Add .serializer() to enum companion and object with custom serializer

Fixes Kotlin/kotlinx.serialization#1386

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

@@ -43,7 +43,7 @@ fun AbstractSerialGenerator.findAddOnSerializer(propertyType: KotlinType, module
     return null
 }
 
-fun KotlinType.isSerializableObject() =
+fun KotlinType.isGeneratedSerializableObject() =
     toClassDescriptor?.run { kind == ClassKind.OBJECT && hasSerializableAnnotationWithoutArgs } == true
 
 @Suppress("FunctionName", "LocalVariableName")
@@ -151,7 +151,7 @@ fun findTypeSerializer(module: ModuleDescriptor, kType: KotlinType): ClassDescri
     if (userOverride != null) return userOverride.toClassDescriptor
     if (kType.isTypeParameter()) return null
     if (KotlinBuiltIns.isArray(kType)) return module.getClassFromInternalSerializationPackage(SpecialBuiltins.referenceArraySerializer)
-    if (kType.isSerializableObject()) return module.getClassFromInternalSerializationPackage(SpecialBuiltins.objectSerializer)
+    if (kType.isGeneratedSerializableObject()) return module.getClassFromInternalSerializationPackage(SpecialBuiltins.objectSerializer)
     val stdSer = findStandardKotlinTypeSerializer(module, kType) // see if there is a standard serializer
         ?: findEnumTypeSerializer(module, kType)
     if (stdSer != null) return stdSer
@@ -216,7 +216,7 @@ fun findStandardKotlinTypeSerializer(module: ModuleDescriptor, kType: KotlinType
 
 fun findEnumTypeSerializer(module: ModuleDescriptor, kType: KotlinType): ClassDescriptor? {
     val classDescriptor = kType.toClassDescriptor ?: return null
-    return if (classDescriptor.kind == ClassKind.ENUM_CLASS && !classDescriptor.isSerializableEnum())
+    return if (classDescriptor.kind == ClassKind.ENUM_CLASS && !classDescriptor.isInternallySerializableEnum())
         module.findClassAcrossModuleDependencies(enumSerializerId)
     else null
 }

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

@@ -572,7 +572,7 @@ open class SerializerIrGenerator(
         ) {
             val serializableDesc = getSerializableClassDescriptorBySerializer(irClass.symbol.descriptor) ?: return
             val generator = when {
-                serializableDesc.isSerializableEnum() -> SerializerForEnumsGenerator(irClass, context, bindingContext, serialInfoJvmGenerator)
+                serializableDesc.isInternallySerializableEnum() -> SerializerForEnumsGenerator(irClass, context, bindingContext, serialInfoJvmGenerator)
                 serializableDesc.isInlineClass() -> SerializerForInlineClassGenerator(irClass, context, bindingContext, serialInfoJvmGenerator)
                 else -> SerializerIrGenerator(irClass, context, bindingContext, metadataPlugin, serialInfoJvmGenerator)
             }

plugins/kotlin-serialization/kotlin-serialization-compiler/src/org/jetbrains/kotlinx/serialization/compiler/backend/js/SerializerJsTranslator.kt

@@ -373,7 +373,7 @@ open class SerializerJsTranslator(
             metadataPlugin: SerializationDescriptorSerializerPlugin?
         ) {
             val serializableDesc = getSerializableClassDescriptorBySerializer(descriptor) ?: return
-            if (serializableDesc.isSerializableEnum()) {
+            if (serializableDesc.isInternallySerializableEnum()) {
                 SerializerForEnumsTranslator(descriptor, translator, context).generate()
             } else {
                 SerializerJsTranslator(descriptor, translator, context, metadataPlugin).generate()

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

@@ -38,7 +38,7 @@ open class SerializerCodegenImpl(
     companion object {
         fun generateSerializerExtensions(codegen: ImplementationBodyCodegen, metadataPlugin: SerializationDescriptorSerializerPlugin?) {
             val serializableClass = getSerializableClassDescriptorBySerializer(codegen.descriptor) ?: return
-            val serializerCodegen = if (serializableClass.isSerializableEnum()) {
+            val serializerCodegen = if (serializableClass.isInternallySerializableEnum()) {
                 SerializerForEnumsCodegen(codegen, serializableClass)
             } else {
                 SerializerCodegenImpl(codegen, serializableClass, metadataPlugin)

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

@@ -97,9 +97,12 @@ val KotlinType?.toClassDescriptor: ClassDescriptor?
     }
 
 internal val ClassDescriptor.shouldHaveGeneratedMethodsInCompanion: Boolean
-    get() = this.isSerializableObject || this.isSerializableEnum() || this.kind == ClassKind.CLASS && annotations.hasAnnotation(SerializationAnnotations.serializableAnnotationFqName)
+    get() = this.isSerializableObject || this.isSerializableEnum() || this.kind == ClassKind.CLASS && hasSerializableAnnotation
 
 internal val ClassDescriptor.isSerializableObject: Boolean
+    get() = kind == ClassKind.OBJECT && hasSerializableAnnotation
+
+internal val ClassDescriptor.isInternallySerializableObject: Boolean
     get() = kind == ClassKind.OBJECT && hasSerializableAnnotationWithoutArgs
 
 internal val ClassDescriptor.isInternalSerializable: Boolean //todo normal checking
@@ -108,14 +111,12 @@ internal val ClassDescriptor.isInternalSerializable: Boolean //todo normal check
         return hasSerializableAnnotationWithoutArgs
     }
 
-internal fun ClassDescriptor.isSerializableEnum(): Boolean {
+internal fun ClassDescriptor.isSerializableEnum(): Boolean = kind == ClassKind.ENUM_CLASS && hasSerializableAnnotation
-    if (this.kind != ClassKind.ENUM_CLASS) return false
+
-    if (hasSerializableAnnotationWithoutArgs) return true
+internal fun ClassDescriptor.isInternallySerializableEnum(): Boolean = kind == ClassKind.ENUM_CLASS && hasSerializableAnnotationWithoutArgs
-    return false
-}
 
 internal val ClassDescriptor.shouldHaveGeneratedSerializer: Boolean
-    get() = (isInternalSerializable && (modality == Modality.FINAL || modality == Modality.OPEN)) || isSerializableEnum()
+    get() = (isInternalSerializable && (modality == Modality.FINAL || modality == Modality.OPEN)) || isInternallySerializableEnum()
 
 internal fun ClassDescriptor.enumEntries(): List<ClassDescriptor> {
     check(this.kind == ClassKind.ENUM_CLASS)
@@ -128,9 +129,12 @@ internal fun ClassDescriptor.enumEntries(): List<ClassDescriptor> {
 internal val Annotations.hasAnySerialAnnotation: Boolean
     get() = serialNameValue != null || any { it.annotationClass?.isSerialInfoAnnotation == true }
 
+private val ClassDescriptor.hasSerializableAnnotation
+    get() = annotations.hasAnnotation(SerializationAnnotations.serializableAnnotationFqName)
+
 internal val ClassDescriptor.hasSerializableAnnotationWithoutArgs: Boolean
     get() {
-        if (!annotations.hasAnnotation(SerializationAnnotations.serializableAnnotationFqName)) return false
+        if (!hasSerializableAnnotation) return false
         // If provided descriptor is lazy, carefully look at psi in order not to trigger full resolve which may be recursive.
         // Otherwise, this descriptor is deserialized from another module and it is OK to check value right away.
         val psi = findSerializableAnnotationDeclaration() ?: return (serializableWith == null)
@@ -178,7 +182,7 @@ internal val ClassDescriptor?.classSerializer: ClassDescriptor?
     }
 
 internal val ClassDescriptor.hasCompanionObjectAsSerializer: Boolean
-    get() = isSerializableObject || companionObjectDescriptor?.serializerForClass == this.defaultType
+    get() = isInternallySerializableObject || companionObjectDescriptor?.serializerForClass == this.defaultType
 
 // returns only user-overriden Serializer
 internal val KotlinType.overridenSerializer: KotlinType?

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

@@ -68,7 +68,7 @@ class SerializableProperties(private val serializableClass: ClassDescriptor, val
             .let { unsort(serializableClass, it) }
 
         isExternallySerializable =
-            serializableClass.isSerializableEnum() || primaryConstructorParameters.size == primaryConstructorProperties.size
+            serializableClass.isInternallySerializableEnum() || primaryConstructorParameters.size == primaryConstructorProperties.size
 
     }