Use an aar library cause missing dependencies using api in Gradle 4.x

When I build an app with a *.aar file instead of the module with Gradle 4.x and following the docu concerning implements and api, I expect using api the included aar file has all dependencies included, but it hasn't.

When you do

git clone https://github.com/hannesa2/aar_dependency
./gradlew clean assembleDebug

means

dependencies {
    api project(':mylibrary')

it works properly.

But when I use insted of lib-module the previous generated *.aar file as dependency

 dependencies {
    api 'com.example.my.mylibrary:mylibrary-debug@aar'

(in demo app just do)

git checkout with_aar
./gradlew clean assembleDebug

I run into this

Task :app:transformClassesWithDesugarForDebug Exception in thread "main" java.lang.TypeNotPresentException: Type io.reactivex.ObservableTransformer not present at sun.invoke.util.BytecodeDescriptor.parseSig(BytecodeDescriptor.java:85) at sun.invoke.util.BytecodeDescriptor.parseMethod(BytecodeDescriptor.java:63) at sun.invoke.util.BytecodeDescriptor.parseMethod(BytecodeDescriptor.java:41) at java.lang.invoke.MethodType.fromMethodDescriptorString(MethodType.java:1067) at com.google.devtools.build.android.desugar.LambdaDesugaring$InvokedynamicRewriter.visitInvokeDynamicInsn(LambdaDesugaring.java:399) at org.objectweb.asm.MethodVisitor.visitInvokeDynamicInsn(Unknown Source) at org.objectweb.asm.MethodVisitor.visitInvokeDynamicInsn(Unknown Source)

Because I ordinary run into this with uploading the aar artifacts into our company Maven Nexus, I created this demo-repo to show exactly what's wrong. In demo app or using Maven I see the same issue.

Does someone knows what I did wrong ?

I was able to solve it. The main issue was Android O with Gradle 4.x using api

dependencies {
    api 'com.squareup.okhttp3:logging-interceptor:3.4.1'
    api "io.reactivex.rxjava2:rxandroid:$versions.libs.rxAndroid"

Most answers are concerning something like this

publishing {
    publications {
        mipartner(MavenPublication) {
            groupId '...'
            artifactId '..'
            version 1.0
            artifact "$buildDir/outputs/aar/myLib-release.aar"

            //generate pom nodes for dependencies
            pom.withXml {
                def dependenciesNode = asNode().appendNode('dependencies')
                configurations.compile.allDependencies.each { dependency ->
                    def dependencyNode = dependenciesNode.appendNode('dependency')
                    dependencyNode.appendNode('groupId', dependency.group)
                    dependencyNode.appendNode('artifactId', dependency.name)
                    dependencyNode.appendNode('version', dependency.version)
                }
            }
        }
    }

    repositories{
        maven {
            url "https://some.url.com"
        }
    }
}

but here in the resulting *.pom there are no dependencies included, after change this line to api the dependencies are included in deployed pom !

configurations.api.allDependencies.each { dependency ->

after this you can easily consume the aar file

dependencies {
    api "com.mylib.net:mylib:1.0"