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Thanks for class name. The issue here is that R8 is optimizing better now and will remove additional methods that are statically known to not be called. The concrete change for this case was in CL: https://r8-review.googlesource.com/c/r8/+/65722

In your case, there is no statically determined point that ever calls the constructor of InvitationCreditModel and so R8 makes it abstract if possible or when not, as in the case of a constructor, it creates a throw null method body. To avoid this you will need a keep rule on the class and its <init> method.

Now, the point I'm not sure about is that the keep rules for the members are active, namely:

-keepclassmembers class com.careem.acma.**.models.** {
    <fields>;
}

which keeps the field names in place (verified that it does actually do that), then the default constructor should be kept too.

Your build is in R8 compatibility mode, which usually means that a keep rule will implicitly keep the default constructor, so it might be most consistent that when the above rule is active, it should imply the default constructor is kept too (in R8 compatibility mode only).

I'll get back to you once we have a resolution on that. For the time being, your amended rule is a good workaround and is R8 full-mode ready.

Thanks for your detailed replied. That makes sense to me now.

For the time being, would you suggest I open an issue on GSON project to amend their R8 rules ?

I'll take it up with the team and get back on that point as well.

After some discussion, it appears to be an error that R8 in compatibility mode does not implicitly retain the default constructor <init>(). We will look into a fix for this. In the meantime, the workaround will need to remain in place. We do not see a way of updating the GSON rules as the library does not give a way to quantify which types need their default constructors kept. It will need to be detailed by the applications using GSON.

Thanks about this.

I agree from library side I dont see a way to update the gson rules within the library.

I meant the suggested rules in https://r8.googlesource.com/r8/+/refs/heads/master/compatibility-faq.md#gson and https://github.com/google/gson/blob/master/examples/android-proguard-example/proguard.cfg

Looking further into this there are a few more details:

1. Neither PG or R8 (compat) will keep the default constructor with the keepclassmembers rule.
2. The GSON library makes several attempts at finding an object allocator, first by looking for a default constructor, and if not found it creates an "unsafe" allocator using runtime internal allocation.

Due to 1. the shrinkers and rules are WAI, so there should not need to be any changes to the suggested GSON rules or to the interpretation of the rules. Due to 2. R8 will cause failures as it does not remove the default constructor but removes its body. Thus GSON thinks it has a valid constructor that then fails when invoked.

I filed b/248473941 as R8 should remove them when possible instead.

A fix for this has landed on the R8 release branches. Let us know if it resolves the issue for you locally.

To update your AGP 7.3 based build, you can manually link to the R8 version 3.3.81 or above using:

pluginManagement {
    buildscript {
        repositories {
            mavenCentral()
            maven {
                url = uri("https://storage.googleapis.com/r8-releases/raw")
            }
        }
        dependencies {
            classpath("com.android.tools:r8:3.3.81")
        }
    }
}

tested. looks like the problem has been fixed from our side.

Thanks for the help and the detailed explanations. Appreciated!

Hi everyone,

I am facing a very similar issue with AGP 7.3.1 (which is using r8 3.3.83).

My GSON rules are exactly same with https://github.com/google/gson/blob/master/examples/android-proguard-example/proguard.cfg

Fatal Exception: java.lang.RuntimeException: Failed to invoke public n5.b$d0() with no args
       at com.google.gson.internal.ConstructorConstructor$9.construct(ConstructorConstructor.java:252)
       at com.google.gson.internal.bind.ReflectiveTypeAdapterFactory$Adapter.read(ReflectiveTypeAdapterFactory.java:256)
       at com.google.gson.Gson.fromJson(Gson.java:1058)
       at com.google.gson.Gson.fromJson(Gson.java:1016)
       at com.google.gson.Gson.fromJson(Gson.java:959)

On below model as one of its values is default.

class Model(
    @SerializedName("first") val first: String? = null,
    @SerializedName("second") val second: String
)

If I remove the default value, constructor remains ok after r8 optimization. Otherwise I need to keep init explicitly as mentioned above in the issue.

I have put this here since it seems related with the issue, but I can create another if it will be more appropriate.

Where are you seeing the version? As per my understanding AGP 7.3.1 is still 3.3.70 so you will need to upgrade R8 to 3.3.81 as per #22

Thanks for reaching out. I filed a new issue b/261151062 for this. Lets move discussion to that issue.