Dispatch warn level to logging.warning, not deprecated .warn (#89)

On the asyncio backend, _log() did `getattr(logger._logger, level)(msg)`
with level == "warn", which resolves to logging.Logger.warn — the
deprecated alias of .warning — emitting "DeprecationWarning: The 'warn'
method is deprecated, use 'warning' instead".

Remap the "warn" level name to "warning" for stdlib dispatch, mirroring
the existing "trace" -> "debug" handling, while keeping the txaio-facing
level name "warn" in kwargs["log_level"]. The Twisted backend is
unaffected (it maps to LogLevel.warn, not stdlib method names).

Add a cross-backend regression test (test_warn) that turns
DeprecationWarning into an error and asserts the message is emitted.
Verified red before the fix (asyncio) and green after, both backends.

Note: This work was completed with AI assistance (Claude Code).

Author: oberstet

docs/changelog.rst

@@ -11,6 +11,10 @@ This document contains a reverse-chronological list of changes to txaio.
 26.6.1
 ------
 
+**Fix**
+
+* Logging at ``warn`` level on the asyncio backend no longer triggers a ``DeprecationWarning`` from the standard library: ``txaio`` now dispatches the ``warn`` level to ``logging.Logger.warning`` instead of the deprecated ``.warn`` alias (`#89 <https://github.com/crossbario/txaio/issues/89>`_)
+
 **Other**
 
 * Bumped the shared ``wamp-ai`` and ``wamp-cicd`` Git submodules to match the rest of the WAMP project group (zlmdb / autobahn-python 26.6.1) for the coordinated release. The ``wamp-cicd`` bump picks up the GHSA-6658 shell-injection hardening in the shared ``identifiers.yml`` reusable workflow (untrusted GitHub event fields are now passed via ``env:`` as quoted data with a fail-closed branch-name allowlist) (`#218 <https://github.com/crossbario/txaio/issues/218>`_)

src/txaio/aio.py

@@ -162,6 +162,10 @@ def _log(logger, level, format="", **kwargs):
     if level == "trace":
         level = "debug"
         kwargs["txaio_trace"] = True
+    elif level == "warn":
+        # stdlib logging.Logger.warn() is the deprecated alias of .warning();
+        # dispatch to the non-deprecated method to avoid a DeprecationWarning (#89)
+        level = "warning"
 
     msg = format.format(**kwargs)
     getattr(logger._logger, level)(msg)

tests/test_logging.py

@@ -139,6 +139,28 @@ def test_info(handler, framework):
     assert handler.messages[0].endswith(b"hilarious elephant")
 
 
+def test_warn(handler, framework):
+    """
+    Logging at "warn" level emits the message and must not trigger the
+    deprecated stdlib ``logging.Logger.warn`` alias (#89): on the asyncio
+    backend the level name is dispatched to ``.warning``, not ``.warn``.
+    """
+    import warnings
+
+    logger = txaio.make_logger()
+
+    with warnings.catch_warnings():
+        warnings.simplefilter("error", DeprecationWarning)
+        logger.warn(
+            "{adjective} {nouns[0]}",
+            adjective="hilarious",
+            nouns=["skunk", "elephant", "wombat"],
+        )
+
+    assert len(handler.messages) == 1
+    assert handler.messages[0].endswith(b"hilarious skunk")
+
+
 def test_legacy_error_with_traceback(handler, framework):
     if framework.using_twisted:
         return pytest.skip("test only for asyncio users")