fix flowName variable (#819)

runtime/v2/runner/src/main/java/com/walmartlabs/concord/runtime/v2/runner/StackTraceCollector.java

@@ -34,7 +34,7 @@ public Result afterCommand(Runtime runtime, VM vm, State state, ThreadId threadI
         if (cmd instanceof FlowCallCommand) {
             FlowCallCommand fcc = (FlowCallCommand) cmd;
             FlowCall step = fcc.getStep();
-            String flowName = VMUtils.getLocal(state, threadId, "flowName");
+            String flowName = FlowCallCommand.getFlowName(state, threadId);
             if (flowName == null) {
                 flowName = step.getFlowName();
             }

runtime/v2/runner/src/main/java/com/walmartlabs/concord/runtime/v2/runner/vm/FlowCallCommand.java

@@ -41,6 +41,8 @@
 
 public class FlowCallCommand extends StepCommand<FlowCall> {
 
+    private static final String FLOW_NAME_VARIABLE = "__flowName__b6bc6c58-c2bc-434c-9a6b-b0092237720b";
+
     private static final long serialVersionUID = 1L;
 
     public FlowCallCommand(FlowCall step) {
@@ -93,7 +95,11 @@ protected void execute(Runtime runtime, State state, ThreadId threadId) {
         // push the out handler first so it executes after the called flow's frame is done
         state.peekFrame(threadId).push(processOutVars);
         state.pushFrame(threadId, innerFrame);
-        VMUtils.putLocal(innerFrame, "flowName", flowName);
+        VMUtils.putLocal(innerFrame, FLOW_NAME_VARIABLE, flowName);
+    }
+
+    public static String getFlowName(State state, ThreadId threadId) {
+        return VMUtils.getLocal(state, threadId, FLOW_NAME_VARIABLE);
     }
 
     private static class EvalVariablesCommand implements Command {

runtime/v2/runner/src/test/java/com/walmartlabs/concord/runtime/v2/runner/MainTest.java

@@ -231,6 +231,19 @@ public void test() throws Exception {
         verify(processStatusCallback, times(1)).onRunning(instanceId);
     }
 
+    @Test
+    public void testFlowNameVariable() throws Exception {
+        deploy("doNotTouchFlowNameVariable");
+
+        save(ProcessConfiguration.builder()
+                .build());
+
+        byte[] log = run();
+        assertLog(log, ".*flowName in inner flow: 'This is MY variable'.*");
+
+        verify(processStatusCallback, times(1)).onRunning(instanceId);
+    }
+
     @Test
     public void testStackTrace() throws Exception {
         deploy("stackTrace");

runtime/v2/runner/src/test/resources/com/walmartlabs/concord/runtime/v2/runner/doNotTouchFlowNameVariable/concord.yaml

@@ -0,0 +1,13 @@
+flows:
+  default:
+    - set:
+        testvar1: "test123"
+        flowName: "This is MY variable"
+    - log: "flowName: ${flowName}"
+    - call: innerFlow
+
+  innerFlow:
+    - log: "flowName in inner flow: '${flowName}'"
+    - if: "${flowName != 'This is MY variable'}"
+      then:
+        - throw: "Hands off my variable!!!!"