Angular CLI 1.7.4 在使用 ng build --prod 會構建失敗，而 ng build 是正常的。比較好的解決辦法是使用 ng build --prod --extract-licenses=false 或者 ng build --prod --no-extract-licenses。
最近將 Angular CLI 升級到 6.X 之后，直接 ng build 會報以下錯誤，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。同樣地，使用 ng build --extract-licenses=false 也可以解決問題。
簡單看一下，問題是由 license-webpack-plugin 插件引起的。這款插件用於輸出第三方插件的許可協議。老外比較重視版權吧。但是不知道為什么總是在這個地方出問題。
--- 2018.7.13 ---
新增解決方法：今天突然發現使用 yarn 安裝依賴則沒有問題。使用 npm 安裝依賴之后，由於某些 angular 插件的文件夾沒有 package.json（在下一層文件夾），所以 license-webpack-plugin 在抽取許可協議時會出錯，但是使用 yarn 安裝依賴時則不會出現這類文件夾，所以運行正常。