Access Transformers

Since some parts of the Minecraft code were not designed to be used from the outside, you may find yourself in a situation in which you need to access a field or method that is not public. While you would normally use reflection to access the field or method, MCP will make this more difficult since you have two different names - the MCP names in the development environment and the Searge names in production.

For example to access the method tick() using reflection you would need to use tick in the development environment, but func_71217_p in production. The re-obfuscation step only handles direct references to methods and fields, not the string parameter passed to the reflection call.

As a solution, ForgeGradle supports using access transformers (or AT) that automatically make the specified methods/fields public so you can reference them directly (without reflection). While they are primarily intended for usage with the Minecraft code base, they can be also applied to classes from other projects. If configured in the JAR manifest of the plugin, SpongeVanilla and Forge will also apply them in production.

Setup

ForgeGradle will automatically scan for access transformer files with the file name suffix _at.cfg in your resource folders. To be able to use the access transformer at runtime, you need to add them to a META-INF folder in your resource directory, for example META-INF/myplugin_at.cfg.

There are 3 different types of access transformers: you can change the modifiers of classes, fields and methods. An access transformer line is defined by 2 parts (for classes) or 3 parts (for fields and methods), each separated by a space.

  • The access type you want to change the method/field to, e.g. public or protected. To remove final from a field, append -f after the access type, e.g. public-f.
  • Full qualified class name, e.g. net.minecraft.server.MinecraftServer
  • For fields and methods: Searge field name or method name and method signature, e.g. field_54654_a or func_4444_a()V

Tip

You can add comments by prefixing them with #. A good convention is to add the MCP name after each access transformer line so you know which field/method the line is referring to.

Here are two examples for access transformer lines:

public-f net.minecraft.server.MinecraftServer field_71308_o # anvilFile
public net.minecraft.server.MinecraftServer func_71260_j()V # stopServer
public-f net.minecraft.item.ItemStack

To apply the access transformers to your development environment, run the Gradle setupDecompWorkspace task again and refresh your Gradle project:

gradle setupDecompWorkspace

Tip

You can use the MCP bot which is present in the MCP and Sponge IRC channels, or in the #bot-spam channel on Discord, to quickly get the access transformer line for a field or method. After looking up a method using !gm <mcp method name> or a field using !gf <mcp field name>, simply copy the listed AT line to your access transformer file.

Note

Making a field/method less accessible (e.g. public -> private) is not supported.

Production

To apply the access transformers in production, you need to add a FMLAT manifest entry to your plugin with the file name of your access transformer in the META-INF directory.

jar {
    manifest.attributes('FMLAT': 'myplugin_at.cfg')
}