Suppress spurious "Failed to detach context" log in OTel interceptor

temporalio/contrib/opentelemetry/_interceptor.py

@@ -2,7 +2,9 @@
 
 from __future__ import annotations
 
+import contextvars
 import dataclasses
+import logging
 from collections.abc import Callable, Iterator, Mapping, Sequence
 from contextlib import contextmanager
 from dataclasses import dataclass
@@ -58,6 +60,33 @@
 _ContextT = TypeVar("_ContextT", bound=nexusrpc.handler.OperationContext)
 
 
+_otel_context_logger = logging.getLogger("opentelemetry.context")
+
+
+class _SuppressDetachFailureFilter(logging.Filter):
+    def filter(self, record: logging.LogRecord) -> bool:
+        return not record.getMessage().startswith("Failed to detach context")
+
+
+def _safe_detach(token: contextvars.Token[Context]) -> None:
+    """Detach an OTel context token, suppressing OTel's spurious failure log.
+
+    A detach can run inside a different ``contextvars.Context`` than the one the
+    token was created on -- the workflow event loop runs portions of the workflow
+    inside ``contextvars.copy_context().run(...)``. A copy preserves the OTel
+    context value but invalidates the token, so OTel's ``detach`` logs "Failed to
+    detach context". We still call ``opentelemetry.context.detach`` (rather than
+    e.g. restoring via ``attach``) so attach/detach calls stay balanced -- a leak
+    invariant the interceptor tests enforce -- and only drop that one log record.
+    """
+    detach_filter = _SuppressDetachFailureFilter()
+    _otel_context_logger.addFilter(detach_filter)
+    try:
+        opentelemetry.context.detach(token)
+    finally:
+        _otel_context_logger.removeFilter(detach_filter)
+
+
 class TracingInterceptor(temporalio.client.Interceptor, temporalio.worker.Interceptor):
     """Interceptor that supports client and worker OpenTelemetry span creation
     and propagation.
@@ -568,7 +597,7 @@ async def handle_query(self, input: temporalio.worker.HandleQueryInput) -> Any:
             # on. As such we do a best effort detach to avoid using a mismatched
             # token.
             if context is opentelemetry.context.get_current():
-                opentelemetry.context.detach(token)
+                _safe_detach(token)
 
     def handle_update_validator(
         self, input: temporalio.worker.HandleUpdateInput
@@ -663,7 +692,7 @@ def _top_level_workflow_context(
             # on. As such we do a best effort detach to avoid using a mismatched
             # token.
             if context is opentelemetry.context.get_current():
-                opentelemetry.context.detach(token)
+                _safe_detach(token)
 
     def _context_to_headers(
         self, headers: Mapping[str, temporalio.api.common.v1.Payload]