Require explicit extern members in extern class/object and update docs

lynglib/src/commonMain/kotlin/net/sergeych/lyng/Compiler.kt

@@ -7727,6 +7727,7 @@ class Compiler(
 
         val annotation = lastAnnotation
         val parentContext = codeContexts.last()
+        val parentClassCtx = parentContext as? CodeContext.ClassBody
 
         // Is extension?
         if (looksLikeExtensionReceiver()) {
@@ -7760,6 +7761,9 @@ class Compiler(
             name = t.value
             nameStartPos = t.pos
         }
+        if (parentClassCtx?.isExtern == true && !isExtern) {
+            throw ScriptError(nameStartPos, "members of extern classes/objects must be marked extern")
+        }
         val extensionWrapperName = extTypeName?.let { extensionCallableName(it, name) }
         val classCtx = codeContexts.asReversed().firstOrNull { it is CodeContext.ClassBody } as? CodeContext.ClassBody
         var memberMethodId = if (extTypeName == null) classCtx?.memberMethodIds?.get(name) else null
@@ -8782,6 +8786,10 @@ class Compiler(
             name = nameToken.value
             nameStartPos = nameToken.pos
         }
+        val parentClassCtx = codeContexts.lastOrNull() as? CodeContext.ClassBody
+        if (parentClassCtx?.isExtern == true && !isExtern) {
+            throw ScriptError(nameStartPos, "members of extern classes/objects must be marked extern")
+        }
 
         val receiverNormalization = normalizeReceiverTypeDecl(receiverTypeDecl, emptySet())
         val implicitTypeParams = receiverNormalization.second

lynglib/src/commonMain/kotlin/net/sergeych/lyng/stdlib_included/observable_lyng.kt

@@ -24,46 +24,46 @@ package lyng.observable
 extern class ChangeRejectionException : Exception
 
 extern class Subscription {
-    fun cancel(): Void
+    extern fun cancel(): Void
 }
 
 extern class Observable<Change> {
-    fun beforeChange(listener: (Change)->Void): Subscription
-    fun onChange(listener: (Change)->Void): Subscription
-    fun changes(): Flow<Change>
+    extern fun beforeChange(listener: (Change)->Void): Subscription
+    extern fun onChange(listener: (Change)->Void): Subscription
+    extern fun changes(): Flow<Change>
 }
 
 extern class ListChange<T>
 
 extern class ListSet<T> : ListChange<T> {
-    val index: Int
-    val oldValue: Object
-    val newValue: Object
+    extern val index: Int
+    extern val oldValue: Object
+    extern val newValue: Object
 }
 
 extern class ListInsert<T> : ListChange<T> {
-    val index: Int
-    val values: List<T>
+    extern val index: Int
+    extern val values: List<T>
 }
 
 extern class ListRemove<T> : ListChange<T> {
-    val index: Int
-    val oldValue: Object
+    extern val index: Int
+    extern val oldValue: Object
 }
 
 extern class ListClear<T> : ListChange<T> {
-    val oldValues: List<T>
+    extern val oldValues: List<T>
 }
 
 extern class ListReorder<T> : ListChange<T> {
-    val oldValues: List<T>
-    val newValues: Object
+    extern val oldValues: List<T>
+    extern val newValues: Object
 }
 
 extern class ObservableList<T> : List<T> {
-    fun beforeChange(listener: (ListChange<T>)->Void): Subscription
-    fun onChange(listener: (ListChange<T>)->Void): Subscription
-    fun changes(): Flow<ListChange<T>>
+    extern fun beforeChange(listener: (ListChange<T>)->Void): Subscription
+    extern fun onChange(listener: (ListChange<T>)->Void): Subscription
+    extern fun changes(): Flow<ListChange<T>>
 }
 
 fun List<T>.observable(): ObservableList<T> {