prevent ng build from overwriting source files

Okay, that one was scarry as hell. I am sooo lucky I pushed my project to GH before building ng sources prepared for prod....

What I did was opening .angular-cli.json and setting
"outDir": "../../",

as I wanted to store built files next to my project so that I could simply exclude project in gradle. Turns out that was a terrible mistake as ng build --prod decided to nuked my whole UI project for good. Yes sir it did. 10 days of work have been completely vanished from my harddrive. Good thing is that I did push it all to git before...

I would strongly suggest to add safety switches preventing self-destruction in the whole ng-cli project.

从 .angular-cli.json 开始，使用 ../../ 作为 outDir，复现报告的 ng build --prod 行为。跟踪 Angular CLI 如何处理该输出路径，并定义一个安全开关，以防止在项目外进行破坏性写入。

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