Don't report error for properties and functions without body that either external by themselves or are members of external classes

compiler/frontend/src/org/jetbrains/kotlin/resolve/DeclarationsChecker.kt

@@ -28,6 +28,7 @@ import org.jetbrains.kotlin.diagnostics.Errors
 import org.jetbrains.kotlin.diagnostics.Errors.*
 import org.jetbrains.kotlin.lexer.KtTokens
 import org.jetbrains.kotlin.psi.*
+import org.jetbrains.kotlin.psi.psiUtil.containingClassOrObject
 import org.jetbrains.kotlin.psi.psiUtil.visibilityModifier
 import org.jetbrains.kotlin.resolve.BindingContext.*
 import org.jetbrains.kotlin.resolve.DescriptorUtils.classCanHaveAbstractMembers
@@ -724,7 +725,8 @@ class DeclarationsChecker(
         }
         else {
             val isUninitialized = trace.bindingContext.get(BindingContext.IS_UNINITIALIZED, propertyDescriptor) ?: false
-            if (backingFieldRequired && !inTrait && !propertyDescriptor.isLateInit && !isPlatform && isUninitialized) {
+            val isExternal = DescriptorUtils.isEffectivelyExternal(propertyDescriptor)
+            if (backingFieldRequired && !inTrait && !propertyDescriptor.isLateInit && !isPlatform && isUninitialized && !isExternal) {
                 if (containingDeclaration !is ClassDescriptor || hasAccessorImplementation) {
                     trace.report(MUST_BE_INITIALIZED.on(property))
                 }
@@ -760,7 +762,7 @@ class DeclarationsChecker(
 
         val containingDescriptor = functionDescriptor.containingDeclaration
         val hasAbstractModifier = function.hasModifier(KtTokens.ABSTRACT_KEYWORD)
-        val hasExternalModifier = function.hasModifier(KtTokens.EXTERNAL_KEYWORD)
+        val hasExternalModifier = DescriptorUtils.isEffectivelyExternal(functionDescriptor)
 
         if (containingDescriptor is ClassDescriptor) {
             val inInterface = containingDescriptor.kind == ClassKind.INTERFACE

core/descriptors/src/org/jetbrains/kotlin/resolve/DescriptorUtils.java

@@ -575,4 +575,16 @@ public class DescriptorUtils {
     public static Collection<DeclarationDescriptor> getAllDescriptors(@NotNull MemberScope scope) {
         return scope.getContributedDescriptors(DescriptorKindFilter.ALL, MemberScope.Companion.getALL_NAME_FILTER());
     }
+
+    public static boolean isEffectivelyExternal(@NotNull MemberDescriptor descriptor) {
+        if (descriptor.isExternal()) return true;
+
+        if (descriptor instanceof PropertyAccessorDescriptor) {
+            PropertyDescriptor variableDescriptor = ((PropertyAccessorDescriptor) descriptor).getCorrespondingProperty();
+            if (isEffectivelyExternal(variableDescriptor)) return true;
+        }
+
+        ClassDescriptor containingClass = getContainingClass(descriptor);
+        return containingClass != null && isEffectivelyExternal(containingClass);
+    }
 }

js/js.frontend/src/org/jetbrains/kotlin/js/translate/utils/AnnotationsUtils.java

@@ -133,10 +133,7 @@ public final class AnnotationsUtils {
     }
 
     private static boolean isEffectivelyExternal(@NotNull DeclarationDescriptor descriptor) {
-        if (descriptor instanceof MemberDescriptor && ((MemberDescriptor) descriptor).isExternal()) return true;
+        return descriptor instanceof MemberDescriptor && DescriptorUtils.isEffectivelyExternal((MemberDescriptor) descriptor);
-
-        ClassDescriptor containingClass = DescriptorUtils.getContainingClass(descriptor);
-        return containingClass != null && isEffectivelyExternal(containingClass);
     }
 
     public static boolean isLibraryObject(@NotNull DeclarationDescriptor descriptor) {