create-react-app 修改为多入口编译的方法

- project
  - build
  - config
  - public
  - scripts
  - src
    - api
    - component
    - site
      - site1
        - index.html
        - index.js
        - ...
      - site2
        - index.html
        - index.js
        - ...
  - package.json

// all site paths
function allSitePath(source) {
 const { lstatSync, readdirSync } = fs
 const { join } = path
 const result = {}
 const isDirectory = source => lstatSync(source).isDirectory()
 readdirSync(source).map(name => {
  let path = join(resolveApp(source), name)
  if (isDirectory(path)) result[name] = path
 })
 return result
}

module.exports = {
 ...
 allSites: allSitePath('src/site'),
}

// 动态生成 entry
const entry = {}
Object.keys(paths.allSites).forEach(item => {
 entry[item] = [
  require.resolve('./polyfills'),
  require.resolve('react-dev-utils/webpackHotDevClient'),
  require.resolve('react-error-overlay'),
  paths.allSites[item]
 ]
})

module.exports = {
 ...
 entry: entry,
 ...
}

module.exports = {
 ...
 output: {
  path: paths.appBuild,
  pathinfo: true,
  filename: 'static/js/[name].bundle.js',
  chunkFilename: 'static/js/[name].chunk.js',
  publicPath: publicPath,
  devtoolModuleFilenameTemplate: info =>
   path.resolve(info.absoluteResourcePath).replace(/\\/g, '/'),
 },
 ...
} 

// 动态生成 plugins
const plugins = []
Object.keys(paths.allSites).forEach(item => {
 plugins.push(new HtmlWebpackPlugin({
  inject: true,
  chunks: [item],
  template: `${paths.allSites[item]}/index.html`,
  filename: `${item}/index.html`,
 }))
})

module.exports = {
 ...
 plugins: [
  ...
 ].concat(plugins),  
 ...
}

const rewrites = []
Object.keys(paths.allSites).forEach(item => {
 rewrites.push({
  from: new RegExp(`^\\/${item}/`, 'i'),
  to: `/${item}/index.html`,
 })
})

...

module.exports = function(proxy, allowedHost) {
 return {
  ...
  historyApiFallback: {
   // Paths with dots should still use the history fallback.
   // See https://github.com/facebookincubator/create-react-app/issues/387.
   disableDotRule: true,
   // 指明哪些路径映射到哪个html
   rewrites: rewrites,
  },
  ...
 };
};