fix: validate inputs_from_state when a tool has no input parameters

haystack/tools/tool.py

@@ -205,7 +205,7 @@ def __post_init__(self) -> None:  # noqa: C901, PLR0912
                         f"inputs_from_state values must be str, not {type(param_name).__name__}. "
                         f"Got {param_name!r} for key '{state_key}'."
                     )
-                if valid_inputs and param_name not in valid_inputs:
+                if param_name not in valid_inputs:
                     raise ValueError(
                         f"inputs_from_state maps '{state_key}' to unknown parameter '{param_name}'. "
                         f"Valid parameters are: {valid_inputs}."

releasenotes/notes/tool-empty-inputs-from-state-validation-bc8460226991e1ba.yaml

@@ -0,0 +1,7 @@
+---
+fixes:
+  - |
+    ``Tool`` now validates ``inputs_from_state`` against the tool's actual input parameters even when the tool takes no input
+    at all. Previously, mapping a state key to a non-existent parameter was accepted at construction time for tools with
+    an empty set of valid parameters (e.g. a function with no arguments, or a ``ComponentTool`` wrapping a component without
+    input sockets), and the typo only surfaced later as a ``ToolInvocationError`` when the agent invoked the tool.

test/tools/test_component_tool.py

@@ -148,6 +148,18 @@ def run(self, documents: list[Document], top_k: int = 5) -> dict[str, str]:
         return {"concatenated": "\n".join(doc.content for doc in documents[:top_k] if doc.content)}
 
 
+@component
+class NoInputComponent:
+    """A component that takes no input at all."""
+
+    @component.output_types(reply=str)
+    def run(self) -> dict[str, str]:
+        """
+        Returns a fixed reply.
+        """
+        return {"reply": "Hello!"}
+
+
 def output_handler(old, new):
     """
     Output handler to test serialization.
@@ -194,6 +206,14 @@ def test_from_component_with_invalid_inputs_from_state_nested_dict(self):
         with pytest.raises(TypeError, match="must be str, not dict"):
             ComponentTool(component=SimpleComponent(), inputs_from_state={"documents": {"source": "documents"}})  # type: ignore[dict-item]
 
+    def test_from_component_with_inputs_from_state_and_no_input_sockets(self):
+        """A component without input sockets has no valid mapping target, so the typo must not pass silently."""
+        tool = ComponentTool(component=NoInputComponent())
+        assert tool.parameters == {"type": "object", "properties": {}}
+
+        with pytest.raises(ValueError, match="unknown parameter 'text'. Valid parameters are: set\\(\\)\\."):
+            ComponentTool(component=NoInputComponent(), inputs_from_state={"state_text": "text"})
+
     def test_from_component_with_outputs_to_state(self):
         tool = ComponentTool(component=SimpleComponent(), outputs_to_state={"replies": {"source": "reply"}})
         assert tool.outputs_to_state == {"replies": {"source": "reply"}}

test/tools/test_tool.py

@@ -296,6 +296,22 @@ def test_inputs_from_state_validation_with_invalid_parameter(self):
                 inputs_from_state={"state_key": "nonexistent"},
             )
 
+    def test_inputs_from_state_validation_with_no_valid_parameters(self):
+        """A tool that takes no input has a known-empty set of valid parameters, so any mapping is a typo."""
+        with pytest.raises(
+            ValueError,
+            match=re.escape(
+                "inputs_from_state maps 'city' to unknown parameter 'nonexistent'. Valid parameters are: set()."
+            ),
+        ):
+            Tool(
+                name="clock",
+                description="What time is it?",
+                parameters={"type": "object", "properties": {}},
+                function=lambda: {"time": "12:00"},
+                inputs_from_state={"city": "nonexistent"},
+            )
+
     def test_inputs_from_state_validation_with_non_string_value(self):
         """Test that inputs_from_state values must be strings"""
         with pytest.raises(TypeError, match=re.escape("inputs_from_state values must be str, not dict")):