Fix circular import: do not import temporalio.client in temporalio.nexus (#973)

Author: dandavison

temporalio/client.py

@@ -56,6 +56,7 @@
 import temporalio.common
 import temporalio.converter
 import temporalio.exceptions
+import temporalio.nexus
 import temporalio.runtime
 import temporalio.service
 import temporalio.workflow
@@ -7323,23 +7324,8 @@ def api_key(self, value: Optional[str]) -> None:
         self.service_client.update_api_key(value)
 
 
-@dataclass(frozen=True)
-class NexusCallback:
-    """Nexus callback to attach to events such as workflow completion.
-
-    .. warning::
-        This API is experimental and unstable.
-    """
-
-    url: str
-    """Callback URL."""
-
-    headers: Mapping[str, str]
-    """Header to attach to callback request."""
-
-
 # Intended to become a union of callback types
-Callback = NexusCallback
+Callback = temporalio.nexus.NexusCallback
 
 
 async def _encode_user_metadata(

temporalio/nexus/__init__.py

@@ -9,6 +9,7 @@
 from ._decorators import workflow_run_operation as workflow_run_operation
 from ._operation_context import Info as Info
 from ._operation_context import LoggerAdapter as LoggerAdapter
+from ._operation_context import NexusCallback as NexusCallback
 from ._operation_context import (
     WorkflowRunOperationContext as WorkflowRunOperationContext,
 )

temporalio/nexus/_decorators.py

@@ -16,16 +16,10 @@
     StartOperationContext,
 )
 
-from temporalio.nexus._operation_context import (
-    WorkflowRunOperationContext,
-)
-from temporalio.nexus._operation_handlers import (
-    WorkflowRunOperationHandler,
-)
-from temporalio.nexus._token import (
-    WorkflowHandle,
-)
-from temporalio.nexus._util import (
+from ._operation_context import WorkflowRunOperationContext
+from ._operation_handlers import WorkflowRunOperationHandler
+from ._token import WorkflowHandle
+from ._util import (
     get_callable_name,
     get_workflow_run_start_method_input_and_output_type_annotations,
     set_operation_factory,

temporalio/nexus/_link_conversion.py

@@ -4,6 +4,7 @@
 import re
 import urllib.parse
 from typing import (
+    TYPE_CHECKING,
     Any,
     Optional,
 )
@@ -12,7 +13,9 @@
 
 import temporalio.api.common.v1
 import temporalio.api.enums.v1
-import temporalio.client
+
+if TYPE_CHECKING:
+    import temporalio.client
 
 logger = logging.getLogger(__name__)
 

temporalio/nexus/_operation_context.py

@@ -7,6 +7,7 @@
 from dataclasses import dataclass
 from datetime import timedelta
 from typing import (
+    TYPE_CHECKING,
     Any,
     Callable,
     Optional,
@@ -19,7 +20,6 @@
 
 import temporalio.api.common.v1
 import temporalio.api.workflowservice.v1
-import temporalio.client
 import temporalio.common
 from temporalio.nexus import _link_conversion
 from temporalio.nexus._token import WorkflowHandle
@@ -32,6 +32,9 @@
     SelfType,
 )
 
+if TYPE_CHECKING:
+    import temporalio.client
+
 # The Temporal Nexus worker always builds a nexusrpc StartOperationContext or
 # CancelOperationContext and passes it as the first parameter to the nexusrpc operation
 # handler. In addition, it sets one of the following context vars.
@@ -122,7 +125,7 @@ def _get_callbacks(
         ctx = self.nexus_context
         return (
             [
-                temporalio.client.NexusCallback(
+                NexusCallback(
                     url=ctx.callback_url,
                     headers=ctx.callback_headers,
                 )
@@ -449,6 +452,21 @@ async def start_workflow(
         return WorkflowHandle[ReturnType]._unsafe_from_client_workflow_handle(wf_handle)
 
 
+@dataclass(frozen=True)
+class NexusCallback:
+    """Nexus callback to attach to events such as workflow completion.
+
+    .. warning::
+        This API is experimental and unstable.
+    """
+
+    url: str
+    """Callback URL."""
+
+    headers: Mapping[str, str]
+    """Header to attach to callback request."""
+
+
 @dataclass(frozen=True)
 class _TemporalCancelOperationContext:
     """Context for a Nexus cancel operation being handled by a Temporal Nexus Worker."""

temporalio/nexus/_operation_handlers.py

@@ -22,7 +22,6 @@
     StartOperationResultAsync,
 )
 
-from temporalio import client
 from temporalio.nexus._operation_context import (
     _temporal_cancel_operation_context,
 )
@@ -67,15 +66,14 @@ async def start(
         """Start the operation, by starting a workflow and completing asynchronously."""
         handle = await self._start(ctx, input)
         if not isinstance(handle, WorkflowHandle):
-            if isinstance(handle, client.WorkflowHandle):
-                raise RuntimeError(
-                    f"Expected {handle} to be a nexus.WorkflowHandle, but got a client.WorkflowHandle. "
-                    f"You must use WorkflowRunOperationContext.start_workflow "
-                    "to start a workflow that will deliver the result of the Nexus operation, "
-                    "not client.Client.start_workflow."
-                )
             raise RuntimeError(
                 f"Expected {handle} to be a nexus.WorkflowHandle, but got {type(handle)}. "
+                f"When using @workflow_run_operation you must use "
+                "WorkflowRunOperationContext.start_workflow() "
+                "to start a workflow that will deliver the result of the Nexus operation, "
+                "and you must return the nexus.WorkflowHandle that it returns. "
+                "It is not possible to use client.Client.start_workflow() and client.WorkflowHandle "
+                "for this purpose."
             )
         return StartOperationResultAsync(handle.to_token())
 

temporalio/nexus/_token.py

@@ -3,15 +3,16 @@
 import base64
 import json
 from dataclasses import dataclass
-from typing import Any, Generic, Literal, Optional, Type
+from typing import TYPE_CHECKING, Any, Generic, Literal, Optional
 
 from nexusrpc import OutputT
 
-from temporalio import client
-
 OperationTokenType = Literal[1]
 OPERATION_TOKEN_TYPE_WORKFLOW: OperationTokenType = 1
 
+if TYPE_CHECKING:
+    import temporalio.client
+
 
 @dataclass(frozen=True)
 class WorkflowHandle(Generic[OutputT]):
@@ -32,8 +33,10 @@ class WorkflowHandle(Generic[OutputT]):
     version: Optional[int] = None
 
     def _to_client_workflow_handle(
-        self, client: client.Client, result_type: Optional[Type[OutputT]] = None
-    ) -> client.WorkflowHandle[Any, OutputT]:
+        self,
+        client: temporalio.client.Client,
+        result_type: Optional[type[OutputT]] = None,
+    ) -> temporalio.client.WorkflowHandle[Any, OutputT]:
         """Create a :py:class:`temporalio.client.WorkflowHandle` from the token."""
         if client.namespace != self.namespace:
             raise ValueError(
@@ -46,7 +49,7 @@ def _to_client_workflow_handle(
     # handle type.
     @classmethod
     def _unsafe_from_client_workflow_handle(
-        cls, workflow_handle: client.WorkflowHandle[Any, OutputT]
+        cls, workflow_handle: temporalio.client.WorkflowHandle[Any, OutputT]
     ) -> WorkflowHandle[OutputT]:
         """Create a :py:class:`WorkflowHandle` from a :py:class:`temporalio.client.WorkflowHandle`.