Don't generate writeSelf/internal constructor if corresponding serialize/deserialize aren't auto-generated

plugins/kotlin-serialization/kotlin-serialization-compiler/src/org/jetbrains/kotlinx/serialization/compiler/backend/common/SerializableCodegen.kt

@@ -22,6 +22,8 @@ import org.jetbrains.kotlin.descriptors.FunctionDescriptor
 import org.jetbrains.kotlin.resolve.BindingContext
 import org.jetbrains.kotlinx.serialization.compiler.resolve.KSerializerDescriptorResolver
 import org.jetbrains.kotlinx.serialization.compiler.resolve.SerializableProperties
+import org.jetbrains.kotlinx.serialization.compiler.resolve.classSerializer
+import org.jetbrains.kotlinx.serialization.compiler.resolve.toClassDescriptor
 
 abstract class SerializableCodegen(
     protected val serializableDescriptor: ClassDescriptor,
@@ -35,13 +37,19 @@ abstract class SerializableCodegen(
     }
 
     private fun generateSyntheticInternalConstructor() {
-        val constrDesc = KSerializerDescriptorResolver.createLoadConstructorDescriptor(serializableDescriptor, bindingContext)
+        val serializerDescriptor = serializableDescriptor.classSerializer?.toClassDescriptor ?: return
-        generateInternalConstructor(constrDesc)
+        if (SerializerCodegen.getSyntheticLoadMember(serializerDescriptor) != null) {
+            val constrDesc = KSerializerDescriptorResolver.createLoadConstructorDescriptor(serializableDescriptor, bindingContext)
+            generateInternalConstructor(constrDesc)
+        }
     }
 
     private fun generateSyntheticMethods() {
-        val func = KSerializerDescriptorResolver.createWriteSelfFunctionDescriptor(serializableDescriptor)
+        val serializerDescriptor = serializableDescriptor.classSerializer?.toClassDescriptor ?: return
-        generateWriteSelfMethod(func)
+        if (SerializerCodegen.getSyntheticSaveMember(serializerDescriptor) != null) {
+            val func = KSerializerDescriptorResolver.createWriteSelfFunctionDescriptor(serializableDescriptor)
+            generateWriteSelfMethod(func)
+        }
     }
 
     protected abstract fun generateInternalConstructor(constructorDescriptor: ClassConstructorDescriptor)

plugins/kotlin-serialization/kotlin-serialization-compiler/src/org/jetbrains/kotlinx/serialization/compiler/backend/common/SerializerCodegen.kt

@@ -110,22 +110,14 @@ abstract class SerializerCodegen(
     }
 
     private fun generateSaveIfNeeded(): Boolean {
-        val function = getMemberToGenerate(
+        val function = getSyntheticSaveMember(serializerDescriptor) ?: return false
-            serializerDescriptor, SerialEntityNames.SAVE,
-            serializerDescriptor::checkSaveMethodResult, serializerDescriptor::checkSaveMethodParameters
-        )
-            ?: return false
         checkSerializability()
         generateSave(function)
         return true
     }
 
     private fun generateLoadIfNeeded(): Boolean {
-        val function = getMemberToGenerate(
+        val function = getSyntheticLoadMember(serializerDescriptor) ?: return false
-            serializerDescriptor, SerialEntityNames.LOAD,
-            serializerDescriptor::checkLoadMethodResult, serializerDescriptor::checkLoadMethodParameters
-        )
-            ?: return false
         checkSerializability()
         generateLoad(function)
         return true
@@ -160,4 +152,16 @@ abstract class SerializerCodegen(
 
     protected fun ClassDescriptor.getFuncDesc(funcName: String): Sequence<FunctionDescriptor> =
         unsubstitutedMemberScope.getDescriptorsFiltered { it == Name.identifier(funcName) }.asSequence().filterIsInstance<FunctionDescriptor>()
+
+    companion object {
+        fun getSyntheticLoadMember(serializerDescriptor: ClassDescriptor): FunctionDescriptor? = getMemberToGenerate(
+            serializerDescriptor, SerialEntityNames.LOAD,
+            serializerDescriptor::checkLoadMethodResult, serializerDescriptor::checkLoadMethodParameters
+        )
+
+        fun getSyntheticSaveMember(serializerDescriptor: ClassDescriptor): FunctionDescriptor? = getMemberToGenerate(
+            serializerDescriptor, SerialEntityNames.SAVE,
+            serializerDescriptor::checkSaveMethodResult, serializerDescriptor::checkSaveMethodParameters
+        )
+    }
 }