Added diagnostic for external serializers

Relates Kotlin/kotlinx.serialization#532

plugins/kotlin-serialization/kotlin-serialization-compiler/src/org/jetbrains/kotlinx/serialization/compiler/diagnostic/SerializationErrors.java

@@ -42,6 +42,9 @@ public interface SerializationErrors {
 
     DiagnosticFactory2<PsiElement, KotlinType, KotlinType> INCONSISTENT_INHERITABLE_SERIALINFO = DiagnosticFactory2.create(ERROR);
 
+    DiagnosticFactory2<PsiElement, KotlinType, KotlinType> EXTERNAL_CLASS_NOT_SERIALIZABLE = DiagnosticFactory2.create(ERROR);
+    DiagnosticFactory2<PsiElement, KotlinType, KotlinType> EXTERNAL_CLASS_IN_ANOTHER_MODULE = DiagnosticFactory2.create(ERROR);
+
     @SuppressWarnings("UnusedDeclaration")
     Object _initializer = new Object() {
         {

plugins/kotlin-serialization/kotlin-serialization-compiler/src/org/jetbrains/kotlinx/serialization/compiler/diagnostic/SerializationPluginDeclarationChecker.kt

@@ -41,6 +41,8 @@ open class SerializationPluginDeclarationChecker : DeclarationChecker {
     final override fun check(declaration: KtDeclaration, descriptor: DeclarationDescriptor, context: DeclarationCheckerContext) {
         if (descriptor !is ClassDescriptor) return
 
+        checkExternalSerializer(descriptor, declaration, context.trace)
+
         if (!canBeSerializedInternally(descriptor, declaration, context.trace)) return
         if (declaration !is KtPureClassOrObject) return
         if (!isIde) {
@@ -58,6 +60,21 @@ open class SerializationPluginDeclarationChecker : DeclarationChecker {
         checkInheritedAnnotations(descriptor, declaration, context.trace)
     }
 
+    private fun checkExternalSerializer(classDescriptor: ClassDescriptor, declaration: KtDeclaration, trace: BindingTrace) {
+        val serializableKType = classDescriptor.serializerForClass ?: return
+        val serializableDescriptor = serializableKType.toClassDescriptor ?: return
+        val props = SerializableProperties(serializableDescriptor, trace.bindingContext)
+
+        if (!props.isExternallySerializable) {
+            val entry = classDescriptor.findAnnotationDeclaration(SerializationAnnotations.serializerAnnotationFqName)
+            val inSameModule =
+                trace.bindingContext[BindingContext.FQNAME_TO_CLASS_DESCRIPTOR, serializableDescriptor.fqNameUnsafe] != null
+            val diagnostic = if (inSameModule) SerializationErrors.EXTERNAL_CLASS_NOT_SERIALIZABLE else SerializationErrors.EXTERNAL_CLASS_IN_ANOTHER_MODULE
+
+            trace.report(diagnostic.on(entry ?: declaration, classDescriptor.defaultType, serializableKType))
+        }
+    }
+
     private fun checkInheritedAnnotations(descriptor: ClassDescriptor, declaration: KtDeclaration, trace: BindingTrace) {
         val annotationsFilter: (Annotations) -> List<Pair<FqName, AnnotationDescriptor>> = { an ->
             an.map { it.annotationClass!!.fqNameSafe to it }

plugins/kotlin-serialization/kotlin-serialization-compiler/src/org/jetbrains/kotlinx/serialization/compiler/diagnostic/SerializationPluginErrorsRendering.kt

@@ -124,5 +124,19 @@ object SerializationPluginErrorsRendering : DefaultErrorMessages.Extension {
             Renderers.RENDER_TYPE,
             Renderers.RENDER_TYPE
         )
+
+        MAP.put(
+            SerializationErrors.EXTERNAL_CLASS_NOT_SERIALIZABLE,
+            "Cannot generate external serializer ''{0}'': class ''{1}'' have constructor parameters which are not properties and therefore it is not serializable automatically",
+            Renderers.RENDER_TYPE,
+            Renderers.RENDER_TYPE
+        )
+
+        MAP.put(
+            SerializationErrors.EXTERNAL_CLASS_IN_ANOTHER_MODULE,
+            "Cannot generate external serializer ''{0}'': class ''{1}'' is defined in another module",
+            Renderers.RENDER_TYPE,
+            Renderers.RENDER_TYPE
+        )
     }
 }

plugins/kotlin-serialization/kotlin-serialization-compiler/src/org/jetbrains/kotlinx/serialization/compiler/resolve/KSerializationUtil.kt

@@ -198,6 +198,11 @@ internal fun Annotated.findSerializableOrMetaAnnotationDeclaration(): KtAnnotati
     return lazyDesc?.annotationEntry
 }
 
+internal fun Annotated.findAnnotationDeclaration(fqName: FqName): KtAnnotationEntry? {
+    val lazyDesc = annotations.findAnnotation(fqName) as? LazyAnnotationDescriptor
+    return lazyDesc?.annotationEntry
+}
+
 // For abstract classes marked with @Serializable,
 // methods are generated anyway, although they shouldn't have
 // generated $serializer and use Polymorphic one.

plugins/kotlin-serialization/kotlin-serialization-compiler/test/org/jetbrains/kotlinx/serialization/SerializationPluginDiagnosticTestGenerated.java

@@ -34,6 +34,11 @@ public class SerializationPluginDiagnosticTestGenerated extends AbstractSerializ
         runTest("plugins/kotlin-serialization/kotlin-serialization-compiler/testData/diagnostics/DuplicateSerialName.kt");
     }
 
+    @TestMetadata("ExternalSerializers.kt")
+    public void testExternalSerializers() throws Exception {
+        runTest("plugins/kotlin-serialization/kotlin-serialization-compiler/testData/diagnostics/ExternalSerializers.kt");
+    }
+
     @TestMetadata("IncorrectTransient.kt")
     public void testIncorrectTransient() throws Exception {
         runTest("plugins/kotlin-serialization/kotlin-serialization-compiler/testData/diagnostics/IncorrectTransient.kt");

plugins/kotlin-serialization/kotlin-serialization-compiler/testData/diagnostics/ExternalSerializers.kt

@@ -0,0 +1,10 @@
+// !DIAGNOSTICS: -UNUSED_PARAMETER,-UNUSED_VARIABLE, -OPT_IN_USAGE
+// SKIP_TXT
+
+// FILE: test.kt
+import kotlinx.serialization.*
+
+class Foo(i: Int, val j: Int)
+
+<!EXTERNAL_CLASS_NOT_SERIALIZABLE!>@Serializer(forClass = Foo::class)<!>
+object ExternalSerializer