feat: Add warm_up() method to ChatGenerators for tool initialization (#9942)

* Add warm_up() method to OpenAIChatGenerator

- Add warm_up() method that calls warm_up_tools()
- Add _is_warmed_up flag for idempotency
- Import warm_up_tools from haystack.tools
- Add comprehensive tests:
  - test_warm_up_with_tools: single tool case
  - test_warm_up_with_no_tools: no tools case
  - test_warm_up_with_multiple_tools: multiple tools case
- All tests passing

Part of issue #9907

* Add warm_up() method to AzureOpenAIChatGenerator

- Add warm_up() method that calls warm_up_tools()
- Add _is_warmed_up flag for idempotency
- Import warm_up_tools from haystack.tools
- Add comprehensive tests:
  - test_warm_up_with_tools: single tool case
  - test_warm_up_with_no_tools: no tools case
  - test_warm_up_with_multiple_tools: multiple tools case
- All tests passing

Part of issue #9907

* Add warm_up() method to HuggingFaceAPIChatGenerator

- Add warm_up() method that calls warm_up_tools()
- Add _is_warmed_up flag for idempotency
- Import warm_up_tools from haystack.tools
- Add comprehensive tests:
  - test_warm_up_with_tools: single tool case
  - test_warm_up_with_no_tools: no tools case
  - test_warm_up_with_multiple_tools: multiple tools case
- All tests passing

Part of issue #9907

* Enhance warm_up() method in HuggingFaceLocalChatGenerator

- Add warm_up_tools import from haystack.tools.utils
- Add _is_warmed_up flag for idempotency
- Enhance existing warm_up() to also warm up tools
- Preserve existing pipeline initialization logic
- Add comprehensive tests:
  - test_warm_up_with_tools: single tool case
  - test_warm_up_with_no_tools: no tools case
  - test_warm_up_with_multiple_tools: multiple tools case

Part of issue #9907

* Add warm_up() method to FallbackChatGenerator

- Add warm_up() method that delegates to underlying generators
- Uses hasattr check to gracefully handle generators without warm_up
- Add comprehensive tests:
  - test_warm_up_delegates_to_generators: verify delegation works
  - test_warm_up_with_no_warm_up_method: handle missing warm_up gracefully
  - test_warm_up_mixed_generators: mix of generators with/without warm_up
- All tests passing

Part of issue #9907

* docs: Add release notes for warm_up() feature

---------

Co-authored-by: HamidOna13 <abdulhamid.onawole@aizatron.com>

Author: HamidOna

haystack/components/generators/chat/azure.py

@@ -18,6 +18,7 @@
     deserialize_tools_or_toolset_inplace,
     flatten_tools_or_toolsets,
     serialize_tools_or_toolset,
+    warm_up_tools,
 )
 from haystack.utils import Secret, deserialize_callable, deserialize_secrets_inplace, serialize_callable
 from haystack.utils.http_client import init_http_client
@@ -201,6 +202,18 @@ def __init__(  # pylint: disable=too-many-positional-arguments
         self.async_client = AsyncAzureOpenAI(
             http_client=init_http_client(self.http_client_kwargs, async_client=True), **client_args
         )
+        self._is_warmed_up = False
+
+    def warm_up(self):
+        """
+        Warm up the Azure OpenAI chat generator.
+
+        This will warm up the tools registered in the chat generator.
+        This method is idempotent and will only warm up the tools once.
+        """
+        if not self._is_warmed_up:
+            warm_up_tools(self.tools)
+            self._is_warmed_up = True
 
     def to_dict(self) -> dict[str, Any]:
         """

haystack/components/generators/chat/fallback.py

@@ -81,6 +81,16 @@ def from_dict(cls, data: dict[str, Any]) -> FallbackChatGenerator:
         data["init_parameters"] = init_params
         return default_from_dict(cls, data)
 
+    def warm_up(self) -> None:
+        """
+        Warm up all underlying chat generators.
+
+        This method calls warm_up() on each underlying generator that supports it.
+        """
+        for gen in self.chat_generators:
+            if hasattr(gen, "warm_up") and callable(gen.warm_up):
+                gen.warm_up()
+
     def _run_single_sync(  # pylint: disable=too-many-positional-arguments
         self,
         gen: Any,

haystack/components/generators/chat/hugging_face_api.py

@@ -26,6 +26,7 @@
     deserialize_tools_or_toolset_inplace,
     flatten_tools_or_toolsets,
     serialize_tools_or_toolset,
+    warm_up_tools,
 )
 from haystack.utils import Secret, deserialize_callable, deserialize_secrets_inplace, serialize_callable
 from haystack.utils.hf import HFGenerationAPIType, HFModelType, check_valid_model, convert_message_to_hf_format
@@ -384,6 +385,18 @@ def __init__(  # pylint: disable=too-many-positional-arguments
             model_or_url, token=token.resolve_value() if token else None, **resolved_api_params
         )
         self.tools = tools
+        self._is_warmed_up = False
+
+    def warm_up(self):
+        """
+        Warm up the Hugging Face API chat generator.
+
+        This will warm up the tools registered in the chat generator.
+        This method is idempotent and will only warm up the tools once.
+        """
+        if not self._is_warmed_up:
+            warm_up_tools(self.tools)
+            self._is_warmed_up = True
 
     def to_dict(self) -> dict[str, Any]:
         """

haystack/components/generators/chat/hugging_face_local.py

@@ -23,6 +23,7 @@
     flatten_tools_or_toolsets,
     serialize_tools_or_toolset,
 )
+from haystack.tools.utils import warm_up_tools
 from haystack.utils import (
     ComponentDevice,
     Secret,
@@ -249,6 +250,7 @@ def __init__(  # pylint: disable=too-many-positional-arguments
             if async_executor is None
             else async_executor
         )
+        self._is_warmed_up = False
 
     def __del__(self) -> None:
         """
@@ -274,11 +276,21 @@ def _get_telemetry_data(self) -> dict[str, Any]:
 
     def warm_up(self) -> None:
         """
-        Initializes the component.
+        Initializes the component and warms up tools if provided.
         """
+        if self._is_warmed_up:
+            return
+
+        # Initialize the pipeline (existing logic)
         if self.pipeline is None:
             self.pipeline = pipeline(**self.huggingface_pipeline_kwargs)
 
+        # Warm up tools (new logic)
+        if self.tools:
+            warm_up_tools(self.tools)
+
+        self._is_warmed_up = True
+
     def to_dict(self) -> dict[str, Any]:
         """
         Serializes the component to a dictionary.

haystack/components/generators/chat/openai.py

@@ -41,6 +41,7 @@
     deserialize_tools_or_toolset_inplace,
     flatten_tools_or_toolsets,
     serialize_tools_or_toolset,
+    warm_up_tools,
 )
 from haystack.utils import Secret, deserialize_callable, deserialize_secrets_inplace, serialize_callable
 from haystack.utils.http_client import init_http_client
@@ -200,6 +201,18 @@ def __init__(  # pylint: disable=too-many-positional-arguments
         self.async_client = AsyncOpenAI(
             http_client=init_http_client(self.http_client_kwargs, async_client=True), **client_kwargs
         )
+        self._is_warmed_up = False
+
+    def warm_up(self):
+        """
+        Warm up the OpenAI chat generator.
+
+        This will warm up the tools registered in the chat generator.
+        This method is idempotent and will only warm up the tools once.
+        """
+        if not self._is_warmed_up:
+            warm_up_tools(self.tools)
+            self._is_warmed_up = True
 
     def _get_telemetry_data(self) -> dict[str, Any]:
         """

releasenotes/notes/add-warm-up-to-chat-generators-cb0fa9429d721074.yaml

@@ -0,0 +1,9 @@
+---
+features:
+  - |
+    Added warm_up() method to all ChatGenerator components (OpenAIChatGenerator,
+    AzureOpenAIChatGenerator, HuggingFaceAPIChatGenerator, HuggingFaceLocalChatGenerator,
+    and FallbackChatGenerator) to properly initialize tools that require warm-up before
+    pipeline execution. The warm_up() method is idempotent and follows the same pattern
+    used in Agent and ToolInvoker components. This enables proper tool initialization
+    in pipelines that use ChatGenerators with tools but without an Agent component.

test/components/generators/chat/test_azure.py

@@ -428,6 +428,110 @@ def test_to_dict_with_toolset(self, tools, monkeypatch):
         }
         assert data["init_parameters"]["tools"] == expected_tools_data
 
+    def test_warm_up_with_tools(self, monkeypatch):
+        """Test that warm_up() calls warm_up on tools and is idempotent."""
+        monkeypatch.setenv("AZURE_OPENAI_API_KEY", "test-api-key")
+
+        # Create a mock tool that tracks if warm_up() was called
+        class MockTool(Tool):
+            warm_up_call_count = 0  # Class variable to track calls
+
+            def __init__(self):
+                super().__init__(
+                    name="mock_tool",
+                    description="A mock tool for testing",
+                    parameters={"x": {"type": "string"}},
+                    function=lambda x: x,
+                )
+
+            def warm_up(self):
+                MockTool.warm_up_call_count += 1
+
+        # Reset the class variable before test
+        MockTool.warm_up_call_count = 0
+        mock_tool = MockTool()
+
+        # Create AzureOpenAIChatGenerator with the mock tool
+        component = AzureOpenAIChatGenerator(azure_endpoint="some-non-existing-endpoint", tools=[mock_tool])
+
+        # Verify initial state - warm_up not called yet
+        assert MockTool.warm_up_call_count == 0
+        assert not component._is_warmed_up
+
+        # Call warm_up() on the generator
+        component.warm_up()
+
+        # Assert that the tool's warm_up() was called
+        assert MockTool.warm_up_call_count == 1
+        assert component._is_warmed_up
+
+        # Call warm_up() again and verify it's idempotent (only warms up once)
+        component.warm_up()
+
+        # The tool's warm_up should still only have been called once
+        assert MockTool.warm_up_call_count == 1
+        assert component._is_warmed_up
+
+    def test_warm_up_with_no_tools(self, monkeypatch):
+        """Test that warm_up() works when no tools are provided."""
+        monkeypatch.setenv("AZURE_OPENAI_API_KEY", "test-api-key")
+
+        component = AzureOpenAIChatGenerator(azure_endpoint="some-non-existing-endpoint")
+
+        # Verify initial state
+        assert not component._is_warmed_up
+        assert component.tools is None
+
+        # Call warm_up() - should not raise an error
+        component.warm_up()
+
+        # Verify the component is warmed up
+        assert component._is_warmed_up
+
+        # Call warm_up() again - should be idempotent
+        component.warm_up()
+        assert component._is_warmed_up
+
+    def test_warm_up_with_multiple_tools(self, monkeypatch):
+        """Test that warm_up() works with multiple tools."""
+        monkeypatch.setenv("AZURE_OPENAI_API_KEY", "test-api-key")
+
+        # Track warm_up calls
+        warm_up_calls = []
+
+        class MockTool(Tool):
+            def __init__(self, tool_name):
+                super().__init__(
+                    name=tool_name,
+                    description=f"Mock tool {tool_name}",
+                    parameters={"type": "object", "properties": {"x": {"type": "string"}}, "required": ["x"]},
+                    function=lambda x: f"{tool_name} result: {x}",
+                )
+
+            def warm_up(self):
+                warm_up_calls.append(self.name)
+
+        mock_tool1 = MockTool("tool1")
+        mock_tool2 = MockTool("tool2")
+
+        # Use a LIST of tools, not a Toolset
+        component = AzureOpenAIChatGenerator(
+            azure_endpoint="some-non-existing-endpoint", tools=[mock_tool1, mock_tool2]
+        )
+
+        # Call warm_up()
+        component.warm_up()
+
+        # Assert that both tools' warm_up() were called
+        assert "tool1" in warm_up_calls
+        assert "tool2" in warm_up_calls
+        assert component._is_warmed_up
+
+        # Test idempotency - warm_up should not call tools again
+        initial_count = len(warm_up_calls)
+        component.warm_up()
+        assert len(warm_up_calls) == initial_count
+
 
 class TestAzureOpenAIChatGeneratorAsync:
     def test_init_should_also_create_async_client_with_same_args(self, tools):

test/components/generators/chat/test_fallback.py

@@ -354,3 +354,71 @@ async def test_failover_trigger_401_authentication_async():
     assert result["replies"][0].text == "success_after_auth"
     assert result["meta"]["successful_chat_generator_index"] == 1
     assert result["meta"]["failed_chat_generators"] == ["_DummyHTTPErrorGen"]
+
+
+@component
+class _DummyGenWithWarmUp:
+    """Dummy generator that tracks warm_up calls."""
+
+    def __init__(self, text: str = "ok"):
+        self.text = text
+        self.warm_up_called = False
+
+    def warm_up(self) -> None:
+        self.warm_up_called = True
+
+    def run(
+        self,
+        messages: list[ChatMessage],
+        generation_kwargs: Optional[dict[str, Any]] = None,
+        tools: Optional[ToolsType] = None,
+        streaming_callback: Optional[StreamingCallbackT] = None,
+    ) -> dict[str, Any]:
+        return {"replies": [ChatMessage.from_assistant(self.text)], "meta": {}}
+
+
+def test_warm_up_delegates_to_generators():
+    """Test that warm_up() is called on each underlying generator."""
+    gen1 = _DummyGenWithWarmUp(text="A")
+    gen2 = _DummyGenWithWarmUp(text="B")
+    gen3 = _DummyGenWithWarmUp(text="C")
+
+    fallback = FallbackChatGenerator(chat_generators=[gen1, gen2, gen3])
+    fallback.warm_up()
+
+    assert gen1.warm_up_called
+    assert gen2.warm_up_called
+    assert gen3.warm_up_called
+
+
+def test_warm_up_with_no_warm_up_method():
+    """Test that warm_up() handles generators without warm_up() gracefully."""
+    gen1 = _DummySuccessGen(text="A")
+    gen2 = _DummySuccessGen(text="B")
+
+    fallback = FallbackChatGenerator(chat_generators=[gen1, gen2])
+    # Should not raise any error
+    fallback.warm_up()
+
+    # Verify generators still work
+    result = fallback.run([ChatMessage.from_user("test")])
+    assert result["replies"][0].text == "A"
+
+
+def test_warm_up_mixed_generators():
+    """Test warm_up() with a mix of generators with and without warm_up()."""
+    gen1 = _DummyGenWithWarmUp(text="A")
+    gen2 = _DummySuccessGen(text="B")
+    gen3 = _DummyGenWithWarmUp(text="C")
+    gen4 = _DummyFailGen()
+
+    fallback = FallbackChatGenerator(chat_generators=[gen1, gen2, gen3, gen4])
+    fallback.warm_up()
+
+    # Only generators with warm_up() should have been called
+    assert gen1.warm_up_called
+    assert gen3.warm_up_called
+
+    # Verify the fallback still works correctly
+    result = fallback.run([ChatMessage.from_user("test")])
+    assert result["replies"][0].text == "A"