Implement API for mods to control their server status response..

Signed-off-by: cpw <cpw+github@weeksfamily.ca>

src/main/java/net/minecraftforge/fml/ExtensionPoint.java

@@ -24,17 +24,28 @@ import net.minecraft.client.gui.GuiScreen;
 import net.minecraft.resources.IResourcePack;
 import net.minecraftforge.fml.network.FMLPlayMessages;
 import net.minecraftforge.fml.packs.ModFileResourcePack;
+import org.apache.commons.lang3.tuple.Pair;
 
 import java.util.function.BiFunction;
+import java.util.function.BiPredicate;
 import java.util.function.Function;
+import java.util.function.Supplier;
 
 public class ExtensionPoint<T>
 {
     public static final ExtensionPoint<BiFunction<Minecraft, GuiScreen, GuiScreen>> CONFIGGUIFACTORY = new ExtensionPoint<>();
     public static final ExtensionPoint<BiFunction<Minecraft, ModFileResourcePack, IResourcePack>> RESOURCEPACK = new ExtensionPoint<>();
+    /**
+     * Compatibility display test for the mod.
+     * Used for displaying compatibility with remote servers with the same mod, and on disk saves.
+     *
+     * The supplier provides my "local" version for sending across the network or writing to disk
+     * The predicate tests the version from a remote instance or save for acceptability (Boolean is true for network, false for local save)
+     */
+    public static final ExtensionPoint<Pair<Supplier<String>, BiPredicate<String, Boolean>>> DISPLAYTEST = new ExtensionPoint<>();
 
     /**
-     * Register with {@link ModLoadingContext#}
+     * Register with {@link ModLoadingContext#registerExtensionPoint(ExtensionPoint, Supplier)}
      */
     public static final ExtensionPoint<Function<FMLPlayMessages.OpenContainer, GuiScreen>> GUIFACTORY = new ExtensionPoint<>();