Gradle setup for Kotlin multi-module project structure - kotlin

Question

I have a gradle project setup which looks similar to the one graphed below and I have some trouble setting up the dependencies between the different modules
┌Top Kotlin Project
│
├── Project1
│ │
│ ├── ModuleA1 (uses C1)
│ ├── ModuleA2
│ ├── ModuleA3
│ └── settings.gradle
├── ModuleB1 (uses C1)
├── ModuleC1 (library project)
└── settings.gradle
The Modules in A1,A2,A3 and B1 are basically isolated Gradle applications with their own build.gradle.kts
Module C1 is supposed to be a library module with shared code, that is used by Module A1, and Module B1.
Originally I thought I only had to declare C1 as an implementation dependency in the build.gradle.kts files of A1 and B1, like this
implementation(project(":ModuleC1"))
and include it in the settings.gradle of the Top Kotlin Project and also Project 1
include(":ModuleC1")
project(":ModuleC1").projectDir = File("../modulec1") #this line only needed in settings.gradle of Project1
However this does not work for multiple reasons.
First of all, all other projects/modules need to include all the repositories ModuleC needs, which means, whenever ModuleC changes I might need to also change the build files of other modules.
Most importantly though, all modules need the kotlin gradle plugin to build.
However if ModuleC1 includes the plugin and ModuleA1 as well, I get error that
> Plugin request for plugin already on the classpath must not include a version
If I do not include the Plugin in ModuleC1 it works for ModuleA1, but ModuleC1 cannot be built alone anymore.
The gradle.build.kts of ModuleC1 currently looks like this:
plugins {
kotlin("jvm") version "1.6.20"
`java-library`
}
group = "org.test.project"
version = "0.1"
repositories {
mavenCentral()
}
dependencies {
testImplementation("org.junit.jupiter:junit-jupiter-api:5.8.1")
testRuntimeOnly("org.junit.jupiter:junit-jupiter-engine:5.8.1")
}
tasks.getByName<Test>("test") {
useJUnitPlatform()
}
In conclusion I think, this setup of simply including the ModuleC1 in the other projects/modules is pretty flawed and there must be a better way to do this.
In summary, my goals are to be able to develop ModuleC1 independently but be able to use it in the other modules as if it was just another package there.