Kotlinx.serialization: Cannot compile class with default value that depends on parameters

[ansman]

When using version 0.5.0 trying to compile this class:

@Serializable
data class Name(
    val first: String,
    val last: String,
    @Optional val full: String = "$first $last"
)

gives this compile error:

Cause: Don't know how to generate outer expression: Class: class Name
The root cause was thrown at: CodegenContext.java:215
    at org.jetbrains.kotlin.codegen.ExpressionCodegen.genQualified(ExpressionCodegen.java:319)
    at org.jetbrains.kotlin.codegen.ExpressionCodegen.genQualified(ExpressionCodegen.java:280)
    at org.jetbrains.kotlin.codegen.ExpressionCodegen.gen(ExpressionCodegen.java:325)
    at org.jetbrains.kotlin.codegen.ExpressionCodegen.gen(ExpressionCodegen.java:333)
    at org.jetbrains.kotlin.codegen.ExpressionCodegen.gen(ExpressionCodegen.java:329)
    at org.jetbrains.kotlinx.serialization.compiler.backend.jvm.SerializableCodegenImpl.genInitProperty(SerializableCodegenImpl.kt:216)
    at org.jetbrains.kotlinx.serialization.compiler.backend.jvm.SerializableCodegenImpl.doGenerateConstructorImpl(SerializableCodegenImpl.kt:153)
    at org.jetbrains.kotlinx.serialization.compiler.backend.jvm.SerializableCodegenImpl.access$doGenerateConstructorImpl(SerializableCodegenImpl.kt:41)
    at org.jetbrains.kotlinx.serialization.compiler.backend.jvm.SerializableCodegenImpl$generateInternalConstructor$1.invoke(SerializableCodegenImpl.kt:65)
    at org.jetbrains.kotlinx.serialization.compiler.backend.jvm.SerializableCodegenImpl$generateInternalConstructor$1.invoke(SerializableCodegenImpl.kt:41)
    at org.jetbrains.kotlinx.serialization.compiler.backend.jvm.JVMCodegenUtilKt$generateMethod$1.doGenerateBody(JVMCodegenUtil.kt:109)
    at org.jetbrains.kotlin.codegen.FunctionGenerationStrategy$CodegenBased.generateBody(FunctionGenerationStrategy.java:80)
    at org.jetbrains.kotlin.codegen.FunctionCodegen.generateMethodBody(FunctionCodegen.java:620)
    at org.jetbrains.kotlin.codegen.FunctionCodegen.generateMethodBody(FunctionCodegen.java:391)
    at org.jetbrains.kotlin.codegen.FunctionCodegen.generateMethod(FunctionCodegen.java:244)
    at org.jetbrains.kotlin.codegen.FunctionCodegen.generateMethod(FunctionCodegen.java:168)
    at org.jetbrains.kotlinx.serialization.compiler.backend.jvm.JVMCodegenUtilKt.generateMethod(JVMCodegenUtil.kt:106)
    at org.jetbrains.kotlinx.serialization.compiler.backend.jvm.SerializableCodegenImpl.generateInternalConstructor(SerializableCodegenImpl.kt:65)
    at org.jetbrains.kotlinx.serialization.compiler.backend.common.SerializableCodegen.generateSyntheticInternalConstructor(SerializableCodegen.kt:39)
    at org.jetbrains.kotlinx.serialization.compiler.backend.common.SerializableCodegen.generate(SerializableCodegen.kt:33)
    at org.jetbrains.kotlinx.serialization.compiler.backend.jvm.SerializableCodegenImpl$Companion.generateSerializableExtensions(SerializableCodegenImpl.kt:52)
    at org.jetbrains.kotlinx.serialization.compiler.extensions.SerializationCodegenExtension.generateClassSyntheticParts(SerializationCodegenExtension.kt:29)
    at org.jetbrains.kotlin.codegen.ImplementationBodyCodegen.generateSyntheticPartsAfterBody(ImplementationBodyCodegen.java:424)
    at org.jetbrains.kotlin.codegen.MemberCodegen.generate(MemberCodegen.java:134)
    at org.jetbrains.kotlin.codegen.MemberCodegen.genClassOrObject(MemberCodegen.java:305)
    at org.jetbrains.kotlin.codegen.MemberCodegen.genClassOrObject(MemberCodegen.java:289)
    at org.jetbrains.kotlin.codegen.PackageCodegenImpl.generateClassOrObject(PackageCodegenImpl.java:161)
    at org.jetbrains.kotlin.codegen.PackageCodegenImpl.generateClassesAndObjectsInFile(PackageCodegenImpl.java:86)
    at org.jetbrains.kotlin.codegen.PackageCodegenImpl.generateFile(PackageCodegenImpl.java:119)
    at org.jetbrains.kotlin.codegen.PackageCodegenImpl.generate(PackageCodegenImpl.java:66)
    at org.jetbrains.kotlin.codegen.DefaultCodegenFactory.generatePackage(CodegenFactory.kt:97)
    at org.jetbrains.kotlin.codegen.DefaultCodegenFactory.generateModule(CodegenFactory.kt:68)
    at org.jetbrains.kotlin.codegen.KotlinCodegenFacade.doGenerateFiles(KotlinCodegenFacade.java:47)
    at org.jetbrains.kotlin.codegen.KotlinCodegenFacade.compileCorrectFiles(KotlinCodegenFacade.java:39)
    at org.jetbrains.kotlin.cli.jvm.compiler.KotlinToJVMBytecodeCompiler.generate(KotlinToJVMBytecodeCompiler.kt:454)
    at org.jetbrains.kotlin.cli.jvm.compiler.KotlinToJVMBytecodeCompiler.compileModules$cli(KotlinToJVMBytecodeCompiler.kt:150)
    at org.jetbrains.kotlin.cli.jvm.K2JVMCompiler.doExecute(K2JVMCompiler.kt:161)
    at org.jetbrains.kotlin.cli.jvm.K2JVMCompiler.doExecute(K2JVMCompiler.kt:63)
    at org.jetbrains.kotlin.cli.common.CLICompiler.execImpl(CLICompiler.java:107)
    at org.jetbrains.kotlin.cli.common.CLICompiler.execImpl(CLICompiler.java:51)
    at org.jetbrains.kotlin.cli.common.CLITool.exec(CLITool.kt:96)
    at org.jetbrains.kotlin.incremental.IncrementalJvmCompilerRunner.runCompiler(IncrementalJvmCompilerRunner.kt:463)
    at org.jetbrains.kotlin.incremental.IncrementalJvmCompilerRunner.runCompiler(IncrementalJvmCompilerRunner.kt:98)
    at org.jetbrains.kotlin.incremental.IncrementalCompilerRunner.compileIncrementally(IncrementalCompilerRunner.kt:228)
    at org.jetbrains.kotlin.incremental.IncrementalCompilerRunner.compile(IncrementalCompilerRunner.kt:99)
    at org.jetbrains.kotlin.daemon.CompileServiceImpl.execIncrementalCompiler(CompileServiceImpl.kt:538)
    at org.jetbrains.kotlin.daemon.CompileServiceImpl.access$execIncrementalCompiler(CompileServiceImpl.kt:98)
    at org.jetbrains.kotlin.daemon.CompileServiceImpl$compile$$inlined$ifAlive$lambda$2.invoke(CompileServiceImpl.kt:418)
    at org.jetbrains.kotlin.daemon.CompileServiceImpl$compile$$inlined$ifAlive$lambda$2.invoke(CompileServiceImpl.kt:98)
    at org.jetbrains.kotlin.daemon.CompileServiceImpl$doCompile$$inlined$ifAlive$lambda$2.invoke(CompileServiceImpl.kt:920)
    at org.jetbrains.kotlin.daemon.CompileServiceImpl$doCompile$$inlined$ifAlive$lambda$2.invoke(CompileServiceImpl.kt:98)
    at org.jetbrains.kotlin.daemon.common.DummyProfiler.withMeasure(PerfUtils.kt:137)
    at org.jetbrains.kotlin.daemon.CompileServiceImpl.checkedCompile(CompileServiceImpl.kt:950)
    at org.jetbrains.kotlin.daemon.CompileServiceImpl.doCompile(CompileServiceImpl.kt:919)
    at org.jetbrains.kotlin.daemon.CompileServiceImpl.compile(CompileServiceImpl.kt:417)
    at sun.reflect.GeneratedMethodAccessor94.invoke(Unknown Source)
    at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
    at java.lang.reflect.Method.invoke(Method.java:498)
    at sun.rmi.server.UnicastServerRef.dispatch(UnicastServerRef.java:357)
    at sun.rmi.transport.Transport$1.run(Transport.java:200)
    at sun.rmi.transport.Transport$1.run(Transport.java:197)
    at java.security.AccessController.doPrivileged(Native Method)
    at sun.rmi.transport.Transport.serviceCall(Transport.java:196)
    at sun.rmi.transport.tcp.TCPTransport.handleMessages(TCPTransport.java:568)
    at sun.rmi.transport.tcp.TCPTransport$ConnectionHandler.run0(TCPTransport.java:826)
    at sun.rmi.transport.tcp.TCPTransport$ConnectionHandler.lambda$run$0(TCPTransport.java:683)
    at java.security.AccessController.doPrivileged(Native Method)
    at sun.rmi.transport.tcp.TCPTransport$ConnectionHandler.run(TCPTransport.java:682)
    at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1149)
    at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:624)
    at java.lang.Thread.run(Thread.java:748)
Caused by: java.lang.UnsupportedOperationException: Don't know how to generate outer expression: Class: class Name
    at org.jetbrains.kotlin.codegen.context.CodegenContext.getOuterExpression(CodegenContext.java:215)
    at org.jetbrains.kotlin.codegen.context.CodegenContext.lookupInContext(CodegenContext.java:540)
    at org.jetbrains.kotlin.codegen.context.MethodContext.lookupInContext(MethodContext.java:81)
    at org.jetbrains.kotlin.codegen.ExpressionCodegen.findCapturedValue(ExpressionCodegen.java:1854)
    at org.jetbrains.kotlin.codegen.ExpressionCodegen.findLocalOrCapturedValue(ExpressionCodegen.java:1845)
    at org.jetbrains.kotlin.codegen.ExpressionCodegen.visitSimpleNameExpression(ExpressionCodegen.java:1760)
    at org.jetbrains.kotlin.codegen.ExpressionCodegen.visitSimpleNameExpression(ExpressionCodegen.java:110)
    at org.jetbrains.kotlin.psi.KtNameReferenceExpression.accept(KtNameReferenceExpression.kt:59)
    at org.jetbrains.kotlin.codegen.ExpressionCodegen.genQualified(ExpressionCodegen.java:298)
    ... 70 more

[sandwwraith]

I suppose that supporting that specific case would require a lot of effort. In general, for every serialization framework you can apply recommendation 'if value can be computed from other values, better to make it transient'.

[ansman]

Well, it not always computed from a default value. Perhaps the user has a middle name that is in the full name.

Does it take a lot of effort because you are not calling the generated constructor for default values but rather compute them yourselves?

[SUPERCILEX]

Any updates on this?

[bjonnh]

Adding transient does not solve it for me either (it does not exist in my json)

Moshi was handling that without complaining or requiring any special decoration.

[ln-12]

I got the exact same problem. Anyone got a solution?

[RaphaelTarita]

I can confirm that this bug is still present and that there are use cases where this would be very useful. I now have to decide how to circumvent this problem in my application. If someone knows some kind of workaround, I'd be very thankful for that.

[benkuly]

If I remeber it right, it worked for me to use init:

@Serializable
data class Name(
    val first: String,
    val last: String
){
    val full:String
    init{
        full = "$first $last"
    }
}