[FIR] Don't lose non-serializable properties during metadata deserialization

^KT-57941 Fixed

compiler/fir/fir-deserialization/src/org/jetbrains/kotlin/fir/deserialization/ClassDeserialization.kt

@@ -327,10 +327,15 @@ private fun ProtoBuf.ClassOrBuilder.propertiesInOrder(context: FirDeserializatio
     if (versionRequirements.any { it.version.major >= 2 }) return properties
     val order = getExtension(SerializationPluginMetadataExtensions.propertiesNamesInProgramOrder)
         .takeIf { it.isNotEmpty() }
+        ?.toSet()
         ?: return properties
     val propertiesByName = properties.groupBy { it.name }
-    return order.flatMap { propertiesByName[it] ?: emptyList() }.also {
-        assert(it.size == properties.size)
+    val orderedProperties = order.flatMap { propertiesByName[it] ?: emptyList() }
+    // non-serializable properties are not saved in SerializationPluginMetadataExtensions, so we need to pick up them if any
+    return if (orderedProperties.size == properties.size) {
+        orderedProperties
+    } else {
+        orderedProperties + properties.filter { it.name !in order }
     }
 }
 

libraries/tools/kotlin-gradle-plugin-integration-tests/src/test/kotlin/org/jetbrains/kotlin/gradle/K2KotlinxSerializationIT.kt

@@ -23,7 +23,7 @@ class K2KotlinxSerializationIT : KGPBaseTest() {
         }
     }
 
-    @DisplayName("Compile code with kotlinx.serialization with K2 against K1")
+    @DisplayName("Compile code with kotlinx.serialization with K2 against K1. KT-57941")
     @GradleTest
     fun `test kotlinx serialization K2 against K1`() {
         project("kotlinxSerializationK2AgainstK1", gradleVersion) {

libraries/tools/kotlin-gradle-plugin-integration-tests/src/test/resources/testProject/kotlinxSerializationK2AgainstK1/app/src/main/kotlin/Main.kt

@@ -19,6 +19,12 @@ class Derived(val d: Long = 1000000000000) : Base(2, "world", listOf("b", "c"))
     }
 }
 
+fun processAbstractBase(abstractBase: AbstractBase) {
+    println(abstractBase.x)
+    println(abstractBase.y)
+    println(abstractBase.nonSerializableProp)
+}
+
 fun main() {
     val expected = Derived(12)
     val result = Json.encodeToString(Derived.serializer(), expected)

libraries/tools/kotlin-gradle-plugin-integration-tests/src/test/resources/testProject/kotlinxSerializationK2AgainstK1/lib/src/main/kotlin/Base.kt

@@ -12,3 +12,11 @@ open class Base(
     val b: String = "hello",
     val a: List<String> = listOf("a")
 )
+
+@Serializable
+abstract class AbstractBase(
+    val x: Int = 1,
+    val y: Int = 2
+) {
+    abstract val nonSerializableProp: String
+}