How to get IDEA to detect kotlin generated sources using Gradle

So I recently got my hands on Kotlin and it's been great so far.

However one of the things that the IDEA kotlin plugin doesn't do¹ is detect the kapt folder which contains any sources generated from annotation processing. This can be fixed using the IDEA gradle plugin².

The idea plugin isn't able to mark the kapt folder as a source directory unless it's been added to the gradle source set.

sourceSets.main.java.srcDir file("$buildDir/generated/source/kapt/")

The next step is to tell the idea plugin to mark the kapt folder as a generated sources root in the module³.

idea {  
    module {
        // Tell idea to mark the folder as generated sources
        generatedSourceDirs += file("$buildDir/generated/source/kapt/")
    }
}

When put together your build script should look a little like this.

apply plugin: 'idea'

...

kapt {  
    generateStubs = true
}

// Add kapt directory to sources
sourceSets.main.java.srcDir file("$buildDir/generated/source/kapt/")

idea {  
    module {
// Tell idea to mark the folder as generated sources
        generatedSourceDirs += file("$buildDir/generated/source/kapt/")
    }
}

Footnotes and references

1. →, V. (2015). Better Annotation Processing: Supporting Stubs in kapt. [online] Kotlin Blog. Available at: https://blog.jetbrains.com/kotlin/2015/06/better-annotation-processing-supporting-stubs-in-kapt/#comment-36065 [Accessed 25 Jun. 2016]. ↩

2. Docs.gradle.org. (2016). The IDEA Plugin - Gradle User Guide Version 2.14. [online] Available at: https://docs.gradle.org/current/userguide/idea_plugin.html [Accessed 25 Jun. 2016]. ↩

3. Docs.gradle.org. (2016). IdeaModule - Gradle DSL Version 2.14. [online] Available at: https://docs.gradle.org/current/dsl/org.gradle.plugins.ide.idea.model.IdeaModule.html [Accessed 25 Jun. 2016]. ↩