CropBlockMixin.java

/**
 * Allows for any block to be farmland, if it's tagged correctly.
 */
@Mixin(CropBlock.class)
public abstract class CropBlockMixin {


    @Inject(method = "Lnet/minecraft/block/CropBlock;canPlantOnTop(Lnet/minecraft/block/BlockState;Lnet/minecraft/world/BlockView;Lnet/minecraft/util/math/BlockPos;)Z",
            at = @At("HEAD"))
    protected void canPlantOn(BlockState blockState_1, BlockView blockView_1, BlockPos blockPos_1, CallbackInfoReturnable<Boolean> cir) {
        if (canPlantOn(blockState_1, blockView_1, blockPos_1))
            cir.setReturnValue(true);
    }

    private static boolean canPlantOn(BlockState blockState_1, BlockView blockView_1, BlockPos blockPos_1) {
        if(blockState_1.getBlock() instanceof FarmlandInterface)
            return true;
        Collection<Identifier> tagsFor = BlockTags.getContainer().getTagsFor(blockState_1.getBlock());
        return tagsFor.contains(new Identifier(Arcanum.INSTANCE.getMODID(), "farmland"));
    }

    /**
     * Providing hooks to be able to create custom farmland.
     *
     * @author Frontrider
     */
    @Overwrite
    public static float method_9830(Block block_1, BlockView blockView_1, BlockPos blockPos_1) {
        float float_1 = 1.0F;
        BlockPos blockPos_2 = blockPos_1.down();

        for (int int_1 = -1; int_1 <= 1; ++int_1) {
            for (int int_2 = -1; int_2 <= 1; ++int_2) {
                float float_2 = 0.0F;
                BlockState blockState_1 = blockView_1.getBlockState(blockPos_2.add(int_1, 0, int_2));
                if (blockState_1.getBlock() == Blocks.FARMLAND) {
                    float_2 = 1.0F;
                    if (blockState_1.get(FarmlandBlock.field_11009) > 0) {
                        float_2 = 3.0F;
                    }
                }
                //the added code starts here
                else {
                    if ((blockState_1.getBlock() instanceof FarmlandInterface)) {
                        float_2 = 1.0F;
                        if (((FarmlandInterface) blockState_1.getBlock()).getWetness(blockState_1, blockPos_2, blockView_1) > 0) {
                            float_2 = 3.0F;
                        }
                    } else {
                        if (canPlantOn(blockState_1, blockView_1, blockPos_2))
                            float_2 = 3.0F;
                    }

                }//the added code ends here.

                if (int_1 != 0 || int_2 != 0) {
                    float_2 /= 4.0F;
                }

                float_1 += float_2;
            }
        }

        BlockPos blockPos_3 = blockPos_1.north();
        BlockPos blockPos_4 = blockPos_1.south();
        BlockPos blockPos_5 = blockPos_1.west();
        BlockPos blockPos_6 = blockPos_1.east();
        boolean boolean_1 = block_1 == blockView_1.getBlockState(blockPos_5).getBlock() || block_1 == blockView_1.getBlockState(blockPos_6).getBlock();
        boolean boolean_2 = block_1 == blockView_1.getBlockState(blockPos_3).getBlock() || block_1 == blockView_1.getBlockState(blockPos_4).getBlock();
        if (boolean_1 && boolean_2) {
            float_1 /= 2.0F;
        } else {
            boolean boolean_3 = block_1 == blockView_1.getBlockState(blockPos_5.north()).getBlock() || block_1 == blockView_1.getBlockState(blockPos_6.north()).getBlock() || block_1 == blockView_1.getBlockState(blockPos_6.south()).getBlock() || block_1 == blockView_1.getBlockState(blockPos_5.south()).getBlock();
            if (boolean_3) {
                float_1 /= 2.0F;
            }
        }

        return float_1;
    }
}

FarmlandInterface.java

/**
 * Allows blocks NOT extending the farmland to serve as such.
 * */
public interface FarmlandInterface {
    int getWetness(BlockState blockState, BlockPos pos, BlockView blockView);
}