[1.20.2] Mixin @ModifyConstant Errors

[Bittripbrit]

Hi there!

I'm experimenting with creating larger jigsaw structures and am attempting to override the base class JigsawStructure. It currently caps the maximum range from the center of a structure to 128 blocks and I'm trying to bump that to 256.

The JigsawStructure class has a, to be honest, horrible variable with a nested series of lambas that I am trying to modify, specifically the intRange (1, 128) into intRange (1,256).

public static final Codec<JigsawStructure> CODEC = ExtraCodecs.validate(RecordCodecBuilder.mapCodec((p_227640_) -> {
      return p_227640_.group(settingsCodec(p_227640_), StructureTemplatePool.CODEC.fieldOf("start_pool").forGetter((p_227656_) -> {
         return p_227656_.startPool;
      }), ResourceLocation.CODEC.optionalFieldOf("start_jigsaw_name").forGetter((p_227654_) -> {
         return p_227654_.startJigsawName;
      }), Codec.intRange(0, 7).fieldOf("size").forGetter((p_227652_) -> {
         return p_227652_.maxDepth;
      }), HeightProvider.CODEC.fieldOf("start_height").forGetter((p_227649_) -> {
         return p_227649_.startHeight;
      }), Codec.BOOL.fieldOf("use_expansion_hck").forGetter((p_227646_) -> {
         return p_227646_.useExpansionHck;
      }), Heightmap.Types.CODEC.optionalFieldOf("project_start_to_heightmap").forGetter((p_227644_) -> {
         return p_227644_.projectStartToHeightmap;
      }), Codec.intRange(1, 128).fieldOf("max_distance_from_center").forGetter((p_227642_) -> {
         return p_227642_.maxDistanceFromCenter;
      })).apply(p_227640_, JigsawStructure::new);
   }), JigsawStructure::verifyRange).codec();

I've found it in bytecode (it's too big to put in all in here due to the number of lambdas, but is very easy to see in IntelliJ by viewing the bytecode of JigsawStructure.java). You can see the SIPUSH 128 that I'm trying to modify in the edited example below:

// access flags 0x100A
  private static synthetic lambda$static$7(Lcom/mojang/serialization/codecs/RecordCodecBuilder$Instance;)Lcom/mojang/datafixers/kinds/App;

...

 INVOKEVIRTUAL com/mojang/serialization/MapCodec.forGetter (Ljava/util/function/Function;)Lcom/mojang/serialization/codecs/RecordCodecBuilder;
    ICONST_1
    SIPUSH 128
   L6
    LINENUMBER 35 L6
    INVOKESTATIC com/mojang/serialization/Codec.intRange (II)Lcom/mojang/serialization/Codec; (itf)
    LDC "max_distance_from_center"
    INVOKEINTERFACE com/mojang/serialization/Codec.fieldOf (Ljava/lang/String;)Lcom/mojang/serialization/MapCodec; (itf)
    INVOKEDYNAMIC apply()Ljava/util/function/Function; [
      // handle kind 0x6 : INVOKESTATIC
      java/lang/invoke/LambdaMetafactory.metafactory(Ljava/lang/invoke/MethodHandles$Lookup;Ljava/lang/String;Ljava/lang/invoke/MethodType;Ljava/lang/invoke/MethodType;Ljava/lang/invoke/MethodHandle;Ljava/lang/invoke/MethodType;)Ljava/lang/invoke/CallSite;
      // arguments:
      (Ljava/lang/Object;)Ljava/lang/Object;, 
      // handle kind 0x6 : INVOKESTATIC
      net/minecraft/world/level/levelgen/structure/structures/JigsawStructure.lambda$static$6(Lnet/minecraft/world/level/levelgen/structure/structures/JigsawStructure;)Ljava/lang/Integer;, 
      (Lnet/minecraft/world/level/levelgen/structure/structures/JigsawStructure;)Ljava/lang/Integer;
    ]

 And as such I've written my Mixin as follows:

    @ModifyConstant(method = "lambda$static$7", constant = @Constant(intValue = 128))
    private static int aldarinmod$modifyMaxJigsawRange(int old)
    {
        return 256;
    }

However, when compiling I get this warning (which causes the Mixin to fail at runtime):

warning: Unable to determine descriptor for @ModifyConstant target method
    @ModifyConstant(method = "lambda$static$7", constant = @Constant(intValue = 128))

I'm not sure what's going wrong here. I'm a C++ programmer rather than a Java programmer so I'm not sure if there's something here that I'm not Java enough to understand. I'm fairly new to Mixins but from my reading, this seems like the correct way of doing this. Happy to pop this up onto github as well if that would help in debugging the issue.

Cheers!