PaperMC/CONTRIBUTING.md

Contributing to Paper
==========================
PaperMC 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.

**Table of contents:**
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* [Use a Personal Fork and not Organization](#use-a-personal-fork-and-not-organization)
* [Requirements](#requirements)
* [Understanding Patches](#understanding-patches)
* [Adding Patches](#adding-patches)
* [Modifying Patches](#modifying-patches)
  * [Method 1](#method-1)
    * [Using the Paper tool](#using-the-paper-tool)
    * [Manual method: Stashing](#manual-method-stashing)
  * [Method 2 - Fixup commits](#method-2---fixup-commits)
    * [Manual method](#manual-method)
    * [Automatic method](#automatic-method)
* [PR Policy](#pr-policy)
* [Formatting](#formatting)
* [Patch Notes](#patch-notes)
* [Obfuscation Helpers](#obfuscation-helpers)
* [Configuration files](#configuration-files)
  * [PaperConfig example](#paperconfig-example)
  * [PaperWorldConfig example](#paperworldconfig-example)
* [Frequently Asked Questions](#frequently-asked-questions)
  * [I can't find the NMS file I need!](#i-cant-find-the-nms-file-i-need)
  * [Where can I learn how to name method/field?](#where-can-i-learn-how-to-name-methodfield)
  * [My commit doesn't need a build, what do I do?](#my-commit-doesnt-need-a-build-what-do-i-do)
  * [Patching and building is *really* slow, what can I do?](#patching-and-building-is-really-slow-what-can-i-do)
  * [I wrote some API, how do I use it in Paper-Server?](#i-wrote-some-api-how-do-i-use-it-in-paper-server)

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## Use a Personal Fork and not Organization

Paper 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 it yourself.

Unfortunately, if you use an organization for your PR, it prevents Paper from
modifying it. This requires us to manually merge your PR, resulting in us
closing the PR instead of marking it as merged.

We much prefer to have PRs show as merged, so please do not use repositories
on organizations for PRs.

See <https://github.com/isaacs/github/issues/1681> for more information on the
issue.

## Requirements

To get started with PRing 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);
- `patch` (often package `patch`);
- A Java 8 or later JDK (packages vary, use Google/DuckDuckGo/etc.).  
If you need one, you can find them on [AdoptOpenJDK](https://adoptopenjdk.net/).
- `maven` (often package `maven`; can be found on
[Apache's site](https://maven.apache.org/download.cgi) too);
- `curl` (package `curl` everywhere).

If you're on Windows, check
[the section on WSL](#patching-and-building-is-really-slow-what-can-i-do).

If you're compiling with Docker, you can use the
[`adoptopenjdk`](https://hub.docker.com/_/adoptopenjdk/) images like so:

```console
# docker run -it -v "$(pwd)":/data --rm adoptopenjdk:8-jdk-hotspot bash
Pulling image...

root@abcdefg1234:/# javac -version
javac 1.8.0_252
```

## Understanding Patches

Paper is mostly patches and extensions to Spigot. These patches/extensions are
split into different directories which target certain parts of the code. These
directories are:

- `Paper-API` - Modifications to `Spigot-API`/`Bukkit`;
- `Paper-MojangAPI` - An API for
[Mojang's Brigadier](https://github.com/Mojang/brigadier);
- `Paper-Server` - Modifications to `Spigot`/`CraftBukkit`.

Because the 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:

1. Clone your fork to your local machine;
1. Type `./paper patch` in a terminal to apply the changes from upstream;
1. cd into `Paper-Server` for server changes, and `Paper-API` for API changes.  
You can also run `./paper server` or `./paper api` for these same directories
respectively.
1. You can also run `./paper setup`, which allows you to type `paper <command>`
from anywhere in the Paper structure in most cases.

`Paper-Server` and `Paper-API` aren't git repositories in the traditional sense:

- Every single commit in `Paper-Server`/`Paper-API` is a patch;
- `origin/master` points to a directory similar to `Paper-Server`/`Paper-API`
but for Paper;
- Typing `git status` should show that we are 10 or 11 commits ahead of master,
meaning we have 10 or 11 patches Spigot and CraftBukkit don't.
   - If it says something like `212 commits ahead, 207 commits behind`,
   cd into the root directory of the cloned repository and type `git fetch` to
   update your upstream. Setting up a remote for the upstream Paper repository
   might be necessary.

## Adding Patches

Adding patches to Paper is very simple:

1. Modify `Paper-Server` and/or `Paper-API` with the appropriate changes;
1. Type `git add .` inside these directories to add your changes;
1. Run `git commit` with the desired patch message;
1. Run `./paper rebuild` in the main directory to convert your commit into a new
patch;
1. PR the generated patch file(s) back to this repository.

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

> ❗ 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 Patches

Modifying previous patches is a bit more complex:

### Method 1

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

> ❗ While in the middle of an edit, you will not be able to compile unless you
> *also* reset the opposing module(s) to a related commit. In the API's case,
> you must reset the Server, and reset the API if you're editing the Server.

#### Using the Paper tool

The PaperMC build tool provides a handy command to automatically do this type of
patch modification.

1. Type `./paper edit server` or `./paper edit api` depending on which project
you want to edit;
   - It should show something like
   [this](https://gist.github.com/zachbr/21e92993cb99f62ffd7905d7b02f3159) 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.
1. Replace `pick` with `edit` for the commit/patch you want to modify, and
"save" the changes;
   - Only do this for **one** commit at a time.
1. Make the changes you want to make to the patch;
1. Type `./paper edit continue` in the root directory to finish and rebuild
patches;
1. PR your modified patch file(s) back to this repository.

#### Manual method: Stashing

In case you need something more complex or want more control, these step-by-step
instruction do exactly what the above slightly automated system above does.

1. 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.
1. Type `git rebase -i upstream/upstream`;
   - It should show something like
   [this](https://gist.github.com/zachbr/21e92993cb99f62ffd7905d7b02f3159) 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.
1. Replace `pick` with `edit` for the commit/patch you want to modify, and
"save" the changes;
   - Only do this for **one** commit at a time.
1. Make the changes you want to make to the patch;
1. Type `git add .` to add your changes;
1. Type `git commit --amend` to commit;
   - **Make sure to add `--amend`** or else a new patch will be created.
   - You can also modify the commit message and author here.
1. Type `git rebase --continue` to finish rebasing;
1. Type `./paper rebuild` in the root directory;
   - This will modify the appropriate patches based on your commits.
1. PR your modified patch file(s) back to this repository.

### Method 2 - Fixup commits

If you are simply editing a more recent commit or your change is small, simply
making the change at HEAD and then moving the commit after you have tested it
may be easier.

This method has the benefit of being able to compile to test your change without
messing with your HEADs.

#### Manual method

1. Make your change while at HEAD;
1. Make a temporary commit. You don't need to make a message for this;
1. Type `git rebase -i upstream/upstream`, move (cut) your temporary commit and
move it under the line of the patch you wish to modify;
1. Change the `pick` to the appropriate action:
   1. `f`/`fixup`: Merge your changes into the patch without touching the
  message.
   1. `s`/`squash`: Merge your changes into the patch and use your commit message
  and subject.
1. Type `./paper rebuild` in the root directory;
   - This will modify the appropriate patches based on your commits.
1. PR your modified patch file(s) back to this repository.

#### Automatic method

1. Make your change while at HEAD;
1. Make a fixup commit. `git commit -a --fixup <hashOfPatchToFix>`;
   - 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"`.
1. Rebase with autosquash: `git rebase --autosquash -i upstream/upstream`.
This will automatically move your fixup commit to the right place, and you just
need to "save" the changes.
1. Type `./paper rebuild` in the root directory;
   - This will modify the appropriate patches based on your commits.
1. PR your modified patch file(s) back to this repository.

## 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](#obfuscation-helpers) aids in the maintenance costs.
Remember that these changes will affect everyone who runs Paper, 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 non-Paper files should be marked.

- Multi-line changes start with `// Paper start` and end with `// Paper end`;
- You can put a comment with an explanation if it isn't obvious, like this:
`// Paper start - reason`.
   - The comments should generally be about the reason the change was made, what
  it was before, or what the change is.
   - Multi-line messages should start with `// Paper start` and use `/* Multi
  line message here */` for the message itself.
- One-line changes should have `// Paper` or `// Paper - reason`.

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

```java
entity.getWorld().dontbeStupid(); // Paper - was beStupid() which is bad
entity.getFriends().forEach(Entity::explode);
entity.a();
entity.b();
// Paper 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()));
// Paper end
```

We generally follow 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.

## Patch Notes

When submitting patches to Paper, we may ask you to add notes to the patch
header. While we do not require it for all changes, you should add patch notes
when the changes you're making are technical, complex, or require an explanation
of some kind. It is very likely that your patch will remain long after we've all
forgotten about the details of your PR; patch notes will help us maintain it
without having to dig back through GitHub history looking for your PR.

These notes should express the intent of your patch, as well as any pertinent
technical details we should keep in mind long-term. Ultimately, they exist to
make it easier for us to maintain the patch across major version changes.

If you add a message to your commit in the `Paper-Server`/`Paper-API`
directories, the rebuild patches script will handle these patch notes
automatically as part of generating the patch file. If you are not
extremely careful, you should always just `squash` or `amend` a patch (see the
above sections on modifying patches) and rebuild.

Editing messages and patches by hand is possible, but you should patch and
rebuild afterwards to make sure you did it correctly. This is slower than just
modifying the patches properly after a few times, so you will not really gain
anything but headaches from doing it by hand.

Underneath is an example patch header/note:

```patch
From 02abc033533f70ef3165a97bfda3f5c2fa58633a Mon Sep 17 00:00:00 2001
From: Shane Freeder <theboyetronic@gmail.com>
Date: Sun, 15 Oct 2017 00:29:07 +0100
Subject: [PATCH] revert serverside behavior of keepalives

This patch intends to bump up the time that a client has to reply to the
server back to 30 seconds as per pre 1.12.2, which allowed clients
more than enough time to reply potentially allowing them to be less
tempermental due to lag spikes on the network thread, e.g. that caused
by plugins that are interacting with netty.

We also add a system property to allow people to tweak how long the server
will wait for a reply. There is a compromise here between lower and higher
values, lower values will mean that dead connections can be closed sooner,
whereas higher values will make this less sensitive to issues such as spikes
from networking or during connections flood of chunk packets on slower clients,
 at the cost of dead connections being kept open for longer.

diff --git a/src/main/java/net/minecraft/server/PlayerConnection.java b/src/main/java/net/minecraft/server/PlayerConnection.java
index a92bf8967..d0ab87d0f 100644
--- a/src/main/java/net/minecraft/server/PlayerConnection.java
+++ b/src/main/java/net/minecraft/server/PlayerConnection.java
```

## Obfuscation Helpers

In an effort to make future updates easier on ourselves, Paper tries to use
obfuscation helpers whenever possible. The purpose of these helpers is to make
the code more readable and maintainable. These helpers should be be made as easy
to inline as possible by the JVM whenever possible.

An obfuscation helper to access an obfuscated item may be as simple as something
like this:

```java
public final int getStuckArrows() { return this.bY(); } // Paper - OBFHELPER
```

Or it may be as complex as forwarding an entire method so that it can be
overridden later:

```java
public boolean be() {
    // Paper start - OBFHELPER
    return this.pushedByWater();
}

public boolean pushedByWater() {
    // Paper end
    return true;
}
```

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
`PaperConfig` or `PaperWorldConfig` classes. Use `PaperConfig` 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.

### PaperConfig example

```java
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:

```java
if (!PaperConfig.saveEmptyScoreboardTeams) {
```

It is often preferred that you use the fully qualified name for the
configuration class when accessing it, like so:
`com.destroystokyo.paper.PaperConfig.valueHere`.  
If this is not done, a developer for Paper 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.

### PaperWorldConfig example

```java
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`
object:

```java
return this.world.paperConfig.useInhabitedTime ? this.w : 0;
```

## Frequently Asked Questions

### I can't find the NMS file I need!

By default, Paper (and upstream) only import files we make changes to. If you
would like to make changes to a file that isn't present in `Paper-Server`'s
source directory, you just need to add it to our import script ran during the
patching process.

1. Save (rebuild) any patches you are in the middle of working on! Their
progress will be lost if you do not;
1. Identify the name(s) of the file(s) you want to import.
   - A complete list of all possible file names can be found at
   `./work/Minecraft/$MCVER/spigot/net/minecraft/server`. You might find
   [MiniMappingViewer] very useful to find the file you need.
1. Open the file at `./scripts/importmcdev.sh` and add the name of your file to
the script. Skip to the 2nd last header and follow the instructions there;
1. Re-patch the server `./paper patch`;
1. Edit away!

> ❗ This change is temporary! **DO NOT COMMIT CHANGES TO THIS FILE!**  
> Once you have made your changes to the new file, and rebuilt patches, you may
> undo your changes to `importmcdev.sh`.

Any file modified in a patch file gets automatically imported, so you only need
this temporarily to import it to create the first patch.

To undo your changes to the file, type `git checkout scripts/importmcdev.sh`.

### Where can I learn how to name method/field?

For most cases, it is preferred if you use [yarn], as their license works with
Paper's license. If you can't do that, [MiniMappingViewer] is always around to
provide you with more of a general idea, *but* you cannot use the Mojang names
for more than understanding the code.

[yarn] is in general more thorough than Mojang's own mappings, as they include
method arguments as well, whereas Mojang's do not. If you need local variables
to understand the code, you might be more lucky with ModCoderPack.

For more information on the Mojang name licensing issues, check this out:
<https://cpw.github.io/MinecraftMappingData.html>

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

Well, 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 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
out of date, update your system with the
[Windows Update Assistant](https://www.microsoft.com/en-us/software-download/windows10).

To setup WSL 2, follow the information here:
<https://docs.microsoft.com/en-us/windows/wsl/install-win10>

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](#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://www.howtogeek.com/426749/how-to-access-your-linux-wsl-files-in-windows-10/>

### I wrote some API, how do I use it in Paper-Server?

To install the API to your local maven repository, do the following:

- Enter the API directory by running `./paper api`;
- Run `mvn install`.
   - If you are working on a patch without much care for whether the tests
   pass, you can instead run `mvn install -DskipTests`. Do not PR changes
   without running tests first.
   - If a test failed, you have to identify the failing tests by scrolling up a
   couple lines (i.e. around 50-200). You should find it fairly quickly.
   - If you later need to use the Paper-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.

You can now use the API in your plugin to test it before PRing. You will also
need to do this to build the Server with the implemented API.

[MiniMappingViewer]: https://minidigger.github.io/MiniMappingViewer/
[yarn]: https://github.com/FabricMC/yarn