Notes on porting Minecraft mods from 1.15.2 to 1.16.3 Forge

[dragoness_e]

A number of things to fix when you branch your 1.15.2 code and try to compile it under 1.16.3:

General

• Use the mapping snapshot for 20200723 or later; before that, the mappings were incomplete in some important areas, such as client-side GUIs.
• Don't forget to update mods.toml as well as your gradle properties
• The 'license' field is now required in mods.toml.
• A number of Minecraft class paths were changed (such as the Loot stuff). Your IDE should handle that for you. Shift-Ctrl-O in Eclipse; I don't know what IntelliJ's keybind is.
• Join the Forge Project Discord and mind your manners; they can provide invaluable advice on modding current versions of Minecraft. You will be expected to heed the Discord rules and already know basic Java programming

Server-side

Items & Blocks

• IArmorMaterial enums have a new mandatory method to implement that returns the knockback resistance.
• Blocks need to have .setRequiresTool() added to initialization, or else they can be harvested bare-handed, no matter the harvestLevel.
• Your DeferredRegister classes now must use the create() method rather than new. This was introduced late in 1.15.2, so if you have used the more recent 1.15.2 Forge versions to develop against, it will not be a surprise.
• Setting the light_level for a block got slightly more complicated. 1.16.1 now enforces setting it in the BlockState (not the Block) via the new setLightLevel() Property method that takes a ToIntFunction<BlockState> value as an argument. See vanilla code for examples of how this works--I'm not doing all your work for you ;-)
• A block being a beacon base is now a tag in 'data/minecraft/tags/blocks/beacon_base_blocks.json', rather than a boolean function in the block class.
• (Introduced late in 1.15.2) Forge finally added a tag, 'data/forge/tags/items/shears.json' that lists modded items that should act like vanilla shears. No more complicated workarounds using GlobalLootModifiers needed!
• (Also introduced in 1.15.2) Minecraft added a tag for plants that are affected by bee pollination, 'data/minecraft/tags/blocks/bee_growables.json'. However, this includes everything included in the 'data/minecraft/tags/blocks/crops.json tag, so if your plant is a harvestable crop, tag it in #minecraft:crops
• In general, vanilla Minecraft now has a lot of tags that add special handling to blocks and items, check them out and be aware of them.
• Coding tags has changed slightly.
• Entities no longer have a registerAttributes() override, but instead prepare their attributes in a static method and add them to GlobalEntityTypeAttributes in the FMLCommonSetupEvent event handler. Example:

      @SubscribeEvent
      public static void onCommonSetup(final FMLCommonSetupEvent event)
      {
          DeferredWorkQueue.runLater( ()-> {
                GlobalEntityTypeAttributes.put(ModEntities.silver_golem.get(), 
                                         SilverGolemEntity.prepareAttributes().create());
          });
      } // end onCommonSetup
  

  And for SilverGolemEntity.prepareAttributes():

      public static AttributeModifierMap.MutableAttribute prepareAttributes()
      {
          return MobEntity.func_233666_p_()
                  .createMutableAttribute(Attributes.MAX_HEALTH, 35.0D)
                  .createMutableAttribute(Attributes.MOVEMENT_SPEED, 0.5D)
                  .createMutableAttribute(Attributes.KNOCKBACK_RESISTANCE, 1.0D)
                  .createMutableAttribute(Attributes.ATTACK_DAMAGE, 15.0D);
      }
  

World Generation

• Has all changed drastically, as vanilla world generation is now JSON driven.
• Forge provides an Event, BiomeLoadingEvent, that you use to add features to a biome as it is loaded.
• Use too complex to explain here. To see it in action, see my SimpleOres2 1.16.3 GitHub. Helper classes are in SimpleCoreLib for 1.16.3.

Client-side

• Client-side GUI methods all have a new argument in front, MatrixStack. It's passed in from the caller and needs to be passed to most subordinate methods, including blit().
• The code for displaying arrows on bows was removed from BowItem and moved to some private method. Either use access transformers to access that private method, or just cut & paste the initialization code to a static method somewhere and call it in your FMLClientSetupEvent handler.
  It looks something like this:
  

      private static void setupBowModelProperties(Item bow) 
      {
          ItemModelsProperties.registerProperty(bow, new ResourceLocation("pull"), (p0, p1, p2) -> {
              if (p2 == null) {
                 return 0.0F;
              } else {
                 return p2.getActiveItemStack() != p0 ? 0.0F : (float)(p0.getUseDuration() - p2.getItemInUseCount()) / 20.0F;
              }
           });
          ItemModelsProperties.registerProperty(bow, new ResourceLocation("pulling"), (p0, p1, p2) -> {
              return p2 != null && p2.isHandActive() && p2.getActiveItemStack() == p0 ? 1.0F : 0.0F;
           });
      }