FIR/LC: fix modality of enum class

enum class, which is extended by enum entries, should not be final.
(Those enum entries should be, instead.)

enum class itself wouldn't be instantiated, and thus it's technically
abstract, but having a private ctor() would be an option.
For the latter case, we can simply put no modality modifier.

compiler/light-classes/src/org/jetbrains/kotlin/asJava/classes/KtLightClassForSourceDeclaration.kt

@@ -8,7 +8,6 @@ package org.jetbrains.kotlin.asJava.classes
 import com.intellij.openapi.components.ServiceManager
 import com.intellij.openapi.diagnostic.Logger
 import com.intellij.openapi.project.Project
-import com.intellij.openapi.util.Comparing
 import com.intellij.openapi.util.Key
 import com.intellij.openapi.util.TextRange
 import com.intellij.psi.*
@@ -222,18 +221,24 @@ abstract class KtLightClassForSourceDeclaration(
             psiModifiers.add(PsiModifier.PUBLIC)
         }
 
-
-        // FINAL
-        if (isAbstract() || isSealed()) {
-            psiModifiers.add(PsiModifier.ABSTRACT)
-        } else if (!(classOrObject.hasModifier(OPEN_KEYWORD) || (classOrObject is KtClass && classOrObject.isEnum()))) {
-            val descriptor = lazy { getDescriptor() }
-            var modifier = PsiModifier.FINAL
-            project.applyCompilerPlugins {
-                modifier = it.interceptModalityBuilding(kotlinOrigin, descriptor, modifier)
+        // ABSTRACT | FINAL
+        when {
+            isAbstract() || isSealed() -> {
+                psiModifiers.add(PsiModifier.ABSTRACT)
             }
-            if (modifier == PsiModifier.FINAL) {
-                psiModifiers.add(PsiModifier.FINAL)
+            isEnum -> {
+                // Enum class should not be `final`, since its enum entries extend it.
+                // It could be either `abstract` w/o ctor, or empty modality w/ private ctor.
+            }
+            !(classOrObject.hasModifier(OPEN_KEYWORD)) -> {
+                val descriptor = lazy { getDescriptor() }
+                var modifier = PsiModifier.FINAL
+                project.applyCompilerPlugins {
+                    modifier = it.interceptModalityBuilding(kotlinOrigin, descriptor, modifier)
+                }
+                if (modifier == PsiModifier.FINAL) {
+                    psiModifiers.add(PsiModifier.FINAL)
+                }
             }
         }
 
@@ -620,4 +625,4 @@ private fun hasParseErrorsAround(psi: PsiElement): Boolean {
     }
 
     return false
-}
+}