Add main entry to the extension

extension/build.xml

@@ -184,6 +184,7 @@ spotbugs.home_dir        - Location of the spotbugs tool. If not set, spotbugs i
             <zipfileset dir="${zserio_cpp17.base_dir}/freemarker" includes="*.ftl"
                 prefix="freemarker/cpp17"/>
             <manifest>
+                <attribute name="Main-Class" value="zserio.extension.cpp17.Cpp17ExtensionMain"/>
                 <attribute name="Implementation-Version" value="${zserio_cpp17.version}"/>
             </manifest>
             <metainf dir="${zserio_cpp17.build_dir}/metainf" includes="**/*"/>

extension/src/zserio/extension/cpp17/Cpp17Extension.java

@@ -15,7 +15,7 @@
 import zserio.tools.ExtensionParameters;
 
 /**
- * The extension which generates C++ API sources.
+ * The extension which generates C++17 API sources.
  */
 public final class Cpp17Extension implements Extension
 {

extension/src/zserio/extension/cpp17/Cpp17ExtensionMain.java

@@ -0,0 +1,22 @@
+package zserio.extension.cpp17;
+
+/**
+ * The main entry of the Zserio C++17 extension.
+ *
+ * This just prints the usage.
+ */
+public final class Cpp17ExtensionMain
+{
+    public static void main(String[] args)
+    {
+        System.out.println(
+                "C++17 Generator version " + Cpp17ExtensionVersion.CPP17_EXTENSION_VERSION_STRING + "\n");
+        System.out.println("This generator cannot be run standalone and is designed as an extension to the " +
+                           "Zserio version " +
+                Cpp17ExtensionVersion.EXPECTED_ZSERIO_VERSION_STRING + ".\n");
+        System.out.println("How to run it using Zserio bundle:");
+        System.out.println("  java -cp zserio.jar:zserio_cpp17.jar zserio.tools.ZserioTool\n");
+        System.out.println("How to run it using Zserio core:");
+        System.out.println("  java -cp zserio_core.jar:zserio_cpp17.jar zserio.tools.ZserioTool");
+    }
+}