fix(langfuse): stop relying on haystack.utils.base_serialization helpers

[davidsbatista]

Related Issues

• related to chore!: removing deadcode haystack#11905 (review)

Proposed Changes:

• serialize_class_instance/deserialize_class_instance in haystack.utils.base_serialization are being removed from haystack-ai as dead code (see chore!: removing deadcode haystack#11905).

• to_dict: serialize span_handler with component_to_dict (from haystack.core.serialization) instead of serialize_class_instance.

• from_dict: deserialize span_handler with deserialize_component_inplace (from haystack.utils) instead of deserialize_class_instance

How did you test it?

• Updated test_langfuse_connector.py fixtures to match the new (flatter) span_handler serialization format.
• Ran the full unit test suite, ruff, and mypy for the langfuse integration.

Checklist

• I have read the contributors guidelines and the code of conduct
• I have updated the related issue with new insights and changes
• I added unit tests and updated the docstrings
• I've used one of the conventional commit types for my PR title: fix:, feat:, build:, chore:, ci:, docs:, style:, refactor:, perf:, test:.

[github-actions]

Coverage report (langfuse)

Click to see where and how coverage changed

File	Statements	Missing	Coverage	Coverage (new stmts)	Lines missing
integrations/langfuse/src/haystack_integrations/components/connectors/langfuse
langfuse_connector.py
Project Total

This report was generated by python-coverage-comment-action

[anakin87]

Would it be possible to keep the old serialization format working (handling this in from_dict)? Otherwise, this would break serialized pipelines

[davidsbatista]

What do you mean by the "old serialization format working"? Using the

def serialize_class_instance(obj: Any) -> dict[str, Any]:

The purpose of the PR is to avoid using that.

[davidsbatista]

or wait, you mean still being able to deserialise old formats?

[anakin87]

I mean: if a user has a serialized Pipeline with LangfuseConnector and langfuse-haystack==5.0.2, the new from_dict method would not be able to load it.

So, to ease the transition, we could modify the from_dict method so it does not break deserialization and add a test covering this case.

[anakin87]

Thank you!

Please release 5.1.0 after merging