test-repo/docs/plugins.md

---
id: plugins
title: Plugins
---

Plugins are ways of adding new languages to Prettier. Prettier’s own implementations of all languages are expressed using the plugin API. The core `prettier` package contains JavaScript and other web-focused languages built in. For additional languages you’ll need to install a plugin.

## Using Plugins

Plugins are automatically loaded if you have them installed in the same `node_modules` directory where `prettier` is located. Plugin package names must start with `@prettier/plugin-` or `prettier-plugin-` or `@<scope>/prettier-plugin-` to be registered.

> `<scope>` should be replaced by a name, read more about [NPM scope](https://docs.npmjs.com/misc/scope.html).

When plugins cannot be found automatically, you can load them with:

- The [CLI](cli.md), via the `--plugin` and `--plugin-search-dir`:

  ```bash
  prettier --write main.foo --plugin-search-dir=./dir-with-plugins --plugin=./foo-plugin
  ```

  > Tip: You can set `--plugin` or `--plugin-search-dir` options multiple times.

- Or the [API](api.md), via the `plugins` and `pluginSearchDirs` options:

  ```js
  prettier.format("code", {
    parser: "foo",
    pluginSearchDirs: ["./dir-with-plugins"],
    plugins: ["./foo-plugin"],
  });
  ```

Prettier expects each of `pluginSearchDirs` to contain `node_modules` subdirectory, where `@prettier/plugin-*`, `@*/prettier-plugin-*` and `prettier-plugin-*` will be searched. For instance, this can be your project directory or the location of global npm modules.

Providing at least one path to `--plugin-search-dir`/`pluginSearchDirs` turns off plugin autoloading in the default directory (i.e. `node_modules` above `prettier` binary).

## Official Plugins

- [`@prettier/plugin-php`](https://github.com/prettier/plugin-php)
- [`@prettier/plugin-pug`](https://github.com/prettier/plugin-pug) by [**@Shinigami92**](https://github.com/Shinigami92)
- [`@prettier/plugin-ruby`](https://github.com/prettier/plugin-ruby)
- [`@prettier/plugin-xml`](https://github.com/prettier/plugin-xml)

## Community Plugins

- [`prettier-plugin-apex`](https://github.com/dangmai/prettier-plugin-apex) by [**@dangmai**](https://github.com/dangmai)
- [`prettier-plugin-elm`](https://github.com/gicentre/prettier-plugin-elm) by [**@giCentre**](https://github.com/gicentre)
- [`prettier-plugin-erb`](https://github.com/adamzapasnik/prettier-plugin-erb) by [**@adamzapasnik**](https://github.com/adamzapasnik)
- [`prettier-plugin-go-template`](https://github.com/NiklasPor/prettier-plugin-go-template) by [**@NiklasPor**](https://github.com/NiklasPor)
- [`prettier-plugin-java`](https://github.com/jhipster/prettier-java) by [**@JHipster**](https://github.com/jhipster)
- [`prettier-plugin-kotlin`](https://github.com/Angry-Potato/prettier-plugin-kotlin) by [**@Angry-Potato**](https://github.com/Angry-Potato)
- [`prettier-plugin-properties`](https://github.com/eemeli/prettier-plugin-properties) by [**@eemeli**](https://github.com/eemeli)
- [`prettier-plugin-solidity`](https://github.com/prettier-solidity/prettier-plugin-solidity) by [**@mattiaerre**](https://github.com/mattiaerre)
- [`prettier-plugin-svelte`](https://github.com/UnwrittenFun/prettier-plugin-svelte) by [**@UnwrittenFun**](https://github.com/UnwrittenFun)
- [`prettier-plugin-toml`](https://github.com/bd82/toml-tools/tree/master/packages/prettier-plugin-toml) by [**@bd82**](https://github.com/bd82)
- [`prettier-plugin-sh`](https://github.com/rx-ts/prettier/tree/master/packages/sh) by [**@JounQin**](https://github.com/JounQin)

## Developing Plugins

Prettier plugins are regular JavaScript modules with five exports:

- `languages`
- `parsers`
- `printers`
- `options`
- `defaultOptions`

### `languages`

Languages is an array of language definitions that your plugin will contribute to Prettier. It can include all of the fields specified in [`prettier.getSupportInfo()`](api.md#prettiergetsupportinfo).

It **must** include `name` and `parsers`.

```js
export const languages = [
  {
    // The language name
    name: "InterpretedDanceScript",
    // Parsers that can parse this language.
    // This can be built-in parsers, or parsers you have contributed via this plugin.
    parsers: ["dance-parse"],
  },
];
```

### `parsers`

Parsers convert code as a string into an [AST](https://en.wikipedia.org/wiki/Abstract_syntax_tree).

The key must match the name in the `parsers` array from `languages`. The value contains a parse function, an AST format name, and two location extraction functions (`locStart` and `locEnd`).

```js
export const parsers = {
  "dance-parse": {
    parse,
    // The name of the AST that
    astFormat: "dance-ast",
    hasPragma,
    locStart,
    locEnd,
    preprocess,
  },
};
```

The signature of the `parse` function is:

```ts
function parse(text: string, parsers: object, options: object): AST;
```

The location extraction functions (`locStart` and `locEnd`) return the starting and ending locations of a given AST node:

```ts
function locStart(node: object): number;
```

_(Optional)_ The pragma detection function (`hasPragma`) should return if the text contains the pragma comment.

```ts
function hasPragma(text: string): boolean;
```

_(Optional)_ The preprocess function can process the input text before passing into `parse` function.

```ts
function preprocess(text: string, options: object): string;
```

### `printers`

Printers convert ASTs into a Prettier intermediate representation, also known as a Doc.

The key must match the `astFormat` that the parser produces. The value contains an object with a `print` function. All other properties (`embed`, `preprocess`, etc.) are optional.

```js
export const printers = {
  "dance-ast": {
    print,
    embed,
    preprocess,
    insertPragma,
    canAttachComment,
    isBlockComment,
    printComment,
    handleComments: {
      ownLine,
      endOfLine,
      remaining,
    },
  },
};
```

#### The printing process

Prettier uses an intermediate representation, called a Doc, which Prettier then turns into a string (based on options like `printWidth`). A _printer_'s job is to take the AST generated by `parsers[<parser name>].parse` and return a Doc. A Doc is constructed using [builder commands](https://github.com/prettier/prettier/blob/main/commands.md):

```js
const { join, line, ifBreak, group } = require("prettier").doc.builders;
```

The printing process works as follows:

1. `preprocess(ast: AST, options: object): AST`, if available, is called. It is passed the AST from the _parser_. The AST returned by `preprocess` will be used by Prettier. If `preprocess` is not defined, the AST returned from the _parser_ will be used.
2. Comments are attached to the AST (see _Handling comments in a printer_ for details).
3. A Doc is recursively constructed from the AST. i) `embed(path: AstPath, print, textToDoc, options: object): Doc | null` is called on each AST node. If `embed` returns a Doc, that Doc is used. ii) If `embed` is undefined or returns a falsy value, `print(path: AstPath, options: object, print): Doc` is called on each AST node.

#### `print`

Most of the work of a plugin's printer will take place in its `print` function, whose signature is:

```ts
function print(
  // Path to the AST node to print
  path: AstPath,
  options: object,
  // Recursively print a child node
  print: (selector?: string | number | Array<string | number> | AstPath) => Doc
): Doc;
```

The `print` function is passed the following parameters:

- **`path`**: An object, which can be used to access nodes in the AST. It’s a stack-like data structure that maintains the current state of the recursion. It is called “path” because it represents the path to the current node from the root of the AST. The current node is returned by `path.getValue()`.
- **`options`**: A persistent object, which contains global options and which a plugin may mutate to store contextual data.
- **`print`**: A callback for printing sub-nodes. This function contains the core printing logic that consists of steps whose implementation is provided by plugins. In particular, it calls the printer’s `print` function and passes itself to it. Thus, the two `print` functions – the one from the core and the one from the plugin – call each other while descending down the AST recursively.

Here’s a simplified example to give an idea of what a typical implementation of `print` looks like:

```js
const {
  builders: { group, indent, join, line, softline },
} = require("prettier").doc;

function print(path, options, print) {
  const node = path.getValue();

  switch (node.type) {
    case "list":
      return group([
        "(",
        indent([softline, join(line, path.map(print, "elements"))]),
        softline,
        ")",
      ]);

    case "pair":
      return group([
        "(",
        indent([softline, print("left"), line, ". ", print("right")]),
        softline,
        ")",
      ]);

    case "symbol":
      return node.name;
  }

  throw new Error(`Unknown node type: ${node.type}`);
}
```

Check out [prettier-python's printer](https://github.com/prettier/prettier-python/blob/034ba8a9551f3fa22cead41b323be0b28d06d13b/src/printer.js#L174) for some examples of what is possible.

#### (optional) `embed`

The `embed` function is called when the plugin needs to print one language inside another. Examples of this are printing CSS-in-JS or fenced code blocks in Markdown. Its signature is:

```ts
function embed(
  // Path to the current AST node
  path: AstPath,
  // Print a node with the current printer
  print: (selector?: string | number | Array<string | number> | AstPath) => Doc,
  // Parse and print some text using a different parser.
  // You should set `options.parser` to specify which parser to use.
  textToDoc: (text: string, options: object) => Doc,
  // Current options
  options: object
): Doc | null;
```

The `embed` function acts like the `print` function, except that it is passed an additional `textToDoc` function, which can be used to render a doc using a different plugin. The `embed` function returns a Doc or a falsy value. If a falsy value is returned, the `print` function is called with the current `path`. If a Doc is returned, that Doc is used in printing and the `print` function is not called.

For example, a plugin that had nodes with embedded JavaScript might have the following `embed` function:

```js
function embed(path, print, textToDoc, options) {
  const node = path.getValue();
  if (node.type === "javascript") {
    return textToDoc(node.javaScriptText, { ...options, parser: "babel" });
  }
  return false;
}
```

#### (optional) `preprocess`

The preprocess function can process the AST from parser before passing into `print` function.

```ts
function preprocess(ast: AST, options: object): AST;
```

#### (optional) `insertPragma`

A plugin can implement how a pragma comment is inserted in the resulting code when the `--insert-pragma` option is used, in the `insertPragma` function. Its signature is:

```ts
function insertPragma(text: string): string;
```

#### Handling comments in a printer

Comments are often not part of a language's AST and present a challenge for pretty printers. A Prettier plugin can either print comments itself in its `print` function or rely on Prettier's comment algorithm.

By default, if the AST has a top-level `comments` property, Prettier assumes that `comments` stores an array of comment nodes. Prettier will then use the provided `parsers[<plugin>].locStart`/`locEnd` functions to search for the AST node that each comment "belongs" to. Comments are then attached to these nodes **mutating the AST in the process**, and the `comments` property is deleted from the AST root. The `*Comment` functions are used to adjust Prettier's algorithm. Once the comments are attached to the AST, Prettier will automatically call the `printComment(path, options): Doc` function and insert the returned doc into the (hopefully) correct place.

#### (optional) `printComment`

Called whenever a comment node needs to be printed. It has the signature:

```ts
function printComment(
  // Path to the current comment node
  commentPath: AstPath,
  // Current options
  options: object
): Doc;
```

#### (optional) `canAttachComment`

```ts
function canAttachComment(node: AST): boolean;
```

This function is used for deciding whether a comment can be attached to a particular AST node. By default, _all_ AST properties are traversed searching for nodes that comments can be attached to. This function is used to prevent comments from being attached to a particular node. A typical implementation looks like

```js
function canAttachComment(node) {
  return node.type && node.type !== "comment";
}
```

#### (optional) `isBlockComment`

```ts
function isBlockComment(node: AST): boolean;
```

Returns whether or not the AST node is a block comment.

#### (optional) `handleComments`

The `handleComments` object contains three optional functions, each with signature

```ts
function(
	// The AST node corresponding to the comment
	comment: AST,
	// The full source code text
	text: string,
	// The global options object
	options: object,
	// The AST
	ast: AST,
	// Whether this comment is the last comment
	isLastComment: boolean
): boolean
```

These functions are used to override Prettier's default comment attachment algorithm. `ownLine`/`endOfLine`/`remaining` is expected to either manually attach a comment to a node and return `true`, or return `false` and let Prettier attach the comment.

Based on the text surrounding a comment node, Prettier dispatches:

- `ownLine` if a comment has only whitespace preceding it and a newline afterwards,
- `endOfLine` if a comment has a newline afterwards but some non-whitespace preceding it,
- `remaining` in all other cases.

At the time of dispatching, Prettier will have annotated each AST comment node (i.e., created new properties) with at least one of `enclosingNode`, `precedingNode`, or `followingNode`. These can be used to aid a plugin's decision process (of course the entire AST and original text is also passed in for making more complicated decisions).

#### Manually attaching a comment

The `util.addTrailingComment`/`addLeadingComment`/`addDanglingComment` functions can be used to manually attach a comment to an AST node. An example `ownLine` function that ensures a comment does not follow a "punctuation" node (made up for demonstration purposes) might look like:

```js
const { util } = require("prettier");

function ownLine(comment, text, options, ast, isLastComment) {
  const { precedingNode } = comment;
  if (precedingNode && precedingNode.type === "punctuation") {
    util.addTrailingComment(precedingNode, comment);
    return true;
  }
  return false;
}
```

Nodes with comments are expected to have a `comments` property containing an array of comments. Each comment is expected to have the following properties: `leading`, `trailing`, `printed`.

<!-- TODO: add a note that this might change in the future -->

The example above uses `util.addTrailingComment`, which automatically sets `comment.leading`/`trailing`/`printed` to appropriate values and adds the comment to the AST node's `comments` array.

The `--debug-print-comments` CLI flag can help with debugging comment attachment issues. It prints a detailed list of comments, which includes information on how every comment was classified (`ownLine`/`endOfLine`/`remaining`, `leading`/`trailing`/`dangling`) and to which node it was attached. For Prettier’s built-in languages, this information is also available on the Playground (the 'show comments' checkbox in the Debug section).

### `options`

`options` is an object containing the custom options your plugin supports.

Example:

```js
options: {
  openingBraceNewLine: {
    type: "boolean",
    category: "Global",
    default: true,
    description: "Move open brace for code blocks onto new line."
  }
}
```

### `defaultOptions`

If your plugin requires different default values for some of Prettier’s core options, you can specify them in `defaultOptions`:

```
defaultOptions: {
  tabWidth: 4
}
```

### Utility functions

A `util` module from Prettier core is considered a private API and is not meant to be consumed by plugins. Instead, the `util-shared` module provides the following limited set of utility functions for plugins:

<!-- prettier-ignore -->
```ts
type Quote = '"' | "'";
type SkipOptions = { backwards?: boolean };
function getMaxContinuousCount(str: string, target: string): number;
function getStringWidth(text: string): number;
function getAlignmentSize(value: string, tabWidth: number, startIndex?: number): number;
function getIndentSize(value: string, tabWidth: number): number;
function skip(chars: string | RegExp): (text: string, index: number | false, opts?: SkipOptions) => number | false;
function skipWhitespace(text: string, index: number | false, opts?: SkipOptions): number | false;
function skipSpaces(text: string, index: number | false, opts?: SkipOptions): number | false;
function skipToLineEnd(text: string, index: number | false, opts?: SkipOptions): number | false;
function skipEverythingButNewLine(text: string, index: number | false, opts?: SkipOptions): number | false;
function skipInlineComment(text: string, index: number | false): number | false;
function skipTrailingComment(text: string, index: number | false): number | false;
function skipNewline(text: string, index: number | false, opts?: SkipOptions): number | false;
function hasNewline(text: string, index: number, opts?: SkipOptions): boolean;
function hasNewlineInRange(text: string, start: number, end: number): boolean;
function hasSpaces(text: string, index: number, opts?: SkipOptions): boolean;
function makeString(rawContent: string, enclosingQuote: Quote, unescapeUnnecessaryEscapes?: boolean): string;
function getNextNonSpaceNonCommentCharacterIndex<N>(text: string, node: N, locEnd: (node: N) => number): number | false;
function isNextLineEmptyAfterIndex(text: string, index: number): boolean;
function isNextLineEmpty<N>(text: string, node: N, locEnd: (node: N) => number): boolean;
function isPreviousLineEmpty<N>(text: string, node: N, locStart: (node: N) => number): boolean;
```

### Tutorials

- [How to write a plugin for Prettier](https://medium.com/@fvictorio/how-to-write-a-plugin-for-prettier-a0d98c845e70): Teaches you how to write a very basic Prettier plugin for TOML.

## Testing Plugins

Since plugins can be resolved using relative paths, when working on one you can do:

```js
const prettier = require("prettier");
const code = "(add 1 2)";
prettier.format(code, {
  parser: "lisp",
  plugins: ["."],
});
```

This will resolve a plugin relative to the current working directory.