Hey, I just ran into a weird issue with custom ser...

# serialization

[molikuner]

Hey, I just ran into a weird issue with custom serializers. I have following code:

class InlineSerializerTest {
    @Test
    fun `simple TestClass serialization test`() {
        val json = "\"test\""
        val parsed = Json.parse(TestClass.Companion, json)
        assertEquals(
            TestClass("test"),
            parsed
        )
    }
}


@Serializable(with = TestClass.Companion::class)
data class TestClass(val a: String) {

    @Serializer(forClass = TestClass::class)
    companion object : TestSerializer {
        override val descriptor: SerialDescriptor = StringDescriptor

        // when removing this function the serialization crashes.
        override fun deserialize(decoder: Decoder): TestClass {
            return TestClass(decoder.decodeString())
        }

        override fun serialize(encoder: Encoder, obj: TestClass) = throw UnsupportedOperationException()
    }
}

interface TestSerializer: KSerializer<TestClass> {
    override fun deserialize(decoder: Decoder): TestClass {
        return TestClass(decoder.decodeString())
    }
}

As you can see in the companion object, I redefined the deserialize function with the same body as the extending interface. When removing this implementation the deserialization crashes:

Invalid JSON at 0: Expected '{, kind: CLASS'
kotlinx.serialization.json.JsonDecodingException: Invalid JSON at 0: Expected '{, kind: CLASS'
	at kotlinx.serialization.json.internal.JsonReader.fail(JsonReader.kt:293)
	at kotlinx.serialization.json.internal.StreamingJsonInput.beginStructure(StreamingJsonInput.kt:39)
	... // if needed I can provide the full stack later

Any idea how to resolve this? Whats really weird is that the error says that a class kind descriptor would be used, but String is definetly not a class kind type.

[molikuner]

After looking into the bytecode, I found out, that the @Serializable annotation generates a default implementation for the deserialization function even though the super class / interface implements it. I will open an issue later and post the link here.

[molikuner]

https://github.com/Kotlin/kotlinx.serialization/issues/636