Fix UNKNOWN gRPC error on describe (temporalio#2672)

Author: Quinn-With-Two-Ns

temporal-test-server/src/main/java/io/temporal/internal/testservice/StateMachines.java

@@ -393,14 +393,22 @@ public String toString() {
   static final class ChildWorkflowData {
 
     final TestWorkflowService service;
+    final String workflowId;
+    final String workflowType;
     final UserMetadata metadata;
     StartChildWorkflowExecutionInitiatedEventAttributes initiatedEvent;
     long initiatedEventId;
     long startedEventId;
     WorkflowExecution execution;
 
-    public ChildWorkflowData(TestWorkflowService service, UserMetadata metadata) {
+    public ChildWorkflowData(
+        TestWorkflowService service,
+        String workflowId,
+        String workflowType,
+        UserMetadata metadata) {
       this.service = service;
+      this.workflowId = workflowId;
+      this.workflowType = workflowType;
       this.metadata = metadata;
     }
 
@@ -568,8 +576,8 @@ public static StateMachine<ActivityTaskData> newActivityStateMachine(
   }
 
   public static StateMachine<ChildWorkflowData> newChildWorkflowStateMachine(
-      TestWorkflowService service, UserMetadata metadata) {
-    return new StateMachine<>(new ChildWorkflowData(service, metadata))
+      TestWorkflowService service, String workflowId, String workflowType, UserMetadata metadata) {
+    return new StateMachine<>(new ChildWorkflowData(service, workflowId, workflowType, metadata))
         .add(NONE, INITIATE, INITIATED, StateMachines::initiateChildWorkflow)
         .add(INITIATED, START, STARTED, StateMachines::childWorkflowStarted)
         .add(INITIATED, FAIL, FAILED, StateMachines::startChildWorkflowFailed)

temporal-test-server/src/main/java/io/temporal/internal/testservice/TestWorkflowMutableStateImpl.java

@@ -1150,7 +1150,8 @@ private void processStartChildWorkflow(
       long workflowTaskCompletedId) {
     a = validateStartChildExecutionAttributes(a);
     StateMachine<ChildWorkflowData> child =
-        StateMachines.newChildWorkflowStateMachine(service, metadata);
+        StateMachines.newChildWorkflowStateMachine(
+            service, a.getWorkflowId(), a.getWorkflowType().getName(), metadata);
     childWorkflows.put(ctx.getNextEventId(), child);
     child.action(StateMachines.Action.INITIATE, ctx, a, workflowTaskCompletedId);
     ctx.lockTimer("processStartChildWorkflow");
@@ -3253,13 +3254,20 @@ private DescribeWorkflowExecutionResponse describeWorkflowExecutionInsideLock()
   private static PendingChildExecutionInfo constructPendingChildExecutionInfo(
       StateMachine<ChildWorkflowData> sm) {
     ChildWorkflowData data = sm.getData();
-    return PendingChildExecutionInfo.newBuilder()
-        .setWorkflowId(data.execution.getWorkflowId())
-        .setRunId(data.execution.getRunId())
-        .setWorkflowTypeName(data.initiatedEvent.getWorkflowType().getName())
-        .setInitiatedId(data.initiatedEventId)
-        .setParentClosePolicy(data.initiatedEvent.getParentClosePolicy())
-        .build();
+    PendingChildExecutionInfo.Builder builder =
+        PendingChildExecutionInfo.newBuilder()
+            .setWorkflowId(data.workflowId)
+            .setWorkflowTypeName(data.workflowType);
+    // These fields may not be set if the child workflow hasn't been started yet
+    if (data.execution != null) {
+      builder.setRunId(data.execution.getRunId());
+    }
+    if (data.initiatedEvent != null) {
+      builder
+          .setInitiatedId(data.initiatedEventId)
+          .setParentClosePolicy(data.initiatedEvent.getParentClosePolicy());
+    }
+    return builder.build();
   }
 
   private static PendingActivityInfo constructPendingActivityInfo(