Angular CLI 1.7.4 在使用 ng build --prod 会构建失败，而 ng build 是正常的。比较好的解决办法是使用 ng build --prod --extract-licenses=false 或者 ng build --prod --no-extract-licenses。

最近将 Angular CLI 升级到 6.X 之后，直接 ng build 会报以下错误，ng serve 也是如此。

95% emitting LicenseWebpackPlugin(node:6252) UnhandledPromiseRejectionWarning: Error: ENOENT: no such file or directory, open 'D:\X\project\Angular-examples\angular-test\node_modules\_@angular_common@6.0.2@@angular\package.json'

    at Object.fs.openSync (fs.js:646:18)

    at Object.fs.readFileSync (fs.js:551:33)

    at LicenseExtractor.readPackageJson (D:\X\project\Angular-examples\angular-test\node_modules\_license-webpack-plugin@1.3.1@license-webpack-plugin\dist\LicenseExtractor.js:126:23)

    at LicenseExtractor.parsePackage (D:\X\project\Angular-examples\angular-test\node_modules\_license-webpack-plugin@1.3.1@license-webpack-plugin\dist\LicenseExtractor.js:23:32)

    at ModuleProcessor.processPackage (D:\X\project\Angular-examples\angular-test\node_modules\_license-webpack-plugin@1.3.1@license-webpack-plugin\dist\ModuleProcessor.js:39:46)

    at ModuleProcessor.processFile (D:\X\project\Angular-examples\angular-test\node_modules\_license-webpack-plugin@1.3.1@license-webpack-plugin\dist\ModuleProcessor.js:36:21)

    at fileCallback (D:\X\project\Angular-examples\angular-test\node_modules\_license-webpack-plugin@1.3.1@license-webpack-plugin\dist\LicenseWebpackPlugin.js:101:61)

    at moduleCallback (D:\X\project\Angular-examples\angular-test\node_modules\_license-webpack-plugin@1.3.1@license-webpack-plugin\dist\LicenseWebpackPlugin.js:108:21)

    at D:\X\project\Angular-examples\angular-test\node_modules\_license-webpack-plugin@1.3.1@license-webpack-plugin\dist\LicenseWebpackPlugin.js:120:29

    at Array.forEach (<anonymous>)

    at emitCallback (D:\X\project\Angular-examples\angular-test\node_modules\_license-webpack-plugin@1.3.1@license-webpack-plugin\dist\LicenseWebpackPlugin.js:86:32)

    at _err0 (eval at create (D:\X\project\Angular-examples\angular-test\node_modules\_tapable@1.0.0@tapable\lib\HookCodeFactory.js:24:12), <anonymous>:19:1)

    at callback (D:\X\project\Angular-examples\angular-test\node_modules\_copy-webpack-plugin@4.5.1@copy-webpack-plugin\dist\index.js:77:17)

    at D:\X\project\Angular-examples\angular-test\node_modules\_copy-webpack-plugin@4.5.1@copy-webpack-plugin\dist\index.js:118:24

    at <anonymous>

(node:6252) UnhandledPromiseRejectionWarning: Unhandled promise rejection. This error originated either by throwing inside of an async function without a catch block, or by rejecting a promise which was not handled with .catch(). (rejection id: 1)

(node:6252) [DEP0018] DeprecationWarning: Unhandled promise rejections are deprecated. In the future, promise rejections that are not handled will terminate the Node.js process with a non-zero exit code.

但是使用 ng build --prod 是正常的。同样地，使用 ng build --extract-licenses=false 也可以解决问题。

简单看一下，问题是由 license-webpack-plugin 插件引起的。这款插件用于输出第三方插件的许可协议。老外比较重视版权吧。但是不知道为什么总是在这个地方出问题。

--- 2018.7.13 ---

新增解决方法：今天突然发现使用 yarn 安装依赖则没有问题。使用 npm 安装依赖之后，由于某些 angular 插件的文件夹没有 package.json（在下一层文件夹），所以 license-webpack-plugin 在抽取许可协议时会出错，但是使用 yarn 安装依赖时则不会出现这类文件夹，所以运行正常。