Value classes: Allow nested inline classes

compiler/frontend/src/org/jetbrains/kotlin/diagnostics/rendering/DefaultErrorMessages.java

@@ -704,7 +704,7 @@ public class DefaultErrorMessages {
         MAP.put(NON_PRIVATE_CONSTRUCTOR_IN_ENUM, "Constructor must be private in enum class");
         MAP.put(NON_PRIVATE_CONSTRUCTOR_IN_SEALED, "Constructor must be private in sealed class");
 
-        MAP.put(INLINE_CLASS_NOT_TOP_LEVEL, "Inline classes are only allowed on top level");
+        MAP.put(INLINE_CLASS_NOT_TOP_LEVEL, "Inline classes cannot be local or inner");
         MAP.put(INLINE_CLASS_NOT_FINAL, "Inline classes can be only final");
         MAP.put(ABSENCE_OF_PRIMARY_CONSTRUCTOR_FOR_INLINE_CLASS, "Primary constructor is required for inline class");
         MAP.put(INLINE_CLASS_CONSTRUCTOR_WRONG_PARAMETERS_SIZE, "Inline class must have exactly one primary constructor parameter");

compiler/frontend/src/org/jetbrains/kotlin/resolve/checkers/InlineClassDeclarationChecker.kt

@@ -29,7 +29,7 @@ object InlineClassDeclarationChecker : DeclarationChecker {
         require(inlineOrValueKeyword != null) { "Declaration of inline class must have 'inline' keyword" }
 
         val trace = context.trace
-        if (!DescriptorUtils.isTopLevelDeclaration(descriptor)) {
+        if (descriptor.isInner || DescriptorUtils.isLocal(descriptor)) {
             trace.report(Errors.INLINE_CLASS_NOT_TOP_LEVEL.on(inlineOrValueKeyword))
             return
         }