Add annotation processor for generating keep rules for types mentioned only inside generics

[piotrros]

Otherwise they will be removed by R8 since it cannot determine whether we are doing reflection on them.

Old issue below:

---

Using com.squareup.retrofit2:retrofit:2.9.0

After upgrading gradle plugin from

com.android.tools.build:gradle:4.1.3

to

com.android.tools.build:gradle:4.2.2

I'm getting following error when running with minifyEnabled true:

java.lang.IllegalArgumentException: Method return type must not include a type variable or wildcard

Here's how looks the method, which generates the error:

    @FormUrlEncoded
    @POST("view_ad") //NON-NLS
    Call<GenericDataResponse<EmptyData>> viewAd(
            @Field("session_id") String sessionId, //NON-NLS
            @Field("id") int id //NON-NLS
    );

    public class EmptyData {

        public EmptyData(){}

    }

    public class GenericDataResponse<T> {

        @SerializedName("result") //NON-NLS
        public String result;

        @SerializedName("data") //NON-NLS
        public T data;

        @SerializedName("mess") //NON-NLS
        public String[] messages;
    }

In order to fix this I have to either:

• downgrade to the previous gradle plugin version
• add proguard rule: -keep class com.example.app.EmptyData
• disable proguard/r8

I've read the docs about gradle 4.2 changes and nothing seems to be related to proguard directly.
Can someone explain what's going on?

[piotrros]

Even after adding rule: -keep class com.example.app.EmptyData I still had strange crashes like NullPointerExceptions so this rule isn't enough. I had to disable proguard for all app classes like this:

-keep class com.example.app.**

[piotrros]

Anyone :) ? It's pretty important.

[ulmaxy]

I have a similar issue with gradle plugin 4.2.1. Have you figured out what the issue is?

[piotrros]

No, I'm still waiting for a response. Downgrading to gradle 4.1.3 is the best option right now.

[ulmaxy]

It's strange, but simply downgrading to gradle 4.1.3 is not working for me

[ulmaxy]

In my case it was caused by data structure being removed by proguard, so adding the @keep annotation helped me

[piotrros]

You used @keep on some class or whole code?

[ulmaxy]

On a class, the signature I've got is similar to this:
@GET("endpoint") fun getData(): Single<List<SomeClass>>

And adding the @Keep annotation to SomeClass helped

[nvkleban]

I have similar issue with Retrofit 2.9 (checked versions down to 2.6.2 too) and gradle plugin 4.2.2 with minifyEnabled=true
Method return type must not include a type variable or wildcard: io.reactivex.Single<?>
But I have simple object not generic type as a response

    @POST("...")
    fun registerPushToken(
        @Body request: RegisterPushTokenRequest
    ): Single<RegisterPushTokenResponse>

class RegisterPushTokenResponse(
    @field:SerializedName("value") val token: String
)

Downgrading plugin to com.android.tools.build:gradle:4.1.3 fixes issue.

[alexxkovalchuk]

@piotrros

Updating plugin to
classpath 'com.android.tools.build:gradle:7.0.1'
fixed the issue for me

(Android Studio Arctic Fox | 2020.3.1 Patch 1)

[piotrros]

@piotrros

Updating plugin to
classpath 'com.android.tools.build:gradle:7.0.1'
fixed the issue for me

(Android Studio Arctic Fox | 2020.3.1 Patch 1)

Thanks, that worked.
It required some more work though like updating java (I was using 1.8 and had to switch to 11).

For that reason I'm not closing this issue yet, because it should be possible using 4.x

[JakeWharton]

If something changed solely with an AGP version change then it's like a result of a newer version of R8. The easiest way for me to look at the problem would be a minimal, self-contained sample project that exhibits the problem.

[piotrros]

Though using 7.0.1 I've discovered new issue, but it's not leading to a crash like before.

But I'll be hard to reproduce on your side probably.

I have an api call to receive a list of items (for example articles), inside a model I have an object named PagingInfo - it's a simple class containing information about number of items and if there's more of the to get.

When I'm using 7.0.1 this class becomes null in ALL api calls I have, but only when using R8. If I disable R8 it's working fine. Could this a GSON issue? I fixed the issue like this:

-keep class com.example.PagingInfo

Class looks like this:

public class PagingInfo {

    @Nullable
    @SerializedName("offset") //NON-NLS
    public int offset;

    @Nullable
    @SerializedName("page_size") //NON-NLS
    public int pageSize;

    @SerializedName("total_items") //NON-NLS
    public int totalItems;

    @SerializedName("has_more_items") //NON-NLS
    public boolean hasMoreItems;

    @Nullable
    @SerializedName("last_message_id") //NON-NLS
    public Integer lastMessageId;

    public PagingInfo() {}

}

Inside a JSON response this looks like this:

"paging": {
    "offset": 0,
    "page_size": 10,
    "total_items": 72,
    "has_more_items": true
  },

I have tons of models and api calls - everything but this one works completely fine. But by some reason using 7.0.1 and R8 leads to retrofit (or gson) unable to deserialise this one class. Simply disabling R8, adding an exception in proguard file or rolling back to the older gradle plugin solves the issue.

[TWiStErRob]

@JakeWharton here's a repro:

1. https://github.com/TWiStErRob/repros/tree/master/retrofit/proguard-removed-return-type
2. Run the app (debug variant)

Expected: Activity starts and reads the header:

I/okhttp.OkHttpClient: <-- 200 OK https://httpstat.us/200 (556ms)
I/okhttp.OkHttpClient: Content-Length: 31
I/okhttp.OkHttpClient: Content-Type: application/json
I/okhttp.OkHttpClient: Server: Kestrel
I/okhttp.OkHttpClient: Request-Context: appId=cid-v1:1e93d241-20e4-4513-bbd7-f452a16a5d69
I/okhttp.OkHttpClient: Strict-Transport-Security: max-age=2592000
I/okhttp.OkHttpClient: Set-Cookie: ARRAffinity=a9cebb550e254ba9270d015acd372767c78fa4f3f79fc353fb793f2912e673b3;Path=/;HttpOnly;Secure;Domain=httpstat.us
I/okhttp.OkHttpClient: Set-Cookie: ARRAffinitySameSite=a9cebb550e254ba9270d015acd372767c78fa4f3f79fc353fb793f2912e673b3;Path=/;HttpOnly;SameSite=None;Secure;Domain=httpstat.us
I/okhttp.OkHttpClient: Date: Thu, 31 Mar 2022 22:43:38 GMT
I/okhttp.OkHttpClient: {"code":200,"description":"OK"}
I/okhttp.OkHttpClient: <-- END HTTP (31-byte body)
I/System.out: 31

Actual:

E/AndroidRuntime: FATAL EXCEPTION: main
    Process: com.example, PID: 9204
    java.lang.RuntimeException: Unable to start activity ComponentInfo{com.example/com.example.MainActivity}: java.lang.IllegalArgumentException: Method return type must not include a type variable or wildcard: b.a.i<g.u<?>>
        for method c.a
        at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:3449)
        at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:3601)
        at android.app.servertransaction.LaunchActivityItem.execute(LaunchActivityItem.java:85)
        at android.app.servertransaction.TransactionExecutor.executeCallbacks(TransactionExecutor.java:135)
        at android.app.servertransaction.TransactionExecutor.execute(TransactionExecutor.java:95)
        at android.app.ActivityThread$H.handleMessage(ActivityThread.java:2066)
        at android.os.Handler.dispatchMessage(Handler.java:106)
        at android.os.Looper.loop(Looper.java:223)
        at android.app.ActivityThread.main(ActivityThread.java:7656)
        at java.lang.reflect.Method.invoke(Native Method)
        at com.android.internal.os.RuntimeInit$MethodAndArgsCaller.run(RuntimeInit.java:592)
        at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:947)
     Caused by: java.lang.IllegalArgumentException: Method return type must not include a type variable or wildcard: b.a.i<g.u<?>>
        for method c.a
        at g.z.n(:54)
        at g.z.m(:43)
        at g.w.b(:30)
        at g.v.c(:202)
        at g.v$a.invoke(:160)
        at java.lang.reflect.Proxy.invoke(Proxy.java:1006)
        at $Proxy1.a(Unknown Source)
        at com.example.MainActivity.onCreate(:39)
        at android.app.Activity.performCreate(Activity.java:7994)
        at android.app.Activity.performCreate(Activity.java:7978)
        at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1309)
        at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:3422)
        	... 11 more

Notable points on what makes it work:

• Change AGP to 7.1.1
• Change isMinifyEnabled = false
• Uncomment println(response.body()!!.description)
• -keep,allowobfuscation,allowoptimization class com.example.ResponseDTO { }

---

I think this is a valid scenario in ProGuard/R8, it just removes an unused class. No-on ever accesses the class except that erased generics. Although the fix in future versions might be that generics -> used.