'Unresolved reference' errors for android library module referenced in app module

Question

I have problems referencing my android library modules in my projects. Beside the main app module I use to have an android library module with either util stuff or as data module. I reference it in app module like that:

dependencies {
    implementation project(":data")
}

When I build the project, it´s giving me lot of error messages 'Unresolved reference: ...' for all stuff that I reference in the app module to the android library module. But the IDE itself doesn´t have a problem, Intelligent finds all classes, interfaces etc., imports are fine, nothing is red. The android library module itself builds and creates aar-file in the output. It´s the compileDebugKotlin task that fails

Any general idea what may be related to that?

Answer 1

Found the problem, my android library module was missing the kotlin configuration:

apply plugin: 'kotlin-android'

dependencies {
    implementation "org.jetbrains.kotlin:kotlin-stdlib-jre7:$kotlinVersion:<version>"
}

Although I used kotlin .kt files in it, it could build without and also

Tools -> Kotlin -> 'Configure Kotlin in projects'

had told me 'All modules with Kotlin files are configured'