fix: crash when a tool parameter is named properties (create_tool_from_function, @tool, ComponentTool)

[sohumt123]

Related Issues

• No existing issue: searched open and closed issues/PRs for remove_title_from_schema, 'str' object has no attribute 'items', and tool-schema AttributeError and found no report of this bug.

Proposed Changes:

Creating a Tool from any function whose signature has a parameter named properties crashes with AttributeError: 'str' object has no attribute 'items'. All of create_tool_from_function, the @tool decorator, and ComponentTool (which imports the same helper) are affected, and a parameter named properties is quite realistic for LLM tools (e.g. "set/update entity properties" tools for graph or DB backends):

from typing import Annotated
from haystack.tools import tool

@tool
def set_properties(
    entity_id: Annotated[str, "the entity"],
    properties: Annotated[dict, "properties to set"],
) -> str:
    """Set properties on an entity."""
    return "ok"
# AttributeError: 'str' object has no attribute 'items'
#   (raised from _remove_title_from_schema, haystack/tools/from_function.py:346)

Root cause: _remove_title_from_schema special-cases key == "properties" and isinstance(value, dict) and "title" in value so that a property named title is not deleted. But the keys of a properties mapping are property names, not schema keywords, and the guard only fires when a property named title happens to exist. When a property is named properties, one level deeper the iteration hits key == "properties" whose value is that property's Pydantic sub-schema — which always contains a title keyword — so the branch triggers and recurses into raw scalar values like "Properties" and "string", calling .items() on a str.

Fix: the properties branch now applies unconditionally and only recurses into dict sub-schemas, so property names are never interpreted as schema keywords. The existing behavior of preserving a property named title (while still stripping the title keyword inside its sub-schema) is unchanged and remains covered by test_remove_title_from_schema_do_not_remove_title_property.

Also added a release note under releasenotes/notes/.

How did you test it?

• Added test_remove_title_from_schema_property_named_properties (unit test for the helper) and test_from_function_with_parameter_named_properties (end-to-end create_tool_from_function test). Both fail on main with the AttributeError above and pass with the fix.
• Ran the full tools unit-test suite locally: pytest test/tools/ -m "not integration" → 269 passed, 11 deselected.
• ruff check / ruff format --check and mypy haystack/tools/from_function.py pass on the changed files.

Notes for the reviewer

• Open PR feat: derive Tool description and parameters from function #12023 refactors from_function.py but only moves the _remove_title_from_schema(schema) call site; it does not touch the helper, so this fix is orthogonal (trivial rebase either way).
• This PR was fully generated with an AI assistant. I have reviewed the changes and run the relevant tests.

Checklist

• I have read the contributors guidelines and the code of conduct.
• I have updated the related issue with new insights and changes.
• I have 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: and added ! in case the PR includes breaking changes.
• I have documented my code.
• I have added a release note file, following the contributors guidelines.
• I have run pre-commit hooks and fixed any issue.

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Coverage report

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File	Statements	Missing	Coverage	Coverage (new stmts)	Lines missing
haystack/tools
from_function.py
Project Total

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[sjrl]

Thanks!