Hocon encoder

formats/hocon/api/kotlinx-serialization-hocon.api

@@ -1,7 +1,8 @@
 public abstract class kotlinx/serialization/hocon/Hocon : kotlinx/serialization/SerialFormat {
 	public static final field Default Lkotlinx/serialization/hocon/Hocon$Default;
-	public synthetic fun <init> (ZZLjava/lang/String;Lkotlinx/serialization/modules/SerializersModule;Lkotlin/jvm/internal/DefaultConstructorMarker;)V
+	public synthetic fun <init> (ZZZLjava/lang/String;Lkotlinx/serialization/modules/SerializersModule;Lkotlin/jvm/internal/DefaultConstructorMarker;)V
 	public final fun decodeFromConfig (Lkotlinx/serialization/DeserializationStrategy;Lcom/typesafe/config/Config;)Ljava/lang/Object;
+	public final fun encodeToConfig (Lkotlinx/serialization/SerializationStrategy;Ljava/lang/Object;)Lcom/typesafe/config/Config;
 	public fun getSerializersModule ()Lkotlinx/serialization/modules/SerializersModule;
 }
 
@@ -10,10 +11,12 @@ public final class kotlinx/serialization/hocon/Hocon$Default : kotlinx/serializa
 
 public final class kotlinx/serialization/hocon/HoconBuilder {
 	public final fun getClassDiscriminator ()Ljava/lang/String;
+	public final fun getEncodeDefaults ()Z
 	public final fun getSerializersModule ()Lkotlinx/serialization/modules/SerializersModule;
 	public final fun getUseArrayPolymorphism ()Z
 	public final fun getUseConfigNamingConvention ()Z
 	public final fun setClassDiscriminator (Ljava/lang/String;)V
+	public final fun setEncodeDefaults (Z)V
 	public final fun setSerializersModule (Lkotlinx/serialization/modules/SerializersModule;)V
 	public final fun setUseArrayPolymorphism (Z)V
 	public final fun setUseConfigNamingConvention (Z)V

formats/hocon/build.gradle

@@ -12,17 +12,9 @@ compileKotlin {
     }
 }
 
-configurations {
-    apiElements {
-        attributes {
-            attribute(TargetJvmVersion.TARGET_JVM_VERSION_ATTRIBUTE, 8)
-        }
-    }
-    runtimeElements {
-        attributes {
-            attribute(TargetJvmVersion.TARGET_JVM_VERSION_ATTRIBUTE, 8)
-        }
-    }
+java {
+    sourceCompatibility = JavaVersion.VERSION_1_8
+    targetCompatibility = JavaVersion.VERSION_1_8
 }
 
 

formats/hocon/src/main/kotlin/kotlinx/serialization/hocon/Hocon.kt

@@ -25,24 +25,45 @@ import kotlinx.serialization.modules.*
  */
 @ExperimentalSerializationApi
 public sealed class Hocon(
-        internal val useConfigNamingConvention: Boolean,
-        internal val useArrayPolymorphism: Boolean,
-        internal val classDiscriminator: String,
-        override val serializersModule: SerializersModule
+    internal val encodeDefaults: Boolean,
+    internal val useConfigNamingConvention: Boolean,
+    internal val useArrayPolymorphism: Boolean,
+    internal val classDiscriminator: String,
+    override val serializersModule: SerializersModule,
 ) : SerialFormat {
 
+    /**
+     * Decodes the given [config] into a value of type [T] using the given serializer.
+     */
     @ExperimentalSerializationApi
     public fun <T> decodeFromConfig(deserializer: DeserializationStrategy<T>, config: Config): T =
         ConfigReader(config).decodeSerializableValue(deserializer)
 
     /**
-     * The default instance of Hocon parser.
+     * Encodes the given [value] into a [Config] using the given [serializer].
+     * @throws SerializationException If list or primitive type passed as a [value].
      */
     @ExperimentalSerializationApi
-    public companion object Default : Hocon(false, false, "type", EmptySerializersModule) {
-        private val NAMING_CONVENTION_REGEX by lazy { "[A-Z]".toRegex() }
+    public fun <T> encodeToConfig(serializer: SerializationStrategy<T>, value: T): Config {
+        lateinit var configValue: ConfigValue
+        val encoder = HoconConfigEncoder(this) { configValue = it }
+        encoder.encodeSerializableValue(serializer, value)
+
+        if (configValue !is ConfigObject) {
+            throw SerializationException(
+                "Value of type '${configValue.valueType()}' can't be used at the root of HOCON Config. " +
+                        "It should be either object or map."
+            )
+        }
+        return (configValue as ConfigObject).toConfig()
     }
 
+    /**
+     * The default instance of Hocon parser.
+     */
+    @ExperimentalSerializationApi
+    public companion object Default : Hocon(false, false, false, "type", EmptySerializersModule)
+
     private abstract inner class ConfigConverter<T> : TaggedDecoder<T>() {
         override val serializersModule: SerializersModule
             get() = this@Hocon.serializersModule
@@ -59,8 +80,7 @@ public sealed class Hocon(
                 }
             } catch (e: ConfigException) {
                 val configOrigin = e.origin()
-                val requiredType = E::class.simpleName
-                throw SerializationException("${configOrigin.description()} required to be of type $requiredType")
+                throw ConfigValueTypeCastException<E>(configOrigin)
             }
         }
 
@@ -109,13 +129,7 @@ public sealed class Hocon(
             if (parentName.isEmpty()) childName else "$parentName.$childName"
 
         override fun SerialDescriptor.getTag(index: Int): String =
-            composeName(currentTagOrNull ?: "", getConventionElementName(index))
-
-        private fun SerialDescriptor.getConventionElementName(index: Int): String {
-            val originalName = getElementName(index)
-            return if (!useConfigNamingConvention) originalName
-            else originalName.replace(NAMING_CONVENTION_REGEX) { "-${it.value.lowercase()}" }
-        }
+            composeName(currentTagOrNull.orEmpty(), getConventionElementName(index, useConfigNamingConvention))
 
         override fun decodeNotNullMark(): Boolean {
             // Tag might be null for top-level deserialization
@@ -133,24 +147,14 @@ public sealed class Hocon(
             val reader = ConfigReader(config)
             val type = reader.decodeTaggedString(classDiscriminator)
             val actualSerializer = deserializer.findPolymorphicSerializerOrNull(reader, type)
-                    ?: throwSerializerNotFound(type)
+                ?: throw SerializerNotFoundException(type)
 
             @Suppress("UNCHECKED_CAST")
             return (actualSerializer as DeserializationStrategy<T>).deserialize(reader)
         }
 
-        private fun throwSerializerNotFound(type: String?): Nothing {
-            val suffix = if (type == null) "missing class discriminator ('null')" else "class discriminator '$type'"
-            throw SerializationException("Polymorphic serializer was not found for $suffix")
-        }
-
         override fun beginStructure(descriptor: SerialDescriptor): CompositeDecoder {
-            val kind = when (descriptor.kind) {
-                is PolymorphicKind -> {
-                    if (useArrayPolymorphism) StructureKind.LIST else StructureKind.MAP
-                }
-                else -> descriptor.kind
-            }
+            val kind = descriptor.hoconKind(useArrayPolymorphism)
 
             return when {
                 kind.listLike -> ListConfigReader(conf.getList(currentTag))
@@ -239,28 +243,31 @@ public sealed class Hocon(
             throw SerializationException("$serialName does not contain element with name '$name'")
         return index
     }
-
-    private val SerialKind.listLike get() = this == StructureKind.LIST || this is PolymorphicKind
-    private val SerialKind.objLike get() = this == StructureKind.CLASS || this == StructureKind.OBJECT
 }
 
 /**
- * Decodes the given [config] into a value of type [T] using a deserialize retrieved
- * from reified type parameter.
+ * Decodes the given [config] into a value of type [T] using a deserializer retrieved
+ * from the reified type parameter.
  */
 @ExperimentalSerializationApi
 public inline fun <reified T> Hocon.decodeFromConfig(config: Config): T =
     decodeFromConfig(serializersModule.serializer(), config)
 
+/**
+ * Encodes the given [value] of type [T] into a [Config] using a serializer retrieved
+ * from the reified type parameter.
+ */
+@ExperimentalSerializationApi
+public inline fun <reified T> Hocon.encodeToConfig(value: T): Config =
+    encodeToConfig(serializersModule.serializer(), value)
+
 /**
  * Creates an instance of [Hocon] configured from the optionally given [Hocon instance][from]
  * and adjusted with [builderAction].
  */
 @ExperimentalSerializationApi
 public fun Hocon(from: Hocon = Hocon, builderAction: HoconBuilder.() -> Unit): Hocon {
-    val builder = HoconBuilder(from)
-    builder.builderAction()
-    return HoconImpl(builder.useConfigNamingConvention, builder.useArrayPolymorphism, builder.classDiscriminator, builder.serializersModule)
+    return HoconImpl(HoconBuilder(from).apply(builderAction))
 }
 
 /**
@@ -273,6 +280,12 @@ public class HoconBuilder internal constructor(hocon: Hocon) {
      */
     public var serializersModule: SerializersModule = hocon.serializersModule
 
+    /**
+     * Specifies whether default values of Kotlin properties should be encoded.
+     * `false` by default.
+     */
+    public var encodeDefaults: Boolean = hocon.encodeDefaults
+
     /**
      * Switches naming resolution to config naming convention: hyphen separated.
      */
@@ -293,9 +306,10 @@ public class HoconBuilder internal constructor(hocon: Hocon) {
 }
 
 @OptIn(ExperimentalSerializationApi::class)
-private class HoconImpl(
-        useConfigNamingConvention: Boolean,
-        useArrayPolymorphism: Boolean,
-        classDiscriminator: String,
-        serializersModule: SerializersModule
-) : Hocon(useConfigNamingConvention, useArrayPolymorphism, classDiscriminator, serializersModule)
+private class HoconImpl(hoconBuilder: HoconBuilder) : Hocon(
+    encodeDefaults = hoconBuilder.encodeDefaults,
+    useConfigNamingConvention = hoconBuilder.useConfigNamingConvention,
+    useArrayPolymorphism = hoconBuilder.useArrayPolymorphism,
+    classDiscriminator = hoconBuilder.classDiscriminator,
+    serializersModule = hoconBuilder.serializersModule
+)

formats/hocon/src/main/kotlin/kotlinx/serialization/hocon/HoconEncoder.kt

@@ -0,0 +1,140 @@
+/*
+ * Copyright 2017-2021 JetBrains s.r.o. Use of this source code is governed by the Apache 2.0 license.
+ */
+
+package kotlinx.serialization.hocon
+
+import com.typesafe.config.*
+import kotlinx.serialization.*
+import kotlinx.serialization.descriptors.*
+import kotlinx.serialization.encoding.*
+import kotlinx.serialization.internal.*
+import kotlinx.serialization.modules.*
+
+@ExperimentalSerializationApi
+internal abstract class AbstractHoconEncoder(
+    private val hocon: Hocon,
+    private val valueConsumer: (ConfigValue) -> Unit,
+) : NamedValueEncoder() {
+
+    override val serializersModule: SerializersModule
+        get() = hocon.serializersModule
+
+    private var writeDiscriminator: Boolean = false
+
+    override fun elementName(descriptor: SerialDescriptor, index: Int): String {
+        return descriptor.getConventionElementName(index, hocon.useConfigNamingConvention)
+    }
+
+    override fun composeName(parentName: String, childName: String): String = childName
+
+    protected abstract fun encodeTaggedConfigValue(tag: String, value: ConfigValue)
+    protected abstract fun getCurrent(): ConfigValue
+
+    override fun encodeTaggedValue(tag: String, value: Any) = encodeTaggedConfigValue(tag, configValueOf(value))
+    override fun encodeTaggedNull(tag: String) = encodeTaggedConfigValue(tag, configValueOf(null))
+    override fun encodeTaggedChar(tag: String, value: Char) = encodeTaggedString(tag, value.toString())
+
+    override fun encodeTaggedEnum(tag: String, enumDescriptor: SerialDescriptor, ordinal: Int) {
+        encodeTaggedString(tag, enumDescriptor.getElementName(ordinal))
+    }
+
+    override fun shouldEncodeElementDefault(descriptor: SerialDescriptor, index: Int): Boolean = hocon.encodeDefaults
+
+    override fun <T> encodeSerializableValue(serializer: SerializationStrategy<T>, value: T) {
+        if (serializer !is AbstractPolymorphicSerializer<*> || hocon.useArrayPolymorphism) {
+            serializer.serialize(this, value)
+            return
+        }
+
+        @Suppress("UNCHECKED_CAST")
+        val casted = serializer as AbstractPolymorphicSerializer<Any>
+        val actualSerializer = casted.findPolymorphicSerializer(this, value as Any)
+        writeDiscriminator = true
+
+        actualSerializer.serialize(this, value)
+    }
+
+    override fun beginStructure(descriptor: SerialDescriptor): CompositeEncoder {
+        val consumer =
+            if (currentTagOrNull == null) valueConsumer
+            else { value -> encodeTaggedConfigValue(currentTag, value) }
+        val kind = descriptor.hoconKind(hocon.useArrayPolymorphism)
+
+        return when {
+            kind.listLike -> HoconConfigListEncoder(hocon, consumer)
+            kind.objLike -> HoconConfigEncoder(hocon, consumer)
+            kind == StructureKind.MAP -> HoconConfigMapEncoder(hocon, consumer)
+            else -> this
+        }.also { encoder ->
+            if (writeDiscriminator) {
+                encoder.encodeTaggedString(hocon.classDiscriminator, descriptor.serialName)
+                writeDiscriminator = false
+            }
+        }
+    }
+
+    override fun endEncode(descriptor: SerialDescriptor) {
+        valueConsumer(getCurrent())
+    }
+
+    private fun configValueOf(value: Any?) = ConfigValueFactory.fromAnyRef(value)
+}
+
+@ExperimentalSerializationApi
+internal class HoconConfigEncoder(hocon: Hocon, configConsumer: (ConfigValue) -> Unit) :
+    AbstractHoconEncoder(hocon, configConsumer) {
+
+    private val configMap = mutableMapOf<String, ConfigValue>()
+
+    override fun encodeTaggedConfigValue(tag: String, value: ConfigValue) {
+        configMap[tag] = value
+    }
+
+    override fun getCurrent(): ConfigValue = ConfigValueFactory.fromMap(configMap)
+}
+
+@ExperimentalSerializationApi
+internal class HoconConfigListEncoder(hocon: Hocon, configConsumer: (ConfigValue) -> Unit) :
+    AbstractHoconEncoder(hocon, configConsumer) {
+
+    private val values = mutableListOf<ConfigValue>()
+
+    override fun elementName(descriptor: SerialDescriptor, index: Int): String = index.toString()
+
+    override fun encodeTaggedConfigValue(tag: String, value: ConfigValue) {
+        values.add(tag.toInt(), value)
+    }
+
+    override fun getCurrent(): ConfigValue = ConfigValueFactory.fromIterable(values)
+}
+
+@ExperimentalSerializationApi
+internal class HoconConfigMapEncoder(hocon: Hocon, configConsumer: (ConfigValue) -> Unit) :
+    AbstractHoconEncoder(hocon, configConsumer) {
+
+    private val configMap = mutableMapOf<String, ConfigValue>()
+
+    private lateinit var key: String
+    private var isKey: Boolean = true
+
+    override fun encodeTaggedConfigValue(tag: String, value: ConfigValue) {
+        if (isKey) {
+            key = when (value.valueType()) {
+                ConfigValueType.OBJECT, ConfigValueType.LIST -> throw InvalidKeyKindException(value)
+                else -> value.unwrappedNullable().toString()
+            }
+            isKey = false
+        } else {
+            configMap[key] = value
+            isKey = true
+        }
+    }
+
+    override fun getCurrent(): ConfigValue = ConfigValueFactory.fromMap(configMap)
+
+    // Without cast to `Any?` Kotlin will assume unwrapped value as non-nullable by default
+    // and will call `Any.toString()` instead of extension-function `Any?.toString()`.
+    // We can't cast value in place using `(value.unwrapped() as Any?).toString()` because of warning "No cast needed".
+    private fun ConfigValue.unwrappedNullable(): Any? = unwrapped()
+}

formats/hocon/src/main/kotlin/kotlinx/serialization/hocon/HoconExceptions.kt

@@ -0,0 +1,22 @@
+/*
+ * Copyright 2017-2021 JetBrains s.r.o. Use of this source code is governed by the Apache 2.0 license.
+ */
+
+package kotlinx.serialization.hocon
+
+import com.typesafe.config.*
+import kotlinx.serialization.*
+
+internal fun SerializerNotFoundException(type: String?) = SerializationException(
+    "Polymorphic serializer was not found for " +
+            if (type == null) "missing class discriminator ('null')" else "class discriminator '$type'"
+)
+
+internal inline fun <reified T> ConfigValueTypeCastException(valueOrigin: ConfigOrigin) = SerializationException(
+    "${valueOrigin.description()} required to be of type ${T::class.simpleName}."
+)
+
+internal fun InvalidKeyKindException(value: ConfigValue) = SerializationException(
+    "Value of type '${value.valueType()}' can't be used in HOCON as a key in the map. " +
+            "It should have either primitive or enum kind."
+)