Android - How can an app with only debug & release buildTypes use a multi flavor library?

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Question

How can an app with only debug & release buildTypes use a multi flavor library?

Details

I have a project containing two modules: app and mymodule.

The app module has no flavor with only debug and release buildTypes. This is the app build.gradle.

apply plugin: 'com.android.application'
android {
    default {
    ....
    }

    buildTypes {
        debug {
        }
        release {
        }
    }
}

dependencies {

}

The mymodule has two flavors: login and registration which share the same base codes. This is mymodule build.gradle.

apply plugin: 'com.android.library'
android {
    default {
    ....
    }

    buildTypes {
        debug {
        }
        release {
        }
    }

    flavorDimensions 'version'
    productFlavors {
        login {
        }
        registration {
        }
    }
}

dependencies {

}

In mymodule, the codes are separated into source set like this so that I can build login.aar or registration.aar, but also let them share the base code from src/main/java. I also would like to use mymodule in app module.

|-src/main/java/
|-src/login/java
|-src/registration/java

This is settings.gradle.

include ':app', ':mymodule'

What I’ve tried

I’ve added the dependency implementation project(':mymodule') into app build.gradle, but I received the following error:

ERROR: Unable to resolve dependency for ':app@debug/compileClasspath': Could not resolve project :mymodule.
Show Details
Affected Modules: app


ERROR: Unable to resolve dependency for ':app@debugAndroidTest/compileClasspath': Could not resolve project :mymodule.
Show Details
Affected Modules: app


ERROR: Unable to resolve dependency for ':app@debugUnitTest/compileClasspath': Could not resolve project :mymodule.
Show Details
Affected Modules: app


ERROR: Unable to resolve dependency for ':app@release/compileClasspath': Could not resolve project :mymodule.
Show Details
Affected Modules: app


ERROR: Unable to resolve dependency for ':app@releaseUnitTest/compileClasspath': Could not resolve project :mymodule.
Show Details
Affected Modules: app