vue-cli/packages/@vue/cli-service/lib/command-plugins/inspect.js

module.exports = (api, options) => {
  api.registerCommand('inspect', {
    description: 'inspect internal webpack config',
    usage: 'vue-cli-service inspect [...keys]',
    options: {
      '--env': 'specify NODE_ENV (default: development)'
    }
  }, args => {
    api.setEnv(args.env || 'development')

    const stringify = require('javascript-stringify')
    const config = api.resolveWebpackConfig()
    const keys = args._

    let res
    if (keys.length) {
      res = {}
      keys.forEach(key => {
        res[key] = config[key]
      })
    } else {
      res = config
    }

    // TODO improve stringification for loaders, plugins etc.
    console.log(stringify(res, null, 2))
  })
}