Allow using value classes with primitive carriers as map keys without… (#1470)

Allow using value classes with primitive carriers as map keys without 'allowStructuredMapKeys'

Fixes #1459

Author: qwwdfsad

formats/json/commonMain/src/kotlinx/serialization/json/internal/WriteMode.kt

@@ -32,7 +32,7 @@ internal inline fun <T, R1 : T, R2 : T> Json.selectMapMode(
     ifMap: () -> R1,
     ifList: () -> R2
 ): T {
-    val keyDescriptor = mapDescriptor.getElementDescriptor(0)
+    val keyDescriptor = mapDescriptor.getElementDescriptor(0).carrierDescriptor
     val keyKind = keyDescriptor.kind
     return if (keyKind is PrimitiveKind || keyKind == SerialKind.ENUM) {
         ifMap()
@@ -42,3 +42,6 @@ internal inline fun <T, R1 : T, R2 : T> Json.selectMapMode(
         throw InvalidKeyKindException(keyDescriptor)
     }
 }
+
+internal val SerialDescriptor.carrierDescriptor: SerialDescriptor
+    get() = if (isInline) getElementDescriptor(0) else this

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

@@ -7,18 +7,33 @@ package kotlinx.serialization.json
 import kotlinx.serialization.*
 import kotlinx.serialization.json.internal.*
 import kotlinx.serialization.test.*
+import kotlin.jvm.*
 import kotlin.test.*
 
+@JvmInline
+@Serializable
+value class ComplexCarrier(val c: IntData)
+
+@JvmInline
+@Serializable
+value class PrimitiveCarrier(val c: String)
+
 class JsonMapKeysTest : JsonTestBase() {
     @Serializable
     private data class WithMap(val map: Map<Long, Long>)
 
+    @Serializable
+    private data class WithValueKeyMap(val map: Map<PrimitiveCarrier, Long>)
+
     @Serializable
     private data class WithEnum(val map: Map<SampleEnum, Long>)
 
     @Serializable
     private data class WithComplexKey(val map: Map<IntData, String>)
 
+    @Serializable
+    private data class WithComplexValueKey(val map: Map<ComplexCarrier, String>)
+
     @Test
     fun testMapKeysShouldBeStrings() = parametrizedTest(default) {
         assertStringFormAndRestored(
@@ -30,13 +45,16 @@ class JsonMapKeysTest : JsonTestBase() {
     }
 
     @Test
-    fun structuredMapKeysShouldBeBannedByDefault() = parametrizedTest { streaming ->
+    fun testStructuredMapKeysShouldBeProhibitedByDefault() = parametrizedTest { streaming ->
+        noLegacyJs {
+            verifyProhibition(WithComplexKey(mapOf(IntData(42) to "42")), streaming)
+            verifyProhibition(WithComplexValueKey(mapOf(ComplexCarrier(IntData(42)) to "42")), streaming)
+        }
+    }
+
+    private inline fun <reified T: Any> verifyProhibition(value: T, streaming: Boolean) {
         val e = assertFailsWith<JsonException> {
-            Json.encodeToString(
-                WithComplexKey.serializer(),
-                WithComplexKey(mapOf(IntData(42) to "42")),
-                streaming
-            )
+            Json.encodeToString(value, streaming)
         }
         assertTrue(e.message?.contains("can't be used in JSON as a key in the map") == true)
     }
@@ -49,11 +67,31 @@ class JsonMapKeysTest : JsonTestBase() {
         Json { allowStructuredMapKeys = true }
     )
 
+    @Test
+    fun testStructuredValueMapKeysAllowedWithFlag() =  noLegacyJs {
+        assertJsonFormAndRestored(
+            WithComplexValueKey.serializer(),
+            WithComplexValueKey(mapOf(ComplexCarrier(IntData(42)) to "42")),
+            """{"map":[{"intV":42},"42"]}""",
+            Json { allowStructuredMapKeys = true }
+        )
+    }
+
     @Test
     fun testEnumsAreAllowedAsMapKeys() = assertJsonFormAndRestored(
         WithEnum.serializer(),
         WithEnum(mapOf(SampleEnum.OptionA to 1L, SampleEnum.OptionC to 3L)),
         """{"map":{"OptionA":1,"OptionC":3}}""",
         Json
     )
+
+    @Test
+    fun testPrimitivesAreAllowedAsValueMapKeys() =  noLegacyJs {
+        assertJsonFormAndRestored(
+            WithValueKeyMap.serializer(),
+            WithValueKeyMap(mapOf(PrimitiveCarrier("fooKey") to 1)),
+            """{"map":{"fooKey":1}}""",
+            Json
+        )
+    }
 }