webpack source code - webpack compiles react into weapp

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perkz
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    introduction

    webpack @5.69.0
    Before using taro@3.5.5 to create a taro-react project and then build a weapp project

    编译.png

    The last step is to enable webpack and compile the react code into weapp

    webpack entry

    The entry file can be found in package.json . The function of this file is to introduce webpack核心函数 (lib/webpack.js) and tool files, and throw out the sorted webpack core functions

     "main": "lib/index.js",

    1. Final output:

       // lib/index.js
// mergeExports是处理fn的，最后输出的就是结果处理的fn
module.exports = mergeExports(fn, {
 // 很多webpack内置插件
 get webpack() {
     return require("./webpack"); // 核心文件
 },
 ......
})

    2. mergeExports

       // lib/index.js
// 第一个参数是对象（函数继承于Fuction，Fuction继承于Object）
const mergeExports = (obj, exports) => {
 // 克隆exports对象，传入这个对象里有很多的文件的引入
 const descriptors = Object.getOwnPropertyDescriptors(exports);
 // 遍历这个对象
 for (const name of Object.keys(descriptors)) {
     const descriptor = descriptors[name];
     if (descriptor.get) {
         const fn = descriptor.get;
         // 遍历出的属性一个个添加getter到传入的webpack函数
         Object.defineProperty(obj, name, {
             configurable: false,
             enumerable: true,
             /**
               * memoize就是执行了传入的fn返回一个返回执行之后的结果的一个函数
               * memoize(fn)等于
               * function(){
               *   return fn();
               * } 
               */
             get: memoize(fn)
         });
     } else if (typeof descriptor.value === "object") {
         Object.defineProperty(obj, name, {
             configurable: false,
             enumerable: true,
             writable: false,
             value: mergeExports({}, descriptor.value) // 递归
         });
     } else {
         throw new Error(
             "Exposed values must be either a getter or an nested object"
         );
     }
 }
 // 返回了一个冻结之后的对象，这个对象是个函数，函数里面有很多添加进去的属性方法
 return /** @type {A & B} */ (Object.freeze(obj)); 
};

      Printing descriptor can get the following

       {
  get: [Function: get webpack],
  set: undefined,
  enumerable: true,
  configurable: true
}
...
{
  value: {
 ModuleDependency: [Getter],
 ConstDependency: [Getter],
 NullDependency: [Getter]
  },
  writable: true,
  enumerable: true,
  configurable: true
}
...

    3. fn:

       // lib/index.js
// fn懒加载出来的webpack核心函数
const fn = lazyFunction(() => require("./webpack"));

    4. lazyFunction: Here we can know how webpack核心函数（lib/webpack） accepts parameters

       // lib/index.js
const lazyFunction = factory => {
 // 和mergeExports一样返回一个返回执行了factory后的函数
 const fac = memoize(factory); // fac函数一个函数
 const f = (
     // 这里args就是我们传入的webpack配置参数
     (...args) => {
        /** 
          * fac() 等于 factory()
          * fac()(...args) 等于 factory()(...args)
          * factory 等于 () => require("./webpack")
          * require("./webpack")(...args)
          */
         return fac()(...args); 
     }
 );
 return (f);// 最后返回f这个函数，在mergeExports里getter添加之后作为入口抛出，在前端工程化项目中webpack启动器里传入webpack配置参数执行
};

    webpack.js

    lib/webpack.js
    Throws the compiler (compiles the compiler if there is a callback)

    1. webpack method main method, throws the compiler compiler (compiler is executed if there is a callback)
      options is a webpack configuration object or an array of configuration objects, the callback function callback , if there is callback it can be compiled directly here, if not, it needs to be called externally compiler.run()
      In the packages/taro-webpack5-runner/src/index.mini.ts of "build a weapp" const compiler = webpack(webpackConfig) no transmission callback only transmission webpack配置 ， It happens to be called in the webpack launcher run、watch、close method

       // lib/webpack.js
const webpack = (options, callback) => {
 // create返回一个对象对象里有编译器、是否监听、监听参数
 const create = () => {
     // options作为数组然后用webpackOptionsSchemaCheck校验参数
     if (!asArray(options).every(webpackOptionsSchemaCheck)) { // false
        ...
     }
     let compiler; // MultiCompiler多个编译器或Compiler单个编译器
     let watch = false; // 是否热更新监听，只要有一个webpack配置是热更新就监听
     let watchOptions; // 热更新监听的参数可以是对象也可以是个对象数组
     if (Array.isArray(options)) {
         compiler = createMultiCompiler(options,options);
         watch = options.some(options => options.watch);
         watchOptions = options.map(options => options.watchOptions || {});
     } else {
         const webpackOptions = options;
         compiler = createCompiler(webpackOptions);
         watch = webpackOptions.watch;
         watchOptions = webpackOptions.watchOptions || {};
     }
     return { compiler, watch, watchOptions };
 };
 if (callback) {
     try {
         const { compiler, watch, watchOptions } = create();
         if (watch) {
             // 开始监听
             compiler.watch(watchOptions, callback);
         } else {
             // 开始编译
             compiler.run((err, stats) => {
                 compiler.close(err2 => {
                     callback(err || err2, stats);
                 });
             });
         }
         // 抛出编译器
         return compiler;
     } catch (err) {
         process.nextTick(() => callback(err));
         return null;
     }
 } else {
     const { compiler, watch } = create();
     if (watch) {
         util.deprecate(
             () => {},
             "A 'callback' argument needs to be provided to the 'webpack(options, callback)' function when the 'watch' option is set. There is no way to handle the 'watch' option without a callback.",
             "DEP_WEBPACK_WATCH_WITHOUT_CALLBACK"
         )();
     }
     // 抛出编译器
     return compiler;
 }
};

    2. createCompiler Create a compiler

       // 参数就是webpack配置参数对象
const createCompiler = rawOptions => {
 // 把webpack配置参数标准化
 const options = getNormalizedWebpackOptions(rawOptions);
 // 基础参数的初始化
 applyWebpackOptionsBaseDefaults(options);
 // 实例化Compiler编译器
 const compiler = new Compiler(options.context, options);
 // 拓展compiler，添加对文件的输入缓存、监听、输出、注册beforeRun钩子
 new NodeEnvironmentPlugin({
     infrastructureLogging: options.infrastructureLogging
 }).apply(compiler);
 // 注册plugin插件this指向编译器compiler
 if (Array.isArray(options.plugins)) {
     for (const plugin of options.plugins) {
         if (typeof plugin === "function") {
             plugin.call(compiler, compiler);
         } else {
             // packages/taro-webpack5-runner/src/plugins/MiniPlugin.ts
             // 插件入口 TaroMiniPlugin.apply(compiler)，这里会调用编译器里的compilation.addEntry、compilation.dependencyFactories
             plugin.apply(compiler); 
         }
     }
 }
 // 基础参数的初始化
 applyWebpackOptionsDefaults(options);
 // 执行environment钩子和afterEnvironment钩子
 compiler.hooks.environment.call(); // 获取环境信息
 compiler.hooks.afterEnvironment.call(); // 获取环境信息之后
 // 根据不同的环境不同的平台等等注册内置插件，多个hook的tag挂载
 new WebpackOptionsApply().process(options, compiler);
 // 执行initialize钩子
 compiler.hooks.initialize.call(); // 初始化
 return compiler;
};

    Note: The following is a brief introduction of related functions and classes in createCompiler :

    1. applyWebpackOptionsBaseDefaults Initialization of basic parameters<br>Initialization of standard webpack configuration parameters context and infrastructureLogging

       const applyWebpackOptionsBaseDefaults = options => {
 // context设置，如果options.context是undefined，options.context就等于项目路径
 F(options, "context", () => process.cwd());
 // 日志输出格式设置
 applyInfrastructureLoggingDefaults(options.infrastructureLogging);
};

    2. applyWebpackOptionsDefaults Initialization of basic parameters<br>Initialization of standard webpack configuration parameters context、target、devtool...

       const applyWebpackOptionsDefaults = options => {
  ...
};

    3. NodeEnvironmentPlugin Expand compiler, add input cache, monitor, output, and register beforeRun hooks for files

       class NodeEnvironmentPlugin {
 constructor(options) {
     this.options = options; // webpack配置参数标准化
 }

 apply(compiler) {
     // infrastructureLogging：日志输出格式设置
     const { infrastructureLogging } = this.options;
     // 日志打印器ConsoleLogger打印器
     compiler.infrastructureLogger = createConsoleLogger({
       ...
     });
     // 输入缓存文件操作
     compiler.inputFileSystem = new CachedInputFileSystem(fs, 60000);
     // 输入文件系统
     const inputFileSystem = compiler.inputFileSystem;
     // 输出文件系统，挂载到compiler对象（graceful-fs就是对node原生fs做了一层封装本质还是node的fs）
     compiler.outputFileSystem = fs;
     compiler.intermediateFileSystem = fs;
     // 监听文件系统，挂载到compiler对象
     compiler.watchFileSystem = new NodeWatchFileSystem(
         compiler.inputFileSystem
     );
     // 注册beforeRun钩子 在执行compiler.run前执行
     compiler.hooks.beforeRun.tap("NodeEnvironmentPlugin", compiler => {
         if (compiler.inputFileSystem === inputFileSystem) {
             compiler.fsStartTime = Date.now();
             inputFileSystem.purge(); // 清除缓存
         }
     });
 }
}

    4. WebpackOptionsApply Register built-in plugin

       class WebpackOptionsApply extends OptionsApply {
 constructor() {
     super();
 }
 process(options, compiler) {
    // 注册内置插件
    ...
    new ExternalsPlugin(...).apply(compiler); // web 配置外部文件的模块加载
    new ChunkPrefetchPreloadPlugin().apply(compiler);
    new ArrayPushCallbackChunkFormatPlugin().apply(compiler);
    new EnableChunkLoadingPlugin(type).apply(compiler);
    new EnableWasmLoadingPlugin(type).apply(compiler);
    ...
    // 执行完成注册内置插件钩子
    compiler.hooks.afterPlugins.call(compiler);
    ...
    compiler.hooks.afterResolvers.call(compiler);
 }
}

    [Plugins].apply

    Take MiniPlugin as an example
    node_modules/@tarojs/webpack5-runner/dist/plugins/MiniPlugin.js
    We said above that in lib/webpack.js called MiniPlugin.apply , here we register multiple hooks

     // 插件入口
apply (compiler: Compiler) {
   ...
    // 配置获取入口文件路径
   this.appEntry = this.getAppEntry(compiler)
   ...
   // 注册钩子run， lib/Compiler.js的run中使用也就是在开始编译的时候只用
   compiler.hooks.run.tapAsync(
     ...
   )
   // 注册钩子watchRun lib/Watching.js里使用用于监听文件改变重新注册run钩子
   compiler.hooks.watchRun.tapAsync(
     ...
   ）
   // 注册钩子make，lib/Compiler.js的compile里使用
   compiler.hooks.make.tapAsync(
     ...
   )
   // 注册钩子compilation，lib/Compiler.js的new Compilation后执行
   compiler.hooks.compilation.tap(
     ...
   )
   // 注册钩子afterEmit
   compiler.hooks.afterEmit.tapAsync(
     ...
   ）
   // 实例化TaroNormalModulesPlugin并调用apply
   new TaroNormalModulesPlugin(this.options.onParseCreateElement).apply(compiler)
}

    Hook registration and use

    Take this.hooks.make.callAsync as an example

    1. AsyncParallelHook asynchronous hook

       AsyncParallelHook

    2. call hook

       // lib/Compiler.js的compile里
this.hooks.make.callAsync(compilation, () => {...})

    3. instantiate hook

       // lib/Compiler.js的constructor里初始化
this.hooks = Object.freeze({
   ...
   // 传入了要执行的钩子compilation，实例化异步钩子AsyncParallelHook
   make: new AsyncParallelHook(["compilation"]), 
   ...
})

    4. AsyncParallelHook async hook

       // node_modules/tapable/lib/AsyncParallelHook.js
function AsyncParallelHook(args = [], name = undefined) {
 // args = ["compilation"]
 const hook = new Hook(args, name); // 实例化一个钩子
 hook.constructor = AsyncParallelHook;
 // 重写hook.compile
 hook.compile = COMPILE;
 hook._call = undefined;
 hook.call = undefined;
 // 返回hook可以在第一步hook.callAsync(compilation, () => {...})执行
 return hook;
}

    5. hook.callAsync

       // node_modules/tapable/lib/Hook.js
constructor(args = [], name = undefined) {
  ...
  this.callAsync = CALL_ASYNC_DELEGATE;
  ...
}

    6. CALL_ASYNC_DELEGATE

       // node_modules/tapable/lib/Hook.js
const CALL_ASYNC_DELEGATE = function(...args) {
 this.callAsync = this._createCall("async"); // this执行Hooks，创建一个异步
 return this.callAsync(...args); // 执行异步并返回结果
};

    7. _createCall

       // node_modules/tapable/lib/Hook.js
 _createCall(type) {
     // 执行this.compile，this.compile在AsyncParallelHook重写为COMPILE
     return this.compile({
         taps: this.taps,
         interceptors: this.interceptors,
         args: this._args,
         type: type // "async"
     });
 }

    8. COMPILE

       // node_modules/tapable/lib/AsyncParallelHook.js
const factory = new AsyncParallelHookCodeFactory(); // 用于创建函数体
const COMPILE = function(options) {
 factory.setup(this, options); // 收集函数this指向Hook
 return factory.create(options); // 创建函数体
};
       setup(instance, options) {
     instance._x = options.taps.map(t => t.fn);
 }

    9. AsyncParallelHookCodeFactory Basic HookCodeFactory Hook function to create factory asynchronously

       // node_modules/tapable/lib/HookCodeFactory.js
create(options) {
  ...
  let fn;
  // 在5中this._createCall("async")，_createCall里又把"async"作为type传给this.compile
  // 这里的this.options.type = "async"
  switch (this.options.type) {
     ...
     case "async":
        fn = new Function(
             this.args({after: "_callback"}), // 结尾加一个_callback参数
             '"use strict";\n' + this.header() +
              this.contentWithInterceptors({
                 onError: err => `_callback(${err});\n`,
                 onResult: result => `_callback(null, ${result});\n`,
                 onDone: () => "_callback();\n"
              }) // 创建一个异步函数体
           );   
      break;
      ...    
  }
return fn
}

    10. The created function body fn

       // CALL_ASYNC_DELEGATE执行this.callAsync(...args)也就睡fn(compilation, () => {})
 function fn(compilation, _callback) {
     "use strict";
     var _context;
     var _x = this._x; // 5. COMPILE收集到的fn（this指向Hook）
     var _taps = this.taps;
     var _interceptors = this.interceptors; 
     _interceptors[0].call(compilation);
     var _fn0 = _x[0]; // 收集的第一个fn执行
     _fn0(compilation, (function (_err0) {
         if (_err0) {
             _callback(_err0);
         } else {
             _interceptors[0].done(); // ProgressPlugin进度条完成完成
             _callback();
         }
     }));
 }

      options printing this is incoming compilation , also executing taps[0].fn(compilation, () => {})

       {
  taps: [
     {
       type: 'async',
       fn: [Function (anonymous)],
       name: 'TaroMiniPlugin' // 从taro项目转入的插件
     }
  ],
  interceptors: [
     {
       name: 'ProgressPlugin', // 进度条
       call: [Function: call],
       done: [Function: done]
     }
  ],
  args: [ 'compilation' ],
  type: 'async'
}

    11. apply
      taps怎么来，MiniPlugin的apply里compiler.hooks.make.tapAsync cceef557485bc6e1a586d5644d8fac89---钩子生成tags ， apply createCompiler （lib/ webpack.js) called

       //node_modules/@tarojs/webpack5-runner/dist/plugins/MiniPlugin.js
apply (compiler: Compiler) {
  ...
  compiler.hooks.make.tapAsync( // tapAsync
   PLUGIN_NAME,
   this.tryAsync<Compilation>(async compilation => {
     const dependencies = this.dependencies
     const promises: Promise<null>[] = []
     this.compileIndependentPages(compiler, compilation, dependencies, promises)
     dependencies.forEach(dep => {
       promises.push(new Promise<null>((resolve, reject) => {
         compilation.addEntry(this.options.sourceDir, dep, {
           name: dep.name,
           ...dep.options
         }, err => err ? reject(err) : resolve(null))
       }))
     })
     await Promise.all(promises)
     await this.options.onCompilerMake?.(compilation)
   })
 )
...
}

    12. Hooks.tapAsync register hook <br>call tapAsync back to node_modules/tapable/lib/Hook.js

       node_modules/tapable/lib/Hook.js
// 传入的参数options, fn，options = 'TaroMiniPlugin'，fn就是上面那个this.tryAsync(...)的结果，结果也是tags里的fn
tapAsync(options, fn) {
 this._tap("async", options, fn);
}
       // node_modules/tapable/lib/Hook.js
_tap(type, options, fn) {
 if (typeof options === "string") {
     options = {
         name: options.trim() //添加name
     };
 } ... 
 if (typeof options.context !== "undefined") {
     deprecateContext();
 }
 options = Object.assign({ type, fn }, options);// 添加fn，type以及options里的其他值，fn这里就是我们最终的tags
 options = this._runRegisterInterceptors(options);
 this._insert(options);// 把钩子注册到taps
}
       // 注册成这样
[
  {
     type: 'async',
     fn: [Function (anonymous)],
     name: 'TaroMiniPlugin'
  }
]

      Summarize:
      (1) It is through the tapAsync、tap、tapPromise registration hook,
      (2) Execute the hook through callAsync、call、callPromise (3) Execute the registration fn is this.tryAsync(...)(compilation, () => {})

    Compiler

    lib/Compiler.js will output the compiled file
    The main engine of ---8739de4645d74e0e72770e76d2da4ebf webpack , at compiler object records complete webpack environment information, at webpack end from startup to 5 compiler afcc024e1695 compiler will only be generated once. You can read the webpack config information on the compiler object, outputPath etc.

     class Compiler {
    constructor(context, options = ({})) {
       super();
       this.hooks = Object.freeze({
          initialize: new SyncHook([]),
          shouldEmit: new SyncBailHook(["compilation"]),
          ...
       });
       this.webpack = webpack;
       ...
    }
    watch(watchOptions, handler) { ... }
    run(callback) { ... }
    purgeInputFileSystem() { ... }
    compile(callback) { ... }
    close(callback) { ... }
    ...    
}

    1. run

       run(callback) {
     // 重复执行报错
     if (this.running) {
         return callback(new ConcurrentCompilationError());
     }

     let logger; // 日志打印
     // 结束回调（无论执行成功还是失败）
     const finalCallback = (err, stats) => {
         ...
     };
     // 此刻时间
     const startTime = Date.now();
     // 执行过了将running变为true，用于判断是否重复执行
     this.running = true;
     const onCompiled = (err, compilation) => {
         ...
     };
     // 执行
     const run = () => {
         this.hooks.beforeRun.callAsync(this, err => {
             if (err) return finalCallback(err);

             this.hooks.run.callAsync(this, err => {
                 if (err) return finalCallback(err);

                 this.readRecords(err => {
                     if (err) return finalCallback(err);
                     // 传入onCompiled，this.compile继续执行
                     this.compile(onCompiled);
                 });
             });
         });
     };

     if (this.idle) {
         this.cache.endIdle(err => {
             if (err) return finalCallback(err);
             this.idle = false;
             run();
         });
     } else {
         run();
     }
 }

    2. compile Compiling done

       compile(callback) {
     //  参数是：普通模块工厂normalModuleFactory、上下文模块工厂contextModuleFactory
     const params = this.newCompilationParams();
     // 异步调用beforeCompile钩子
     this.hooks.beforeCompile.callAsync(params, err => {
         if (err) return callback(err);
         // 调用compile钩子
         this.hooks.compile.call(params);
         // 获取一个编译器Compilation！！！！！！
         const compilation = this.newCompilation(params);

         const logger = compilation.getLogger("webpack.Compiler");

         logger.time("make hook");
         // 入口文件开始，构建模块，直到所有模块创建结束
         // 执行make钩子会调用compilation上的addEntry
         this.hooks.make.callAsync(compilation, err => {
             logger.timeEnd("make hook");
             if (err) return callback(err);

             logger.time("finish make hook");
             this.hooks.finishMake.callAsync(compilation, err => {
                 logger.timeEnd("finish make hook");
                 if (err) return callback(err);

                 process.nextTick(() => {
                     logger.time("finish compilation");
                     // 编译完成
                     compilation.finish(err => {
                         logger.timeEnd("finish compilation");
                         if (err) return callback(err);

                         logger.time("seal compilation");
                         compilation.seal(err => {
                             logger.timeEnd("seal compilation");
                             if (err) return callback(err);

                             logger.time("afterCompile hook");
                             // 异步调用afterCompile，返回回调函数
                             this.hooks.afterCompile.callAsync(compilation, err => {
                                 logger.timeEnd("afterCompile hook");
                                 if (err) return callback(err);
                                 // 执行一些列钩子后，执行run里的onCompiled，onCompiled(null, compilation)
                                 return callback(null, compilation);
                             });
                         });
                     });
                 });
             });
         });
     });
 }

    3. onCompiled in run

       const onCompiled = (err, compilation) => {
         if (err) return finalCallback(err);
         //如果没有编译完成
         if (this.hooks.shouldEmit.call(compilation) === false) {
             compilation.startTime = startTime;
             compilation.endTime = Date.now();
             const stats = new Stats(compilation);
             this.hooks.done.callAsync(stats, err => {
                 if (err) return finalCallback(err);
                 return finalCallback(null, stats);
             });
             return;
         }

         process.nextTick(() => {
             logger = compilation.getLogger("webpack.Compiler");
             logger.time("emitAssets");
             // 输出编译后的文件，调用emitAsset方法，emitAsset主要负责写入文件输出文件，不影响我们先看编译（通过this.outputFileSystem、mkdirp、emitFiles输出文件）
             this.emitAssets(compilation, err => {
                 logger.timeEnd("emitAssets");
                 if (err) return finalCallback(err);
                 // 如果上传的编译没有完成则重来一遍编译
                 if (compilation.hooks.needAdditionalPass.call()) {
                     compilation.needAdditionalPass = true;

                     compilation.startTime = startTime;
                     compilation.endTime = Date.now();
                     logger.time("done hook");
                     const stats = new Stats(compilation);
                     this.hooks.done.callAsync(stats, err => {
                         logger.timeEnd("done hook");
                         if (err) return finalCallback(err);

                         this.hooks.additionalPass.callAsync(err => {
                             if (err) return finalCallback(err);
                             this.compile(onCompiled);
                         });
                     });
                     return;
                 }
                 // 完成编译
                 logger.time("emitRecords");
                 this.emitRecords(err => {
                     logger.timeEnd("emitRecords");
                     if (err) return finalCallback(err);
                     // 编译开始和编译结束时间
                     compilation.startTime = startTime;
                     compilation.endTime = Date.now();
                     logger.time("done hook");
                     const stats = new Stats(compilation);
                     this.hooks.done.callAsync(stats, err => {
                         logger.timeEnd("done hook");
                         if (err) return finalCallback(err);
                         this.cache.storeBuildDependencies(
                             compilation.buildDependencies,
                             err => {
                                 if (err) return finalCallback(err);
                                 // 编译完成返回new Stats(compilation)表示完成编译
                                 return finalCallback(null, stats);
                             }
                         );
                     });
                 });
             });
         });
     };

    4. emitAssets Create files after collecting compiled files

       emitAssets(compilation, callback) {
let outputPath;
// 收集编译好的文件
const emitFiles = err => {
    const assets = compilation.getAssets();
    compilation.assets = { ...compilation.assets };
    const caseInsensitiveMap = new Map();
    const allTargetPaths = new Set();
    // 对每个file资源文件进行路径拼接，将每个source源码转换为buffer(为了性能提升)，最后将文件写入真实目标路径
    asyncLib.forEachLimit(...)
    ...
}
// 创建文件
this.hooks.emit.callAsync(compilation, err => {
    if (err) return callback(err);
    outputPath = compilation.getPath(this.outputPath, {});
    mkdirp(this.outputFileSystem, outputPath, emitFiles);
  });
}
    5. Compiler flow line
      Compiler的流程线.png

    Compilation

    lib/Compilation.js
    loader ，解析文件的ast语法树， bundles ， chunks Compiler.js Instantiated for compilation, representing a single version build and generate resources. Compiler call hooks.make hook will execute Compilation.addEntry .
    (1) addEntry : Start the construction of the entry module, add the entry module to the program after success, call hooks.addEntry , and execute Compilation.addModule .
    (2) finish : Complete the compilation and collect the problems that each module builds.
    (3) seal : End compilation, generate chunks, and perform a series of optimizations on chunks.

    1. addEntry Parameters: context project path, entry entry dependency, optionsOrName project configuration or project name, callback callback.
      (1) addEntry Organize optionsOrName After execution Compilation._addEntryItem

       // Compilation._addEntryItem
_addEntryItem(context, entry, target, options, callback) {
 // 第一步生成entryData大致如下
 let entryData = {
     dependencies: [],
     includeDependencies: [],
     options: {
        name: undefined,
        ...options
     },
     [target]: entry
 }
 ...
 // 把entryData存入entries
 this.entries.set(name, entryData);
 ...
 // 调用hooks.addEntry 让this.entries.get(name)的options变成{ name: 名对应字, runtime: 'runtime'}
 this.hooks.addEntry.call(entry, options);
 // 调用Compilation.addModuleTree
 this.addModuleTree({...参数}, 一个callback函数);
}

      (2) hooks.addEntry mounts two fn , ProgressPlugin are progress bars.

       taps: [
  {
    type: 'sync',
    fn: [Function (anonymous)],
    name: 'RuntimeChunkPlugin'
  },
  { 
    type: 'sync', 
    fn: [Function: entryAdd], 
    name: 'ProgressPlugin' 
  }
],

      (3) RuntimeChunkPlugin in addEntry.tap

       // lib/optimize/RuntimeChunkPlugin.js
compilation.hooks.addEntry.tap(
  "RuntimeChunkPlugin",
  (_, { name: entryName }) => {
   if (entryName === undefined) return;
   const data = compilation.entries.get(entryName);
   if (data.options.runtime === undefined && !data.options.dependOn) {
       // 确定运行时区块名称
       let name = this.options.name;
       if (typeof name === "function") {
           name = name({ name: entryName });
       }
       data.options.runtime = name; // 让entries里对应entryName的值的runtime = 'runtime'
   }
  }
);

      (4) addModuleTree

       addModuleTree({ context, dependency, contextInfo }, callback) {
  ...
  // this.dependencyFactories是Map，在初始化注册插件apply的时候set
  const Dep = dependency.constructor; // class TaroSingleEntryDependency extends ModuleDependency
  // 根据对应的Dep获取对应的模块工厂，在Compiler.compile中可以知道分成普通模块工厂normalModuleFactory和上下文模块工厂contextModuleFactory
  const moduleFactory = this.dependencyFactories.get(Dep);
  // 执行Compilation.handleModuleCreation
  this.handleModuleCreation({...参数}, 一个callback函数）     
}

      (5) handleModuleCreation

       handleModuleCreation({ factory, dependencies, originModule, contextInfo, context, recursive = true, connectOrigin = recursive },callback) {
  // ModuleGraph用于记录依赖关系
  const moduleGraph = this.moduleGraph;  
  // 配置文件 = undefined
  const currentProfile = this.profile ? new ModuleProfile() : undefined;
  
  this.factorizeModule({...参数}, 一个callback函数)
}

      (6) factorizeModule

       Compilation.prototype.factorizeModule = function (options, callback) {
  this.factorizeQueue.add(options, callback); // 放入到异步队列里
};
       constructor(compiler, params) {
  ...
  // factorizeQueue是AsyncQueue的实例，作用是异步队列控制，将callback存入callbacks
  this.factorizeQueue = new AsyncQueue({
     name: "factorize",
     parent: this.addModuleQueue,
     // 达到条件会后执行processor，会返回一个【modulefactory】，执行factory.create，执行完成之后会执行回调callbacks里的callback
     processor: this._factorizeModule.bind(this)
  });
  ...
}
       _factorizeModule({currentProfile, factory, dependencies, originModule, factoryResult, contextInfo, context}, callback){
  ...
  factory.create({...参数}, 个callback函数);
}

      (7) normalModuleFactory and contextModuleFactory

       【normalModuleFactory】常用来处理import A from './a'这种导入语句的文件

【contextModuleFactory】常用来处理const b = require('./b/' + c)这种带变量的导入语句，在编译阶段webpack没办法识别真正运行时该用哪个文件，因此会将b目录下的所有文件都进行编译

      (8) factory.create We all use normal in the project to introduce it to build the module

       // lib/NormalModuleFactory.js
create(data, callback) {
 ...
 // 创建resolveData
 const resolveData = {....};
 // 执行hooks.beforeResolve
 this.hooks.beforeResolve.callAsync(resolveData, (err, result) => {
     ...
     // 执行hooks.factorize（NormalModuleFactory初始化的时候挂载），内部会执行hooks.resolve和hooks.createModule
     this.hooks.factorize.callAsync(resolveData, (err, module) => {
         ...
         const factoryResult = {...};
         callback(null, factoryResult); // 获得factoryResult执行回调
     })   
 })
}

      (9) hooks.factorize

       // NormalModuleFactory初始化
this.hooks.factorize.tapAsync({ name: "NormalModuleFactory", stage: 100},(resolveData, callback) => {
  // 生成对应的`loader`和依赖信息
  this.hooks.resolve.callAsync(resolveData, (err, result) => {
      ...
      this.hooks.afterResolve.callAsync(resolveData, (err, result) => {
          ...
          this.hooks.createModule.callAsync(createData, resolveData, () => {
              ...
              createdModule = this.hooks.module.call(
                 createdModule,
                 createData,
                 resolveData
              );
              return callback(null, createdModule); // module构建完成
          })
      })
  })
})

      (10) hooks.resolve , parse NormalModuleFactory , generate corresponding loader and dependency information

       // NormalModuleFactory初始化 data = resolveData
this.hooks.resolve.tapAsync({ name: "NormalModuleFactory", stage: 100},(data, callback) => {
  ...
  // 获取一个解析loader的工具
  const loaderResolver = this.getResolver("loader");
  // ...
}
       // type = "loader" resolveOptions = undefined
getResolver(type, resolveOptions) {
  return this.resolverFactory.get(type, resolveOptions);
}
       // lib/ResolverFactory.js
// ResolverFactory.get
get(type, resolveOptions = EMPTY_RESOLVE_OPTIONS) {
  // 获取缓存
  let typedCaches = this.cache.get(type);
  // 没有则创建缓存并存入
  if (!typedCaches) {
      ...
      this.cache.set(type, typedCaches);
  }  
  // 如果存在resolver直接返回resolver
  const cachedResolver = typedCaches.direct.get(resolveOptions);  
  if (cachedResolver) {
      return cachedResolver;
  } 
  ...
  // 创建了一个resolver并返回
  // this._create通过require("enhanced-resolve").ResolverFactory.createResolver(resolveOptions)来创建resolver
  const newResolver = this._create(type, resolveOptions);
  ...
  return newResolver;     
}
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