fix: bind_tools should not force tool_choice_option='auto' by default

The tool_choice docstring documents that None/False should have "no
effect, default OpenAI behavior", but the else branch unconditionally
set tool_choice_option="auto", causing WatsonX models to always attempt
a tool call even when no tool was relevant to the query.

Added unit tests covering the unset, 'auto', required/True, and named-tool
cases for bind_tools, since none previously existed.

Fixes #152

Author: SpiliosDimakopoulos

libs/ibm/langchain_ibm/chat_models.py

@@ -1752,8 +1752,12 @@ def bind_tools(
                 kwargs["tool_choice_option"] = tool_choice
             else:
                 kwargs["tool_choice"] = tool_choice
-        else:
-            kwargs["tool_choice_option"] = "auto"
+        # When tool_choice is not specified (None/False), leave tool_choice_option
+        # unset so the request has no effect on tool selection, matching the
+        # documented default OpenAI-style behavior (see `tool_choice` docstring
+        # above). Previously this branch forced tool_choice_option="auto",
+        # which caused WatsonX models to always attempt a tool call even when
+        # no tools were relevant to the user's query.
 
         return super().bind(tools=formatted_tools, **kwargs)
 

libs/ibm/tests/unit_tests/test_chat_models.py

@@ -503,3 +503,56 @@ def test_initialize_chat_watsonx_model_id_without_project_or_space_id(
             url="https://us-south.ml.cloud.ibm.com",
             apikey="test_apikey",
         )
+
+
+# ── bind_tools should not force tool use when tool_choice is unset (#152) ───────
+
+_WEATHER_TOOL = {
+    "type": "function",
+    "function": {
+        "name": "get_weather",
+        "description": "Get the weather for a city.",
+        "parameters": {
+            "type": "object",
+            "properties": {"city": {"type": "string"}},
+        },
+    },
+}
+
+
+def test_bind_tools_without_tool_choice_has_no_effect() -> None:
+    """No tool_choice given should not force tool_choice_option at all.
+
+    Previously this branch defaulted to `tool_choice_option="auto"`, which
+    caused WatsonX models to always attempt a tool call even when no tool was
+    relevant to the user's query. The documented contract for `tool_choice`
+    is that `None`/`False` should have "no effect, default OpenAI behavior".
+    """
+    chat = ChatWatsonx(watsonx_model=model_inference_mock)
+    bound = chat.bind_tools([_WEATHER_TOOL])
+    assert "tool_choice_option" not in bound.kwargs
+    assert "tool_choice" not in bound.kwargs
+
+
+def test_bind_tools_with_explicit_auto_sets_tool_choice_option() -> None:
+    """Explicitly passing tool_choice='auto' should still set tool_choice_option."""
+    chat = ChatWatsonx(watsonx_model=model_inference_mock)
+    bound = chat.bind_tools([_WEATHER_TOOL], tool_choice="auto")
+    assert bound.kwargs["tool_choice_option"] == "auto"
+
+
+def test_bind_tools_with_required_forces_tool_choice() -> None:
+    """tool_choice=True (or 'required'/'any') should force tool_choice_option."""
+    chat = ChatWatsonx(watsonx_model=model_inference_mock)
+    bound = chat.bind_tools([_WEATHER_TOOL], tool_choice=True)
+    assert bound.kwargs["tool_choice_option"] == "required"
+
+
+def test_bind_tools_with_specific_tool_name() -> None:
+    """tool_choice=<tool name> should force that specific tool via a dict."""
+    chat = ChatWatsonx(watsonx_model=model_inference_mock)
+    bound = chat.bind_tools([_WEATHER_TOOL], tool_choice="get_weather")
+    assert bound.kwargs["tool_choice"] == {
+        "type": "function",
+        "function": {"name": "get_weather"},
+    }