Stabilize EmptySerializersModule (#1921)

Fixes #1765

core/api/kotlinx-serialization-core.api

@@ -1205,6 +1205,7 @@ public final class kotlinx/serialization/modules/SerializersModuleBuilder : kotl
 }
 
 public final class kotlinx/serialization/modules/SerializersModuleBuildersKt {
+	public static final fun EmptySerializersModule ()Lkotlinx/serialization/modules/SerializersModule;
 	public static final fun SerializersModule (Lkotlin/jvm/functions/Function1;)Lkotlinx/serialization/modules/SerializersModule;
 	public static final fun polymorphic (Lkotlinx/serialization/modules/SerializersModuleBuilder;Lkotlin/reflect/KClass;Lkotlinx/serialization/KSerializer;Lkotlin/jvm/functions/Function1;)V
 	public static synthetic fun polymorphic$default (Lkotlinx/serialization/modules/SerializersModuleBuilder;Lkotlin/reflect/KClass;Lkotlinx/serialization/KSerializer;Lkotlin/jvm/functions/Function1;ILjava/lang/Object;)V

core/commonMain/src/kotlinx/serialization/Serializers.kt

@@ -38,15 +38,15 @@ public inline fun <reified T> SerializersModule.serializer(): KSerializer<T> {
  *  @throws SerializationException if serializer cannot be created (provided [type] or its type argument is not serializable).
  */
 @OptIn(ExperimentalSerializationApi::class)
-public fun serializer(type: KType): KSerializer<Any?> = EmptySerializersModule.serializer(type)
+public fun serializer(type: KType): KSerializer<Any?> = EmptySerializersModule().serializer(type)
 
 /**
  * Creates a serializer for the given [type].
  * [type] argument can be obtained with experimental [typeOf] method.
  * Returns `null` if serializer cannot be created (provided [type] or its type argument is not serializable).
  */
 @OptIn(ExperimentalSerializationApi::class)
-public fun serializerOrNull(type: KType): KSerializer<Any?>? = EmptySerializersModule.serializerOrNull(type)
+public fun serializerOrNull(type: KType): KSerializer<Any?>? = EmptySerializersModule().serializerOrNull(type)
 
 /**
  * Attempts to create a serializer for the given [type] and fallbacks to [contextual][SerializersModule.getContextual]
@@ -122,7 +122,10 @@ private fun SerializersModule.builtinSerializer(
 }
 
 @OptIn(ExperimentalSerializationApi::class)
-internal fun <T : Any> SerializersModule.reflectiveOrContextual(kClass: KClass<T>, typeArgumentsSerializers: List<KSerializer<Any?>>): KSerializer<T>? {
+internal fun <T : Any> SerializersModule.reflectiveOrContextual(
+    kClass: KClass<T>,
+    typeArgumentsSerializers: List<KSerializer<Any?>>
+): KSerializer<T>? {
     return kClass.serializerOrNull() ?: getContextual(kClass, typeArgumentsSerializers)
 }
 

core/commonMain/src/kotlinx/serialization/internal/NoOpEncoder.kt

@@ -14,7 +14,7 @@ import kotlinx.serialization.modules.*
  */
 @OptIn(ExperimentalSerializationApi::class)
 internal object NoOpEncoder : AbstractEncoder() {
-    override val serializersModule: SerializersModule = EmptySerializersModule
+    override val serializersModule: SerializersModule = EmptySerializersModule()
 
     public override fun encodeValue(value: Any): Unit = Unit
 

core/commonMain/src/kotlinx/serialization/internal/Tagged.kt

@@ -24,7 +24,7 @@ public abstract class TaggedEncoder<Tag : Any?> : Encoder, CompositeEncoder {
     protected abstract fun SerialDescriptor.getTag(index: Int): Tag
 
     override val serializersModule: SerializersModule
-        get() = EmptySerializersModule
+        get() = EmptySerializersModule()
 
     // ---- API ----
     protected open fun encodeTaggedValue(tag: Tag, value: Any): Unit =
@@ -177,7 +177,7 @@ public abstract class NamedValueEncoder : TaggedEncoder<String>() {
 @InternalSerializationApi
 public abstract class TaggedDecoder<Tag : Any?> : Decoder, CompositeDecoder {
     override val serializersModule: SerializersModule
-        get() = EmptySerializersModule
+        get() = EmptySerializersModule()
 
     protected abstract fun SerialDescriptor.getTag(index: Int): Tag
 

core/commonMain/src/kotlinx/serialization/modules/SerializersModule.kt

@@ -6,6 +6,7 @@ package kotlinx.serialization.modules
 
 import kotlinx.serialization.*
 import kotlinx.serialization.internal.*
+import kotlin.js.*
 import kotlin.jvm.*
 import kotlin.native.concurrent.*
 import kotlin.reflect.*
@@ -18,6 +19,9 @@ import kotlin.reflect.*
  * To enable runtime serializers resolution, one of the special annotations must be used on target types
  * ([Polymorphic] or [Contextual]), and a serial module with serializers should be used during construction of [SerialFormat].
  *
+ * Serializers module can be built with `SerializersModule {}` builder function.
+ * Empty module can be obtained with `EmptySerializersModule()` factory function.
+ *
  * @see Contextual
  * @see Polymorphic
  */
@@ -28,7 +32,7 @@ public sealed class SerializersModule {
         "Deprecated in favor of overload with default parameter",
         ReplaceWith("getContextual(kclass)"),
         DeprecationLevel.HIDDEN
-    ) // Was stable since 1.0.0, HIDDEN in 1.2.0 in a backwards-compatible manner
+    ) // Was experimental since 1.0.0, HIDDEN in 1.2.0 in a backwards-compatible manner
     public fun <T : Any> getContextual(kclass: KClass<T>): KSerializer<T>? =
         getContextual(kclass, emptyList())
 
@@ -70,7 +74,10 @@ public sealed class SerializersModule {
  * A [SerializersModule] which is empty and always returns `null`.
  */
 @SharedImmutable
-@ExperimentalSerializationApi
+@Deprecated("Deprecated in the favour of 'EmptySerializersModule()'",
+    level = DeprecationLevel.WARNING,
+    replaceWith = ReplaceWith("EmptySerializersModule()"))
+@JsName("EmptySerializersModuleLegacyJs") // Compatibility with JS
 public val EmptySerializersModule: SerializersModule = SerialModuleImpl(emptyMap(), emptyMap(), emptyMap(), emptyMap(), emptyMap())
 
 /**

core/commonMain/src/kotlinx/serialization/modules/SerializersModuleBuilders.kt

@@ -33,6 +33,11 @@ public inline fun SerializersModule(builderAction: SerializersModuleBuilder.() -
     return builder.build()
 }
 
+/**
+ * A [SerializersModule] which is empty and returns `null` from each method.
+ */
+public fun EmptySerializersModule(): SerializersModule = @Suppress("DEPRECATION") EmptySerializersModule
+
 /**
  * A builder class for [SerializersModule] DSL. To create an instance of builder, use [SerializersModule] factory function.
  */

core/commonTest/src/kotlinx/serialization/BasicTypesSerializationTest.kt

@@ -20,7 +20,7 @@ class BasicTypesSerializationTest {
 
     // KeyValue Input/Output
     class KeyValueOutput(private val sb: StringBuilder) : AbstractEncoder() {
-        override val serializersModule: SerializersModule = EmptySerializersModule
+        override val serializersModule: SerializersModule = EmptySerializersModule()
 
         override fun beginStructure(descriptor: SerialDescriptor): CompositeEncoder {
             sb.append('{')
@@ -56,7 +56,7 @@ class BasicTypesSerializationTest {
     }
 
     class KeyValueInput(private val inp: Parser) : AbstractDecoder() {
-        override val serializersModule: SerializersModule = EmptySerializersModule
+        override val serializersModule: SerializersModule = EmptySerializersModule()
 
         override fun beginStructure(descriptor: SerialDescriptor): CompositeDecoder {
             inp.expectAfterWhiteSpace('{')

core/commonTest/src/kotlinx/serialization/CustomPropertyAccessorsTest.kt

@@ -108,9 +108,8 @@ class CustomPropertyAccessorsTest {
      */
 
 
-
     private class CommonStringDecoder(private val elementCount: Int) : AbstractDecoder() {
-        override val serializersModule: SerializersModule = EmptySerializersModule
+        override val serializersModule: SerializersModule = EmptySerializersModule()
         private var elementIndex = 0
 
         override fun decodeString(): String {

core/jvmMain/src/kotlinx/serialization/SerializersJvm.kt

@@ -27,7 +27,7 @@ import kotlin.reflect.*
  * @throws SerializationException if serializer cannot be created (provided [type] or its type argument is not serializable).
  */
 @ExperimentalSerializationApi
-public fun serializer(type: Type): KSerializer<Any> = EmptySerializersModule.serializer(type)
+public fun serializer(type: Type): KSerializer<Any> = EmptySerializersModule().serializer(type)
 
 /**
  * Reflectively constructs a serializer for the given reflective Java [type].
@@ -40,7 +40,7 @@ public fun serializer(type: Type): KSerializer<Any> = EmptySerializersModule.ser
  * Returns `null` if serializer cannot be created (provided [type] or its type argument is not serializable).
  */
 @ExperimentalSerializationApi
-public fun serializerOrNull(type: Type): KSerializer<Any>? = EmptySerializersModule.serializerOrNull(type)
+public fun serializerOrNull(type: Type): KSerializer<Any>? = EmptySerializersModule().serializerOrNull(type)
 
 /**
  * Retrieves serializer for the given reflective Java [type] using
@@ -56,7 +56,8 @@ public fun serializerOrNull(type: Type): KSerializer<Any>? = EmptySerializersMod
  */
 @ExperimentalSerializationApi
 public fun SerializersModule.serializer(type: Type): KSerializer<Any> =
-    serializerByJavaTypeImpl(type, failOnMissingTypeArgSerializer = true) ?: type.prettyClass().serializerNotRegistered()
+    serializerByJavaTypeImpl(type, failOnMissingTypeArgSerializer = true) ?: type.prettyClass()
+        .serializerNotRegistered()
 
 /**
  * Retrieves serializer for the given reflective Java [type] using
@@ -75,7 +76,10 @@ public fun SerializersModule.serializerOrNull(type: Type): KSerializer<Any>? =
     serializerByJavaTypeImpl(type, failOnMissingTypeArgSerializer = false)
 
 @OptIn(ExperimentalSerializationApi::class)
-private fun SerializersModule.serializerByJavaTypeImpl(type: Type, failOnMissingTypeArgSerializer: Boolean = true): KSerializer<Any>? =
+private fun SerializersModule.serializerByJavaTypeImpl(
+    type: Type,
+    failOnMissingTypeArgSerializer: Boolean = true
+): KSerializer<Any>? =
     when (type) {
         is GenericArrayType -> {
             genericArraySerializer(type, failOnMissingTypeArgSerializer)
@@ -85,7 +89,9 @@ private fun SerializersModule.serializerByJavaTypeImpl(type: Type, failOnMissing
             val rootClass = (type.rawType as Class<*>)
             val args = (type.actualTypeArguments)
             val argsSerializers =
-                if (failOnMissingTypeArgSerializer) args.map { serializer(it) } else args.map { serializerOrNull(it) ?: return null }
+                if (failOnMissingTypeArgSerializer) args.map { serializer(it) } else args.map {
+                    serializerOrNull(it) ?: return null
+                }
             when {
                 Set::class.java.isAssignableFrom(rootClass) -> SetSerializer(argsSerializers[0]) as KSerializer<Any>
                 List::class.java.isAssignableFrom(rootClass) || Collection::class.java.isAssignableFrom(rootClass) -> ListSerializer(
@@ -122,7 +128,10 @@ private fun SerializersModule.serializerByJavaTypeImpl(type: Type, failOnMissing
     }
 
 @OptIn(ExperimentalSerializationApi::class)
-private fun SerializersModule.typeSerializer(type: Class<*>, failOnMissingTypeArgSerializer: Boolean): KSerializer<Any>? {
+private fun SerializersModule.typeSerializer(
+    type: Class<*>,
+    failOnMissingTypeArgSerializer: Boolean
+): KSerializer<Any>? {
     return if (type.isArray && !type.componentType.isPrimitive) {
         val eType: Class<*> = type.componentType
         val s = if (failOnMissingTypeArgSerializer) serializer(eType) else (serializerOrNull(eType) ?: return null)
@@ -134,7 +143,10 @@ private fun SerializersModule.typeSerializer(type: Class<*>, failOnMissingTypeAr
 }
 
 @OptIn(ExperimentalSerializationApi::class)
-private fun <T : Any> SerializersModule.reflectiveOrContextual(jClass: Class<T>, typeArgumentsSerializers: List<KSerializer<Any?>>): KSerializer<T>? {
+private fun <T : Any> SerializersModule.reflectiveOrContextual(
+    jClass: Class<T>,
+    typeArgumentsSerializers: List<KSerializer<Any?>>
+): KSerializer<T>? {
     jClass.constructSerializerForGivenTypeArgs(*typeArgumentsSerializers.toTypedArray())?.let { return it }
     val kClass = jClass.kotlin
     return kClass.builtinSerializerOrNull() ?: getContextual(kClass, typeArgumentsSerializers)