fix: ComponentMeta.__call__ handles keyword- and positional-only parameters correctly (#6701)

* fix: `ComponentMeta.__call__` handles keyword- and positional-only parameters correctly

* Update release note

haystack/core/component/component.py

@@ -139,7 +139,10 @@ class ComponentMeta(type):
             instance.__canals_input__ = {}
         run_signature = inspect.signature(getattr(cls, "run"))
         for param in list(run_signature.parameters)[1:]:  # First is 'self' and it doesn't matter.
-            if run_signature.parameters[param].kind == inspect.Parameter.POSITIONAL_OR_KEYWORD:  # ignore `**kwargs`
+            if run_signature.parameters[param].kind not in (
+                inspect.Parameter.VAR_POSITIONAL,
+                inspect.Parameter.VAR_KEYWORD,
+            ):  # ignore variable args
                 socket_kwargs = {"name": param, "type": run_signature.parameters[param].annotation}
                 if run_signature.parameters[param].default != inspect.Parameter.empty:
                     socket_kwargs["default_value"] = run_signature.parameters[param].default

releasenotes/notes/component-kw-only-run-args-eedee8907232d2d4.yaml

@@ -0,0 +1,4 @@
+---
+fixes:
+  - |
+    Fix ComponentMeta ignoring keyword-only parameters in the `run` method. ComponentMeta.__call__ handles the creation of InputSockets for the component's inputs when the latter has not explicitly called _Component.set_input_types(). This logic was not correctly handling keyword-only parameters.

test/core/component/test_component.py

@@ -176,3 +176,17 @@ def test_input_has_default_value():
     comp = MockComponent()
     assert comp.__canals_input__["value"].default_value == 42
     assert not comp.__canals_input__["value"].is_mandatory
+
+
+def test_keyword_only_args():
+    @component
+    class MockComponent:
+        def __init__(self):
+            component.set_output_types(self, value=int)
+
+        def run(self, *, arg: int):
+            return {"value": arg}
+
+    comp = MockComponent()
+    component_inputs = {name: {"type": socket.type} for name, socket in comp.__canals_input__.items()}
+    assert component_inputs == {"arg": {"type": int}}