GetChildWorkflowExecution().Get(...) panics on duplicated ID

[mfateev]

ExecuteChildWorkflow(...).GetChildWorkflowExecution(..).Get(...) panics if the child workflow with the same ID is already running:

2020-01-27T08:22:07.355-0800	ERROR	internal/internal_task_handlers.go:1342	Workflow panic.	{"Domain": "samples-domain", "TaskList": "childWorkflowGroup", "WorkerID": "[email protected]@childWorkflowGroup", "WorkflowID": "parentworkflow_7934c636-0cda-4706-b654-d12f2578825e", "RunID": "a1557a7e-34ad-46b3-94fa-cbe1d918c4c4", "PanicError": "adding duplicate decision DecisionType: ChildWorkflow, ID: child_workflow:a1557a7e-34ad-46b3-94fa-cbe1d918c4c4, state=Created, isDone()=false, history=[Created]", "PanicStack": "coroutine 1 [panic]:\ngo.uber.org/cadence/internal.panicIllegalState(...)\n\t/Users/maxim/go/pkg/mod/go.uber.org/[email protected]/internal/internal_decision_state_machine.go:332\ngo.uber.org/cadence/internal.(*decisionsHelper).addDecision(0xc0004e85d0, 0x197f920, 0xc0000e55a0)\n\t/Users/maxim/go/pkg/mod/go.uber.org/[email protected]/internal/internal_decision_state_machine.go:708 +0x1f3\ngo.uber.org/cadence/internal.(*decisionsHelper).startChildWorkflowExecution(0xc0004e85d0, 0xc0000fe870, 0x15ddbe8, 0xc0004e89c0)\n\t/Users/maxim/go/pkg/mod/go.uber.org/[email protected]/internal/internal_decision_state_machine.go:829 +0x59\ngo.uber.org/cadence/internal.(*workflowEnvironmentImpl).ExecuteChildWorkflow(0xc0000c2000, 0xc0000e5170, 0xc0000e6150, 0xc0000e61b8, 0xc0000e5160, 0xc0002d4100, 0x33, 0x0, 0xc0004e8900, 0xc0004e8930, ...)\n\t/Users/maxim/go/pkg/mod/go.uber.org/[email protected]/internal/internal_event_handlers.go:358 +0x286\ngo.uber.org/cadence/internal.ExecuteChildWorkflow(0x1974080, 0xc0004e8c90, 0x1752660, 0x187f5e8, 0xc00051c7c0, 0x2, 0x2, 0x1973ec0, 0xc0000e50c0)\n\t/Users/maxim/go/pkg/mod/go.uber.org/[email protected]/internal/workflow.go:585 +0x6fc\ngo.uber.org/cadence/workflow.ExecuteChildWorkflow(...)\n\t/Users/maxim/go/pkg/mod/go.uber.org/[email protected]/workflow/workflow.go:177\nmain.SampleParentWorkflow(0x1973e80, 0xc00037c340, 0x0, 0x0)\n\t/Users/maxim/cadence/cadence-samples/cmd/samples/recipes/childworkflow/parent_workflow.go:40 +0x308\nreflect.Value.call(0x1722b40, 0x187f5f0, 0x13, 0x183dd73, 0x4, 0xc00039fe30, 0x1, 0x1, 0x1631c40, 0xc0004e8ae0, ...)\n\t/usr/local/go/src/reflect/value.go:460 +0x5f6\nreflect.Value.Call(0x1722b40, 0x187f5f0, 0x13, 0xc00039fe30, 0x1, 0x1, 0x0, 0x0, 0x0)\n\t/usr/local/go/src/reflect/value.go:321 +0xb4\ngo.uber.org/cadence/internal.(*workflowExecutor).Execute(0xc00051c320, 0x1973e80, 0xc00037c340, 0x0, 0x0, 0x0, 0xc000393701, 0x1020101, 0xc0003936f0, 0x1615418, ...)\n\t/Users/maxim/go/pkg/mod/go.uber.org/[email protected]/internal/internal_worker.go:897 +0x38b\ngo.uber.org/cadence/internal.(*syncWorkflowDefinition).Execute.func1(0x1974080, 0xc0004e8ae0)\n\t/Users/maxim/go/pkg/mod/go.uber.org/[email protected]/internal/internal_workflow.go:414 +0x105"}
go.uber.org/cadence/internal.(*workflowTaskHandlerImpl).completeWorkflow
	/Users/maxim/go/pkg/mod/go.uber.org/[email protected]/internal/internal_task_handlers.go:1342
go.uber.org/cadence/internal.(*workflowExecutionContextImpl).CompleteDecisionTask
	/Users/maxim/go/pkg/mod/go.uber.org/[email protected]/internal/internal_task_handlers.go:987
go.uber.org/cadence/internal.(*workflowExecutionContextImpl).ProcessWorkflowTask
	/Users/maxim/go/pkg/mod/go.uber.org/[email protected]/internal/internal_task_handlers.go:854
go.uber.org/cadence/internal.(*workflowTaskHandlerImpl).ProcessWorkflowTask
	/Users/maxim/go/pkg/mod/go.uber.org/[email protected]/internal/internal_task_handlers.go:684
go.uber.org/cadence/internal.(*workflowTaskPoller).processWorkflowTask
	/Users/maxim/go/pkg/mod/go.uber.org/[email protected]/internal/internal_task_pollers.go:262
go.uber.org/cadence/internal.(*workflowTaskPoller).ProcessTask
	/Users/maxim/go/pkg/mod/go.uber.org/[email protected]/internal/internal_task_pollers.go:235
go.uber.org/cadence/internal.(*baseWorker).processTask
	/Users/maxim/go/pkg/mod/go.uber.org/[email protected]/internal/internal_worker_base.go:301

Here is the code to reproduce:

func SampleParentWorkflow(ctx workflow.Context) error {
	logger := workflow.GetLogger(ctx)
	execution := workflow.GetInfo(ctx).WorkflowExecution
	// Parent workflow can choose to specify it's own ID for child execution.  Make sure they are unique for each execution.
	childID := fmt.Sprintf("child_workflow:%v", execution.RunID)
	cwo := workflow.ChildWorkflowOptions{
		// Do not specify WorkflowID if you want cadence to generate a unique ID for child execution
		WorkflowID:                   childID,
		ExecutionStartToCloseTimeout: time.Minute,
	}
	ctx = workflow.WithChildOptions(ctx, cwo)
	var result string
	workflow.ExecuteChildWorkflow(ctx, SampleChildWorkflow, 0, 5)
	workflow.Sleep(ctx, time.Second)
	f := workflow.ExecuteChildWorkflow(ctx, SampleChildWorkflow, 0, 5)
	f.GetChildWorkflowExecution().Get(ctx, nil)
	err := f.Get(ctx, &result)
	if err != nil {
		logger.Error("Parent execution received child execution failure.", zap.Error(err))
		return err
	}

	logger.Info("Parent execution completed.", zap.String("Result", result))
	return nil
}