JS: prohibit inline external declarations. See KT-15307

js/js.frontend/src/org/jetbrains/kotlin/js/resolve/diagnostics/DefaultErrorMessagesJs.kt

@@ -72,6 +72,7 @@ private val DIAGNOSTIC_FACTORY_TO_RENDERER by lazy {
         put(ErrorsJs.OVERRIDING_EXTERNAL_FUN_WITH_OPTIONAL_PARAMS_WITH_FAKE,
             "Overriding `external` function with optional parameters by declaration from superclass: {0}", Renderers.COMPACT)
         put(ErrorsJs.IMPLEMENTING_FUNCTION_INTERFACE, "Implementing function interface is prohibited in JavaScript")
+        put(ErrorsJs.INLINE_EXTERNAL_DECLARATION, "Inline external declaration")
 
         this
     }

js/js.frontend/src/org/jetbrains/kotlin/js/resolve/diagnostics/ErrorsJs.java

@@ -76,6 +76,8 @@ public interface ErrorsJs {
             DiagnosticFactory1.create(ERROR, PositioningStrategies.DECLARATION_SIGNATURE_OR_DEFAULT);
     DiagnosticFactory0<KtClassOrObject> IMPLEMENTING_FUNCTION_INTERFACE = DiagnosticFactory0.create(
             ERROR, PositioningStrategies.DECLARATION_SIGNATURE_OR_DEFAULT);
+    DiagnosticFactory0<KtDeclaration> INLINE_EXTERNAL_DECLARATION = DiagnosticFactory0.create(
+            ERROR, PositioningStrategies.DECLARATION_SIGNATURE_OR_DEFAULT);
 
     @SuppressWarnings("UnusedDeclaration")
     Object _initializer = new Object() {

js/js.frontend/src/org/jetbrains/kotlin/js/resolve/diagnostics/JsExternalChecker.kt

@@ -18,6 +18,7 @@ package org.jetbrains.kotlin.js.resolve.diagnostics
 
 import org.jetbrains.kotlin.builtins.KotlinBuiltIns
 import org.jetbrains.kotlin.descriptors.*
+import org.jetbrains.kotlin.descriptors.annotations.isInlineOnlyOrReified
 import org.jetbrains.kotlin.diagnostics.DiagnosticSink
 import org.jetbrains.kotlin.js.PredefinedAnnotation
 import org.jetbrains.kotlin.js.translate.utils.AnnotationsUtils
@@ -75,6 +76,10 @@ object JsExternalChecker : SimpleDeclarationChecker {
                 diagnosticHolder.report(ErrorsJs.EXTERNAL_TYPE_EXTENDS_NON_EXTERNAL_TYPE.on(declaration))
             }
         }
+
+        if (descriptor is FunctionDescriptor && descriptor.isInline) {
+            diagnosticHolder.report(ErrorsJs.INLINE_EXTERNAL_DECLARATION.on(declaration))
+        }
     }
 
     private fun isDirectlyExternal(declaration: KtDeclaration, descriptor: DeclarationDescriptor): Boolean {