Contributing to Purpur

Purpur is happy you're willing to contribute to our projects. We are usually very lenient with all submitted PRs, but there are still some guidelines you can follow to make the approval process go more smoothly.

Use a Personal Fork and not an Organization

Purpur will routinely modify your PR, whether it's a quick rebase or to take care of any minor nitpicks we might have. Often, it's better for us to solve these problems for you than make you go back and forth trying to fix them yourself.

Unfortunately, if you use an organization for your PR, it prevents Purpur from modifying it. To avoid this, please do not use repositories on organizations for PRs.

Requirements

To get started with making changes, you'll need the following software, most of which can be obtained in (most) package managers such as apt (Debian / Ubuntu; you will most likely use this for WSL), homebrew (macOS / Linux), and more:

git (package git everywhere);
A Java 21 or later JDK (packages vary, use Google/DuckDuckGo/etc.).
- Adoptium has builds for most operating systems.
- Purpur requires JDK 21 to build, however, makes use of Gradle's Toolchains feature to allow building with only JRE 11 or later installed. (Gradle will automatically provision JDK 21 for compilation if it cannot find an existing install).

If you're on Windows, check the section on WSL.

If you're compiling with Docker, you can use Adoptium's eclipse-temurin images like so:

# docker run -it -v "$(pwd)":/data --rm eclipse-temurin:21.0.5_11-jdk bash
Pulling image...

root@abcdefg1234:/# javac -version
javac 21.0.5

Understanding Patches

Unlike the Purpur API and its implementation, modifications to Paper and Minecraft source files are done through patches. These patches/extensions are split into three different sets of two categories, which are formatted like so:

Under purpur-api:

paper-patches (applies to the paper-server/ git repo)
- sources: Per-file patches to Paper API classes;
- features: Larger feature patches that modify multiple Paper API classes.

Under purpur-server:

minecraft-patches (applies to the purpur-server// git repo)
- sources: Per-file patches to Minecraft classes;
- resources: Per-file patches to Minecraft data files;
- features: Larger feature patches that modify multiple classes.
paper-patches
- sources: Per-file patches to Paper Server classes;
- features: Larger feature patches that modify multiple Paper Server classes.

Because this entire structure is based on patches and git, a basic understanding of how to use git is required. A basic tutorial can be found here: https://git-scm.com/docs/gittutorial.

Assuming you have already forked the repository:

Clone your fork to your local machine;
Type ./gradlew applyAllPatches in a terminal to apply the patches to both paper and minecraft classes. On Windows, remove ./ from the beginning of gradlew commands;
cd into purpur-server for server changes, purpur-api for API changes, paper-api for Paper API changes, and paper-server for Paper Server changes.

purpur-server/src/minecraft/java and purpur-server/src/minecraft/java/resources are not git repositories in the traditional sense. Its initial commits are the decompiled and deobfuscated Minecraft source and resource files. The per-file patches are applied on top of these files as a single, large commit, which is then followed by the individual feature-patch commits. paper-api/ and paper-server/ follow the same concept; each paper "project" has its own git repository that also includes it's own feature and per-file patches.

Understanding the Gradle Tasks

It can be overwhelming when you look over all the available gradle tasks, but it's pretty straightforward. Each "project" that includes a local git repository has the following available gradle tasks attached to it:

./gradlew apply[project]FeaturePatches - Applies [project] feature patches
./gradlew apply[project]FilePatches - Applies [project] file patches
./gradlew apply[project]Patches - Applies all [project] patches
./gradlew fixup[project]FilePatches - Puts the currently tracked source changes into the [project] file patches commit
./gradlew rebuild[project]FeaturePatches - Rebuilds [project] feature patches
./gradlew rebuild[project]FilePatches - Rebuilds [project] file patches
./gradlew rebuild[project]Patches - Rebuilds all [project] patches

Some additional useful tasks are listed below:

./gradlew applyAllPatches - Applies all patches defined in the paperweight-patcher project and the server project. (equivalent to running applyPaperPatches and then applyAllServerPatches in a second Gradle invocation)
./gradlew applyAllServerFeaturePatches - Applies all Minecraft and upstream server feature patches (equivalent to applyMinecraftFeaturePatches applyServerFeaturePatches)
./gradlew applyAllServerFilePatches - Applies all Minecraft and upstream server file patches (equivalent to applyMinecraftFilePatches applyServerFilePatches)
./gradlew applyAllServerPatches - Applies all Minecraft and upstream server patches (equivalent to applyMinecraftPatches applyServerPatches)
./gradlew rebuildPaperSingleFilePatches - Fixups and rebuilds all paper single-file patches. This is how you'd make changes to the build.gradle.kts files located under purpur-api and purpur-server

Modifying (per-file) patches

This is generally what you need to do when editing files. Updating our per-file patches is as easy as:

Making your changes;
Running ./gradlew fixup[project]FilePatches in the root directory;
If nothing went wrong, rebuilding patches with ./gradlew rebuild[project]FilePatches;

Resolving rebase conflicts

If you run into conflicts while running fixup[project]FilePatches, you need to go a more manual route:

This method works by temporarily resetting your HEAD to the desired commit to edit it using git rebase.

If you have changes you are working on, type git stash to store them for later;
- You can type git stash pop to get them back at any point.
cd into the relevant local git repo and run git rebase -i base;
- It should show something like this in the text editor you get.
- If your editor does not have a "menu" at the bottom, you're using vim.
  If you don't know how to use vim and don't want to learn, enter :q! and press enter. Before redoing this step, do export EDITOR=nano for an easier editor to use.
Replace pick with edit for the commit/patch you want to modify (in this case the very first commit, purpur File Patches), and "save" the changes;
Make the changes you want to make to the patch;
Run git add . to add your changes;
Run git commit --amend to commit;
Run git rebase --continue to finish rebasing;
Run ./gradlew rebuild[project]FilePatches in the root directory;

Adding larger feature patches

Feature patches are exclusively used for large-scale changes that are hard to track and maintain and that can be optionally dropped, such as the more involved optimizations we have. This makes it easier to update Purpur during Minecraft updates, since we can temporarily drop these patches and reapply them later.

There is only a very small chance that you will have to use this system, but adding such patches is very simple:

Modify the relevant local git repo with the appropriate changes;
Run git add . inside that directory to add your changes;
Run git commit with the desired patch message;
Run ./gradlew rebuild[project]FeaturePatches in the root directory.

Your commit will be converted into a patch that you can then PR into Purpur.

❗ Please note that if you have some specific implementation detail you'd like to document, you should do so in the patch message or in comments.

Modifying larger feature patches

One way of modifying feature patches is to reset to the patch commit and follow the instructions from the rebase section. If you are sure there won't be any conflicts from later patches, you can also use the fixup method.

Fixup method

Manual method

Make your changes;
Make a temporary commit. You don't need to make a message for this;
Type git rebase -i base, move (cut) your temporary commit and move it under the line of the patch you wish to modify;
Change the pick to the appropriate action:
1. f/fixup: Merge your changes into the patch without touching the message.
2. s/squash: Merge your changes into the patch and use your commit message and subject.
Run ./gradlew rebuild[project]Patches in the root directory;
- This will modify the appropriate patches based on your commits.

Automatic method

Make your changes;
Make a fixup commit: git commit -a --fixup <hash of patch to fix>;
- If you want to modify a per-file patch, use git commit -a --fixup file
- You can also use --squash instead of --fixup if you want the commit message to also be changed.
- You can get the hash by looking at git log or git blame; your IDE can assist you too.
- Alternatively, if you only know the name of the patch, you can do git commit -a --fixup "Subject of Patch name".
Rebase with autosquash: git rebase -i --autosquash base. This will automatically move your fixup commit to the right place, and you just need to "save" the changes.
Run ./gradlew rebuild[project]Patches in the root directory. This will modify the appropriate patches based on your commits.

Rebasing PRs

Steps to rebase a PR to include the latest changes from main.
These steps assume the origin remote is your fork of this repository and upstream is the official PurpurMC repository.

Fetch the latest changes from upstream's main: git fetch upstream.
Checkout your feature/fix branch and rebase on main: git switch patch-branch && git rebase upstream/main.
Apply updated patches: ./gradlew applyPatches.
If there are conflicts, fix them.
If your PR creates new feature patches instead of modifying existing ones, ensure your newly-created patch is the last commit by either:
- Renaming the patch file with a large 4-digit number in front (e.g. 9999-Patch-to-add-some-new-stuff.patch), and re-applying patches.
- Running git rebase --interactive base and moving the commits to the end.
Rebuild patches: ./gradlew rebuildPatches.
Commit modified patches.
Force push changes: git push --force. Make sure you're not deleting any of your commits or changes here!

PR Policy

We'll accept changes that make sense. You should be able to justify their existence, along with any maintenance costs that come with them. Using obfuscation helpers aids in the maintenance costs. Remember that these changes will affect everyone who runs Purpur, not just you and your server.

While we will fix minor formatting issues, you should stick to the guide below when making and submitting changes.

Formatting

All modifications to Minecraft files and Paper files should be marked. For historical reasons, API and API-implementation contain a lot of these too, but they are no longer required.

You need to add a comment with a short and identifiable description of the patch: // Purpur start - <COMMIT DESCRIPTION>
- The comments should generally be about the reason the change was made, what it was before, or what the change is.
- After the general commit description, you can add additional information either after a ; or in the next line.
Multi-line changes start with // Purpur start - <COMMIT DESCRIPTION> and end with // Purpur end - <COMMIT DESCRIPTION>.
One-line changes should have // Purpur - <COMMIT DESCRIPTION> at the end of the line.

[!NOTE] These comments are incredibly important to be able to keep track of changes across files and to remember what they are for, even a decade into the future.

Here's an example of how to mark changes by Purpur:

entity.getWorld().dontBeStupid(); // Purpur - Move away from beStupid()
entity.getFriends().forEach(Entity::explode);
entity.updateFriends();

// Purpur start - Use plugin-set spawn
// entity.getWorld().explode(entity.getWorld().getSpawn());
Location spawnLocation = ((CraftWorld) entity.getWorld()).getSpawnLocation();
entity.getWorld().explode(new BlockPosition(spawnLocation.getX(), spawnLocation.getY(), spawnLocation.getZ()));
// Purpur end - Use plugin-set spawn

We generally follow the usual Java style (aka. Oracle style), or what is programmed into most IDEs and formatters by default. There are a few notes, however:

It is fine to go over 80 lines as long as it doesn't hurt readability.
There are exceptions, especially in Spigot-related files
When in doubt or the code around your change is in a clearly different style, use the same style as the surrounding code.
Usage of the var keyword is discouraged, as it makes reading patch files a lot harder and can lead to confusion during updates due to changed return types. The only exception to this is if a line would otherwise be way too long/filled with hard to parse generics in a case where the base type itself is already obvious.

Imports

When adding new imports to a Minecraft or Paper class, use the fully qualified class name instead of adding a new import to the top of the file. If you are using a type a significant number of times, you can add an import with a comment. However, if it's only used a couple of times, the FQN is preferred to prevent future patch conflicts in the import section of the file.

import net.minecraft.server.MinecraftServer;
// don't add import here, use FQN like below

public class SomeVanillaClass {
    public final org.bukkit.Location newLocation; // Purpur - add location
}

Nullability annotations

We are in the process of switching nullability annotation libraries, so you might need to use one or the other:

For classes we add: Fields, method parameters and return types that are nullable should be marked via the @Nullable annotation from org.jspecify.annotations. Whenever you create a new class, add @NullMarked, meaning types are assumed to be non-null by default. For less obvious placing such as on generics or arrays, see the JSpecify docs.

For other classes: Keep using both @Nullable and @NotNull from org.jetbrains.annotations. These will be replaced later.

Access Transformers

Sometimes, Vanilla code already contains a field, method, or type you want to access but the visibility is too low (e.g. a private field in an entity class). Purpur can use access transformers to change the visibility or remove the final modifier from fields, methods, and classes. Inside the build-data/purpur.at file, you can add ATs that are applied when you ./gradlew applyPatches. You can read about the format of ATs here.

Obfuscation Helpers

While rarely needed, obfuscation helpers are sometimes useful when it comes to unmapped local variables, or poorly named method parameters. In an effort to make future updates easier on ourselves, Purpur tries to use obfuscation helpers wherever it makes sense. The purpose of these helpers is to make the code more readable and maintainable. These helpers should be made easy to inline by the JVM wherever possible.

An example of an obfuscation helper for a local variable:

double d0 = entity.getX(); final double fromX = d0; // Purpur - OBFHELPER
// ...   
this.someMethod(fromX); // Purpur

While they may not always be done in exactly the same way, the general goal is always to improve readability and maintainability. Use your best judgment and do what fits best in your situation.

Configuration files

To use a configurable value in your patch, add a new entry in either the PurpurConfig or PurpurWorldConfig classes. Use PurpurConfig if a value must remain the same throughout all worlds, or the latter if it can change between worlds. World-specific configuration options are preferred whenever possible.

PurpurConfig example

public static boolean saveEmptyScoreboardTeams = false;
private static void saveEmptyScoreboardTeams() {
    // This is called automatically!
    // The name also doesn't matter.
    saveEmptyScoreboardTeams = getBoolean("settings.save-empty-scoreboard-teams", false);
}

Notice that the field is always public, but the setter is always private. This is important to the way the configuration generation system works. To access this value, reference it as you would any other static value:

if (!PurpurConfig.saveEmptyScoreboardTeams) {

It is often preferred that you use the fully qualified name for the configuration class when accessing it, like so: org.purpurmc.purpur.PurpurConfig.valueHere.
If this is not done, a developer for Purpur might fix that for you before merging, but it's always nice if you make it a habit where you only need 1-2 lines changed.

PurpurWorldConfig example

public boolean useInhabitedTime = true;
private void useInhabitedTime() {
    // This is called automatically!
    // The name also doesn't matter.
    useInhabitedTime = getBoolean("use-chunk-inhabited-timer", true);
}

Again, notice that the field is always public, but the setter is always private. To access this value, you'll need an instance of the net.minecraft.world.level.Level object:

return this.level.purpurConfig.useInhabitedTime ? this.inhabitedTime : 0;

Testing API changes

Using the Purpur Test Plugin

The Purpur project has a test-plugin module for easily testing out API changes and additions. To use the test plugin, enable it in test-plugin.settings.gradle.kts, which will be generated after running Gradle at least once. After this, you can edit the test plugin, and run a server with the plugin using ./gradlew runDev (or any of the other Purpur run tasks).

Publishing to Maven local (use in external plugins)

To build and install the Purpur APIs and Server to your local Maven repository, do the following:

Run ./gradlew publishToMavenLocal in the base directory.

If you use Gradle to build your plugin:

Add mavenLocal() as a repository. Gradle checks repositories in the order they are declared, so if you also have the Purpur repository added, put the local repository above Purpur's.
Make sure to remove mavenLocal() when you are done testing, see the Gradle docs for more details.

If you use Maven to build your plugin:

If you later need to use the Purpur-API, you might want to remove the jar from your local Maven repository.
If you use Windows and don't usually build using WSL, you might not need to do this.

Frequently Asked Questions

My commit doesn't need a build, what do I do?

Quite simple: You add [ci skip] to the start of your commit subject.

This case most often applies to changes to files like README.md, this very file (CONTRIBUTING.md), the LICENSE.md file, and so forth.

Patching and building is really slow, what can I do?

This only applies if you're running Windows. If you're running a prior Windows release, either update to Windows 10/11 or move to macOS/Linux/BSD.

In order to speed up patching process on Windows, it's recommended you get WSL 2. This is available in Windows 10 v2004, build 19041 or higher. (You can check your version by running winver in the run window (Windows key + R)). If you're using an out of date version of Windows 10, update your system with the Windows 10 Update Assistant or Windows 11 Update Assistant.

To set up WSL 2, follow the information here: https://docs.microsoft.com/en-us/windows/wsl/install

You will most likely want to use the Ubuntu apps. Once it's set up, install the required tools with sudo apt-get update && sudo apt-get install $TOOL_NAMES -y. Replace $TOOL_NAMES with the packages found in the requirements. You can now clone the repository and do everything like usual.

❗ Do not use the /mnt/ directory in WSL! Instead, mount the WSL directories in Windows like described here: https://docs.microsoft.com/en-us/windows/wsl/filesystems#view-your-current-directory-in-windows-file-explorer

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CONTRIBUTING.md

CONTRIBUTING.md

Contributing to Purpur

Use a Personal Fork and not an Organization

Requirements

Understanding Patches

Understanding the Gradle Tasks

Modifying (per-file) patches

Resolving rebase conflicts

Adding larger feature patches

Modifying larger feature patches

Fixup method

Manual method

Automatic method

Rebasing PRs

PR Policy

Formatting

Imports

Nullability annotations

Access Transformers

Obfuscation Helpers

Configuration files

PurpurConfig example

PurpurWorldConfig example

Testing API changes

Using the Purpur Test Plugin

Publishing to Maven local (use in external plugins)

Frequently Asked Questions

My commit doesn't need a build, what do I do?

Patching and building is really slow, what can I do?

Files

CONTRIBUTING.md

Latest commit

History

CONTRIBUTING.md

File metadata and controls

Contributing to Purpur

Use a Personal Fork and not an Organization

Requirements

Understanding Patches

Understanding the Gradle Tasks

Modifying (per-file) patches

Resolving rebase conflicts

Adding larger feature patches

Modifying larger feature patches

Fixup method

Manual method

Automatic method

Rebasing PRs

PR Policy

Formatting

Imports

Nullability annotations

Access Transformers

Obfuscation Helpers

Configuration files

PurpurConfig example

PurpurWorldConfig example

Testing API changes

Using the Purpur Test Plugin

Publishing to Maven local (use in external plugins)

Frequently Asked Questions

My commit doesn't need a build, what do I do?

Patching and building is really slow, what can I do?