breaking: change to webpack 5

[lwr]

drop compatibility for webpack 1~4 and then rollup version to 2

about defer and stage options

1. by defaults plugin run at processAssets phase in stage PROCESS_ASSETS_STAGE_DEV_TOOLING (that is, after all optimizations liked CssMinimizerPlugin done)
   • new options.stage added for precise controlling
2. if options.defer is true, then the plugin will run in afterProcessAssets phase

known problems

ref webpack-contrib/mini-css-extract-plugin#256, now css-split-webpack-plugin can not work with mini-css-extract-plugin (even in webpack 4) for async chunks, there are tow workarounds

1. use option {imports: true}
2. or add stylesheet links staticcally and patch to remove __webpack_require__.f.miniCss

   config = {
       // ...
       plugins: [
           new MiniCssExtractPlugin({/* ... */}),
           {   // remove `__webpack_require__.f.miniCss`
               apply(compiler) {
                   compiler.hooks.thisCompilation.tap('remove require.f.miniCss', compilation => {
                       compilation.hooks.afterRuntimeRequirements.tap('remove require.f.miniCss', () => {
                           [...compilation.modules].find(x => x.name === 'css loading').generate = () => null;
                       });
                   });
               },
           },
           new CSSSplitWebpackPlugin(),
       ]
   }

simple example to demonstrate this issue

// index.js
// using dynamic import to split chunk
import('./index.less')

now we must config the plugin with {imports: true} to avoid chunk load problem

[yibn2008]

@lwr Great job! I'll review your PR in the next few days.

[aleen42]

@yibn2008 Any progress?

[yibn2008]

v2.0.0 released