Response Type Keeper

Generates keep rules for types mentioned in generic parameter positions of Retrofit service methods.

Problem

Given a service method like

@GET("users/{id}")
Call<User> getUser(
  @Path("id") String id);

If you execute this request and do not actually use the returned User instance, R8 will remove it and replace the return type as Call<?>. This fails Retrofit's runtime validation since a wildcard is not a valid type to pass to a converter. Note: this removal only occurs if the Retrofit's service method definition is the only reference to User.

Solution

This module contains an annotation processor which looks at each Retrofit method and generates explicit -keep rules for the types mentioned.

Add it to Gradle Java projects with

annotationProcessor 'com.squareup.retrofit2:response-type-keeper:<version>'

Or Gradle Kotlin projects with

kapt 'com.squareup.retrofit2:response-type-keeper:<version>'

For other build systems, the com.squareup.retrofit2:response-type-keeper needs added to the Java compiler -processor classpath.

For the example above, the annotation processor's generated file would contain

-keep com.example.User

This works for nested generics, such as Call<ApiResponse<User>>, which would produce:

-keep com.example.ApiResponse
-keep com.example.User

It also works on Kotlin suspend functions which turn into a type like Continuation<? extends User> in the Java bytecode.