Annotation processors must be explicitly declared now

Android Studio升级到最新版3.0 Canary 8后，当使用到注解时，报了如下错误：

Error:Execution failed for task ':app:javaPreCompileDebug'.> Annotation processors must be explicitly declared now.  The following dependencies on the compile classpath are found to contain annotation processor.  Please add them to the annotationProcessor configuration.    - butterknife-8.8.1.jar  Alternatively, set android.defaultConfig.javaCompileOptions.annotationProcessorOptions.includeCompileClasspath = true to continue with previous behavior.  Note that this option is deprecated and will be removed in the future.  See https://developer.android.com/r/tools/annotation-processor-error-message.html for more details.

借鉴网友的解决方法，在引用注解库的module下的build.gradle文件中，添加了如下配置。

android {    ...    defaultConfig {        ...        javaCompileOptions {             annotationProcessorOptions {                 includeCompileClasspath = true             }         }    }    ...}

遗憾的是，添加上述配置之后，仍然出现这个错误；

这个时候转念一想，工程结构是多module形式的，会不会是重复依赖导致的呢？顺着这个想法，到每个module下的build.gradle文件搜索，发现的确在两个module下都依赖了butterknife注解库。

找到问题就很好解决了，只要去除掉其中一个依赖就可以了。