[FIR Serialization] Fix serialization of generated nested classifiers

^KT-55759 Fixed

compiler/fir/fir-serialization/src/org/jetbrains/kotlin/fir/serialization/FirElementSerializer.kt

@@ -28,14 +28,14 @@ import org.jetbrains.kotlin.fir.extensions.typeAttributeExtensions
 import org.jetbrains.kotlin.fir.resolve.*
 import org.jetbrains.kotlin.fir.resolve.providers.symbolProvider
 import org.jetbrains.kotlin.fir.scopes.FakeOverrideTypeCalculator
+import org.jetbrains.kotlin.fir.scopes.getSingleClassifier
 import org.jetbrains.kotlin.fir.scopes.processAllFunctions
 import org.jetbrains.kotlin.fir.scopes.processAllProperties
 import org.jetbrains.kotlin.fir.serialization.constant.EnumValue
 import org.jetbrains.kotlin.fir.serialization.constant.IntValue
 import org.jetbrains.kotlin.fir.serialization.constant.StringValue
 import org.jetbrains.kotlin.fir.serialization.constant.toConstantValue
-import org.jetbrains.kotlin.fir.symbols.impl.ConeClassLikeLookupTagImpl
-import org.jetbrains.kotlin.fir.symbols.impl.FirCallableSymbol
+import org.jetbrains.kotlin.fir.symbols.impl.*
 import org.jetbrains.kotlin.fir.types.*
 import org.jetbrains.kotlin.fir.types.builder.buildResolvedTypeRef
 import org.jetbrains.kotlin.fir.types.impl.ConeClassLikeTypeImpl
@@ -148,12 +148,19 @@ class FirElementSerializer private constructor(
             }
         }
 
-        val nestedClassifiers = klass.declarations.filterIsInstance<FirClassLikeDeclaration>()
+        fun FirClass.nestedClassifiers(): List<FirClassifierSymbol<*>> {
+            val scope = defaultType().scope(session, scopeSession, FakeOverrideTypeCalculator.DoNothing) ?: return emptyList()
+            return buildList {
+                scope.getClassifierNames().mapNotNullTo(this) { scope.getSingleClassifier(it) }
+            }
+        }
+
+        val nestedClassifiers = klass.nestedClassifiers()
         for (nestedClassifier in nestedClassifiers) {
-            if (nestedClassifier is FirTypeAlias) {
-                typeAliasProto(nestedClassifier)?.let { builder.addTypeAlias(it) }
-            } else if (nestedClassifier is FirRegularClass) {
-                if (!extension.shouldSerializeNestedClass(nestedClassifier)) {
+            if (nestedClassifier is FirTypeAliasSymbol) {
+                typeAliasProto(nestedClassifier.fir)?.let { builder.addTypeAlias(it) }
+            } else if (nestedClassifier is FirRegularClassSymbol) {
+                if (!extension.shouldSerializeNestedClass(nestedClassifier.fir)) {
                     continue
                 }
 

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

@@ -0,0 +1,23 @@
+// ISSUE: KT-55759
+// TARGET_BACKEND: JVM_IR
+// WITH_STDLIB
+
+// MODULE: lib
+// TARGET_PLATFORM: JVM
+// FILE: lib.kt
+
+import kotlinx.serialization.*
+
+@Serializable
+class Test
+
+// MODULE: jvm(lib)()()
+// TARGET_PLATFORM: JVM
+// FILE: main.kt
+
+import kotlinx.serialization.*
+import kotlinx.serialization.descriptors.*
+
+fun box(): String {
+    return if (Test.serializer().descriptor.toString() == "Test()") "OK" else "FAIL"
+}

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

@@ -69,6 +69,12 @@ public class SerializationFirBlackBoxTestGenerated extends AbstractSerialization
             runTest("plugins/kotlinx-serialization/testData/boxIr/externalSerialierJava.kt");
         }
 
+        @Test
+        @TestMetadata("generatedClassifiersViaLibraryDependency.kt")
+        public void testGeneratedClassifiersViaLibraryDependency() throws Exception {
+            runTest("plugins/kotlinx-serialization/testData/boxIr/generatedClassifiersViaLibraryDependency.kt");
+        }
+
         @Test
         @TestMetadata("genericBaseClassMultiple.kt")
         public void testGenericBaseClassMultiple() throws Exception {

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

@@ -67,6 +67,12 @@ public class SerializationIrBoxTestGenerated extends AbstractSerializationIrBoxT
         runTest("plugins/kotlinx-serialization/testData/boxIr/externalSerialierJava.kt");
     }
 
+    @Test
+    @TestMetadata("generatedClassifiersViaLibraryDependency.kt")
+    public void testGeneratedClassifiersViaLibraryDependency() throws Exception {
+        runTest("plugins/kotlinx-serialization/testData/boxIr/generatedClassifiersViaLibraryDependency.kt");
+    }
+
     @Test
     @TestMetadata("genericBaseClassMultiple.kt")
     public void testGenericBaseClassMultiple() throws Exception {