Why cant a Kotlin library Module depend on an Android Library Module?

Question

I am trying to have this dependency graph:

presentation (Android Module) -> domain (Kotlin Module) -> data (Android module)

And whenever I make domain to depend on data implementation(projects.data) it throws an error like this:

Could not determine the dependencies of task ':domain:compileJava'.
> Could not resolve all task dependencies for configuration ':domain:compileClasspath'.
   > Could not resolve project :data.
     Required by:
         project :domain
      > No matching variant of project :data was found. The consumer was configured to find a library for use during compile-time, compatible with Java 21, preferably in the form of class files, preferably optimized for standard JVMs, and its dependencies declared externally, as well as attribute 'org.jetbrains.kotlin.platform.type' with value 'jvm' but:
          - Variant 'debugApiElements' declares a library for use during compile-time, preferably optimized for Android:
              - Incompatible because this component declares a component, as well as attribute 'org.jetbrains.kotlin.platform.type' with value 'androidJvm' and the consumer needed a component, as well as attribute 'org.jetbrains.kotlin.platform.type' with value 'jvm'
              - Other compatible attributes:
                  - Doesn't say anything about how its dependencies are found (required its dependencies declared externally)
                  - Doesn't say anything about its elements (required them preferably in the form of class files)
                  - Doesn't say anything about its target Java version (required compatibility with Java 21)
          - Variant 'debugRuntimeElements' declares a library for use during runtime, preferably optimized for Android:
              - Incompatible because this component declares a component, as well as attribute 'org.jetbrains.kotlin.platform.type' with value 'androidJvm' and the consumer needed a component, as well as attribute 'org.jetbrains.kotlin.platform.type' with value 'jvm'
              - Other compatible attributes:
                  - Doesn't say anything about how its dependencies are found (required its dependencies declared externally)
                  - Doesn't say anything about its elements (required them preferably in the form of class files)
                  - Doesn't say anything about its target Java version (required compatibility with Java 21)
          - Variant 'debugSourcesElements' declares a component for use during runtime, packaged as a jar, preferably optimized for Android, and its dependencies declared externally:     
              - Incompatible because this component declares documentation, as well as attribute 'org.jetbrains.kotlin.platform.type' with value 'androidJvm' and the consumer needed a library, as well as attribute 'org.jetbrains.kotlin.platform.type' with value 'jvm'
              - Other compatible attribute:
                  - Doesn't say anything about its target Java version (required compatibility with Java 21)
          - Variant 'releaseApiElements' declares a library for use during compile-time, preferably optimized for Android:
              - Incompatible because this component declares a component, as well as attribute 'org.jetbrains.kotlin.platform.type' with value 'androidJvm' and the consumer needed a component, as well as attribute 'org.jetbrains.kotlin.platform.type' with value 'jvm'
              - Other compatible attributes:
                  - Doesn't say anything about how its dependencies are found (required its dependencies declared externally)
                  - Doesn't say anything about its elements (required them preferably in the form of class files)
                  - Doesn't say anything about its target Java version (required compatibility with Java 21)
          - Variant 'releaseRuntimeElements' declares a library for use during runtime, preferably optimized for Android:
              - Incompatible because this component declares a component, as well as attribute 'org.jetbrains.kotlin.platform.type' with value 'androidJvm' and the consumer needed a component, as well as attribute 'org.jetbrains.kotlin.platform.type' with value 'jvm'
              - Other compatible attributes:
                  - Doesn't say anything about how its dependencies are found (required its dependencies declared externally)
                  - Doesn't say anything about its elements (required them preferably in the form of class files)
                  - Doesn't say anything about its target Java version (required compatibility with Java 21)
          - Variant 'releaseSourcesElements' declares a component for use during runtime, packaged as a jar, preferably optimized for Android, and its dependencies declared externally:   
rary, as well as attribute 'org.jetbrains.kotlin.platform.type' with value 'jvm'
              - Other compatible attribute:
                  - Doesn't say anything about its target Java version (required compatibility with Java 21)

the build.gradle of domain:

plugins {
    alias(libs.plugins.jetbrains.kotlin.jvm)
}

java {
    sourceCompatibility = JavaVersion.VERSION_21
    targetCompatibility = JavaVersion.VERSION_21
}

tasks.withType<org.jetbrains.kotlin.gradle.tasks.KotlinCompile>().configureEach {
    kotlinOptions {
        jvmTarget = "21"
    }
}


dependencies {
    implementation(projects.data)
}

The build.gradle of data

plugins {
    alias(libs.plugins.android.library)
    alias(libs.plugins.jetbrains.kotlin.android)
}

android {
    namespace = "com.your.mom"
    compileSdk = 34

    defaultConfig {
        minSdk = 28

        testInstrumentationRunner = "androidx.test.runner.AndroidJUnitRunner"
        consumerProguardFiles("consumer-rules.pro")
    }

    buildTypes {
        release {
            isMinifyEnabled = false
            proguardFiles(
                getDefaultProguardFile("proguard-android-optimize.txt"),
                "proguard-rules.pro"
            )
        }
    }
    compileOptions {
        sourceCompatibility = JavaVersion.VERSION_21
        targetCompatibility = JavaVersion.VERSION_21
    }
    kotlinOptions {
        jvmTarget = "21"
    }
}

dependencies {

    implementation(libs.androidx.core.ktx)
    implementation(libs.androidx.appcompat)
    implementation(libs.material)
    testImplementation(libs.junit)
    androidTestImplementation(libs.androidx.junit)
    androidTestImplementation(libs.androidx.espresso.core)
}

A Kotlin library module shouldn't depend on an Android library module because Kotlin libraries should only have pure Kotlin code, not Android-specific code. If you need Android-specific stuff, use an Android library module instead. — Abdo21
– Abdo21, Commented Jul 13, 2024 at 21:14

JustSightseeing · Accepted Answer · 2024-07-25 19:15:14Z

3

Just to prevent people from doing... confusing stuff.

if the android lib module (M) would expose certain android methods / calls to the Kotlin module (K) then we could use and call android methods from the K module, which would turn it into a kotlin module, that can use android resources / methods (which basically is an Android Lib Module)

answered Jul 25, 2024 at 19:15

JustSightseeing

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