# Contributing extensions

Before you submit extensions, please read the custom extension tutorial **in full**:

 - https://docs.turbowarp.org/development/extensions/introduction

Please pay special attention to:

 - Unsandboxed extensions: https://docs.turbowarp.org/development/extensions/unsandboxed
 - Maintaining backward compatibility: https://docs.turbowarp.org/development/extensions/compatibility
 - A better development server: https://docs.turbowarp.org/development/extensions/better-development-server

Read this document **in full** too. Pull requests that don't follow the guidelines will take *much* longer to be reviewed.

## Acceptance criteria

Strictly, nothing is banned, but the following are *highly* discouraged:

 - Broad "Utilities" extensions (break them up into multiple extensions, see https://github.com/TurboWarp/extensions/issues/674)
 - Extensions that are very similar to existing ones (consider modifying the existing one instead)
 - One-use personal extensions (load the extension as a local file instead)
 - Extensions whose primary purpose is monetization (not in the spirit of an open source project)
 - Joke extensions (they aren't funny when they cause us to get bug reports)

Some extensions were added before these rules existed. That doesn't mean you will be exempted too.

## Important context

Every merged extension is more code that we will be expected to maintain indefinitely, even if you disappear. Remember: broken extensions mean that real projects by real people no longer work. If the renderer is rewritten one day, we will have to ensure that extensions like Clipping & Blending, RGB Channels, and Augmented Reality still work. That's not a small commitment.

We're all volunteers who all have lives outside of Scratch extensions. Many have full time jobs or are full time students. We'll get to you as soon as we can, so please be patient.

Every extension is also covered under [our bug bounty](https://github.com/TurboWarp/extensions/security/policy), so mindlessly merging things will have a direct impact on my wallet.

## Writing extensions

Extension source code goes in the [`extensions`](extensions) folder. For example, an extension placed at `extensions/hello-world.js` would be accessible at [http://localhost:8000/hello-world.js](http://localhost:8000/hello-world.js) using our development server.

New extensions should be added in a user folder. You can name your folder anything you want; common choices are your GitHub username or your Scratch username. If your username is `TestMuffin123`, then `TestMuffin123`, `TestMuffin`, or even just `Muffin` would all be accepted -- we are very lenient about this. Do note that user folders are just for organization; other people are still allowed to edit your extension. Renaming your folder later is only allowed in very rare circumstances, so please get it right the first time.

Extensions must be self-contained. All libraries and hardcoded resources should be embedded into the extension's JavaScript file. If you include minified code, please link where to find the unminified code and include a copy of the original license.

## License

**We are not lawyers. This is not legal advice.**

Everything in this repository must be available under an open source license. You can use any license you want, but we **STRONGLY** recommend using the [Mozilla Public License verison 2.0](licenses/MPL-2.0.txt) for all new extensions.

The following licenses are banned for being [incompatible the GPLv3](https://www.gnu.org/licenses/license-list.en.html), so do not use any code, images, etc. under them:

 - Creative Commons Attribution-ShareAlike licenses prior to version 4.0
   - This includes user-generated content on the Scratch website which [uses version 2.0](https://scratch.mit.edu/terms_of_use) of this license.
   - This includes StackOverflow posts contributed before 2018-05-02 which [use several different versions](https://stackoverflow.com/help/licensing).
 - Creative Commons Attribution-NoDerivs and similar "no derivatives" licenses
 - Creative Commons Attribution-NonCommercial and similar "non commercial" or "personal use only" licenses

Once you choose a license for your extension, [find its SPDX identifier from this table](https://spdx.org/licenses/). The "FSF Free/Libre?" and "OSI Approved?" columns should both contain "Y".

## Metadata

All extensions should need a metadata comment at the *very* start of the file, before any code. We have a script that will read these, so to make sure it understands what you write, use this exact format:

```js
// Name: My Cool Extension
// ID: extensionid
// Description: Does a very cool thing. This must have punctuation at the end!
// By: GarboMuffin <https://scratch.mit.edu/users/GarboMuffin/>
// Original: TestMuffin
// License: MPL-2.0
```

You must use line comments; block comments `/* */` will not work. These fields are **REQUIRED**:

 - `Name` will appear on the website. It should be similar to the name returned by getInfo().
 - `ID` should be identical to the id returned by getInfo().
 - `Description` will appear on the website.
 - `License` describes the license that the extension's code is under. It should be a valid [SPDX license](https://spdx.org/licenses/) expression. (use `MPL-2.0` if you are unsure)

`By` is optionally used to credit the author of the extension (you!). `Original` is used if the extension is based on or ported from somewhere else. They both use the same format of `Name` or `Name <https://scratch.mit.edu/users/username>`. Links to places other than Scratch are not allowed at this time. You can repeat both of these as many times as needed, just add another `// By: ...` comment after.

In addition to `// License: ...`, you can also add a larger block comment with more information if you want to.

## Website stuff

Add your extension's path (without `extensions/` and without `.js`) to `extensions/extensions.json`. The order of that list determines the order of the library. Don't worry about putting it in the right spot, we'll move it if we disagree.

New extensions do not *need* images, but they are encouraged. Save the image in the `images` folder with the same folder name and file name (but different file extension) as the extension's source code. For example, if your extension is located in `extensions/TestMuffin/fetch.js`, save the image as `images/TestMuffin/fetch.svg` or `images/TestMuffin/fetch.png`. The homepage generator will detect it automatically. Images are displayed in a 2:1 aspect ratio. SVG (preferred), PNG, or JPG are accepted. PNG or JPG should be 600x300 in resolution. Please add proper attribution to `images/README.md` for *any* resources that were not made by you. The resulting image must be licensed under the [GNU General Public License version 3](licenses/GPL-3.0.txt).

Most extensions shouldn't need external documentation -- it should be obvious what to do just by looking at the blocks. That said, some do need more explanation. Documentation is written in markdown and placed in the `docs` folder with a similar layout to images. For example, documentation for `extensions/TestMuffin/fetch.js` would be saved as `docs/TestMuffin/fetch.md`. Our version of markdown is slightly extended to allow rendering [scratchblocks](https://scratchblocks.github.io/). Just look at the existing documentation for syntax examples. It's not a perfect experience: block colors have to be manually copied, and icons aren't supported, but it's better than what we had before. Once you put your markdown there, you can set a `docsURI` like `https://extensions.turbowarp.org/TestMuffin/fetch`.

Static resources such as example resources used by extensions go in the `website` folder.

## Banned APIs

Don't use these:

 - `eval()`
 - `new Function()`
 - untrusted or remote `<script>` or `<iframe>`
 - other arbitrary JS/CSS/HTML evaluation

## Type checking

If you use our development server, TypeScript aware editors such as Visual Studio Code will give you smart autocomplete suggestions for most Scratch and extension APIs based on [@turbowarp/types](https://github.com/TurboWarp/types) and [@turbowarp/types-tw](https://github.com/TurboWarp/types-tw). Note that these types are not perfect; some methods are missing or incorrect. Please report any issues you find.

If you encounter a TypeScript error, as long as you understand the error, feel free to add `// @ts-ignore`, `// @ts-expect-error`, or just ignore the error entirely. We currently do not require extensions to pass type checking.

## Linting, validation, and formatting

All pull requests are automatically checked by a combination of custom validation scripts, [ESLint](https://eslint.org/), and [Prettier](https://prettier.io/). Don't worry about passing these checks on the first attempt -- most don't. That's why we have these checks.

Our custom validation scripts do things like making sure you have the correct headers at the start of your extension and that the images are the right size. **Your extension must pass validation.** You can run them locally with:

```bash
npm run validate
```

ESLint detects common JavaScript errors such as referencing non-existant variables. **Your extension must pass linting.** You can run it locally with:

```bash
npm run lint
```

You are allowed to [disable ESLint warnings and errors](https://eslint.org/docs/latest/use/configure/rules#disabling-rules) as needed, but please only do so if actually required.

When including third-party code, especially minified code, you may use `/* eslint-disable*/` and `/* eslint-enable */` markers to disable linting for that entire section.

We use Prettier to ensure consistent code formatting. **Your extension does not need to pass format; we will fix it for you if linting and validation pass.** You can format your code automatically with:

```bash
npm run format
```

To just check formatting, use:

```bash
npm run check-format
```