Input Code is not formatted the same as Output

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Current Behavior We’re trying to use parse/generate to read a js config file, modify the config, then write back to the same file. To start I decided to ignore the modification step to verify I could read a config and write it back accurately. This is where we ran into an issue. Formatting and some comments get lost.

I honestly not sure if this is expected, a bug, or I’m missing a critical configuration option. Thanks for the help.

Input code:

module.exports = {
  siteMetadata: {
    title: `Gatsby Default Starter`,
    description: `Kick off your next, great Gatsby project with this default starter. This barebones starter ships with the main Gatsby configuration files you might need.`,
    author: `@gatsbyjs`,
  },
  plugins: [
    `gatsby-plugin-react-helmet`,
    {
      resolve: `gatsby-source-filesystem`,
      options: {
        name: `images`,
        path: `${__dirname}/src/images`,
      },
    },
    `gatsby-transformer-sharp`,
    `gatsby-plugin-sharp`,
    {
      resolve: `gatsby-plugin-manifest`,
      options: {
        name: `gatsby-starter-default`,
        short_name: `starter`,
        start_url: `/`,
        background_color: `#663399`,
        theme_color: `#663399`,
        display: `minimal-ui`,
        icon: `src/images/gatsby-icon.png`, // This path is relative to the root of the site.
      },
    },
    /* this (optional) plugin enables Progressive Web App + Offline functionality */
    // To learn more, visit: https://gatsby.dev/offline
    // 'gatsby-plugin-offline'
  ],
}

What get’s written to a file:

module.exports = {
  siteMetadata: {
    title: `Gatsby Default Starter`,
    description: `Kick off your next, great Gatsby project with this default starter. This barebones starter ships with the main Gatsby configuration files you might need.`,
    author: `@gatsbyjs`
  },
  plugins: [`gatsby-plugin-react-helmet`, {
    resolve: `gatsby-source-filesystem`,
    options: {
      name: `images`,
      path: `${__dirname}/src/images`
    }
  }, `gatsby-transformer-sharp`, `gatsby-plugin-sharp`, {
    resolve: `gatsby-plugin-manifest`,
    options: {
      name: `gatsby-starter-default`,
      short_name: `starter`,
      start_url: `/`,
      background_color: `#663399`,
      theme_color: `#663399`,
      display: `minimal-ui`,
      icon: `src/images/gatsby-icon.png` // This path is relative to the root of the site.

    }
  }]
};

1. Notice the {,[ brackets on the same line and not on a new line.
2. Notice the final 3 lines of comments are missing.

Input Code

• REPL or Repo link if applicable:

const fileLocation = path.join(rootPath, `gatsby-config.js`)
const file = fs.readFileSync(fileLocation).toString()
const currentConfigAST = parse(file)

const configString = generate(currentConfigAST, {
    comments: true,
    compact: false,
    concise: false,
  }).code

fs.writeFile(`gatsby-config-test.js`, configString, err => {
    if (err) throw new Error(`gatsby-config-test.js write error: ${err}`)
  })

Expected behavior/code I would expect these two files to be identical. The brackets on a newline I could probably ignore, but missing comments is definitely not okay for our situation.

Environment

• “@babel/code-frame”: “^7.0.0”, “@babel/core”: “^7.4.3”, “@babel/generator”: “^7.4.0”, “@babel/parser”: “^7.4.3”, “@babel/polyfill”: “^7.0.0”, “@babel/runtime”: “^7.0.0”, “@babel/traverse”: “^7.4.3”,
• Node/npm version: node v10.15.3/npm v6.4.1
• OS: Ubuntu Linux 18.10
• Monorepo: lerna
• How you are using Babel: import

Thanks ya’ll.

[nicolo-ribaudo]

Yeah, comments shouldn’t disappear

[nicolo-ribaudo]

Matching the original formatting is not a goal of Babel. I suggest using recast with Babel if you want to do so.

You can find an example at https://github.com/nicolo-ribaudo/legacy-decorators-migration-utility/blob/master/packages/wrap-legacy-decorators/src/index.js#L105