A small babel transform to switch `getStaticProps` to `getServerProps` in nextjs

transform.js

// getStaticProps, which we use as the primary method for data fetching on all our pages,
// runs at build time and generates page data statically. this data is not regenerated
// unless the site is rebuilt, a lot like a static site generator. therefore, it's not
// helpful when you are trying to live preview content changes without rebuilding the entire
// site, even though its great for performance in production.
//
// In order to solve this, we run this script before pushing the preview version of the website,
// which replaces `getStaticProps` with `getServerProps`, a method with the same signature that
// dynamically fetches data fresh on every page load, making it excellent for fast-changing data,
// which is just what we need for a preview environment.
//
// The nextjs team is working on a "next-native" solution to the preview content problem, as
// soon as this is released we will remove this script and shift our code into the native solution.
// The result may look something like returning { props: { foo: 'bar' }, preview: true } from
// getStaticProps.

const babel = require('@babel/core')
const glob = require('glob')
const path = require('path')
const fs = require('fs')
const prettier = require('prettier')

glob(
  `${path.join(__dirname, '../pages')}/**/*.+(jsx|tsx)`,
  {},
  (err, files) => {
    if (err) throw err
    files.map(file => {
      babel.transformFile(file, babelConfig, (err, result) => {
        if (err) throw err
        fs.writeFile(
          file,
          prettier.format(result.code, {
            parser: file.match(/\.tsx$/) ? 'typescript' : 'babel',
            semi: false,
            singleQuote: true
          }),
          'utf8',
          () => console.log(`Transformed: ${file}`)
        )
      })
    })
  }
)

const babelConfig = {
  plugins: [
    ['@babel/plugin-syntax-typescript', { isTSX: true }],
    '@babel/plugin-syntax-jsx',
    '@babel/plugin-syntax-dynamic-import',
    staticToServerPropsPlugin
  ]
}

function staticToServerPropsPlugin({ types: t }) {
  return {
    visitor: {
      FunctionDeclaration(_path) {
        if (_path.node.id.name === 'unstable_getStaticProps') {
          _path.node.id = t.identifier('unstable_getServerProps')
          _path.replaceWith(_path)
        }
      }
    }
  }
}