const createMultiCompiler = (childOptions, options) =>{...}

const createCompiler = rawOptions => {
    ..
    const compiler = new Compiler(options.context);
	compiler.options = options;
    ...apply(compiler);
    ...
    compiler.hooks.environment.call();
	compiler.hooks.afterEnvironment.call();
	new WebpackOptionsApply().process(options, compiler);
	compiler.hooks.initialize.call();
    return compiler;
}

const webpack =(
    (options, callback) => {..}
)
module.exports = webpack;

const webpack =(
	(options, callback) => {
		const create = () => {
			if (!webpackOptionsSchemaCheck(options)) {
				getValidateSchema()(webpackOptionsSchema, options);//校验
			}
			let compiler;
			let watch = false;
			let watchOptions;
			...
            {
				const webpackOptions = (options);
				compiler = createCompiler(webpackOptions); 
                //applyWebpackOptionsBaseDefaults 里面有
				watch = webpackOptions.watch;
				watchOptions = webpackOptions.watchOptions || {};
			}
			return { compiler, watch, watchOptions }; // 最终配置
		};
		if (callback) {
			try {
				const { compiler, watch, watchOptions } = create(); //创建对象
				if (watch) {
					compiler.watch(watchOptions, callback);
				} else {
					compiler.run((err, stats) => {
						..
					});
				}
			...
		} else {
			const { compiler, watch } = create();
			if (watch) {
			...
			}
			return compiler;
		}
	}
);

const createCompiler = rawOptions => {
	const options = getNormalizedWebpackOptions(rawOptions);
	applyWebpackOptionsBaseDefaults(options); // 合并选项

	const compiler = new Compiler(options.context);
	compiler.options = options;
	new NodeEnvironmentPlugin({
		infrastructureLogging: options.infrastructureLogging
	}).apply(compiler);
	if (Array.isArray(options.plugins)) { //遍历注入plugin
		for (const plugin of options.plugins) {
			if (typeof plugin === "function") {
				plugin.call(compiler, compiler);
			} else {
				plugin.apply(compiler);
			}
		}
	}
	applyWebpackOptionsDefaults(options);
	compiler.hooks.environment.call();
	compiler.hooks.afterEnvironment.call();

	new WebpackOptionsApply().process(options, compiler); // 加载各种内置插件

	compiler.hooks.initialize.call();
	return compiler;
};