How to prevent proguard from modifying the fields in my method

Question

How do I prevent proguard from modifying the field names in my method?

I know we can use -keep , -keepclassmembers ..etc but these seems to only preserve the member names and NOT the variables that are used inside.

Here's what happened:

Before:

private static URL getPluginImageURL(Object plugin, String name) throws Exception {
    // try to work with 'plugin' as with OSGI BundleContext
    try {
        Class<?> BundleClass = Class.forName("org.osgi.framework.Bundle"); //$NON-NLS-1$
        Class<?> BundleContextClass = Class.forName("org.osgi.framework.BundleContext"); //$NON-NLS-1$
        if (BundleContextClass.isAssignableFrom(plugin.getClass())) {
            Method getBundleMethod = BundleContextClass.getMethod("getBundle", new Class[0]); //$NON-NLS-1$
            Object bundle = getBundleMethod.invoke(plugin, new Object[0]);
            //
            Class<?> PathClass = Class.forName("org.eclipse.core.runtime.Path"); //$NON-NLS-1$
            Constructor<?> pathConstructor = PathClass.getConstructor(new Class[]{String.class});
            Object path = pathConstructor.newInstance(new Object[]{name});
            //
            Class<?> IPathClass = Class.forName("org.eclipse.core.runtime.IPath"); //$NON-NLS-1$
            Class<?> PlatformClass = Class.forName("org.eclipse.core.runtime.Platform"); //$NON-NLS-1$
            Method findMethod = PlatformClass.getMethod("find", new Class[]{BundleClass, IPathClass}); //$NON-NLS-1$
            return (URL) findMethod.invoke(null, new Object[]{bundle, path});
        }
    } catch (Throwable e) {
        // Ignore any exceptions
    }
    // else work with 'plugin' as with usual Eclipse plugin
    {
        Class<?> PluginClass = Class.forName("org.eclipse.core.runtime.Plugin"); //$NON-NLS-1$
        if (PluginClass.isAssignableFrom(plugin.getClass())) {
            //
            Class<?> PathClass = Class.forName("org.eclipse.core.runtime.Path"); //$NON-NLS-1$
            Constructor<?> pathConstructor = PathClass.getConstructor(new Class[]{String.class});
            Object path = pathConstructor.newInstance(new Object[]{name});
            //
            Class<?> IPathClass = Class.forName("org.eclipse.core.runtime.IPath"); //$NON-NLS-1$
            Method findMethod = PluginClass.getMethod("find", new Class[]{IPathClass}); //$NON-NLS-1$
            return (URL) findMethod.invoke(plugin, new Object[]{path});
        }
    }
    return null;
}

After proguard:

private static URL getPluginImageURL(Object plugin, String name)
throws Exception
{
try
{
  localClass1 = Class.forName("org.osgi.framework.Bundle");
  localClass2 = Class.forName("org.osgi.framework.BundleContext");
  if (localClass2.isAssignableFrom(plugin.getClass())) {
    localObject1 = localClass2.getMethod("getBundle", new Class[0]);
    localObject2 = ((Method)localObject1).invoke(plugin, new Object[0]);

    localClass3 = Class.forName("org.eclipse.core.runtime.Path");
    localObject3 = localClass3.getConstructor(new Class[] { String.class });
    Object localObject4 = ((Constructor)localObject3).newInstance(new Object[] { name });

    Class localClass4 = Class.forName("org.eclipse.core.runtime.IPath");
    Class localClass5 = Class.forName("org.eclipse.core.runtime.Platform");
    Method localMethod = localClass5.getMethod("find", new Class[] { localClass1, localClass4 });
    return (URL)localMethod.invoke(null, new Object[] { localObject2, localObject4 });
  }
}
catch (Throwable localThrowable)
{
  Class localClass2;
  Object localObject1;
  Object localObject2;
  Class localClass3;
  Object localObject3;
  Class localClass1 = Class.forName("org.eclipse.core.runtime.Plugin");
  if (localClass1.isAssignableFrom(plugin.getClass()))
  {
    localClass2 = Class.forName("org.eclipse.core.runtime.Path");
    localObject1 = localClass2.getConstructor(new Class[] { String.class });
    localObject2 = ((Constructor)localObject1).newInstance(new Object[] { name });

    localClass3 = Class.forName("org.eclipse.core.runtime.IPath");
    localObject3 = localClass1.getMethod("find", new Class[] { localClass3 });
    return (URL)((Method)localObject3).invoke(plugin, new Object[] { localObject2 });
  }
}
return null;

}

Notice how localObject1 and localObject2 no longer have Class declaration? Doesn't this make the code syntactically incorrect?

Help...

Answer 1

It's your decompiler that produces the syntactically incorrect code. You could try a different decompiler.

ProGuard indeed removes the local variable names, since they are just optional debugging information. They are not required by the virtual machine.