prettier-plugin-pegjs

A prettier plugin for formatting Pegjs grammars. You can try it out online in the playground

Intro

Prettier is an opinionated code formatter. It enforces a consistent style by parsing your code and re-printing it with its own rules that take the maximum line length into account, wrapping code when necessary.

This plugin adds support for the Pegjs language to Prettier.

$3

``
Expression = head:Term tail:(_("+"/"-")_ Term) * {
return tail.reduce(function(result, element) {if (element[1] === "+") { return result + element[3]; }
if (element[1] === "-") { return result - element[3]; }
}, head)}
`

$3

`
Expression
= head:Term tail:(_ "+" / "-" _ Term)* {
return tail.reduce(function (result, element) {
if (element[1] === "+") {
return result + element[3];
}
if (element[1] === "-") {
return result - element[3];
}
}, head);
}
`

Install

yarn:

`bash
yarn add --dev prettier prettier-plugin-pegjs


or globally


yarn global add prettier prettier-plugin-pegjs
`

npm:

`bash
npm install --save-dev prettier prettier-plugin-pegjs


or globally


npm install --global prettier prettier-plugin-pegjs
`

Use

$3

If you installed prettier as a local dependency, you can add prettier as a
script in your package.json,

`json
{
"scripts": {
"prettier": "prettier"
}
}
`

and then run it via

`bash
yarn run prettier path/to/grammar.pegjs --write


or


npm run prettier path/to/grammar.pegjs --write
`

If you installed globally, run

`bash
prettier path/to/grammar.pegjs --write
`

$3

This package exposes a standalone.ts that wraps prettier and exports a
printPrettier function that can be called as

`js
printPrettier(YOUR_CODE, {
// example option
tabWidth: 2,
});
`

Options

The standard Prettier options (such as tabWidth) can be used. Additionally,
you may set actionParser to specify how the code inside a Pegjs action is
printed. actionParser can be the parser from any valid Prettier plugin.
It defaults to "babel-ts" for Javascript and Typescript, but it could be set
to a different parser if your actions are written in a different language/dialect.

Development

To make a production build, run

`
npm run build
`

To develop, run

`
npm run watch
`

You can then execute Prettier with

`
prettier --plugin-search-dir=./ ...
`

or

`
prettier --plugin=./build/prettier-plugin-pegjs.js ...
`

and the Pegjs plugin will load from the current directory.

$3

prettier-plugin-pegjs uses a Pegjs grammar (located in grammars/)
to parse Pegjs grammars! This grammar is slightly modified from Pegjs's
official grammar to include delimiters and strings as AST nodes.
For example, the = in Rule = a / b is assigned an AST node.
This is so that prettier-plugin-pegjs can use Prettier's automatic
comment placement algorithm, which searches through the AST and places comments
based on an AST node's start and end position.

prettier-plugin-pegjs uses webpack to dynamically compile imported
Pegjs grammars, so they can be used _like_ native ES6 imports, though
of course they are not.

The plugin is organized as follows:

- prettier-plugin-pegjs.ts This file exports the objects required of a
Prettier plugin.
- standalone.ts This file wraps the Prettier parser and pre-loads
prettier-plugin-pegjs as a plugin.
- grammars/pegjs.peggy The Pegjs grammar that parsers Pegjs/Peggy grammars.
- libs/parser.ts The parser which loads a Pegjs-created parser and creates
an AST from a string.
- libs/printer.ts` Printers take an AST and produce a Doc (the intermediate
format that Prettier uses). This is where most of the details of the plugin lie.