Added support for the kotlin.time.Duration class as built-in

core/api/kotlinx-serialization-core.api

@@ -175,6 +175,7 @@ public final class kotlinx/serialization/builtins/BuiltinSerializersKt {
 	public static final fun serializer (Lkotlin/jvm/internal/LongCompanionObject;)Lkotlinx/serialization/KSerializer;
 	public static final fun serializer (Lkotlin/jvm/internal/ShortCompanionObject;)Lkotlinx/serialization/KSerializer;
 	public static final fun serializer (Lkotlin/jvm/internal/StringCompanionObject;)Lkotlinx/serialization/KSerializer;
+	public static final fun serializer (Lkotlin/time/Duration$Companion;)Lkotlinx/serialization/KSerializer;
 }
 
 public final class kotlinx/serialization/builtins/LongAsStringSerializer : kotlinx/serialization/KSerializer {
@@ -662,6 +663,15 @@ public final class kotlinx/serialization/internal/DoubleSerializer : kotlinx/ser
 	public synthetic fun serialize (Lkotlinx/serialization/encoding/Encoder;Ljava/lang/Object;)V
 }
 
+public final class kotlinx/serialization/internal/DurationSerializer : kotlinx/serialization/KSerializer {
+	public static final field INSTANCE Lkotlinx/serialization/internal/DurationSerializer;
+	public synthetic fun deserialize (Lkotlinx/serialization/encoding/Decoder;)Ljava/lang/Object;
+	public fun deserialize-5sfh64U (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-HG0u8IE (Lkotlinx/serialization/encoding/Encoder;J)V
+}
+
 public final class kotlinx/serialization/internal/ElementMarker {
 	public fun <init> (Lkotlinx/serialization/descriptors/SerialDescriptor;Lkotlin/jvm/functions/Function2;)V
 	public final fun mark (I)V

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

@@ -9,6 +9,7 @@ import kotlinx.serialization.*
 import kotlinx.serialization.internal.*
 import kotlin.reflect.*
 import kotlinx.serialization.descriptors.*
+import kotlin.time.Duration
 
 /**
  * Returns a nullable serializer for the given serializer of non-null type.
@@ -217,3 +218,11 @@ public fun UByte.Companion.serializer(): KSerializer<UByte> = UByteSerializer
 @ExperimentalSerializationApi
 @ExperimentalUnsignedTypes
 public fun UShort.Companion.serializer(): KSerializer<UShort> = UShortSerializer
+
+/**
+ * Returns serializer for [Duration].
+ * It is serialized as a string that represents a duration in the ISO-8601 format.
+ *
+ * The result of serialization is similar to calling [Duration.toIsoString], for deserialization is [Duration.parseIsoString].
+ */
+public fun Duration.Companion.serializer(): KSerializer<Duration> = DurationSerializer

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

@@ -0,0 +1,25 @@
+/*
+ * Copyright 2017-2022 JetBrains s.r.o. Use of this source code is governed by the Apache 2.0 license.
+ */
+package kotlinx.serialization.internal
+
+import kotlinx.serialization.KSerializer
+import kotlinx.serialization.descriptors.PrimitiveKind
+import kotlinx.serialization.descriptors.SerialDescriptor
+import kotlinx.serialization.encoding.Decoder
+import kotlinx.serialization.encoding.Encoder
+import kotlin.time.Duration
+
+
+@PublishedApi
+internal object DurationSerializer : KSerializer<Duration> {
+    override val descriptor: SerialDescriptor = PrimitiveSerialDescriptor("kotlin.time.Duration", PrimitiveKind.STRING)
+
+    override fun serialize(encoder: Encoder, value: Duration) {
+        encoder.encodeString(value.toIsoString())
+    }
+
+    override fun deserialize(decoder: Decoder): Duration {
+        return Duration.parseIsoString(decoder.decodeString())
+    }
+}

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

@@ -13,6 +13,7 @@ import kotlinx.serialization.descriptors.*
 import kotlinx.serialization.encoding.*
 import kotlin.native.concurrent.*
 import kotlin.reflect.*
+import kotlin.time.Duration
 
 @SharedImmutable
 private val BUILTIN_SERIALIZERS = mapOf(
@@ -33,7 +34,8 @@ private val BUILTIN_SERIALIZERS = mapOf(
     ByteArray::class to ByteArraySerializer(),
     Boolean::class to Boolean.serializer(),
     BooleanArray::class to BooleanArraySerializer(),
-    Unit::class to Unit.serializer()
+    Unit::class to Unit.serializer(),
+    Duration::class to Duration.serializer()
 )
 
 internal class PrimitiveSerialDescriptor(

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

@@ -4,12 +4,13 @@
 
 package kotlinx.serialization
 
+import kotlinx.serialization.builtins.serializer
 import kotlinx.serialization.descriptors.*
 import kotlinx.serialization.encoding.*
 import kotlinx.serialization.encoding.CompositeDecoder.Companion.UNKNOWN_NAME
-import kotlinx.serialization.internal.*
 import kotlinx.serialization.modules.*
 import kotlin.test.*
+import kotlin.time.Duration
 
 /*
  * Test ensures that type that aggregate all basic (primitive/collection/maps/arrays)
@@ -170,4 +171,24 @@ class BasicTypesSerializationTest {
         assertEquals(umbrellaInstance, other)
         assertNotSame(umbrellaInstance, other)
     }
+
+    @Test
+    fun testEncodeDuration() {
+        val sb = StringBuilder()
+        val out = KeyValueOutput(sb)
+
+        val duration = Duration.parseIsoString("P4DT12H30M5S")
+        out.encodeSerializableValue(Duration.serializer(), duration)
+
+        assertEquals("\"${duration.toIsoString()}\"", sb.toString())
+    }
+
+    @Test
+    fun testDecodeDuration() {
+        val durationString = "P4DT12H30M5S"
+        val inp = KeyValueInput(Parser(StringReader("\"$durationString\"")))
+        val other = inp.decodeSerializableValue(Duration.serializer())
+        assertEquals(Duration.parseIsoString(durationString), other)
+    }
+
 }

formats/json/commonTest/src/kotlinx/serialization/SerializersLookupTest.kt

@@ -14,6 +14,7 @@ import kotlinx.serialization.modules.*
 import kotlinx.serialization.test.*
 import kotlin.reflect.*
 import kotlin.test.*
+import kotlin.time.Duration
 
 @Suppress("RemoveExplicitTypeArguments") // This is exactly what's being tested
 class SerializersLookupTest : JsonTestBase() {
@@ -243,6 +244,13 @@ class SerializersLookupTest : JsonTestBase() {
         }
     }
 
+// TODO uncomment when Kotlin 1.7.20 is released
+//    @Test
+//    fun testLookupDuration() = noLegacyJs {
+//        assertNotNull(serializerOrNull(typeOf<Duration>()))
+//        assertSame(Duration.serializer(), serializer<Duration>())
+//    }
+
     private inline fun <reified T> assertSerializedWithType(
         expected: String,
         value: T,

formats/json/commonTest/src/kotlinx/serialization/features/DurationTest.kt

@@ -0,0 +1,27 @@
+/*
+ * Copyright 2017-2022 JetBrains s.r.o. Use of this source code is governed by the Apache 2.0 license.
+ */
+
+package kotlinx.serialization.features
+
+import kotlinx.serialization.Serializable
+import kotlinx.serialization.json.JsonTestBase
+import kotlin.test.Test
+import kotlin.time.Duration
+import kotlin.time.DurationUnit
+import kotlin.time.toDuration
+
+
+class DurationTest : JsonTestBase() {
+// TODO uncomment when Kotlin 1.7.20 is released
+//    @Serializable
+//    data class DurationHolder(val duration: Duration)
+//    @Test
+//    fun testDuration() {
+//        assertJsonFormAndRestored(
+//            DurationHolder.serializer(),
+//            DurationHolder(1000.toDuration(DurationUnit.SECONDS)),
+//            """{"duration":"PT16M40S"}"""
+//        )
+//    }
+}