@megalo/entry/lib/extract-config.js

解析配置在 `main.js` 或者 `App.vue` 中的 [小程序全局配置](https://developers.weixin.qq.com/miniprogram/dev/framework/config.html#%E5%85%A8%E5%B1%80%E9%85%8D%E7%BD%AE)并生成webpack所需要的entry键值对

const babelon = require('babelon')
const generate = require('babel-generator').default

module.exports = function ({ types: t }) {
  return {
    visitor: {
      ExportDefaultDeclaration (path) {
        path.node.declaration.properties.forEach(prop => {
          if (
            t.isObjectProperty(prop) &&
            t.isIdentifier(prop.key, { name: 'config' })
          ) {
            const code = generate(prop.value).code

            path.hub.file.metadata.config = {
              code: code,
              node: prop.value,
              value: babelon.eval(code)
            }
          }
        })

        path.remove()
      }
    }
  }
}