feat: Add ComponentTool to Haystack tools

[vblagoje]

Why:

Adds ComponentTool enabling Haystack components to be wrapped and used as LLM-compatible tools thus integrating them into Haystack's new tooling architecture.

What:

• Added ComponentTool class to facilitate the use of Haystack components as callable tools.
• Modified __init__.py to include ComponentTool in the module exports.
• Updated pyproject.toml to include the docstring-parser dependency for documentation extraction.

How can it be used:

This implementation enables the creation of LLM-compatible tools from existing components. Here’s an example of usage:

from haystack import component, Pipeline
from haystack.dataclasses import ChatMessage, ChatRole
from haystack.tools import ComponentTool
from haystack.components.tools import ToolInvoker
from haystack.components.generators.chat import OpenAIChatGenerator

@component
class WeatherComponent:
    @component.output_types(reply=str)
    def run(self, city: str, units: str = "celsius"):
        return {"reply":  f"Weather in {city}: 20°{units}"}

weather_tool = ComponentTool(component=WeatherComponent())

# Create pipeline with OpenAIChatGenerator and ToolInvoker
pipeline = Pipeline()
pipeline.add_component("llm", OpenAIChatGenerator(model="gpt-4o-mini", tools=[weather_tool]))
pipeline.add_component("tool_invoker", ToolInvoker(tools=[weather_tool]))

# Connect components
pipeline.connect("llm.replies", "tool_invoker.messages")

message = ChatMessage.from_user("What's the weather like in S.F.?")

# Run pipeline
result = pipeline.run({"llm": {"messages": [message]}})

With weather_tool assigned to your ChatGenerator and ToolInvoker, you can now invoke the component automatically with given a ChatMessage that will trigger this tool, e.g ChatMessage.from_user("What's the weather like in S.F.?")

How did you test it:

Extensive unit and integration tests were created, validating the functionality of ComponentTool with various components. Tests included invoking tools and ensuring correct parameter handling and responses from LLM integrations.

Notes for the reviewer:

Review the implementation of the ComponentTool for potential edge cases with non-component inputs. The integration tests require an OpenAI API key to run successfully, so consider verifying this before executing the tests.

[julian-risch]

Looks quite good to me. My main request is to make the docstring-parser dependency optional. Let's discuss if @anakin87 disagrees or if we decide to make jsonschema a required dependency too.

[julian-risch]

You mentioned limitations in the call regarding which components are supported. Could you please add them to the release note? If there is a particular Haystack component that is not supported mention it here as an example.

[vblagoje]

Thank you @julian-risch and @anakin87 - great feedback. I haven’t removed support for Pydantic models yet but if both of you are okay with its removal - I’ll proceed. The support is largely effortless thanks to TypeAdapter conversion, but as @anakin87 mentioned it could be counterproductive. I’ll remove it in a separate commit to maintain a reference for its implementation in case our users ask for it or an internal need for it arises in the future.

[anakin87]

Let's also remember to add this module to docs/pydoc/config/tools_api.yml

[coveralls]

Pull Request Test Coverage Report for Build 12715813181

Warning: This coverage report may be inaccurate.

This pull request's base commit is no longer the HEAD commit of its target branch. This means it includes changes from outside the original pull request, including, potentially, unrelated coverage changes.

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Details

• 0 of 0 changed or added relevant lines in 0 files are covered.
• 3 unchanged lines in 2 files lost coverage.
• Overall coverage increased (+0.2%) to 91.309%

---

Files with Coverage Reduction	New Missed Lines	%
components/preprocessors/sentence_tokenizer.py	1	94.12%
components/generators/chat/openai.py	2	96.27%

Totals
Change from base Build 12708466879:	0.2%
Covered Lines:	8962
Relevant Lines:	9815

---

💛 - Coveralls

[anakin87]

I am quite happy with the progress here.

Some of my comments probably went unnoticed. I was proposing to add some tests:

• ComponentTool to_dict/from_dict methods
• check that an attempt to convert a Component that is part of a Pipeline fails

[vblagoje]

@anakin87 have another look. Let's wait with integration of this PR - #8697 because I think I can use some of the errors defined there. Nothing major, just replacing ValueError with a more precise SchemaGenerationError

[anakin87]

@dfokina could you please take a look at docstrings and release note?

[anakin87]

Looks good!

(Nit: I have the impression that some methods can be converted to static methods. See if it makes sense...)

Let's wait for final reviews by @julian-risch and @dfokina

[dfokina]

Mostly unifying the capitalization and punctuation in docstrings. Everything else seems good, inc the release note and the error messages

[vblagoje]

@julian-risch @dfokina have a look again 🙏

[dfokina]

Left one last comment, otherwise LGTM