1 files changed, 110 insertions, 0 deletions
diff --git a/formats/json-tests/commonTest/src/kotlinx/serialization/json/JsonElementDecodingTest.kt b/formats/json-tests/commonTest/src/kotlinx/serialization/json/JsonElementDecodingTest.kt
new file mode 100644
index 00000000..3cdfa082
--- /dev/null
+++ b/formats/json-tests/commonTest/src/kotlinx/serialization/json/JsonElementDecodingTest.kt
@@ -0,0 +1,110 @@
+package kotlinx.serialization.json
+
+import kotlinx.serialization.*
+import kotlinx.serialization.descriptors.*
+import kotlinx.serialization.encoding.*
+import kotlin.test.*
+
+class JsonElementDecodingTest : JsonTestBase() {
+
+    @Serializable
+    data class A(val a: Int = 42)
+
+    @Test
+    fun testTopLevelClass() = assertSerializedForm(A(), """{}""".trimMargin())
+
+    @Test
+    fun testTopLevelNullableClass() {
+        assertSerializedForm<A?>(A(), """{}""")
+        assertSerializedForm<A?>(null, "null")
+    }
+
+    @Test
+    fun testTopLevelPrimitive() = assertSerializedForm(42, """42""")
+
+    @Test
+    fun testTopLevelNullablePrimitive() {
+        assertSerializedForm<Int?>(42, """42""")
+        assertSerializedForm<Int?>(null, """null""")
+    }
+
+    @Test
+    fun testTopLevelList() = assertSerializedForm(listOf(42), """[42]""")
+
+    @Test
+    fun testTopLevelNullableList() {
+        assertSerializedForm<List<Int>?>(listOf(42), """[42]""")
+        assertSerializedForm<List<Int>?>(null, """null""")
+    }
+
+    private inline fun <reified T> assertSerializedForm(value: T, expectedString: String) {
+        val element = Json.encodeToJsonElement(value)
+        assertEquals(expectedString, element.toString())
+        assertEquals(value, Json.decodeFromJsonElement(element))
+    }
+
+    @Test
+    fun testDeepRecursion() {
+        // Reported as https://github.com/Kotlin/kotlinx.serialization/issues/1594
+        var json = """{ "a": %}"""
+        for (i in 0..12) {
+            json = json.replace("%", json)
+        }
+        json = json.replace("%", "0")
+        Json.parseToJsonElement(json)
+    }
+
+    private open class NullAsElementSerializer<T : Any>(private val serializer: KSerializer<T>, val nullElement: T) : KSerializer<T?> {
+        final override val descriptor: SerialDescriptor = serializer.descriptor.nullable
+
+        final override fun serialize(encoder: Encoder, value: T?) {
+            serializer.serialize(encoder, value ?: nullElement)
+        }
+
+        final override fun deserialize(decoder: Decoder): T = serializer.deserialize(decoder)
+    }
+
+    private object NullAsJsonNullJsonElementSerializer : NullAsElementSerializer<JsonElement>(JsonElement.serializer(), JsonNull)
+    private object NullAsJsonNullJsonPrimitiveSerializer : NullAsElementSerializer<JsonPrimitive>(JsonPrimitive.serializer(), JsonNull)
+    private object NullAsJsonNullJsonNullSerializer : NullAsElementSerializer<JsonNull>(JsonNull.serializer(), JsonNull)
+    private val noExplicitNullsOrDefaultsJson = Json {
+        explicitNulls = false
+        encodeDefaults = false
+    }
+
+    @Test
+    fun testNullableJsonElementDecoding() {
+        @Serializable
+        data class Wrapper(
+            @Serializable(NullAsJsonNullJsonElementSerializer::class)
+            val value: JsonElement? = null,
+        )
+
+        assertJsonFormAndRestored(Wrapper.serializer(), Wrapper(value = JsonNull), """{"value":null}""", noExplicitNullsOrDefaultsJson)
+        assertJsonFormAndRestored(Wrapper.serializer(), Wrapper(value = null), """{}""", noExplicitNullsOrDefaultsJson)
+    }
+
+    @Test
+    fun testNullableJsonPrimitiveDecoding() {
+        @Serializable
+        data class Wrapper(
+            @Serializable(NullAsJsonNullJsonPrimitiveSerializer::class)
+            val value: JsonPrimitive? = null,
+        )
+
+        assertJsonFormAndRestored(Wrapper.serializer(), Wrapper(value = JsonNull), """{"value":null}""", noExplicitNullsOrDefaultsJson)
+        assertJsonFormAndRestored(Wrapper.serializer(), Wrapper(value = null), """{}""", noExplicitNullsOrDefaultsJson)
+    }
+
+    @Test
+    fun testNullableJsonNullDecoding() {
+        @Serializable
+        data class Wrapper(
+            @Serializable(NullAsJsonNullJsonNullSerializer::class)
+            val value: JsonNull? = null,
+        )
+
+        assertJsonFormAndRestored(Wrapper.serializer(), Wrapper(value = JsonNull), """{"value":null}""", noExplicitNullsOrDefaultsJson)
+        assertJsonFormAndRestored(Wrapper.serializer(), Wrapper(value = null), """{}""", noExplicitNullsOrDefaultsJson)
+    }
+}