背景：隔了很久的项目，再次打开打包时报错：
FAILURE: Build completed with 2 failures.
1: Task failed with an exception.
-----------
* What went wrong:
Execution failed for task ':app:mergeReleaseResources'.
> Couldn't delete stale output file
* Try:
Run with --stacktrace option to get the stack trace. Run with --info or --debug option to get more log output. Run with --scan to get full insights.
==============================================================================
2: Task failed with an exception.
-----------
* What went wrong:
Execution failed for task ':app:signingConfigWriterRelease'.
> Couldn't delete stale output file
* Try:
Run with --stacktrace option to get the stack trace. Run with --info or --debug option to get more log output. Run with --scan to get full insights.
开始怀疑是studio版本更新了，项目中的gradle版本过低。
修改项目gradle版本，改成其它正常项目中的版本
改完重新打包：
依旧报错，不过解决了一个。
之后点开build.gradle(:app) ：发现右上角有报错提示
点开
修改 targetSdk版本，注意每个modules下的targetSdk版本都要修改
然后依旧报错，之后clean project，不能删除的build文件手动去文件夹中删除，然后rebuild projiect 再打包成功。
以上是我出现bug时记录的解决过程笔记。