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Code Conventions

Security

Keep in mind that your code will be running on hundreds or thousands of servers; security matters. Following these guidelines is vital for all new code. Contributors should also see the dedicated security document.

Our users have an expectation of security and trust; it is important we make sure our code is safe.

Malicious Code

No contributions should contain malicious code designed to harm the user or their machine. Nothing should intend to damage or delete system files, the user's personal files or unrelated parts of the Minecraft server (like other plugins' files).

Runtime.getRuntime().exec("rm -rf /"); // bad, don't do this

While we expect contributors to use common sense, a general rule would be that contributions should not modify or delete resources unless:

  1. They belong to or are associated with Skript (variables, Skript files)
  2. They are expected to be modified by Skript (minecraft world data, player data)

Contributions to Skript should not include code or syntax with an easy potential to be exploited for malicious purposes (e.g. syntax to run exec commands, broad access to the filesystem unrelated to the Minecraft server). While any code has the potential to be abused or cause accidental damage, we would ideally like to limit this where possible.

Secrets and Personal Data

Contributions should never include secret tokens, passwords, personal api keys, GitHub tokens, etc. This code may be run across tens of thousands of servers, giving all those users access to that private resource.

While we would expect to catch an accidental password share at the review stage, please do your best not to commit them! Once a commit is made, the information may be publicly available forever even if deleted by us - if you do commit your password, please change it as quickly as possible.

Please do not include personal or identifying data (names, emails, addresses, etc.) in contributions. Your GitHub account will be automatically credited in the contributor record; you do not need to include your name or by-line in comments or documentation.

Server Safety

Contributions should avoid slowing or making the server unstable. Explicit pauses (sleep/wait) are almost never appropriate, particularly considering Skript's single-threaded design.

Easy infinite loop traps should also be avoided where possible. Please be especially wary of syntax people might accidentally (mis)use.

I/O operations should never be exposed via syntax.
This includes but is not limited to:

  • File syntax
  • Network I/O syntax
  • Remote socket syntax

These operations are natively slow and unsafe (particularly if they involve contacting another machine) and Skript does not currently have the tools for users to employ them safely (e.g. thread support, error catching, resource closing.)

That said, some syntax may be required to use I/O operations (e.g. logging to a file.)
For contributions including necessary I/O please make sure:

  1. All resource streams are handled using a try-with-resources block or closed safely in a finally block.
  2. Output does not needlessly block the server thread.
  3. Operations respect other concurrent I/O (make sure resources are available/safe to use, be careful of concurrent access.)

Operations that access a remote machine will almost never be appropriate for Skript. With the exception of contacting our own resources (e.g. to check for updates) contributions should include no form of automatic installation/fetching or download of third-party resources.

Licensing

Code contributed must be licensed under GPLv3, by you. We expect that any code you contribute is either owned by you or you have explicit permission to provide and license it to us.

Third party code (under a compatible licence) may be accepted in the following cases:

  • It is part of a public, freely-available library or resource.
  • It is somehow necessary to your contribution, and you have been given permission to include it.
  • You have previously co-authored the code, the other contributors have given you permission to include it.

If we receive complaints regarding the licensing of a contribution we will forward the complaints to you the contributor.

If you have questions or complaints regarding the licensing or reproduction of a contribution you may contact us (the organisation) or the contributor of that code directly.

If, in the future, we need to relicense contributed code, we will contact all contributors involved. If we need to remove or alter contributed code due to a licensing issue we will attempt to notify its contributor.

Code Style

Formatting

  • Tabs, no spaces (unless in code imported from other projects) ** No tabs/spaces in empty lines

  • No trailing whitespace

  • At most 120 characters per line

    • In Javadoc/multiline comments, at most 80 characters per line

  • When statements consume multiple lines, all lines but first have two tabs of additional indentation

  • Each class begins with an empty line

  • No squeezing of multiple lines of code on a single line

  • Separate method declarations with empty lines

    • Empty line after last method in a class is not required
    • Otherwise, empty line before and after method is a good rule of thumb

  • If fields have Javadoc, separate them with empty lines

  • Use empty lines liberally inside methods to improve readability

  • Use curly brackets to start and end most blocks

    • Only when a conditional block (if or else) contains a single statement, they may be omitted
    • When omitting brackets, still indent as if the code had brackets
    • Avoid omitting brackets if it produces hard-to-read code

  • Annotations for methods and classes are placed in lines before their declarations, one per line

  • When there are multiple annotations, place them in order:

    • @Override -> @Nullable -> @SuppressWarnings
    • For other annotations, doesn't matter; let your IDE decide

  • When splitting Strings into multiple lines the last part of the string must be (space character included) " " +

    String string = "example string " +
      "with more to add";

  • When extending one of following classes: SimpleExpression, SimplePropertyExpression, Effect, Condition...

    • Put overridden methods in order
    • SimpleExpression: init -> get/getAll -> acceptChange -> change -> setTime -> getTime -> isSingle -> getReturnType -> toString
    • SimplePropertyExpression: -> init -> convert -> acceptChange -> change -> setTime -> getTime -> getReturnType -> getPropertyName
    • Effect: init -> execute -> toString
    • Condition: init -> check -> toString
    • PropertyCondition: (init) -> check -> (getPropertyType) -> getPropertyName
    • Section: init -> walk -> toString
    • Structure: init -> (preLoad) -> load -> (postLoad) -> unload -> (postUnload) -> (getPriority) -> toString

Naming

  • Class names are written in UpperCamelCase
    • The file name should match its primary class name (e.g. MyClass goes in MyClass.java.)
  • Fields and methods named in camelCase
    • Static constant fields should be named in UPPER_SNAKE_CASE
  • Localised messages should be named in lower_snake_case
    • And that is the only place where snake_case is acceptable
  • Use prefixes only where their use has been already estabilished (such as ExprSomeRandomThing)
    • Otherwise, use postfixes where necessary
    • Common occurrences include: Struct (Structure), Sec (Section), EffSec (EffectSection), Eff (Effect), Cond (Condition), Expr (Expression)

Comments

  • Prefer to comment why you're doing things instead of how you're doing them
    • In case the code is particularly complex, though, do both!
  • Write all comments in readable English
    • Remember the basic grammar rules
    • Fun is allowed, if that does not hurt the readability
  • No matter if a comment contains a sentence or not, capitalize the first letter
  • For single line comments
    • Always start with a space; it improves readability
    • You may put them at ends of lines, if the line doesn't get too wide due to that

Your comments should look something like these:

// A single line comment

/**
 * This is a Javadoc comment.
 * @param first Description of the first parameter.
 * @param second Description of the second parameter.
 * @return Description of the return value.
 */
 
/*
 * This is a block comment.
 */

Language Features

Compatibility

  • Contributions should maintain Java 8 source/binary compatibility, even though compiling Skript requires Java 17
    • Users must not need JRE newer than version 8
  • Versions up to and including Java 17 should work too
    • Please avoid using unsafe reflection
  • It is recommended to make fields final, if they are effectively final
  • Local variables and method parameters should not be declared final
  • Methods should be declared final only where necessary
  • Use @Override whenever applicable

Nullness

  • All fields, method parameters and their return values are non-null by default
    • Exceptions: Github API JSON mappings, Metrics
  • When something is nullable, mark it as so
  • Only ignore nullness errors when a variable is effectively non-null - if in doubt: check
    • Most common example is syntax elements, which are not initialised using a constructor
  • Use assertions liberally: if you're sure something is not null, assert so to the compiler
    • Makes finding bugs easier for developers
  • Assertions must not have side-effects - they may be skipped in real environments
  • Avoid checking non-null values for nullability
    • Unless working around buggy addons, it is rarely necessary
    • This is why ignoring nullness errors is particularly dangerous

Assertions

Skript must run with assertations enabled; use them in your development environment.
The JVM flag -ea is used to enable them.

Minecraft Features

Avoid Version-Specific Code

Contributions must never rely on the variable net.minecraft.server package.

import net.minecraft.server.v1_13_1.*; // BAD

This makes updating between versions excessively difficult, and requires us to write different code for all supported versions. If a feature is not accessible via the Bukkit API it should not be included in Skript.

For features requiring 'NMS' please consider making a third-party addon.

Support the Target Versions

The target Minecraft versions are written in our README.

Skript must run on these MC versions, in one way or another. If your contribution breaks compatibility for any of these versions we cannot accept it.

Please try to make sure contributions are future-safe, to the best of your ability. Where possible, avoid using version-specific code to target a feature (e.g. accessing different copies of an internal class via reflection for each minecraft version) as this creates additional maintenance work every time a new version releases. Checking whether a class exists in order to target supported versions is acceptable.

Support the Target Servers

Skript currently supports the 'Spigot' and 'Paper' server implementations. Contributions must not break this cross-compatibility.

This may change in the future as the server landscape shifts - we will note any changes here and in the README.

Paper-specific functionality and syntax are acceptable. Please make sure these contributions do not break compatibility with Spigot.

Skript may also run on other server platforms. While these are not supported, please do not deliberately break compatibility for them.

We do not support Bukkit/CraftBukkit.

Class Use

Prefer Aliases.javaItemType to the Material enum, as this may change in future versions.

Material type = Material.DIRT; // Bad
ItemType type = Aliases.javaItemType("dirt"); // Good

The exceptions are Material.AIR, which is a good way to represent "nothing" and Material.STONE which can be used to get a dummy ItemMeta.

Prefer to avoid referencing the Biome enum directly, since it has changed between versons in the past.