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Yeah notably Retrofit uses Method.getGenericParameterTypes which is framework code which then parses the signature and invokes Class.forName.

Caused by: java.lang.ClassNotFoundException: Didn't find class "java.time.LocalDate" on path: DexPathList[[zip file "/data/app/com.paulwoitaschek.agptest-1/base.apk"],nativeLibraryDirectories=[/data/app/com.paulwoitaschek.agptest-1/lib/x86_64, /vendor/lib64, /system/lib64]]
   at dalvik.system.BaseDexClassLoader.findClass(BaseDexClassLoader.java:56)
   at java.lang.ClassLoader.loadClass(ClassLoader.java:511)
   at java.lang.ClassLoader.loadClass(ClassLoader.java:469)
   at java.lang.Class.classForName(Native Method) 
   at java.lang.Class.forName(Class.java:324) 
   at libcore.reflect.ParameterizedTypeImpl.getRawType(ParameterizedTypeImpl.java:65) 
   at libcore.reflect.ParameterizedTypeImpl.getResolvedType(ParameterizedTypeImpl.java:76) 
   at libcore.reflect.ListOfTypes.resolveTypes(ListOfTypes.java:70) 
   at libcore.reflect.ListOfTypes.getResolvedTypes(ListOfTypes.java:55) 
   at libcore.reflect.Types.getTypeArray(Types.java:50) 
   at java.lang.reflect.Method.getGenericParameterTypes(Method.java:246) 
   at retrofit2.RequestFactory$Builder.<init>(RequestFactory.java:175) 
   at retrofit2.RequestFactory.parseAnnotations(RequestFactory.java:67) 
   at retrofit2.ServiceMethod.parseAnnotations(ServiceMethod.java:26) 
   at retrofit2.Retrofit.loadServiceMethod(Retrofit.java:202) 
   at retrofit2.Retrofit.validateServiceInterface(Retrofit.java:189) 
   at retrofit2.Retrofit.create(Retrofit.java:141) 
   at com.paulwoitaschek.agptest.MainActivity.onCreate(MainActivity.kt:18) 

L8 is currently not rewriting generic signatures. Will update this when it does.

Nice! Is it possible to cherry pic this into a 4.0.x release?

I hope that it is - it will be updated here when cherry-picked.

woitaschek@, could I ask you to verify that the fix works on your project by adding the following to your top-level build.gradle file:

buildscript {

    repositories {
        maven {
            url "https://storage.googleapis.com/r8-releases/raw/master"
        }
    }

    dependencies {
        classpath 'com.android.tools:r8:0c54dd2edb4fd81073cdac5ff487dd1a37330fba'  // Must be before the Gradle Plugin for Android.
        classpath 'com.android.tools.build:gradle:X.Y.Z'     // Your current AGP version.
     }
}

Nice, it works!

.method public abstract test(Lj$/time/LocalDate;)Lretrofit2/Call;
    .param p1    # Lj$/time/LocalDate;
        .annotation runtime Lretrofit2/http/Query;
            value = "meop"
        .end annotation
    .end param
    .annotation system Ldalvik/annotation/Signature;
        value = {
            "(",
            "Lj$/time/LocalDate;",
            ")",
            "Lretrofit2/Call<",
            "Ljava/lang/Void;",
            ">;"
        }
    .end annotation

    .annotation runtime Lretrofit2/http/GET;
        value = "meop"
    .end annotation
.end method

This will hopefully make the next point release for AGP 4.0, but you can try it out by adding the following to your top-level build.gradle:

buildscript {

    repositories {
        maven {
            url 'https://storage.googleapis.com/r8-releases/raw'
        }
    }

    dependencies {
        classpath 'com.android.tools:r8:2.0.85'          // Must be before the Gradle Plugin for Android.
        classpath 'com.android.tools.build:gradle:X.Y.Z' // Your current AGP version.
     }
}

Is this identially to the r8 version bundled in 4.0.0 besides the generic signature rewrite? Do you think this is safe to be used in production?

The version in AGP is 2.0.74. 2.0.85 is build on top of 2.0.74 by cherry-picking various bug-fixes. Version 2.0.85 (or perhaps a later version) will probably be in the next point release. So I regard all 2.0.X versions for X > 74 to be stable.

And if you have problems with that version, please let us know.