@SerialId does not affect enum members

There appears to be an incorrect enum index/value check during protobuf enum decoding (kotlin: 1.3.20, kotlinx.serialization: 0.10.0)

For example using the following .proto definition to generate the incoming serialized message:

syntax = "proto3";
package example;

option java_package = "example.java";
option java_multiple_files = true;

enum EnumA {
    reserved 2 to 9;
    A_ZERO = 0;
    A_ONE = 1;
    A_TEN = 10;
}

enum EnumB {
    B_ZERO = 0;
    B_ONE = 1;
    B_TWO = 2;
}

message ExampleEnumMessage {
    EnumA a = 1;
    EnumB b = 2;
}

Deserializing to the following data class:

enum class EnumA {
    @SerialId(0) A_ZERO,
    @SerialId(1) A_ONE,
    @SerialId(10) A_TEN;

    companion object {
        val defaultValue: EnumA = EnumA.values()[0]
    }
}

enum class EnumB {
    @SerialId(0) B_ZERO,
    @SerialId(1) B_ONE,
    @SerialId(2) B_TWO;

    companion object {
        val defaultValue: EnumB = EnumB.values()[0]
    }
}

@Serializable
data class ExampleEnumMessage(
    @SerialId(1) @Optional val a: EnumA = EnumA.defaultValue,
    @SerialId(2) @Optional val b: EnumB = EnumB.defaultValue) {
}

The following example uses protobuf-java runtime to generate the encoded data to be decoded by kotlinx.serialization:

fun example() {
    val parser = ExampleEnumMessageJava.parser()
    val serializer = ExampleEnumMessage.serializer()

    val message = ExampleEnumMessageJava.newBuilder().setA(EnumAJava.A_TEN).build()
    // Replacing previous line with the following will not have an error.
    // val message = ExampleEnumMessageJava.newBuilder().setB(EnumBJava.B_TWO).build()
    val encodedWithJava = message.toByteArray()
    val decodedWithKotlin = ProtoBuf.load(serializer, encodedWithJava)
}

will fail with:

java.lang.IllegalStateException: 10 is not among valid example.EnumA choices, choices size is 3

	at kotlinx.serialization.internal.CommonEnumSerializer.deserialize(Enums.kt:46)
	at kotlinx.serialization.protobuf.ProtoBuf$ProtobufReader.decodeSerializableValue(ProtoBuf.kt:204)
	at kotlinx.serialization.TaggedDecoder$decodeSerializableElement$1.invoke(Tagged.kt:254)
	at kotlinx.serialization.TaggedDecoder.tagBlock(Tagged.kt:267)
	at kotlinx.serialization.TaggedDecoder.decodeSerializableElement(Tagged.kt:254)

It looks like the decoded value is directly used as the index value into an enum-value choice array, which is causing the range-check condition to fail.

What is the correct way to pass in enum constant information such that it matches the analogous protobuf IDL declaration?

Edited:

• Removed red-herring information on a application-supplied ‘value’ property in the enum class definitions. The example now attempts to tag each enum value with a @SerialId (though probably incorrectly used).

[sandwwraith]

This is the current enums limitation: no serial annotation has any effect on them. We are going to fix this at some point in the future.

[rickygao]

Looking forward it. Actually, values in enums should be easier to be customized any way you like, instead of just in sequence.

I noticed that Int may replace the enum type, however, to make a workaround.