Don't pass cause to HandlerError constructor

Author: dandavison

temporalio/nexus/_operation_handlers.py

@@ -112,8 +112,7 @@ async def fetch_result(
         #         "Failed to decode operation token as workflow operation token. "
         #         "Fetching result for non-workflow operations is not supported.",
         #         type=HandlerErrorType.NOT_FOUND,
-        #         cause=err,
-        #     )
+        #     ) from err
         # ctx = _temporal_fetch_operation_context.get()
         # try:
         #     client_handle = nexus_handle.to_workflow_handle(
@@ -123,8 +122,7 @@ async def fetch_result(
         #     raise HandlerError(
         #         "Failed to construct workflow handle from workflow operation token",
         #         type=HandlerErrorType.NOT_FOUND,
-        #         cause=err,
-        #     )
+        #     ) from err
         # return await client_handle.result()
 
 
@@ -145,8 +143,7 @@ async def cancel_operation(
             "Failed to decode operation token as workflow operation token. "
             "Canceling non-workflow operations is not supported.",
             type=HandlerErrorType.NOT_FOUND,
-            cause=err,
-        )
+        ) from err
 
     ctx = _temporal_cancel_operation_context.get()
     try:
@@ -157,6 +154,5 @@ async def cancel_operation(
         raise HandlerError(
             "Failed to construct workflow handle from workflow operation token",
             type=HandlerErrorType.NOT_FOUND,
-            cause=err,
-        )
+        ) from err
     await client_workflow_handle.cancel(**kwargs)

temporalio/worker/_nexus.py

@@ -381,7 +381,6 @@ async def deserialize(
             raise nexusrpc.HandlerError(
                 "Data converter failed to decode Nexus operation input",
                 type=nexusrpc.HandlerErrorType.BAD_REQUEST,
-                cause=err,
                 retryable=False,
             ) from err
 
@@ -393,36 +392,32 @@ def _exception_to_handler_error(err: BaseException) -> nexusrpc.HandlerError:
     if isinstance(err, nexusrpc.HandlerError):
         return err
     elif isinstance(err, ApplicationError):
-        return nexusrpc.HandlerError(
+        handler_err = nexusrpc.HandlerError(
             # TODO(nexus-prerelease): what should message be?
             err.message,
             type=nexusrpc.HandlerErrorType.INTERNAL,
-            cause=err,
             retryable=not err.non_retryable,
         )
     elif isinstance(err, RPCError):
         if err.status == RPCStatusCode.INVALID_ARGUMENT:
-            return nexusrpc.HandlerError(
+            handler_err = nexusrpc.HandlerError(
                 err.message,
                 type=nexusrpc.HandlerErrorType.BAD_REQUEST,
-                cause=err,
             )
         elif err.status in [
             RPCStatusCode.ALREADY_EXISTS,
             RPCStatusCode.FAILED_PRECONDITION,
             RPCStatusCode.OUT_OF_RANGE,
         ]:
-            return nexusrpc.HandlerError(
+            handler_err = nexusrpc.HandlerError(
                 err.message,
                 type=nexusrpc.HandlerErrorType.INTERNAL,
-                cause=err,
                 retryable=False,
             )
         elif err.status in [RPCStatusCode.ABORTED, RPCStatusCode.UNAVAILABLE]:
-            return nexusrpc.HandlerError(
+            handler_err = nexusrpc.HandlerError(
                 err.message,
                 type=nexusrpc.HandlerErrorType.UNAVAILABLE,
-                cause=err,
             )
         elif err.status in [
             RPCStatusCode.CANCELLED,
@@ -436,37 +431,36 @@ def _exception_to_handler_error(err: BaseException) -> nexusrpc.HandlerError:
             # we convert to internal because this is not a client auth error and happens
             # when the handler fails to auth with Temporal and should be considered
             # retryable.
-            return nexusrpc.HandlerError(
-                err.message, type=nexusrpc.HandlerErrorType.INTERNAL, cause=err
+            handler_err = nexusrpc.HandlerError(
+                err.message, type=nexusrpc.HandlerErrorType.INTERNAL
             )
         elif err.status == RPCStatusCode.NOT_FOUND:
-            return nexusrpc.HandlerError(
-                err.message, type=nexusrpc.HandlerErrorType.NOT_FOUND, cause=err
+            handler_err = nexusrpc.HandlerError(
+                err.message, type=nexusrpc.HandlerErrorType.NOT_FOUND
             )
         elif err.status == RPCStatusCode.RESOURCE_EXHAUSTED:
-            return nexusrpc.HandlerError(
+            handler_err = nexusrpc.HandlerError(
                 err.message,
                 type=nexusrpc.HandlerErrorType.RESOURCE_EXHAUSTED,
-                cause=err,
             )
         elif err.status == RPCStatusCode.UNIMPLEMENTED:
-            return nexusrpc.HandlerError(
+            handler_err = nexusrpc.HandlerError(
                 err.message,
                 type=nexusrpc.HandlerErrorType.NOT_IMPLEMENTED,
-                cause=err,
             )
         elif err.status == RPCStatusCode.DEADLINE_EXCEEDED:
-            return nexusrpc.HandlerError(
+            handler_err = nexusrpc.HandlerError(
                 err.message,
                 type=nexusrpc.HandlerErrorType.UPSTREAM_TIMEOUT,
-                cause=err,
             )
         else:
-            return nexusrpc.HandlerError(
+            handler_err = nexusrpc.HandlerError(
                 f"Unhandled RPC error status: {err.status}",
                 type=nexusrpc.HandlerErrorType.INTERNAL,
-                cause=err,
             )
-    return nexusrpc.HandlerError(
-        str(err), type=nexusrpc.HandlerErrorType.INTERNAL, cause=err
-    )
+    else:
+        handler_err = nexusrpc.HandlerError(
+            str(err), type=nexusrpc.HandlerErrorType.INTERNAL
+        )
+    handler_err.__cause__ = err
+    return handler_err

tests/nexus/test_handler.py

@@ -194,8 +194,7 @@ async def handler_error_internal(
             message="deliberate internal handler error",
             type=HandlerErrorType.INTERNAL,
             retryable=False,
-            cause=RuntimeError("cause message"),
-        )
+        ) from RuntimeError("cause message")
 
     @sync_operation
     async def operation_error_failed(