Prohibit external modifiers on classes and properties in JVM target

compiler/frontend.java/src/org/jetbrains/kotlin/resolve/jvm/checkers/ExternalFunChecker.kt

@@ -18,6 +18,8 @@ package org.jetbrains.kotlin.resolve.jvm.checkers
 
 import org.jetbrains.kotlin.descriptors.*
 import org.jetbrains.kotlin.diagnostics.DiagnosticSink
+import org.jetbrains.kotlin.diagnostics.Errors
+import org.jetbrains.kotlin.lexer.KtTokens
 import org.jetbrains.kotlin.psi.KtDeclaration
 import org.jetbrains.kotlin.psi.KtDeclarationWithBody
 import org.jetbrains.kotlin.psi.KtPropertyAccessor
@@ -34,7 +36,17 @@ class ExternalFunChecker : SimpleDeclarationChecker {
             diagnosticHolder: DiagnosticSink,
             bindingContext: BindingContext
     ) {
-        if (descriptor !is FunctionDescriptor || !descriptor.isExternal) return
+        if (descriptor !is MemberDescriptor || !descriptor.isExternal) return
+
+        if (descriptor !is FunctionDescriptor) {
+            val target = when (descriptor) {
+                is PropertyDescriptor -> "property"
+                is ClassDescriptor -> "class"
+                else -> "non-function declaration"
+            }
+            diagnosticHolder.report(Errors.WRONG_MODIFIER_TARGET.on(declaration, KtTokens.EXTERNAL_KEYWORD, target))
+            return
+        }
 
         if (DescriptorUtils.isInterface(descriptor.containingDeclaration)) {
             diagnosticHolder.report(ErrorsJvm.EXTERNAL_DECLARATION_IN_INTERFACE.on(declaration))

compiler/testData/diagnostics/testsWithStdLib/native/nonFunction.kt

@@ -0,0 +1,9 @@
+<!WRONG_MODIFIER_TARGET!>external class A<!>
+
+<!WRONG_MODIFIER_TARGET!>external val foo: Int = 23<!>
+
+class B {
+    <!WRONG_MODIFIER_TARGET!>external class A<!>
+
+    <!WRONG_MODIFIER_TARGET!>external val foo: Int = 23<!>
+}

compiler/testData/diagnostics/testsWithStdLib/native/nonFunction.txt

@@ -0,0 +1,25 @@
+package
+
+public val foo: kotlin.Int = 23
+
+public final class A {
+    public constructor A()
+    public open override /*1*/ /*fake_override*/ fun equals(/*0*/ other: kotlin.Any?): kotlin.Boolean
+    public open override /*1*/ /*fake_override*/ fun hashCode(): kotlin.Int
+    public open override /*1*/ /*fake_override*/ fun toString(): kotlin.String
+}
+
+public final class B {
+    public constructor B()
+    public final val foo: kotlin.Int = 23
+    public open override /*1*/ /*fake_override*/ fun equals(/*0*/ other: kotlin.Any?): kotlin.Boolean
+    public open override /*1*/ /*fake_override*/ fun hashCode(): kotlin.Int
+    public open override /*1*/ /*fake_override*/ fun toString(): kotlin.String
+
+    public final class A {
+        public constructor A()
+        public open override /*1*/ /*fake_override*/ fun equals(/*0*/ other: kotlin.Any?): kotlin.Boolean
+        public open override /*1*/ /*fake_override*/ fun hashCode(): kotlin.Int
+        public open override /*1*/ /*fake_override*/ fun toString(): kotlin.String
+    }
+}

compiler/tests/org/jetbrains/kotlin/checkers/DiagnosticsTestWithStdLibGenerated.java

@@ -950,6 +950,12 @@ public class DiagnosticsTestWithStdLibGenerated extends AbstractDiagnosticsTestW
             doTest(fileName);
         }
 
+        @TestMetadata("nonFunction.kt")
+        public void testNonFunction() throws Exception {
+            String fileName = KotlinTestUtils.navigationMetadata("compiler/testData/diagnostics/testsWithStdLib/native/nonFunction.kt");
+            doTest(fileName);
+        }
+
         @TestMetadata("override.kt")
         public void testOverride() throws Exception {
             String fileName = KotlinTestUtils.navigationMetadata("compiler/testData/diagnostics/testsWithStdLib/native/override.kt");