Introduction

What?

This Prettier plugin (namely prettier-plugin-embed) provides a configurable solution for formatting embedded languages in the form of template literals within JavaScript or TypeScript files.

Why?

Prettier has introduced an option for formatting embedded languages, named embedded-language-formatting. However, this option only offers two modes: auto and off. This limits its functionality, as it does not permit individual formatting adjustments for specific languages. Additionally, it lacks support for customizing which languages require formatting, as well as specifying block comments or tags for embedded language identification. These constraints hinder the feature's overall usability. For in-depth discussions on this matter, see the GitHub issues: prettier/prettier#4424 and prettier/prettier#5588.

How?

By leveraging Prettier's plugin system, this plugin overrides the default embed function of the estree printer, so varieties of new languages can be hooked in through this function. Check this file to get an idea of how this is accomplished.

Features

• Support for Additional Languages: Extend the embedded language formatting capability to include languages such as XML, SQL, PHP, and more.

• Dual Identification Modes: Identify embedded languages by block comments /* comment */ `...` or tags tag`...` preceding the template literals.

• Customizable Language Comments or Tags: Customize the comments or tags used for identifying the embedded languages.

• Formatting Opt-out Mechanism: Offer the capability to deactivate formatting for certain comments or tags, including the built-in ones (html, css...) supported by the embedded-language-formatting option.

• Configurable Formatting Style: Provide additional options to tailor the formatting style for embedded languages.

• Strongly Typed API: Benefit from comprehensive type support for configuring this plugin's options.

• Easy Integration: Integrate with the existing Prettier setup seamlessly, requiring minimal configuration to get started.

Installation

npm i -D prettier-plugin-embed

Usage

Getting Started

This is a Prettier plugin, which follows the standard usage pattern of many other Prettier plugins:

CLI:

Via --plugin:

prettier --write main.ts --plugin=prettier-plugin-embed

API:

Via the plugins options:

await prettier.format(code, {
  filepath: "main.ts",
  plugins: ["prettier-plugin-embed"],
});

Configuration File:

{
  "plugins": ["prettier-plugin-embed"]
}

Quick Start Config Examples

Here're some quick start config examples to use this plugin for various embedded languages. Check beblow for a detailed explanation of all the available options.

An Overview of the Philosophy

To use this plugin, embedded-language-formatting option must be set to auto (which is the default setting as of now), because this option serves as the main switch for activating embedded language formatting.

This plugin does not aim to implement parsers or printers to support every newly added embedded language. Rather, it aims to leverage existing Prettier plugins for those languages, and only adds a thin layer of formatting support when they are embedded in template literals.

Therefore, to enable formatting for a specific embedded language, the corresponding Prettier plugin for that language must also be loaded. For example, if you wish to format embedded XML language, you will need to load both this plugin and @prettier/plugin-xml. To find out which other plugins are required when using this plugin, please refer to the Language-Specific Options section below.

Embedded languages to be formatted are required to be enclosed in the template literals, and are identified by the preceding block comments /* comment */ `...` or tags tag`...`. This plugin comes pre-configured with a built-in set of comments and tags for identifying various embedded languages. For instance, using comments like /* xml */ or /* svg */ or tags like xml or svg will trigger automatic formatting for the embedded XML language. You can specify an alternative list of comments or tags using the embeddedXmlComments option or the embeddedXmlTags option, respectively. The naming convention for these options follows the pattern of embedded<Language>Comments and embedded<Language>Tags for other languages as well. Further details on these options and how to configure them are also available in the Language-Specific Options section.

To exclude certain comments or tags from being identified, like the default ones supported by the embedded-language-formatting option, add them to the list of the embeddedNoopComments/embeddedNoopTags options. Any matching comments or tags listed in these options will take precedence over other embedded<Language>Comments and embedded<Language>Tags options, effectively disabling their formatting.

[!IMPORTANT]

Until this notice is removed, always specify comments or tags explicitly and do not rely on the built-in defaults, as they may be subject to change.

Language-Specific Options

Supported embedded languages are:

• CSS
• ES (ECMAScript/JavaScript)
• GLSL
• GraphQL
• HTML
• INI
• Java
• JSON
• JSONata
• LaTeX
• Markdown
• NGINX
• Pegjs
• PHP
• Prisma
• Properties
• Pug
• Ruby
• Sh (Shell)
• SQL
• TOML
• TS (TypeScript)
• XML
• YAML

Language-Agnostic Options

Language-Agnostic

noEmbeddedIdentificationByComment

noEmbeddedIdentificationByTag

preserveEmbeddedExteriorWhitespaces

• Type: string[]
• Default: []
• Description: Preserves leading and trailing whitespaces in the formatting results for the specified comments or tags.

noEmbeddedMultiLineIndentation

• Type: string[]
• Default: []
• Description: Turns off auto indentation in the formatting results for the specified comments or tags when they are formatted to span multi lines.

embeddedOverrides

• Type: string
• Default: undefined
• Description: Option overrides for the specified comments or tags. It should either be a stringified JSON or an absolute filepath to the option overrides file. See below for a detailed explanation.

embeddedOverrides

This option is provided for users to override certain options based on comments or tags. Due to the lack of support for using objects in prettier plugin options (https://github.com/prettier/prettier/issues/14671), it accepts a stringified json string, or a file path with an extension of .json, .jsonc, .js, .cjs, .mjs, .ts, .cts or .mts as its value. If no extension is provided, it will be treated as a .json/.jsonc file. For relative paths, it will automatically figure out the prettier config location and use that as the base path.

[!NOTE]

The support for using .ts, .mts or .cts files for embeddedOverrides requires a minimal node version of 18.19.0, and tsx as a dependency in your project. And it currently doesn't work with the Prettier VSCode extension.

The resolved value should be an array of objects. Each object in the array must have 2 fields: comments and options, or tags and options. The options are considerred overrides that will be applied to the global options of prettier for those comments and tags only. It's like the overrides of prettier, but it is comment/tag-based instead of file-based.

In a json file, the root is the array of objects. In a JavaScript/TypeScript file, the array of objects should be a default export, or a named export with the name embeddedOverrides.

An example .json/.jsonc file is:

[
  {
    "comments": ["sql"],
    "options": {
      "keywordCase": "lower"
    }
  },
  {
    "tags": ["mysql"],
    "options": {
      "keywordCase": "upper"
    }
  }
]

[!CAUTION]

Please note that not every option is supported to override. That largely depends on at which phase those options will kick in and take effect. For example, you can't override tabWidth in embeddedOverrides because this option is used in the printDocToString phase, where prettier-plugin-embed cannot override this option for only a set of specified comments or tags. To find the list of unsupported options, please check the interface definition of EmbeddedOverride in the source code.

Typed Options

There're several ways to use the typed options provided by this plugin. Taking the embedded SQL language as an example:

• Augment the Options type from Prettier to use plugin-specific options

  Register options from prettier-plugin-embed (this plugin):

  /// <reference types="prettier-plugin-embed/plugin-embed" />

  Register options from prettier-plugin-sql:

  /// <reference types="prettier-plugin-embed/embedded/sql/plugin-sql" />

  Other embedded languages share the same pattern:

  /// <reference types="prettier-plugin-embed/embedded/<language>/<(no prettier or scope) plugin name>" />

• Import plugin-specific options

  Import options from prettier-plugin-embed (this plugin):

  import type { PluginEmbedOptions } from "prettier-plugin-embed";

  Import options from prettier-plugin-sql:

  import type { PluginSqlOptions } from "prettier-plugin-embed/embedded/sql/plugin-sql-types";

  NOTE: You can also import the types from the prettier-plugin-sql plugin directly. However, not all of the plugins provide types, or provide them in a predictable way, so this plugin exports them in a more unified manner.

  Other embedded languages share the same pattern:

  import type { Plugin<Language>Options } from "prettier-plugin-embed/embedded/<language>/<(no prettier or scope) plugin name>-types";

• Use JSDoc in JavaScript files

  /**
  * @type {import("prettier-plugin-embed").PluginEmbedOptions}
  */
  const pluginEmbedOptions = {
  embeddedSqlTags: ["sql"],
  };
  
  /**
  * @type {import("prettier-plugin-embed/embedded/sql/plugin-sql-types").PluginSqlOptions}
  */
  const pluginSqlOptions = {
  language: "postgresql",
  keywordCase: "upper",
  };

Contributing

Bug fixes, new language support and tests are welcome. Please have a look at the project structure before getting started. Feel free to leave questions or suggestions.

Contributors

Karl Horky 💻 📖

Kelvin Soh 💻

License

MIT