Retrofit converter factory wrapper inspired by Jake Wharton presentation https://speakerdeck.com/jakewharton/making-retrofit-work-for-you-ohio-devfest-2016?slide=91

ConverterFactoryWrapper.kt

// Could create in separate file
annotation class SomeAnnotation

// This annotation should be placed to your Retrofit Api method
@GET("api/v1/data/{id}")
@SomeAnnotation
suspend fun fetchData(@Path("id") id: Int): SomeData

class ConverterFactoryWrapper(
    standardMoshi: Moshi,
    moshiForSomeAnnotation: Moshi
) : Converter.Factory() {

    private val standardFactory = MoshiConverterFactory.create(standardMoshi)
    private val someAnnotationFactory = MoshiConverterFactory.create(moshiForSomeAnnotation)

    override fun responseBodyConverter(
        type: Type,
        annotations: Array<out Annotation>,
        retrofit: Retrofit
    ): Converter<ResponseBody, *>? {

        return if (containsSomeAnnotation(annotations)) {
            someAnnotationFactory.responseBodyConverter(type, annotations, retrofit)
        } else {
            standardFactory.responseBodyConverter(type, annotations, retrofit)
        }
    }
    
    // You also should override requestBodyConverter to proxy that call to standart factory
    override fun requestBodyConverter(
        type: Type,
        parameterAnnotations: Array<Annotation>,
        methodAnnotations: Array<Annotation>,
        retrofit: Retrofit
    ): Converter<*, RequestBody>? {
        return standardFactory.requestBodyConverter(
            type,
            parameterAnnotations,
            methodAnnotations,
            retrofit
        )
    }
    
     // You also should override stringConverter to proxy that call to standart factory
     override fun stringConverter(
        type: Type,
        annotations: Array<Annotation>,
        retrofit: Retrofit
    ): Converter<*, String>? {
        return standardFactory.stringConverter(type, annotations, retrofit)
    }


    private fun containsStoreStatusAnnotation(annotations: Array<out Annotation>): Boolean {
        return annotations.find { it.annotationClass == SomeAnnotation::class } != null
    }
}


// Then add this converer wrapper to retrofit when creting it
Retrofit.Builder()
            .baseUrl(BuildConfig.API_BASE_URL)
            .client(/.../)
            .addConverterFactory(
                // In this example Retrofit initialize in Koin appModule
                ConverterFactoryWrapper(get(named("standard")), get(named("someAnnotaion")))
            )
            .build()
            .create(Api::class.java)