[KxSerialization] Fix "IllegalAccessError: Update to static final field"

Fixes #KT-57647

For value classes, if you add code to companion anonymous init block in IR, it will be executed in the instance constructor. This causes an error when initializing static fields, because writing to them can only occur from the <clinit> method.

The solution is to transfer the static field initialization code from an anonymous init block to the IR initializer of this field

Merge-request: KT-MR-9633
Merged-by: Sergey Shanshin <Sergey.Shanshin@jetbrains.com>

plugins/kotlinx-serialization/kotlinx-serialization.backend/src/org/jetbrains/kotlinx/serialization/compiler/backend/ir/BaseIrGenerator.kt

@@ -398,8 +398,8 @@ abstract class BaseIrGenerator(private val currentClass: IrClass, final override
         val kSerializerType = kSerializerClass.typeWith(compilerContext.irBuiltIns.anyType)
         val arrayType = compilerContext.irBuiltIns.arrayClass.typeWith(kSerializerType)
 
-        return addValPropertyWithJvmField(arrayType, SerialEntityNames.CACHED_CHILD_SERIALIZERS_PROPERTY_NAME) {
-            +createArrayOfExpression(kSerializerType, cacheableSerializers.map { it ?: irNull() })
+        return addValPropertyWithJvmFieldInitializer(arrayType, SerialEntityNames.CACHED_CHILD_SERIALIZERS_PROPERTY_NAME) {
+            createArrayOfExpression(kSerializerType, cacheableSerializers.map { it ?: irNull() })
         }
     }
 

plugins/kotlinx-serialization/kotlinx-serialization.backend/src/org/jetbrains/kotlinx/serialization/compiler/backend/ir/IrBuilderWithPluginContext.kt

@@ -161,6 +161,30 @@ interface IrBuilderWithPluginContext {
         }
     }
 
+    fun IrClass.addValPropertyWithJvmFieldInitializer(
+        type: IrType,
+        name: Name,
+        visibility: DescriptorVisibility = DescriptorVisibilities.PRIVATE,
+        initializer: IrBuilderWithScope.() -> IrExpression
+    ): IrProperty {
+        return generateSimplePropertyWithBackingField(name, type, this, visibility).apply {
+            val field = backingField!!
+
+            val builder = DeclarationIrBuilder(
+                compilerContext,
+                field.symbol,
+                field.startOffset,
+                field.endOffset
+            )
+            field.initializer = IrExpressionBodyImpl(builder.initializer())
+
+            val annotationCtor = compilerContext.jvmFieldClassSymbol.constructors.single { it.owner.isPrimary }
+            val annotationType = compilerContext.jvmFieldClassSymbol.defaultType
+
+            field.annotations += IrConstructorCallImpl.fromSymbolOwner(startOffset, endOffset, annotationType, annotationCtor)
+        }
+    }
+
     /**
      * Add all statements to the builder, except the last one.
      * The last statement should be an expression, it will return as a result