Serializer for class is not found even marked the class as @Serializable

[seventhmoon]

Describe the bug

To Reproduce
Attach a code snippet or test data if possible.

Having a data class JwtResult

@Keep
@Serializable
data class JwtResult(
        val nonce: String,
        val ctsProfileMatch: Boolean,
        val basicIntegrity: Boolean
)

and trying to parse the Json to JwtResult.class by
val returnedPayload = Json { ignoreUnknownKeys = true }.decodeFromString<JwtResult>(decodedPayload)

Exception was thrown in release build (minifyEnabled), but not debug build.
Seem the class was gone during the build process.

Serializer for class 'JwtResult' is not found. Mark the class as @serializable or provide the serializer explicitly.
kotlinx.serialization.internal.Platform_commonKt.serializerNotRegistered

Expected behavior
successfully parsing the JSON

Environment

• Kotlin version: 1.4.10
• Library version: 1.4.10
• Kotlin platforms: Android
• Gradle version: 6.6.1
• IDE version (if bug is related to the IDE) Android Studio 4.2 Canary 12
• Other relevant context [e.g. OS version, JRE version, ... ]

[Arutyun2312]

Try this:
val returnedPayload = Json { ignoreUnknownKeys = true }.decodeFromString(JwtResult.serializer(), decodedPayload)

[pdvrieze]

This seems to be a proguard configuration problem. The suggested solution should fix it as it certainly makes a static reference to the serializer. However decodeFromString should be inline reified and do this too.

[seventhmoon]

Yes. I believe it is an issue from R8.

[webfrea-k]

Stumbled upon this one as well. Downgraded the version to 1.0.0-RC (was RC2) and the issue disappeared.

[qwwdfsad]

It seems to be an Android issue. Could you please provide a reproducing project with your R8 configuration?

[seventhmoon]

https://github.com/seventhmoon/hello-kotlin-serialization

[seventhmoon]

🤦‍♂️ It is fixed by adding the following the instruction about proguard from readme.md
I was expecting the @Keep annotation will handle this well.

-keepattributes Annotation, InnerClasses
-dontnote kotlinx.serialization.SerializationKt
-keep,includedescriptorclasses class com.yourcompany.yourpackage.$$serializer { ; } # <-- change package name to your app's
-keepclassmembers class com.yourcompany.yourpackage. { # <-- change package name to your app's
*** Companion;
}
-keepclasseswithmembers class com.yourcompany.yourpackage.* { # <-- change package name to your app's
kotlinx.serialization.KSerializer serializer(...);
}

[atorrico09]

I had same issue that yours! Serializables data clases seemed dissapear only during build release and I got the same error.
In my case, I just added Keep anotation and try with @Arutyun2312 static serializer solution. It works perfectly!!!
Thank you very much for open this issue!! :)

[gandrewstone]

Note, you will get this error if you have not added serializations to your gradle plugins section:

plugins {
kotlin("plugin.serialization") version "1.4.31"
}

[sandwwraith]

I assume this can be closed now

[p4ulor]

For anyone having issues using this in android studio, check gradle website
Get the latest version and use " instead of '
Like:
id "org.jetbrains.kotlin.plugin.serialization" version "1.6.0-RC"
This is the fundamental line of code you need to add to your plugins { } in the file build.gradle(:app) to fix this problem.

Also make sure you have, on the same file, in dependencies { } the line:
implementation 'org.jetbrains.kotlinx:kotlinx-serialization-json:1.3.0'

And remove comments (specially if they have links) near the build statements. That can interfere according to my tests.

Make sure you have the imports in the .kt files:
import kotlinx.serialization.*
import kotlinx.serialization.json.Json //if you're using json

IDK if this is also part of the problem, but also make sure you have this in your proguard-rules.pro file (which is part of the gradle scripts)
https://github.com/Kotlin/kotlinx.serialization#android

Finally, try using other grade JDK's by going to gradle settings. It's probably best to use Android's. And consider doing invalidate caches and restart. I've been trying on this issue for 5 hours. Yes.

[jmarks213]

I ran into this issue recently after I had refactored my android apps' package in a kotlin multiplatform project. I needed to add rules to keep the serializers from both the androidApp package and the core library. My proguard looks something like:

-keepattributes Annotation, InnerClasses
-dontnote kotlinx.serialization.SerializationKt

-keep,includedescriptorclasses class com.androidApp.package.$$serializer { ; } # <-- change package name to your app's
-keepclassmembers class com.androidApp.package. { # <-- change package name to your app's
*** Companion;
}
-keepclasseswithmembers class com.androidApp.package.* { # <-- change package name to your app's
kotlinx.serialization.KSerializer serializer(...);
}

-keep,includedescriptorclasses class com.kmp.core.$$serializer { ; } # <-- change package name to your app's
-keepclassmembers class com.kmp.core. { # <-- change package name to your app's
*** Companion;
}
-keepclasseswithmembers class com.kmp.core.* { # <-- change package name to your app's
kotlinx.serialization.KSerializer serializer(...);
}

[cyb3rko]

For those where the solutions above were not working.
Here's what I used (taken from this issue here and StreetComplete):

-keepattributes Annotation, InnerClasses
-dontnote kotlinx.serialization.AnnotationsKt
-dontnote kotlinx.serialization.SerializationKt

# Keep Serializers

-keep,includedescriptorclasses class com.company.package.**$$serializer { *; }
-keepclassmembers class com.company.package.** {
    *** Companion;
}
-keepclasseswithmembers class com.company.package.** {
    kotlinx.serialization.KSerializer serializer(...);
}

# When kotlinx.serialization.json.JsonObjectSerializer occurs

-keepclassmembers class kotlinx.serialization.json.** {
    *** Companion;
}
-keepclasseswithmembers class kotlinx.serialization.json.** {
    kotlinx.serialization.KSerializer serializer(...);
}