KT-2752: prohibit JSName on extension properties

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

@@ -45,6 +45,7 @@ private val DIAGNOSTIC_FACTORY_TO_RENDERER by lazy {
         put(ErrorsJs.JS_NAME_ON_ACCESSOR_AND_PROPERTY, "@JsName can be either on a property or its accessors, not both of them")
         put(ErrorsJs.JS_NAME_IS_NOT_ON_ALL_ACCESSORS, "@JsName should be on all of the property accessors")
         put(ErrorsJs.JS_NAME_PROHIBITED_FOR_OVERRIDE, "@JsName is prohibited for overridden members")
+        put(ErrorsJs.JS_NAME_PROHIBITED_FOR_EXTENSION_PROPERTY, "@JsName is prohibited for extension properties")
 
         this
     }

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

@@ -49,6 +49,7 @@ public interface ErrorsJs {
     DiagnosticFactory0<KtElement> JS_NAME_ON_ACCESSOR_AND_PROPERTY = DiagnosticFactory0.create(ERROR);
     DiagnosticFactory0<PsiElement> JS_NAME_IS_NOT_ON_ALL_ACCESSORS = DiagnosticFactory0.create(ERROR);
     DiagnosticFactory0<PsiElement> JS_NAME_PROHIBITED_FOR_OVERRIDE = DiagnosticFactory0.create(ERROR);
+    DiagnosticFactory0<PsiElement> JS_NAME_PROHIBITED_FOR_EXTENSION_PROPERTY = DiagnosticFactory0.create(ERROR);
 
     @SuppressWarnings("UnusedDeclaration")
     Object _initializer = new Object() {

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

@@ -21,6 +21,8 @@ import org.jetbrains.kotlin.diagnostics.DiagnosticSink
 import org.jetbrains.kotlin.js.translate.utils.AnnotationsUtils
 import org.jetbrains.kotlin.psi.KtDeclaration
 import org.jetbrains.kotlin.resolve.BindingContext
+import org.jetbrains.kotlin.resolve.DeclarationChecker
+import org.jetbrains.kotlin.resolve.descriptorUtil.isExtension
 import org.jetbrains.kotlin.resolve.SimpleDeclarationChecker
 
 object JsNameChecker : SimpleDeclarationChecker {
@@ -51,6 +53,11 @@ object JsNameChecker : SimpleDeclarationChecker {
                     diagnosticHolder.report(ErrorsJs.JS_NAME_ON_ACCESSOR_AND_PROPERTY.on(jsNamePsi))
                 }
             }
+            is PropertyDescriptor -> {
+                if (descriptor.isExtension) {
+                    diagnosticHolder.report(ErrorsJs.JS_NAME_PROHIBITED_FOR_EXTENSION_PROPERTY.on(jsNamePsi))
+                }
+            }
         }
     }
 }