Revert back visibility in deserialization ctor to public so inheritors can access it from other modules.

Fix instantiating of polymorphic serializer with generics.
Move context creation below as asked.

compiler/backend/src/org/jetbrains/kotlin/codegen/ConstructorCodegen.java

@@ -127,12 +127,12 @@ public class ConstructorCodegen {
     ) {
         if (!canHaveDeclaredConstructors(descriptor)) return;
 
-        ConstructorContext constructorContext = context.intoConstructor(constructorDescriptor, typeMapper);
-
         KtSecondaryConstructor constructor = (KtSecondaryConstructor) descriptorToDeclaration(constructorDescriptor);
         // Synthetic constructors don't have corresponding declarations
         if (constructor == null) return;
 
+        ConstructorContext constructorContext = context.intoConstructor(constructorDescriptor, typeMapper);
+
         functionCodegen.generateMethod(
                 JvmDeclarationOriginKt.OtherOrigin(constructor, constructorDescriptor),
                 constructorDescriptor, constructorContext,

plugins/kotlin-serialization/kotlin-serialization-compiler/src/org/jetbrains/kotlinx/serialization/compiler/backend/jvm/JVMCodegenUtil.kt

@@ -263,23 +263,9 @@ internal fun AbstractSerialGenerator.stackValueSerializerInstance(codegen: Class
         dup()
         // instantiate all arg serializers on stack
         val signature = StringBuilder("(")
-        when (serializer.classId) {
-            enumSerializerId, contextSerializerId, polymorphicSerializerId -> {
-                // a special way to instantiate enum -- need a enum KClass reference
-                // GENERIC_ARGUMENT forces boxing in order to obtain KClass
-                aconst(codegen.typeMapper.mapType(kType, null, TypeMappingMode.GENERIC_ARGUMENT))
-                AsmUtil.wrapJavaClassIntoKClass(this)
-                signature.append(AsmTypes.K_CLASS_TYPE.descriptor)
-            }
-            referenceArraySerializerId -> {
-                // a special way to instantiate reference array serializer -- need an element KClass reference
-                aconst(codegen.typeMapper.mapType(kType.arguments[0].type, null, TypeMappingMode.GENERIC_ARGUMENT))
-                AsmUtil.wrapJavaClassIntoKClass(this)
-                signature.append(AsmTypes.K_CLASS_TYPE.descriptor)
-            }
-        }
-        // all serializers get arguments with serializers of their generic types
-        argSerializers.forEach { (argType, argSerializer) ->
+
+        fun instantiate(typeArgument: Pair<KotlinType, ClassDescriptor?>) {
+            val (argType, argSerializer) = typeArgument
             assert(
                 stackValueSerializerInstance(
                     codegen,
@@ -295,6 +281,26 @@ internal fun AbstractSerialGenerator.stackValueSerializerInstance(codegen: Class
             if (argType.isMarkedNullable) wrapStackValueIntoNullableSerializer()
             signature.append(kSerializerType.descriptor)
         }
+
+        when (serializer.classId) {
+            enumSerializerId, contextSerializerId, polymorphicSerializerId -> {
+                // a special way to instantiate enum -- need a enum KClass reference
+                // GENERIC_ARGUMENT forces boxing in order to obtain KClass
+                aconst(codegen.typeMapper.mapType(kType, null, TypeMappingMode.GENERIC_ARGUMENT))
+                AsmUtil.wrapJavaClassIntoKClass(this)
+                signature.append(AsmTypes.K_CLASS_TYPE.descriptor)
+            }
+            referenceArraySerializerId -> {
+                // a special way to instantiate reference array serializer -- need an element KClass reference
+                aconst(codegen.typeMapper.mapType(kType.arguments[0].type, null, TypeMappingMode.GENERIC_ARGUMENT))
+                AsmUtil.wrapJavaClassIntoKClass(this)
+                signature.append(AsmTypes.K_CLASS_TYPE.descriptor)
+                // Reference array serializer still needs serializer for its argument type
+                instantiate(argSerializers[0])
+            }
+            // all serializers get arguments with serializers of their generic types
+            else -> argSerializers.forEach(::instantiate)
+        }
         signature.append(")V")
         // invoke constructor
         invokespecial(serializerType.internalName, "<init>", signature.toString(), false)

plugins/kotlin-serialization/kotlin-serialization-compiler/src/org/jetbrains/kotlinx/serialization/compiler/resolve/KSerializerDescriptorResolver.kt

@@ -323,7 +323,7 @@ object KSerializerDescriptorResolver {
 
         functionDescriptor.initialize(
             consParams,
-            Visibilities.INTERNAL
+            Visibilities.PUBLIC
         )
 
         functionDescriptor.returnType = classDescriptor.defaultType