fix: log traceback in logger.exception() of Haystack loggers

[hardness1020]

Related Issues

• fixes logger.exception() from haystack.logging.getLogger does not log the traceback #13188

Proposed Changes:

getLogger wrapped logger.exception with patch_log_method_to_kwargs_only, which always forwards exc_info=None. The stdlib default exc_info=True never applied, so logger.exception(...) logged no traceback in JSON or console output.

• patch_log_method_to_kwargs_only takes a keyword-only default_exc_info (default None), and exception is wrapped with default_exc_info=True. Explicit exc_info still works, and positional-arg errors still name Logger.exception().
• PatchedLogger.exception now declares exc_info: Any = True.

How did you test it?

• New tests in test/test_logging.py: exception() attaches exc_info, and exc_info=False is respected. The traceback test fails without the fix.
• test_haystack_logger_with_positional_args now checks that the TypeError names the called method.
• test/test_logging.py passes on Python 3.14 and 3.10. Tests for the 8 modules that call logger.exception pass, except 2 test_type_serialization failures that also fail on main under 3.14 (Union repr).
• Ran the repro from the issue: JSON has the exception entry, and the console output renders the traceback.
• hatch run fmt and hatch run test:types pass.

Notes for the reviewer

• On Python 3.10 the caller line of exception() records stays wrong for plain logging.Logger instances (two wrapper frames), as on main. It goes away once 3.10 is dropped (Drop Python 3.10 support and add Python 3.15 #13065). See the review thread for a single-wrapper variant that fixes it now.
• Side effects of tracebacks appearing: JSON exc_value is not truncated (same as for stdlib loggers today), and console mode with rich shows locals in tracebacks.

Checklist

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• I have updated the related issue with new insights and changes.
• I have added unit tests and updated the docstrings.
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• 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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[sjrl]

Could we keep the wrapper here instead of relying on stdlib Logger.exception delegating to self.error? Without it a positional call raises Logger.error() takes 1 positional argument ..., which is confusing from exception(). Lets give patch_log_method_to_kwargs_only an exc_info default instead:

Suggested change

	# `exception` stays unpatched: the stdlib version calls the patched `error` with `exc_info=True`. Wrapping it would
	# pass `exc_info=None` and drop the traceback.
	logger.exception = patch_log_method_to_kwargs_only(logger.exception, default_exc_info=True) # type: ignore

with exc_info: Any = default_exc_info in the inner wrapper's signature. WDYT?

[hardness1020]

Good catch, done in 40dc64d: patch_log_method_to_kwargs_only takes a keyword-only default_exc_info, and exception passes True. I also pinned the Logger.<method>() name in test_haystack_logger_with_positional_args.

One trade-off: with two wrappers, the caller line is still wrong on Python 3.10 (it points into haystack/logging.py), as on main. #13065 makes that moot. If you want it fixed now, exception can wrap the unpatched error instead, which keeps the exception() name and passes on 3.10:

logger.exception = functools.wraps(logger.exception)(
    patch_log_method_to_kwargs_only(unpatched_error, default_exc_info=True)
)

Happy to switch.

[github-actions]

Coverage report

Click to see where and how coverage changed

File	Statements	Missing	Coverage	Coverage (new stmts)	Lines missing
haystack
logging.py
haystack/hooks/compaction
__init__.py
tool_result_pruning.py
utils.py
haystack/hooks/tool_result_offloading
hooks.py
Project Total

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