Service interface extending doesn't work with Proguard/R8

[ursusursus]

Hi, since latest versions now support service interface subclassing, as to facilitate versioning, I did just so

interface ConfigApi {
    suspend fun configuration(): Response<ConfigurationResponse>
}

interface V1ConfigAp : ConfigApi {
    @GET("api/v1/config")
    override suspend fun configuration(): Response<ConfigurationResponse>
}

interface V2ConfigAp : ConfigApi {
    @GET("api/v2/config")
    override suspend fun configuration(): Response<ConfigurationResponse>
}

I'm on android. If run in debug, everything works.
If run with R8 turned on, at runtime I get

2021-03-26 18:10:06.503 22986-23211/foo.bar W/Default: HTTP method annotation is required (e.g., @GET, @POST, etc.).
        for method b.a
    java.lang.IllegalArgumentException: HTTP method annotation is required (e.g., @GET, @POST, etc.).
        for method b.a

If I explicitly keep the class -keep class foo.bar.V2ConfigApi { *; } it works

It appears R8 ignores the "implementing" interface V2ConfigApi (Its only reference is in a dagger module provider method, and nowhere else), and just uses the base one, which obviously doesn't have the annotations.

I can live with the keep rule for now, but it's footgunny, since almost nothing requires app level keep rules now
Is there a general rule to be extracted? (and then possibly merged into the library)

Android
AGP 4.1.2
Retrofit 2.9.0

[ursusursus]

Although I'd naively expect this to already be that general rule

https://github.com/square/retrofit/blob/master/retrofit/src/main/resources/META-INF/proguard/retrofit2.pro#L9

[ursusursus]

:/

[rumburake]

As a workaround we could annotate the base class too:

interface ConfigApi {
    @GET("api/v1/config")
    suspend fun configuration(): Response<ConfigurationResponse>
}

interface V1ConfigAp : ConfigApi {
    @GET("api/v1/config")
    override suspend fun configuration(): Response<ConfigurationResponse>
}


interface V2ConfigAp : ConfigApi {
    @GET("api/v2/config")
    override suspend fun configuration(): Response<ConfigurationResponse>
}

[JakeWharton]

I need a project which reproduces the behavior in order to investigate.

[dmytroKarataiev]

@JakeWharton created a reproducible sample here: https://github.com/dmytroKarataiev/RetrofitProguard/tree/master

[Reginer]

-keep class kotlin.coroutines.Continuation