Access current update info with ID inside update handler (#544)

Fixes #542

temporalio/worker/_workflow_instance.py

@@ -463,6 +463,11 @@ def _apply_do_update(
         # inside the task, since the update may not be defined until after we have started the workflow - for example
         # if an update is in the first WFT & is also registered dynamically at the top of workflow code.
         async def run_update() -> None:
+            # Set the current update for the life of this task
+            temporalio.workflow._set_current_update_info(
+                temporalio.workflow.UpdateInfo(id=job.id, name=job.name)
+            )
+
             command = self._add_command()
             command.update_response.protocol_instance_id = job.protocol_instance_id
             past_validation = False

temporalio/workflow.py

@@ -3,6 +3,7 @@
 from __future__ import annotations
 
 import asyncio
+import contextvars
 import inspect
 import logging
 import threading
@@ -424,6 +425,17 @@ class ParentInfo:
     workflow_id: str
 
 
+@dataclass(frozen=True)
+class UpdateInfo:
+    """Information about a workflow update."""
+
+    id: str
+    """Update ID."""
+
+    name: str
+    """Update type name."""
+
+
 class _Runtime(ABC):
     @staticmethod
     def current() -> _Runtime:
@@ -654,6 +666,31 @@ async def workflow_wait_condition(
         ...
 
 
+_current_update_info: contextvars.ContextVar[UpdateInfo] = contextvars.ContextVar(
+    "__temporal_current_update_info"
+)
+
+
+def _set_current_update_info(info: UpdateInfo) -> None:
+    _current_update_info.set(info)
+
+
+def current_update_info() -> Optional[UpdateInfo]:
+    """Info for the current update if any.
+
+    This is powered by :py:mod:`contextvars` so it is only valid within the
+    update handler and coroutines/tasks it has started.
+
+    .. warning::
+       This API is experimental
+
+    Returns:
+        Info for the current update handler the code calling this is executing
+            within if any.
+    """
+    return _current_update_info.get(None)
+
+
 def deprecate_patch(id: str) -> None:
     """Mark a patch as deprecated.
 

tests/worker/test_workflow.py

@@ -4927,3 +4927,78 @@ async def test_workflow_wait_utility(client: Client):
             task_queue=worker.task_queue,
         )
         assert len(result) == 10
+
+
+@workflow.defn
+class CurrentUpdateWorkflow:
+    def __init__(self) -> None:
+        self._pending_get_update_id_tasks: List[asyncio.Task[str]] = []
+
+    @workflow.run
+    async def run(self) -> List[str]:
+        # Confirm no update info
+        assert not workflow.current_update_info()
+
+        # Wait for all tasks to come in, then return the full set
+        await workflow.wait_condition(
+            lambda: len(self._pending_get_update_id_tasks) == 5
+        )
+        assert not workflow.current_update_info()
+        return list(await asyncio.gather(*self._pending_get_update_id_tasks))
+
+    @workflow.update
+    async def do_update(self) -> str:
+        # Check that simple helper awaited has the ID
+        info = workflow.current_update_info()
+        assert info
+        assert info.name == "do_update"
+        assert info.id == await self.get_update_id()
+
+        # Also schedule the task and wait for it in the main workflow to confirm
+        # it still gets the update ID
+        self._pending_get_update_id_tasks.append(
+            asyncio.create_task(self.get_update_id())
+        )
+
+        # Re-fetch and return
+        info = workflow.current_update_info()
+        assert info
+        return info.id
+
+    @do_update.validator
+    def do_update_validator(self) -> None:
+        info = workflow.current_update_info()
+        assert info
+        assert info.name == "do_update"
+
+    async def get_update_id(self) -> str:
+        await asyncio.sleep(0.01)
+        info = workflow.current_update_info()
+        assert info
+        return info.id
+
+
+async def test_workflow_current_update(client: Client, env: WorkflowEnvironment):
+    if env.supports_time_skipping:
+        pytest.skip(
+            "Java test server: https://github.com/temporalio/sdk-java/issues/1903"
+        )
+    async with new_worker(client, CurrentUpdateWorkflow) as worker:
+        handle = await client.start_workflow(
+            CurrentUpdateWorkflow.run,
+            id=f"wf-{uuid.uuid4()}",
+            task_queue=worker.task_queue,
+        )
+        update_ids = await asyncio.gather(
+            handle.execute_update(CurrentUpdateWorkflow.do_update, id="update1"),
+            handle.execute_update(CurrentUpdateWorkflow.do_update, id="update2"),
+            handle.execute_update(CurrentUpdateWorkflow.do_update, id="update3"),
+            handle.execute_update(CurrentUpdateWorkflow.do_update, id="update4"),
+            handle.execute_update(CurrentUpdateWorkflow.do_update, id="update5"),
+        )
+        assert {"update1", "update2", "update3", "update4", "update5"} == set(
+            update_ids
+        )
+        assert {"update1", "update2", "update3", "update4", "update5"} == set(
+            await handle.result()
+        )