Hi there – I’m running into an unusual error link...

# serialization

[Ben Deming]

Hi there –

I’m running into an unusual error linking against an Apple (iOS) framework built from a Kotlin MPP project after adding a dependency to kotlinx-serialization-json.

The project:
– contains androidMain, commonMain, and iosMain sourceSets
– built to a framework using the syncFramework task created by applying the Cocoapods plugin, and run using a pod post_install hook
– already uses kotlinx-serialization-protobuf across all source sets already without incident

Our Kotlin language version is 1.5.21.
The serialization plugin is applied in this manner:

plugins {
    kotlin("multiplatform")
    kotlin("native.cocoapods")
    kotlin("plugin.serialization") version "1.5.21"

And the dependency on kotlinx-serialization-protobuf is defined in this manner:

val commonMain by getting {
            dependsOn(designSystemMain)
            dependencies {
                ...
                implementation("org.jetbrains.kotlin:kotlin-stdlib-common")
                ...
                implementation("org.jetbrains.kotlinx:kotlinx-serialization-protobuf:1.2.1")
                implementation("org.jetbrains.kotlinx:kotlinx-serialization-json:1.3.1")
            }
        }

A serializable class is defined like so:

@ExperimentalSerializationApi
@Serializable
data class AuthorizerRequestInfo(
    @SerialName("token")
    val token: String,
    @SerialName("client-id")
    val clientId: String,
)

Source in iosMain attempts encodes an instance of the data class in this manner:

Json.encodeToString(
    serializer = serializer(),
    value = AuthorizerRequestInfo(
        token = ...,
        clientId = ...
    )
)

The iOS framework is successfully built using the syncFramework command, but a linker issue occurs when statically linking the framework into the application:

Showing All Messages
Ld [redacted]/[redacted].app/[redacted] normal (in target '[redacted]' from project '[redacted]')
    cd 
    ....
Undefined symbols for architecture x86_64:
  "_kfun:kotlinx.serialization.json.JsonClassDiscriminator#<get-discriminator>(){}kotlin.String", referenced from:
      _kfun:kotlinx.serialization.json.internal#classDiscriminator__at__kotlinx.serialization.descriptors.SerialDescriptor(kotlinx.serialization.json.Json){}kotlin.String in [redacted](result.o)
ld: symbol(s) not found for architecture x86_64
clang: error: linker command failed with exit code 1 (use -v to see invocation)

We aren’t making use of class discriminator, note how ‘simple’ the AuthorizerRequestInfo class in question is, so I’m left kind of stumped.

Interestingly, the tasks that compile our iosTest source set & links our unit test target for iOS completes successfully – we can spawn a simulator and run a test executable with them, without incident.

Does anyone have guidance on how we can debug this further?

[Ben Deming]

(Following up for posterity) Filed https://youtrack.jetbrains.com/issue/KT-49888