Use .fullyExpandedType to get serializable annotation from inside typealias

to correctly handle 'global customization via typealias' feature
in K2 serialization plugin.

plugins/kotlinx-serialization/kotlinx-serialization.k2/src/org/jetbrains/kotlinx/serialization/compiler/fir/services/ContextualSerializersProvider.kt

@@ -18,6 +18,7 @@ import org.jetbrains.kotlin.fir.declarations.hasAnnotation
 import org.jetbrains.kotlin.fir.declarations.utils.isEnumClass
 import org.jetbrains.kotlin.fir.expressions.*
 import org.jetbrains.kotlin.fir.extensions.FirExtensionSessionComponent
+import org.jetbrains.kotlin.fir.resolve.fullyExpandedType
 import org.jetbrains.kotlin.fir.resolve.providers.symbolProvider
 import org.jetbrains.kotlin.fir.symbols.impl.FirClassSymbol
 import org.jetbrains.kotlin.fir.types.*
@@ -77,7 +78,7 @@ val FirSession.contextualSerializersProvider: ContextualSerializersProvider by F
 context(CheckerContext)
 fun findTypeSerializerOrContextUnchecked(type: ConeKotlinType): FirClassSymbol<*>? {
     if (type.isTypeParameter) return null
-    val annotations = type.customAnnotations
+    val annotations = type.fullyExpandedType(session).customAnnotations
     annotations.serializableWith?.let { return it.toRegularClassSymbol(session) }
     val classSymbol = type.toRegularClassSymbol(session) ?: return null
     val currentFile = currentFile

plugins/kotlinx-serialization/testData/boxIr/typealiasesTest.kt

@@ -0,0 +1,44 @@
+// TARGET_BACKEND: JVM_IR
+
+// WITH_STDLIB
+
+import kotlinx.serialization.*
+import kotlinx.serialization.json.*
+import kotlinx.serialization.descriptors.*
+import kotlinx.serialization.encoding.*
+import java.util.Date
+
+class NotSerializable(val i: Int)
+
+object SerializerB : KSerializer<NotSerializable> {
+    override val descriptor: SerialDescriptor
+        get() = PrimitiveSerialDescriptor("SerializerB", PrimitiveKind.STRING)
+
+    override fun serialize(encoder: Encoder, value: NotSerializable) = TODO()
+
+    override fun deserialize(decoder: Decoder): NotSerializable = TODO()
+}
+
+object DateSer : KSerializer<Date> {
+    override val descriptor = PrimitiveSerialDescriptor("DateSer", PrimitiveKind.DOUBLE)
+
+    override fun deserialize(decoder: Decoder): Date = TODO()
+
+    override fun serialize(encoder: Encoder, value: Date) = TODO()
+}
+
+typealias S = @Serializable(SerializerB::class) NotSerializable
+typealias BS = @Serializable(DateSer::class) Date
+
+@Serializable
+class Foo(
+    val s: S,
+    val bs: BS,
+    val list: List<BS>
+)
+
+fun box(): String {
+    val list = Foo.serializer().descriptor.elementDescriptors.map { it.serialName }.toList()
+    if (list != listOf("SerializerB", "DateSer", "kotlin.collections.ArrayList")) return list.toString()
+    return "OK"
+}

plugins/kotlinx-serialization/tests-gen/org/jetbrains/kotlinx/serialization/runners/SerializationFirBlackBoxTestGenerated.java

@@ -128,6 +128,12 @@ public class SerializationFirBlackBoxTestGenerated extends AbstractSerialization
         public void testStarProjections() throws Exception {
             runTest("plugins/kotlinx-serialization/testData/boxIr/starProjections.kt");
         }
+
+        @Test
+        @TestMetadata("typealiasesTest.kt")
+        public void testTypealiasesTest() throws Exception {
+            runTest("plugins/kotlinx-serialization/testData/boxIr/typealiasesTest.kt");
+        }
     }
 
     @Nested

plugins/kotlinx-serialization/tests-gen/org/jetbrains/kotlinx/serialization/runners/SerializationIrBoxTestGenerated.java

@@ -126,4 +126,10 @@ public class SerializationIrBoxTestGenerated extends AbstractSerializationIrBoxT
     public void testStarProjections() throws Exception {
         runTest("plugins/kotlinx-serialization/testData/boxIr/starProjections.kt");
     }
+
+    @Test
+    @TestMetadata("typealiasesTest.kt")
+    public void testTypealiasesTest() throws Exception {
+        runTest("plugins/kotlinx-serialization/testData/boxIr/typealiasesTest.kt");
+    }
 }