diff --git a/picocli-codegen/src/main/java/picocli/codegen/util/Util.java b/picocli-codegen/src/main/java/picocli/codegen/util/Util.java
index 6a38716a..fc60f9ef 100644
--- a/picocli-codegen/src/main/java/picocli/codegen/util/Util.java
+++ b/picocli-codegen/src/main/java/picocli/codegen/util/Util.java
@@ -7,9 +7,10 @@ import picocli.CommandLine.Model.CommandSpec;
 import java.io.Closeable;
 import java.io.IOException;
 import java.util.ArrayList;
+import java.util.IdentityHashMap;
 import java.util.List;
 
-public class Util {
+public final class Util {
     private Util() {}
 
     public static List<CommandSpec> getCommandSpecs(String factoryClass, Class<?>[] classes) throws Exception {
@@ -24,6 +25,19 @@ public class Util {
         return specs;
     }
 
+    public static List<CommandSpec> flattenHierarchy(CommandSpec root) {
+        IdentityHashMap<CommandSpec, CommandSpec> result = new IdentityHashMap<CommandSpec, CommandSpec>();
+        addRecursively(root, result);
+        return new ArrayList<CommandSpec>(result.keySet());
+    }
+
+    private static void addRecursively(CommandSpec command, IdentityHashMap<CommandSpec, CommandSpec> result) {
+        result.put(command, command);
+        for (CommandLine sub : command.subcommands().values()) {
+            addRecursively(sub.getCommandSpec(), result);
+        }
+    }
+
     public static void closeSilently(Closeable closeable) {
         if (closeable != null) {
             try {