fix: PythonCodeSplitter emits invalid code for docstring-only bodies

[AmirF194]

Related Issues

• fixes PythonCodeSplitter with strip_docstrings=True emits invalid Python for docstring-only function/method/class bodies #12330

Proposed Changes:

_strip_docstring only refuses to strip a docstring when it shares a line with the def/class header or extends past the caller's slice. It never checks whether the docstring is the unit's only body statement. When it is, the before/after slices it composes leave just the header with no body, which is invalid Python.

This adds a third guard, len(body) == 1, to the existing bail-out check, so a docstring-only unit is left untouched (docstring kept in the chunk content, nothing added to meta["docstrings"]) instead of being reduced to an empty body.

How did you test it?

• New parametrized test, TestDocstringStripping::test_strip_docstrings_skips_body_that_is_only_a_docstring (docstring-only class, function, and method): fails on main with a SyntaxError from ast.parse, passes on this branch.
• Full test/components/preprocessors/test_python_code_splitter.py suite: 72 passed.
• ruff check / ruff format --check and check_imports.py clean on the changed files.
• Not checked: whether the same class of bug exists elsewhere in the splitter for units this fix does not touch.

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.
• I have documented my code.
• I have added a release note file.
• I have run pre-commit hooks and fixed any issue.

[vercel]

@AmirF194 is attempting to deploy a commit to the deepset Team on Vercel.

A member of the Team first needs to authorize it.

[CLAassistant]

Thank you for your submission! We really appreciate it. Like many open source projects, we ask that you sign our Contributor License Agreement before we can accept your contribution.
_{You have signed the CLA already but the status is still pending? Let us recheck it.}

[HaystackBot]

Hi @AmirF194, thanks a lot for your contribution! 🙏

We noticed that the Contributor License Agreement (CLA) check (license/cla) hasn't passed yet, so we've temporarily moved this PR to draft and paused the review assignment.

To get your PR reviewed, please sign the CLA via the link in the license/cla check below (or in the CLA bot comment). As soon as the check turns green, this PR will automatically be marked ready for review again and a reviewer will be re-assigned.