minecraft-kajetans-core-mod/src/main/resources/class_transformer/block.js

var transformerName = "Dedicated Server Transformer";
var ASMAPI = Java.type('net.minecraftforge.coremod.api.ASMAPI');
var Opcodes = Java.type('org.objectweb.asm.Opcodes');
var VarInsnNode = Java.type("org.objectweb.asm.tree.VarInsnNode");
var MethodInsnNode = Java.type("org.objectweb.asm.tree.MethodInsnNode");
var LineNumberNode = Java.type("org.objectweb.asm.tree.LineNumberNode");
var FieldInsnNode = Java.type("org.objectweb.asm.tree.FieldInsnNode");
var InsnNode = Java.type("org.objectweb.asm.tree.InsnNode");

function initializeCoreMod() {
    return {
        transformerName: {
            'target': {
                'type': 'CLASS',
                'name': 'net.minecraft.block.Block'
            },
            'transformer': function (classNode) {
                var methods = classNode.methods;

                var targetMethodNameA = ASMAPI.mapMethod("func_220070_a"); // getDrops
                var targetMethodNameB = ASMAPI.mapMethod("func_220077_a"); // getDrops
                var targetMethodDescA = "(Lnet/minecraft/block/BlockState;Lnet/minecraft/world/server/ServerWorld;Lnet/minecraft/util/math/BlockPos;Lnet/minecraft/tileentity/TileEntity;)Ljava/util/List;";
                var targetMethodDescB = "(Lnet/minecraft/block/BlockState;Lnet/minecraft/world/server/ServerWorld;Lnet/minecraft/util/math/BlockPos;Lnet/minecraft/tileentity/TileEntity;Lnet/minecraft/entity/Entity;Lnet/minecraft/item/ItemStack;)Ljava/util/List;";

                for (var i in methods) {
                    var method = methods[i];
                    if (method.name.equals(targetMethodNameA) && method.desc.equals(targetMethodDescA)) {
                        transformA(method);
                    }
                    if (method.name.equals(targetMethodNameB) && method.desc.equals(targetMethodDescB)) {
                        transformB(method);
                    }
                }
                return classNode;
            }
        }
    };
}

function transformA(method) {
    var instrList = method.instructions;
    instrList.clear();
    instrList.add(new VarInsnNode(Opcodes.ALOAD, 0));
    instrList.add(new VarInsnNode(Opcodes.ALOAD, 1));
    instrList.add(new VarInsnNode(Opcodes.ALOAD, 2));
    instrList.add(new VarInsnNode(Opcodes.ALOAD, 3));
    instrList.add(new MethodInsnNode(Opcodes.INVOKESTATIC, "me/kcm/Hooks",
                    "getDropsA", 
                    "(Lnet/minecraft/block/BlockState;Lnet/minecraft/world/server/ServerWorld;Lnet/minecraft/util/math/BlockPos;Lnet/minecraft/tileentity/TileEntity;)Ljava/util/List;", 
                    false));
    instrList.add(new InsnNode(Opcodes.ARETURN));
}

function transformB(method) {
    var instrList = method.instructions;
    instrList.clear();
    instrList.add(new VarInsnNode(Opcodes.ALOAD, 0));
    instrList.add(new VarInsnNode(Opcodes.ALOAD, 1));
    instrList.add(new VarInsnNode(Opcodes.ALOAD, 2));
    instrList.add(new VarInsnNode(Opcodes.ALOAD, 3));
    instrList.add(new VarInsnNode(Opcodes.ALOAD, 4));
    instrList.add(new VarInsnNode(Opcodes.ALOAD, 5));
    instrList.add(new MethodInsnNode(Opcodes.INVOKESTATIC, "me/kcm/Hooks",
                    "getDropsB", 
                    "(Lnet/minecraft/block/BlockState;Lnet/minecraft/world/server/ServerWorld;Lnet/minecraft/util/math/BlockPos;Lnet/minecraft/tileentity/TileEntity;Lnet/minecraft/entity/Entity;Lnet/minecraft/item/ItemStack;)Ljava/util/List;", 
                    false));
    instrList.add(new InsnNode(Opcodes.ARETURN));
}