How do I change a method of an interface using mixins? using Spongepowered on Minecraft Forge 1.18.2

Question

So I am using IntelliJ IDEA to mod Minecraft Forge 1.18.2 and I am trying to change the isEmptyBlock method of the LevelReader class using SpongePowered mixins.

But LevelReader is an interface, and the mod won't run if I try to edit an Interface. And after looking for quite a while on the InterWebs, I have found nothing.

So the question is:

So how do I change the method of an Interface?

I am using this code: in: MixinLevelReader

package net.iateminecraft.jetpacksfix.mixin;

import com.mojang.logging.LogUtils;
import net.minecraft.core.BlockPos;
import net.minecraft.world.level.LevelReader;
import net.minecraft.world.level.LevelAccessor;
import org.slf4j.Logger;
import org.spongepowered.asm.mixin.Mixin;
import org.spongepowered.asm.mixin.Unique;
import org.spongepowered.asm.mixin.injection.At;
import org.spongepowered.asm.mixin.injection.Inject;
import org.spongepowered.asm.mixin.injection.callback.CallbackInfoReturnable;

@Mixin(LevelReader.class)
public abstract class MixinLevelReader {
    @Unique
    private static final Logger LOGGER = LogUtils.getLogger();
    @Unique
    LevelAccessor world = (LevelAccessor) (Object) this;

    @Inject(at = @At("HEAD"), method = "isEmptyBlock(Lnet/minecraft/core/BlockPos;)Z", cancellable = true)
    private void isEmptyBlock(BlockPos blockposition, CallbackInfoReturnable<Boolean> callback) {
        LOGGER.info(String.valueOf(world.getBlockState(blockposition).isAir()));
        callback.setReturnValue(world.getBlockState(blockposition).isAir());
    }
}

It will compile fine when I run ./gradlew :build, but as soon as I do ./gradlew :runClient it errors with: Caused by: org.spongepowered.asm.mixin.transformer.throwables.InvalidMixinException: @Mixin target type mismatch: net.minecraft.world.level.LevelReader is an interface in org.spongepowered.asm.mixin.transformer.MixinInfo$SubType$Standard@75b6dd5b

gabizou · Accepted Answer · 2024-10-03 03:48:49Z

0

On Forge, you won't be able to as the version used in 1.18.2 is too old to have the newer feature of using @Redirect or @Inject on interfaces. You'd have to use an @Overwrite of the full default method, that way you can add your code in the right place. The alternative is to use an @Override on something like ServerLevel where you can add a method "implementing" the parent method that is defaulted:


    @Override
    public boolean isEmptyBlock(BlockPos pos) {
        // Do something before
        if (net.minecraft.world.level.LevelReader.super.isEmptyBlock(isEmptyBlock)) {
            // do something after if true
        }
        // do something here as well
    }

answered Oct 3, 2024 at 3:48

gabizou

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