Warn when DNET is enabling and there is a physical action

core/src/main/java/org/lflang/federated/extensions/CExtension.java

@@ -43,6 +43,7 @@
 import org.lflang.federated.generator.FederationFileConfig;
 import org.lflang.federated.launcher.RtiConfig;
 import org.lflang.federated.serialization.FedROS2CPPSerialization;
+import org.lflang.generator.ActionInstance;
 import org.lflang.generator.CodeBuilder;
 import org.lflang.generator.LFGeneratorContext;
 import org.lflang.generator.ReactorInstance;
@@ -60,6 +61,7 @@
 import org.lflang.target.property.ClockSyncOptionsProperty;
 import org.lflang.target.property.CoordinationOptionsProperty;
 import org.lflang.target.property.CoordinationProperty;
+import org.lflang.target.property.DNETProperty;
 import org.lflang.target.property.FedSetupProperty;
 import org.lflang.target.property.KeepaliveProperty;
 import org.lflang.target.property.SingleThreadedProperty;
@@ -833,6 +835,22 @@ private String generateCodeForPhysicalActions(
           outputFound = output;
         }
       }
+      if (federate.targetConfig.getOrDefault(DNETProperty.INSTANCE)) {
+        ActionInstance found = federate.findPhysicalAction(instance);
+        if (found != null) {
+          String warning =
+              String.join(
+                  "\n",
+                  "Found a physical action inside the federate "
+                      + addDoubleQuotes(instance.getName()),
+                  "and a signal downstream next event tag (DNET) will be used.",
+                  "The signal DNET may increase the lag, the time difference between ",
+                  "the time this physical action is scheduled and the time it is executed, ",
+                  "specifically when this federate has multiple upstream reactors.",
+                  "Consider disabling the signal DNET with a property {DNET: false}.");
+          messageReporter.at(found.getDefinition()).warning(warning);
+        }
+      }
       if (minDelay != TimeValue.MAX_VALUE) {
         // Unless silenced, issue a warning.
         if (coordinationOptions.advanceMessageInterval == null) {

core/src/main/java/org/lflang/federated/generator/FederateInstance.java

@@ -647,6 +647,27 @@ private boolean containsAllVarRefs(Iterable<VarRef> varRefs) {
     return inFederate;
   }
 
+  /**
+   * Return the first found physical action or null if there is no physical action in this federate.
+   *
+   * @param instance The reactor instance to check whether there is a physical action.
+   */
+  public ActionInstance findPhysicalAction(ReactorInstance instance) {
+    for (ActionInstance action : instance.actions) {
+      if (action.isPhysical()) {
+        return action;
+      }
+    }
+    for (ReactorInstance child : instance.children) {
+      for (ActionInstance action : child.actions) {
+        if (action.isPhysical()) {
+          return action;
+        }
+      }
+    }
+    return null;
+  }
+
   /**
    * Find output ports that are connected to a physical action trigger upstream in the same reactor.
    * Return a list of such outputs paired with the minimum delay from the nearest physical action.