Make Toolset.add chainable and flatten nested toolsets

haystack/tools/toolset.py

@@ -185,7 +185,7 @@ def __contains__(self, item: Any) -> bool:
             return item in self.tools
         return False
 
-    def add(self, tool: Union[Tool, "Toolset"]) -> None:
+    def add(self, tool: Union[Tool, "Toolset"]) -> "Toolset":
         """
         Add a new Tool or merge another Toolset.
 
@@ -207,6 +207,7 @@ def add(self, tool: Union[Tool, "Toolset"]) -> None:
         _check_duplicate_tool_names(combined_tools)
 
         self.tools.extend(new_tools)
+        return self
 
     def to_dict(self) -> Dict[str, Any]:
         """

releasenotes/notes/toolset-add-chainable-f34447fbe9cb733d.yaml

@@ -0,0 +1,4 @@
+
+enhancements:
+  - |
+    Made `Toolset.add()` method chainable and ensured it flattens nested toolsets. This allows chaining calls like `t.add(a).add(b)` and adds all tools correctly.

test/tools/test_toolset.py

@@ -584,3 +584,32 @@ def test_toolinvoker_deserialization_with_custom_toolset(self, weather_tool):
         assert deserialized_invoker._tools_with_names == invoker._tools_with_names
         assert deserialized_invoker.raise_on_failure == invoker.raise_on_failure
         assert deserialized_invoker.convert_result_to_json_string == invoker.convert_result_to_json_string
+
+    def test_toolset_add_can_flatten_nested_toolsets(self):
+        tool_a = Tool(
+            name="add",
+            description="Add two numbers",
+            parameters={
+                "type": "object",
+                "properties": {"a": {"type": "integer"}, "b": {"type": "integer"}},
+                "required": ["a", "b"],
+            },
+            function=add_numbers,
+        )
+        tool_b = Tool(
+            name="multiply",
+            description="Multiply two numbers",
+            parameters={
+                "type": "object",
+                "properties": {"a": {"type": "integer"}, "b": {"type": "integer"}},
+                "required": ["a", "b"],
+            },
+            function=multiply_numbers,
+        )
+        tset_a = Toolset([tool_a])
+        tset_b = Toolset([tool_b])
+
+        master = Toolset()
+        master.add(tset_a).add(tset_b)
+
+        assert {t.name for t in master} == {"add", "multiply"}