Add IDE diagnostic on @Serializable classes for non-applied serialization plugin

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

@@ -18,6 +18,7 @@ import static org.jetbrains.kotlin.diagnostics.Severity.WARNING;
 
 public interface SerializationErrors {
     DiagnosticFactory0<PsiElement> INLINE_CLASSES_NOT_SUPPORTED = DiagnosticFactory0.create(ERROR);
+    DiagnosticFactory0<PsiElement> PLUGIN_IS_NOT_ENABLED = DiagnosticFactory0.create(WARNING);
 
     DiagnosticFactory0<KtAnnotationEntry> SERIALIZABLE_ANNOTATION_IGNORED = DiagnosticFactory0.create(ERROR);
     DiagnosticFactory0<KtAnnotationEntry> NON_SERIALIZABLE_PARENT_MUST_HAVE_NOARG_CTOR = DiagnosticFactory0.create(ERROR);

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

@@ -33,8 +33,8 @@ import org.jetbrains.kotlinx.serialization.compiler.resolve.*
 
 internal val SERIALIZABLE_PROPERTIES: WritableSlice<ClassDescriptor, SerializableProperties> = Slices.createSimpleSlice()
 
-class SerializationPluginDeclarationChecker : DeclarationChecker {
+open class SerializationPluginDeclarationChecker : DeclarationChecker {
-    override fun check(declaration: KtDeclaration, descriptor: DeclarationDescriptor, context: DeclarationCheckerContext) {
+    final override fun check(declaration: KtDeclaration, descriptor: DeclarationDescriptor, context: DeclarationCheckerContext) {
         if (descriptor !is ClassDescriptor) return
 
         if (!canBeSerializedInternally(descriptor, context.trace)) return
@@ -47,6 +47,11 @@ class SerializationPluginDeclarationChecker : DeclarationChecker {
     private fun canBeSerializedInternally(descriptor: ClassDescriptor, trace: BindingTrace): Boolean {
         if (!descriptor.annotations.hasAnnotation(SerializationAnnotations.serializableAnnotationFqName)) return false
 
+        if (!serializationPluginEnabledOn(descriptor)) {
+            trace.reportOnSerializableAnnotation(descriptor, SerializationErrors.PLUGIN_IS_NOT_ENABLED)
+            return false
+        }
+
         if (descriptor.isInline) {
             trace.reportOnSerializableAnnotation(descriptor, SerializationErrors.INLINE_CLASSES_NOT_SUPPORTED)
             return false
@@ -67,6 +72,13 @@ class SerializationPluginDeclarationChecker : DeclarationChecker {
         return true
     }
 
+    open fun serializationPluginEnabledOn(descriptor: ClassDescriptor): Boolean {
+        // In the CLI/Gradle compiler, this diagnostic is located in the plugin itself.
+        // Therefore, if we are here, plugin is in the compile classpath and enabled.
+        // For the IDE case, see SerializationPluginIDEDeclarationChecker
+        return true
+    }
+
     private fun buildSerializableProperties(descriptor: ClassDescriptor, trace: BindingTrace): SerializableProperties? {
         if (!descriptor.annotations.hasAnnotation(SerializationAnnotations.serializableAnnotationFqName)) return null
         if (!descriptor.isInternalSerializable) return null

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

@@ -18,6 +18,11 @@ object SerializationPluginErrorsRendering : DefaultErrorMessages.Extension {
             SerializationErrors.INLINE_CLASSES_NOT_SUPPORTED,
             "Inline classes are not supported by kotlinx.serialization yet"
         )
+        MAP.put(
+            SerializationErrors.PLUGIN_IS_NOT_ENABLED,
+            "kotlinx.serialization compiler plugin is not applied to the module, so this annotation would not be processed. " +
+                    "Make sure that you've setup your buildscript correctly and re-import project."
+        )
         MAP.put(
             SerializationErrors.SERIALIZABLE_ANNOTATION_IGNORED,
             "@Serializable annotation is ignored because it is impossible to serialize automatically interfaces or enums. " +

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

@@ -0,0 +1,17 @@
+/*
+ * Copyright 2010-2019 JetBrains s.r.o. and Kotlin Programming Language contributors.
+ * Use of this source code is governed by the Apache 2.0 license that can be found in the license/LICENSE.txt file.
+ */
+
+package org.jetbrains.kotlinx.serialization.compiler.diagnostic
+
+import org.jetbrains.kotlin.descriptors.ClassDescriptor
+import org.jetbrains.kotlinx.serialization.idea.getIfEnabledOn
+
+class SerializationPluginIDEDeclarationChecker : SerializationPluginDeclarationChecker() {
+    override fun serializationPluginEnabledOn(descriptor: ClassDescriptor): Boolean {
+        // In the IDE, plugin is always in the classpath, but enabled only if corresponding compiler settings
+        // were imported into project model from Gradle.
+        return getIfEnabledOn(descriptor) { true } == true
+    }
+}

plugins/kotlin-serialization/kotlin-serialization-ide/src/org/jetbrains/kotlinx/serialization/compiler/extensions/SerializationIDEContainerContributor.kt

@@ -10,7 +10,7 @@ import org.jetbrains.kotlin.container.useInstance
 import org.jetbrains.kotlin.descriptors.ModuleDescriptor
 import org.jetbrains.kotlin.extensions.StorageComponentContainerContributor
 import org.jetbrains.kotlin.platform.TargetPlatform
-import org.jetbrains.kotlinx.serialization.compiler.diagnostic.SerializationPluginDeclarationChecker
+import org.jetbrains.kotlinx.serialization.compiler.diagnostic.SerializationPluginIDEDeclarationChecker
 
 class SerializationIDEContainerContributor : StorageComponentContainerContributor {
     override fun registerModuleComponents(
@@ -18,6 +18,6 @@ class SerializationIDEContainerContributor : StorageComponentContainerContributo
         platform: TargetPlatform,
         moduleDescriptor: ModuleDescriptor
     ) {
-        container.useInstance(SerializationPluginDeclarationChecker())
+        container.useInstance(SerializationPluginIDEDeclarationChecker())
     }
 }