def __init__(self) -> None:
+            component.set_output_types(self, value=int)
+
+        @component.output_types(value=int)
+        def run(self, value: int):
+            return {"value": 1}
+
+    with pytest.raises(ComponentError, match="Cannot call `set_output_types`"):
+        comp = MockComponent()
+
+
 def test_output_types_decorator_mismatch_run_async_run():
     @component
     class MockComponent: