Add support for incremental annotation processing with Gradle 4.7+

[tudorluca]

Gradle 4.7 added support for incremental annotation processing, docs here.

For additional help, follow up with the gradle dedicated issue.

[greenrobot-team]

Thanks. Already looked into this a while ago and the issue is that our processor does not really fit either mode. @Entity classes cause generation of multiple files (Entity Info, Cursors), but all entity classes are also aggregated in a single class (MyObjectBox).

In addition, for relations multiple @Entity classes may influence the contents of a generated class. This does not seem to fit "isolating" mode.

The ObjectBox processor also can't use "aggregating" mode because it needs access to parameter names (would require a compiler flag with that mode).

Side note: when using the Android Plugin it is still unclear (last time I checked) how to do incremental annotation processing anyhow.
-ut

[tudorluca]

I'm afraid I can't help, I'm no gradle wizard.

[greenrobot-team]

News: with Android Gradle Plugin 3.3.0 incremental annotation processor support is available for Java-only projects. But not for Kotlin or mixed Kotlin+Java projects.

Also, there is a note that it does not work with Gradle 5.1 and higher.
https://developer.android.com/studio/releases/gradle-plugin

So: nothing to do here for now.
-ut

[dbriggsDFleet]

Can this be unblocked with the release of Android Gradle Plugin 3.5.0? "Additionally, KAPT 1.3.30 and higher also support incremental annotation processors, which you can enable by including kapt.incremental.apt=true in your gradle.properties file."
https://developer.android.com/studio/releases/gradle-plugin#3-5-0

[greenrobot-team]

@dbriggsDFleet Sure, but the biggest, unresolved issues are still those described in #620 (comment).

[jrcacd]

This is a must.
With incremental annotation processing we could do really fast unit testing with objectBox, as we would have to wait a lot less for the project to compile

[greenrobot-team]

We just released 2.5.1 which supports incremental annotation processing. It is turned off by default.

To turn it on set objectbox.incremental to true in build.gradle:

android {
    defaultConfig {
        javaCompileOptions {
            annotationProcessorOptions {
                arguments = [ "objectbox.incremental" : "true" ]
            }
        }
    }
}

This configuration works for both Android Java and Android Kotlin projects.

We appreciate your feedback on this feature.

If all goes well, incremental annotation processing will be on by default in a future release.