Experimental support for inline classes (#1244)

* Support for `@Serializable inline class` with generated (requires 1.4.30 IR compiler) and custom serializers

* Standard serializers for UInt, ULong, UByte and UShort

* Unsigned types support for both streaming and tree Json

* Exclude folder with inline classes tests when legacy JVM compiler is used

* Add appendix with info about inline classes to documentation

Co-authored-by: Vsevolod Tolstopyatov <qwwdfsad@gmail.com>

core/api/kotlinx-serialization-core.api

@@ -145,6 +145,10 @@ public final class kotlinx/serialization/builtins/BuiltinSerializersKt {
 	public static final fun ShortArraySerializer ()Lkotlinx/serialization/KSerializer;
 	public static final fun TripleSerializer (Lkotlinx/serialization/KSerializer;Lkotlinx/serialization/KSerializer;Lkotlinx/serialization/KSerializer;)Lkotlinx/serialization/KSerializer;
 	public static final fun getNullable (Lkotlinx/serialization/KSerializer;)Lkotlinx/serialization/KSerializer;
+	public static final fun serializer (Lkotlin/UByte$Companion;)Lkotlinx/serialization/KSerializer;
+	public static final fun serializer (Lkotlin/UInt$Companion;)Lkotlinx/serialization/KSerializer;
+	public static final fun serializer (Lkotlin/ULong$Companion;)Lkotlinx/serialization/KSerializer;
+	public static final fun serializer (Lkotlin/UShort$Companion;)Lkotlinx/serialization/KSerializer;
 	public static final fun serializer (Lkotlin/Unit;)Lkotlinx/serialization/KSerializer;
 	public static final fun serializer (Lkotlin/jvm/internal/BooleanCompanionObject;)Lkotlinx/serialization/KSerializer;
 	public static final fun serializer (Lkotlin/jvm/internal/ByteCompanionObject;)Lkotlinx/serialization/KSerializer;
@@ -242,11 +246,13 @@ public abstract interface class kotlinx/serialization/descriptors/SerialDescript
 	public abstract fun getKind ()Lkotlinx/serialization/descriptors/SerialKind;
 	public abstract fun getSerialName ()Ljava/lang/String;
 	public abstract fun isElementOptional (I)Z
+	public abstract fun isInline ()Z
 	public abstract fun isNullable ()Z
 }
 
 public final class kotlinx/serialization/descriptors/SerialDescriptor$DefaultImpls {
 	public static fun getAnnotations (Lkotlinx/serialization/descriptors/SerialDescriptor;)Ljava/util/List;
+	public static fun isInline (Lkotlinx/serialization/descriptors/SerialDescriptor;)Z
 	public static fun isNullable (Lkotlinx/serialization/descriptors/SerialDescriptor;)Z
 }
 
@@ -315,6 +321,8 @@ public abstract class kotlinx/serialization/encoding/AbstractDecoder : kotlinx/s
 	public fun decodeEnum (Lkotlinx/serialization/descriptors/SerialDescriptor;)I
 	public fun decodeFloat ()F
 	public final fun decodeFloatElement (Lkotlinx/serialization/descriptors/SerialDescriptor;I)F
+	public fun decodeInline (Lkotlinx/serialization/descriptors/SerialDescriptor;)Lkotlinx/serialization/encoding/Decoder;
+	public final fun decodeInlineElement (Lkotlinx/serialization/descriptors/SerialDescriptor;I)Lkotlinx/serialization/encoding/Decoder;
 	public fun decodeInt ()I
 	public final fun decodeIntElement (Lkotlinx/serialization/descriptors/SerialDescriptor;I)I
 	public fun decodeLong ()J
@@ -352,6 +360,8 @@ public abstract class kotlinx/serialization/encoding/AbstractEncoder : kotlinx/s
 	public fun encodeEnum (Lkotlinx/serialization/descriptors/SerialDescriptor;I)V
 	public fun encodeFloat (F)V
 	public final fun encodeFloatElement (Lkotlinx/serialization/descriptors/SerialDescriptor;IF)V
+	public fun encodeInline (Lkotlinx/serialization/descriptors/SerialDescriptor;)Lkotlinx/serialization/encoding/Encoder;
+	public final fun encodeInlineElement (Lkotlinx/serialization/descriptors/SerialDescriptor;I)Lkotlinx/serialization/encoding/Encoder;
 	public fun encodeInt (I)V
 	public final fun encodeIntElement (Lkotlinx/serialization/descriptors/SerialDescriptor;II)V
 	public fun encodeLong (J)V
@@ -382,6 +392,7 @@ public abstract interface class kotlinx/serialization/encoding/CompositeDecoder
 	public abstract fun decodeDoubleElement (Lkotlinx/serialization/descriptors/SerialDescriptor;I)D
 	public abstract fun decodeElementIndex (Lkotlinx/serialization/descriptors/SerialDescriptor;)I
 	public abstract fun decodeFloatElement (Lkotlinx/serialization/descriptors/SerialDescriptor;I)F
+	public abstract fun decodeInlineElement (Lkotlinx/serialization/descriptors/SerialDescriptor;I)Lkotlinx/serialization/encoding/Decoder;
 	public abstract fun decodeIntElement (Lkotlinx/serialization/descriptors/SerialDescriptor;I)I
 	public abstract fun decodeLongElement (Lkotlinx/serialization/descriptors/SerialDescriptor;I)J
 	public abstract fun decodeNullableSerializableElement (Lkotlinx/serialization/descriptors/SerialDescriptor;ILkotlinx/serialization/DeserializationStrategy;Ljava/lang/Object;)Ljava/lang/Object;
@@ -411,6 +422,7 @@ public abstract interface class kotlinx/serialization/encoding/CompositeEncoder
 	public abstract fun encodeCharElement (Lkotlinx/serialization/descriptors/SerialDescriptor;IC)V
 	public abstract fun encodeDoubleElement (Lkotlinx/serialization/descriptors/SerialDescriptor;ID)V
 	public abstract fun encodeFloatElement (Lkotlinx/serialization/descriptors/SerialDescriptor;IF)V
+	public abstract fun encodeInlineElement (Lkotlinx/serialization/descriptors/SerialDescriptor;I)Lkotlinx/serialization/encoding/Encoder;
 	public abstract fun encodeIntElement (Lkotlinx/serialization/descriptors/SerialDescriptor;II)V
 	public abstract fun encodeLongElement (Lkotlinx/serialization/descriptors/SerialDescriptor;IJ)V
 	public abstract fun encodeNullableSerializableElement (Lkotlinx/serialization/descriptors/SerialDescriptor;ILkotlinx/serialization/SerializationStrategy;Ljava/lang/Object;)V
@@ -434,6 +446,7 @@ public abstract interface class kotlinx/serialization/encoding/Decoder {
 	public abstract fun decodeDouble ()D
 	public abstract fun decodeEnum (Lkotlinx/serialization/descriptors/SerialDescriptor;)I
 	public abstract fun decodeFloat ()F
+	public abstract fun decodeInline (Lkotlinx/serialization/descriptors/SerialDescriptor;)Lkotlinx/serialization/encoding/Decoder;
 	public abstract fun decodeInt ()I
 	public abstract fun decodeLong ()J
 	public abstract fun decodeNotNullMark ()Z
@@ -463,6 +476,7 @@ public abstract interface class kotlinx/serialization/encoding/Encoder {
 	public abstract fun encodeDouble (D)V
 	public abstract fun encodeEnum (Lkotlinx/serialization/descriptors/SerialDescriptor;I)V
 	public abstract fun encodeFloat (F)V
+	public abstract fun encodeInline (Lkotlinx/serialization/descriptors/SerialDescriptor;)Lkotlinx/serialization/encoding/Encoder;
 	public abstract fun encodeInt (I)V
 	public abstract fun encodeLong (J)V
 	public abstract fun encodeNotNullMark ()V
@@ -691,6 +705,13 @@ public final class kotlinx/serialization/internal/HashSetSerializer : kotlinx/se
 	public synthetic fun toResult (Ljava/lang/Object;)Ljava/lang/Object;
 }
 
+public final class kotlinx/serialization/internal/InlineClassDescriptor : kotlinx/serialization/internal/PluginGeneratedSerialDescriptor {
+	public fun <init> (Ljava/lang/String;Lkotlinx/serialization/internal/GeneratedSerializer;)V
+	public fun equals (Ljava/lang/Object;)Z
+	public fun hashCode ()I
+	public fun isInline ()Z
+}
+
 public final class kotlinx/serialization/internal/IntArrayBuilder : kotlinx/serialization/internal/PrimitiveArrayBuilder {
 	public synthetic fun build$kotlinx_serialization_core ()Ljava/lang/Object;
 }
@@ -878,6 +899,7 @@ public class kotlinx/serialization/internal/PluginGeneratedSerialDescriptor : ko
 	public fun getSerialNames ()Ljava/util/Set;
 	public fun hashCode ()I
 	public fun isElementOptional (I)Z
+	public fun isInline ()Z
 	public fun isNullable ()Z
 	public final fun pushAnnotation (Ljava/lang/annotation/Annotation;)V
 	public final fun pushClassAnnotation (Ljava/lang/annotation/Annotation;)V
@@ -975,6 +997,8 @@ public abstract class kotlinx/serialization/internal/TaggedDecoder : kotlinx/ser
 	public final fun decodeEnum (Lkotlinx/serialization/descriptors/SerialDescriptor;)I
 	public final fun decodeFloat ()F
 	public final fun decodeFloatElement (Lkotlinx/serialization/descriptors/SerialDescriptor;I)F
+	public final fun decodeInline (Lkotlinx/serialization/descriptors/SerialDescriptor;)Lkotlinx/serialization/encoding/Decoder;
+	public final fun decodeInlineElement (Lkotlinx/serialization/descriptors/SerialDescriptor;I)Lkotlinx/serialization/encoding/Decoder;
 	public final fun decodeInt ()I
 	public final fun decodeIntElement (Lkotlinx/serialization/descriptors/SerialDescriptor;I)I
 	public final fun decodeLong ()J
@@ -997,6 +1021,7 @@ public abstract class kotlinx/serialization/internal/TaggedDecoder : kotlinx/ser
 	protected fun decodeTaggedDouble (Ljava/lang/Object;)D
 	protected fun decodeTaggedEnum (Ljava/lang/Object;Lkotlinx/serialization/descriptors/SerialDescriptor;)I
 	protected fun decodeTaggedFloat (Ljava/lang/Object;)F
+	protected fun decodeTaggedInline (Ljava/lang/Object;Lkotlinx/serialization/descriptors/SerialDescriptor;)Lkotlinx/serialization/encoding/Decoder;
 	protected fun decodeTaggedInt (Ljava/lang/Object;)I
 	protected fun decodeTaggedLong (Ljava/lang/Object;)J
 	protected fun decodeTaggedNotNullMark (Ljava/lang/Object;)Z
@@ -1028,6 +1053,8 @@ public abstract class kotlinx/serialization/internal/TaggedEncoder : kotlinx/ser
 	public final fun encodeEnum (Lkotlinx/serialization/descriptors/SerialDescriptor;I)V
 	public final fun encodeFloat (F)V
 	public final fun encodeFloatElement (Lkotlinx/serialization/descriptors/SerialDescriptor;IF)V
+	public final fun encodeInline (Lkotlinx/serialization/descriptors/SerialDescriptor;)Lkotlinx/serialization/encoding/Encoder;
+	public final fun encodeInlineElement (Lkotlinx/serialization/descriptors/SerialDescriptor;I)Lkotlinx/serialization/encoding/Encoder;
 	public final fun encodeInt (I)V
 	public final fun encodeIntElement (Lkotlinx/serialization/descriptors/SerialDescriptor;II)V
 	public final fun encodeLong (J)V
@@ -1048,6 +1075,7 @@ public abstract class kotlinx/serialization/internal/TaggedEncoder : kotlinx/ser
 	protected fun encodeTaggedDouble (Ljava/lang/Object;D)V
 	protected fun encodeTaggedEnum (Ljava/lang/Object;Lkotlinx/serialization/descriptors/SerialDescriptor;I)V
 	protected fun encodeTaggedFloat (Ljava/lang/Object;F)V
+	protected fun encodeTaggedInline (Ljava/lang/Object;Lkotlinx/serialization/descriptors/SerialDescriptor;)Lkotlinx/serialization/encoding/Encoder;
 	protected fun encodeTaggedInt (Ljava/lang/Object;I)V
 	protected fun encodeTaggedLong (Ljava/lang/Object;J)V
 	protected fun encodeTaggedNull (Ljava/lang/Object;)V
@@ -1074,6 +1102,42 @@ public final class kotlinx/serialization/internal/TripleSerializer : kotlinx/ser
 	public fun serialize (Lkotlinx/serialization/encoding/Encoder;Lkotlin/Triple;)V
 }
 
+public final class kotlinx/serialization/internal/UByteSerializer : kotlinx/serialization/KSerializer {
+	public static final field INSTANCE Lkotlinx/serialization/internal/UByteSerializer;
+	public synthetic fun deserialize (Lkotlinx/serialization/encoding/Decoder;)Ljava/lang/Object;
+	public fun deserialize-Wa3L5BU (Lkotlinx/serialization/encoding/Decoder;)B
+	public fun getDescriptor ()Lkotlinx/serialization/descriptors/SerialDescriptor;
+	public synthetic fun serialize (Lkotlinx/serialization/encoding/Encoder;Ljava/lang/Object;)V
+	public fun serialize-EK-6454 (Lkotlinx/serialization/encoding/Encoder;B)V
+}
+
+public final class kotlinx/serialization/internal/UIntSerializer : kotlinx/serialization/KSerializer {
+	public static final field INSTANCE Lkotlinx/serialization/internal/UIntSerializer;
+	public synthetic fun deserialize (Lkotlinx/serialization/encoding/Decoder;)Ljava/lang/Object;
+	public fun deserialize-OGnWXxg (Lkotlinx/serialization/encoding/Decoder;)I
+	public fun getDescriptor ()Lkotlinx/serialization/descriptors/SerialDescriptor;
+	public synthetic fun serialize (Lkotlinx/serialization/encoding/Encoder;Ljava/lang/Object;)V
+	public fun serialize-Qn1smSk (Lkotlinx/serialization/encoding/Encoder;I)V
+}
+
+public final class kotlinx/serialization/internal/ULongSerializer : kotlinx/serialization/KSerializer {
+	public static final field INSTANCE Lkotlinx/serialization/internal/ULongSerializer;
+	public synthetic fun deserialize (Lkotlinx/serialization/encoding/Decoder;)Ljava/lang/Object;
+	public fun deserialize-I7RO_PI (Lkotlinx/serialization/encoding/Decoder;)J
+	public fun getDescriptor ()Lkotlinx/serialization/descriptors/SerialDescriptor;
+	public synthetic fun serialize (Lkotlinx/serialization/encoding/Encoder;Ljava/lang/Object;)V
+	public fun serialize-2TYgG_w (Lkotlinx/serialization/encoding/Encoder;J)V
+}
+
+public final class kotlinx/serialization/internal/UShortSerializer : kotlinx/serialization/KSerializer {
+	public static final field INSTANCE Lkotlinx/serialization/internal/UShortSerializer;
+	public synthetic fun deserialize (Lkotlinx/serialization/encoding/Decoder;)Ljava/lang/Object;
+	public fun deserialize-BwKQO78 (Lkotlinx/serialization/encoding/Decoder;)S
+	public fun getDescriptor ()Lkotlinx/serialization/descriptors/SerialDescriptor;
+	public synthetic fun serialize (Lkotlinx/serialization/encoding/Encoder;Ljava/lang/Object;)V
+	public fun serialize-i8woANY (Lkotlinx/serialization/encoding/Encoder;S)V
+}
+
 public final class kotlinx/serialization/internal/UnitSerializer : kotlinx/serialization/KSerializer {
 	public static final field INSTANCE Lkotlinx/serialization/internal/UnitSerializer;
 	public synthetic fun deserialize (Lkotlinx/serialization/encoding/Decoder;)Ljava/lang/Object;

core/commonMain/src/kotlinx/serialization/builtins/BuiltinSerializers.kt

@@ -190,3 +190,30 @@ public fun <K, V> MapSerializer(
     valueSerializer: KSerializer<V>
 ): KSerializer<Map<K, V>> = LinkedHashMapSerializer(keySerializer, valueSerializer)
 
+/**
+ * Returns serializer for [UInt].
+ */
+@ExperimentalSerializationApi
+@ExperimentalUnsignedTypes
+public fun UInt.Companion.serializer(): KSerializer<UInt> = UIntSerializer
+
+/**
+ * Returns serializer for [ULong].
+ */
+@ExperimentalSerializationApi
+@ExperimentalUnsignedTypes
+public fun ULong.Companion.serializer(): KSerializer<ULong> = ULongSerializer
+
+/**
+ * Returns serializer for [UByte].
+ */
+@ExperimentalSerializationApi
+@ExperimentalUnsignedTypes
+public fun UByte.Companion.serializer(): KSerializer<UByte> = UByteSerializer
+
+/**
+ * Returns serializer for [UShort].
+ */
+@ExperimentalSerializationApi
+@ExperimentalUnsignedTypes
+public fun UShort.Companion.serializer(): KSerializer<UShort> = UShortSerializer

core/commonMain/src/kotlinx/serialization/descriptors/SerialDescriptor.kt

@@ -161,6 +161,12 @@ public interface SerialDescriptor {
     @ExperimentalSerializationApi
     public val isNullable: Boolean get() = false
 
+    /**
+     * Returns `true` if this descriptor describes a serializable inline class.
+     */
+    @ExperimentalSerializationApi
+    public val isInline: Boolean get() = false
+
     /**
      * The number of elements this descriptor describes, besides from the class itself.
      * [elementsCount] describes the number of **semantic** elements, not the number

core/commonMain/src/kotlinx/serialization/encoding/AbstractDecoder.kt

@@ -34,6 +34,8 @@ public abstract class AbstractDecoder : Decoder, CompositeDecoder {
     override fun decodeString(): String = decodeValue() as String
     override fun decodeEnum(enumDescriptor: SerialDescriptor): Int = decodeValue() as Int
 
+    override fun decodeInline(inlineDescriptor: SerialDescriptor): Decoder = this
+
     // overwrite by default
     public open fun <T : Any?> decodeSerializableValue(
         deserializer: DeserializationStrategy<T>,
@@ -55,6 +57,11 @@ public abstract class AbstractDecoder : Decoder, CompositeDecoder {
     final override fun decodeCharElement(descriptor: SerialDescriptor, index: Int): Char = decodeChar()
     final override fun decodeStringElement(descriptor: SerialDescriptor, index: Int): String = decodeString()
 
+    final override fun decodeInlineElement(
+        descriptor: SerialDescriptor,
+        index: Int
+    ): Decoder = decodeInline(descriptor.getElementDescriptor(index))
+
     final override fun <T> decodeSerializableElement(
         descriptor: SerialDescriptor,
         index: Int,

core/commonMain/src/kotlinx/serialization/encoding/AbstractEncoder.kt

@@ -7,6 +7,7 @@ package kotlinx.serialization.encoding
 import kotlinx.serialization.*
 import kotlinx.serialization.descriptors.*
 import kotlinx.serialization.modules.*
+import kotlinx.serialization.internal.*
 
 /**
  * A skeleton implementation of both [Encoder] and [CompositeEncoder] that can be used
@@ -50,6 +51,8 @@ public abstract class AbstractEncoder : Encoder, CompositeEncoder {
     override fun encodeString(value: String): Unit = encodeValue(value)
     override fun encodeEnum(enumDescriptor: SerialDescriptor, index: Int): Unit = encodeValue(index)
 
+    override fun encodeInline(inlineDescriptor: SerialDescriptor): Encoder = this
+
     // Delegating implementation of CompositeEncoder
     final override fun encodeBooleanElement(descriptor: SerialDescriptor, index: Int, value: Boolean) { if (encodeElement(descriptor, index)) encodeBoolean(value) }
     final override fun encodeByteElement(descriptor: SerialDescriptor, index: Int, value: Byte) { if (encodeElement(descriptor, index)) encodeByte(value) }
@@ -61,6 +64,12 @@ public abstract class AbstractEncoder : Encoder, CompositeEncoder {
     final override fun encodeCharElement(descriptor: SerialDescriptor, index: Int, value: Char) { if (encodeElement(descriptor, index)) encodeChar(value) }
     final override fun encodeStringElement(descriptor: SerialDescriptor, index: Int, value: String) { if (encodeElement(descriptor, index)) encodeString(value) }
 
+    final override fun encodeInlineElement(
+        descriptor: SerialDescriptor,
+        index: Int
+    ): Encoder =
+        if (encodeElement(descriptor, index)) encodeInline(descriptor.getElementDescriptor(index)) else NoOpEncoder
+
     final override fun <T : Any?> encodeSerializableElement(
         descriptor: SerialDescriptor,
         index: Int,