Support for @UseSerializers annotation

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

@@ -14,7 +14,10 @@ import org.jetbrains.kotlin.resolve.constants.KClassValue
 import org.jetbrains.kotlin.resolve.descriptorUtil.firstArgument
 import org.jetbrains.kotlin.resolve.descriptorUtil.module
 import org.jetbrains.kotlin.types.KotlinType
+import org.jetbrains.kotlin.types.typeUtil.supertypes
 import org.jetbrains.kotlinx.serialization.compiler.resolve.SerializationAnnotations
+import org.jetbrains.kotlinx.serialization.compiler.resolve.isKSerializer
+import org.jetbrains.kotlinx.serialization.compiler.resolve.toClassDescriptor
 
 abstract class AbstractSerialGenerator(val bindingContext: BindingContext, val currentDeclaration: ClassDescriptor) {
 
@@ -34,4 +37,15 @@ abstract class AbstractSerialGenerator(val bindingContext: BindingContext, val c
             currentDeclaration
         ).toSet()
     }
+
+    val additionalSerializersInScopeOfCurrentFile: Map<KotlinType, ClassDescriptor> by lazy {
+        getKClassListFromFileAnnotation(SerializationAnnotations.additionalSerializersFqName, currentDeclaration)
+            .associateBy(
+                {
+                    it.supertypes().find(::isKSerializer)?.arguments?.firstOrNull()?.type
+                        ?: throw AssertionError("Argument for ${SerializationAnnotations.additionalSerializersFqName} does not implement KSerializer")
+                },
+                { it.toClassDescriptor!! }
+            )
+    }
 }

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

@@ -49,14 +49,18 @@ open class SerialTypeInfo(
     val unit: Boolean = false
 )
 
+fun AbstractSerialGenerator.findAddOnSerializer(propertyType: KotlinType): ClassDescriptor? =
+    additionalSerializersInScopeOfCurrentFile[propertyType]
+
 @Suppress("FunctionName", "LocalVariableName")
 fun AbstractSerialGenerator.getSerialTypeInfo(property: SerializableProperty): SerialTypeInfo {
     fun SerializableInfo(serializer: ClassDescriptor?) =
         SerialTypeInfo(property, if (property.type.isMarkedNullable) "Nullable" else "", serializer)
 
     val T = property.type
-    T.overridenSerializer?.toClassDescriptor?.let { return SerializableInfo(it) }
     property.serializableWith?.toClassDescriptor?.let { return SerializableInfo(it) }
+    T.overridenSerializer?.toClassDescriptor?.let { return SerializableInfo(it) }
+    findAddOnSerializer(T)?.let { return SerializableInfo(it) }
     return when {
         T.isTypeParameter() -> SerialTypeInfo(property, if (property.type.isMarkedNullable) "Nullable" else "", null)
         T.isPrimitiveNumberType() or T.isBoolean() -> SerialTypeInfo(
@@ -91,6 +95,7 @@ fun AbstractSerialGenerator.findTypeSerializerOrContext(
     annotations: Annotations = kType.annotations,
     sourceElement: PsiElement? = null
 ): ClassDescriptor? {
+    additionalSerializersInScopeOfCurrentFile[kType]?.let { return it }
     if (kType.isTypeParameter()) return null
     fun getContextualSerializer() =
         if (annotations.hasAnnotation(SerializationAnnotations.contextualFqName) || kType in contextualKClassListInCurrentFile)

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

@@ -31,6 +31,7 @@ import org.jetbrains.kotlin.types.KotlinType
 import org.jetbrains.kotlin.types.typeUtil.isTypeParameter
 import org.jetbrains.kotlinx.serialization.compiler.backend.common.AbstractSerialGenerator
 import org.jetbrains.kotlinx.serialization.compiler.backend.common.SerialTypeInfo
+import org.jetbrains.kotlinx.serialization.compiler.backend.common.findAddOnSerializer
 import org.jetbrains.kotlinx.serialization.compiler.backend.common.findTypeSerializerOrContext
 import org.jetbrains.kotlinx.serialization.compiler.resolve.*
 import org.jetbrains.kotlinx.serialization.compiler.resolve.SerialEntityNames.DECODER_CLASS
@@ -109,6 +110,7 @@ fun InstructionAdapter.genKOutputMethodCall(
         ownerVar,
         classCodegen.state
     )
+    StackValue.coerce(propertyType, sti.type, this)
     invokeinterface(
         kOutputType.internalName,
         CallingConventions.encode + sti.elementMethodPrefix + (if (useSerializer) "Serializable" else "") + CallingConventions.elementPostfix,
@@ -309,6 +311,18 @@ class JVMSerialTypeInfo(
 ) : SerialTypeInfo(property, nn, serializer, unit)
 
 fun AbstractSerialGenerator.getSerialTypeInfo(property: SerializableProperty, type: Type): JVMSerialTypeInfo {
+    fun SerializableInfo(serializer: ClassDescriptor?) =
+        JVMSerialTypeInfo(
+            property,
+            Type.getType("Ljava/lang/Object;"),
+            if (property.type.isMarkedNullable) "Nullable" else "",
+            serializer
+        )
+
+    property.serializableWith?.toClassDescriptor?.let { return SerializableInfo(it) }
+    property.type.overridenSerializer?.toClassDescriptor?.let { return SerializableInfo(it) }
+    findAddOnSerializer(property.type)?.let { return SerializableInfo(it) }
+
     if (property.type.isTypeParameter()) return JVMSerialTypeInfo(
         property,
         Type.getType("Ljava/lang/Object;"),

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

@@ -385,6 +385,7 @@ class SerializerCodegenImpl(
                         genValidateProperty(index, ::bitMaskOff)
                         ificmpeq(readLabel)
                         load(propVar, propertyType)
+                        StackValue.coerce(propertyType, sti.type, this)
                         produceCall(true)
                         goTo(endL)
                         visitLabel(readLabel)

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

@@ -22,6 +22,7 @@ object SerializationAnnotations {
     internal val serialInfoFqName = FqName("kotlinx.serialization.SerialInfo")
 
     internal val contextualFqName = FqName("kotlinx.serialization.ContextualSerialization")
+    internal val additionalSerializersFqName = FqName("kotlinx.serialization.UseSerializers")
 }
 
 object SerialEntityNames {