细说webpack源码之compile流程-rules参数处理技巧(1

const params = this.newCompilationParams();

Compiler.prototype.newCompilationParams = () => {
 const params = {
 normalModuleFactory: this.createNormalModuleFactory(),
 contextModuleFactory: this.createContextModuleFactory(),
 compilationDependencies: []
 };
 return params;
}
// 工厂方法1
Compiler.prototype.createNormalModuleFactory = () => {
 const normalModuleFactory = new NormalModuleFactory(this.options.context, this.resolvers, this.options.module || {});
 this.applyPlugins("normal-module-factory", normalModuleFactory);
 return normalModuleFactory;
}
// 工厂方法2
Compiler.prototype.createContextModuleFactory = () => {
 const contextModuleFactory = new ContextModuleFactory(this.resolvers, this.inputFileSystem);
 this.applyPlugins("context-module-factory", contextModuleFactory);
 return contextModuleFactory;
}

class NormalModuleFactory extends Tapable {
 // context默认为命令执行路径
 // resolvers => {...}
 // options => options.module
 constructor(context, resolvers, options) {
 super();
 // 该参数在WebpackOptionsApply方法中被赋值
 this.resolvers = resolvers;
 // 处理module.rules或module.loaders
 // 两者意义一样
 this.ruleSet = new RuleSet(options.rules || options.loaders);
 // 谁会去设置这玩意???默认参数设置那会被置为true
 // 这里会生成一个返回布尔值的函数 可以简单理解为!!
 this.cachePredicate = typeof options.unsafeCache === "function" ? options.unsafeCache : Boolean.bind(null, options.unsafeCache);
 this.context = context || "";
 // 解析缓存
 this.parserCache = {};
 // 这两个方法超级长
 this.plugin("factory", () => (result, callback) => { /**/ });
 this.plugin("resolver", () => (data, callback) => { /**/ })
 }
}

const path = require('path');
// resolve => path.join(__dirname,'..',path)
module.exports = {
 entry: './input.js',
 output: {
 filename: 'output.js'
 },
 module: {
 rules: [
 {
 test: /\.js$/,
 loader: 'babel-loader',
 include: [resolve('src'), resolve('test')]
 },
 {
 test: /\.css/,
 loader: 'css-loader!style-loader'
 }
 ]
 }
};

module.exports = class RuleSet {
 constructor(rules) {
 // 空对象
 this.references = Object.create(null);
 // 格式化
 this.rules = RuleSet.normalizeRules(rules, this.references, "ref-");
 }
}

class RuleSet {
 constructor(rules) { /**/ }
 // rules => 传进来的配置数组
 // refs => 纯净对象
 // ident => 'ref-'
 static normalizeRules(rules, refs, ident) {
 // 分数组与非数组
 if (Array.isArray(rules)) {
 return rules.map((rule, idx) => {
 return RuleSet.normalizeRule(rule, refs, `${ident}-${idx}`);
 });
 } else if (rules) {
 return [RuleSet.normalizeRule(rules, refs, ident)];
 }
 // 未配置rules直接返回空数组 
 else {
 return [];
 }
 }
}

// 数组
module.exports = {
 // ...
 module: {
 rules: [{ test: /\.vue$/, loader: 'vue-loader' }, /*...*/ ]
 }
};
// 非数组
module.exports = {
 // ...
 module: {
 rules: { test: /\.vue$/, loader: 'vue-loader' }
 }
};

class RuleSet {
 constructor(rules) { /**/ };
 // ident => 'ref-${index}'
 static normalizeRule(rule, refs, ident) {
 // 传入字符串
 // 'css-loader' => use:[{loader:'css-loader'}]
 if (typeof rule === "string")
 return {
 use: [{
  loader: rule
 }]
 };
 // 非法参数
 if (!rule)
 throw new Error("Unexcepted null when object was expected as rule");
 if (typeof rule !== "object")
 throw new Error("Unexcepted " + typeof rule + " when object was expected as rule (" + rule + ")");
 const newRule = {};
 let useSource;
 let resourceSource;
 let condition;
 // test
 if (rule.test || rule.include || rule.exclude) { /**/ }
 if (rule.resource) { /**/ }
 // 官网doc都懒得解释 估计是几个很弱智的参数
 if (rule.resourceQuery) { /**/ }
 if (rule.compiler) { /**/ }
 if (rule.issuer) { /**/ }
 // loader、loaders只能用一个
 if (rule.loader && rule.loaders)
 throw new Error(RuleSet.buildErrorMessage(rule, new Error("Provided loader and loaders for rule (use only one of them)")));
 const loader = rule.loaders || rule.loader;
 // 处理loader
 if (typeof loader === "string" && !rule.options && !rule.query) {
 checkUseSource("loader");
 newRule.use = RuleSet.normalizeUse(loader.split("!"), ident);
 }
 else if (typeof loader === "string" && (rule.options || rule.query)) {
 checkUseSource("loader + options/query");
 newRule.use = RuleSet.normalizeUse({
 loader: loader,
 options: rule.options,
 query: rule.query
 }, ident);
 } else if (loader && (rule.options || rule.query)) {
 throw new Error(RuleSet.buildErrorMessage(rule, new Error("options/query cannot be used with loaders (use options for each array item)")));
 } else if (loader) {
 checkUseSource("loaders");
 newRule.use = RuleSet.normalizeUse(loader, ident);
 } else if (rule.options || rule.query) {
 throw new Error(RuleSet.buildErrorMessage(rule, new Error("options/query provided without loader (use loader + options)")));
 }
 // 处理use
 if (rule.use) {
 checkUseSource("use");
 newRule.use = RuleSet.normalizeUse(rule.use, ident);
 }
 // 递归处理内部rules
 if (rule.rules)
 newRule.rules = RuleSet.normalizeRules(rule.rules, refs, `${ident}-rules`);
 // 不知道是啥
 if (rule.oneOf)
 newRule.oneOf = RuleSet.normalizeRules(rule.oneOf, refs, `${ident}-oneOf`);
 //
 const keys = Object.keys(rule).filter((key) => {
 return ["resource", "resourceQuery", "compiler", "test", "include", "exclude", "issuer", "loader", "options", "query", "loaders", "use", "rules", "oneOf"].indexOf(key) < 0;
 });
 keys.forEach((key) => {
 newRule[key] = rule[key];
 });
 function checkUseSource(newSource) { /**/ }
 function checkResourceSource(newSource) { /**/ }
 if (Array.isArray(newRule.use)) {
 newRule.use.forEach((item) => {
 if (item.ident) {
  refs[item.ident] = item.options;
 }
 });
 }
 return newRule;
 }
}