Add function to supertype immediately removes redundant modifiers #KT-12297 Fixed

idea/src/org/jetbrains/kotlin/idea/quickfix/AddFunctionToSupertypeFix.kt

@@ -35,9 +35,12 @@ import org.jetbrains.kotlin.idea.util.IdeDescriptorRenderers
 import org.jetbrains.kotlin.idea.core.ShortenReferences
 import org.jetbrains.kotlin.idea.core.TemplateKind
 import org.jetbrains.kotlin.idea.core.getFunctionBodyTextFromTemplate
+import org.jetbrains.kotlin.idea.core.implicitModality
 import org.jetbrains.kotlin.idea.imports.importableFqName
 import org.jetbrains.kotlin.idea.util.application.executeWriteCommand
+import org.jetbrains.kotlin.lexer.KtModifierKeywordToken
 import org.jetbrains.kotlin.psi.*
+import org.jetbrains.kotlin.psi.psiUtil.modalityModifier
 import org.jetbrains.kotlin.types.KotlinType
 import org.jetbrains.kotlin.types.checker.KotlinTypeChecker
 import org.jetbrains.kotlin.types.typeUtil.supertypes
@@ -87,6 +90,11 @@ class AddFunctionToSupertypeFix private constructor(
             val insertedFunctionElement = classBody.addBefore(functionElement, classBody.rBrace) as KtNamedFunction
 
             ShortenReferences.DEFAULT.process(insertedFunctionElement)
+            val modifierToken = insertedFunctionElement.modalityModifier()?.node?.elementType as? KtModifierKeywordToken
+                                ?: return@executeWriteCommand
+            if (insertedFunctionElement.implicitModality() == modifierToken) {
+                RemoveModifierFix(insertedFunctionElement, modifierToken, true).invoke()
+            }
         }
     }
 
@@ -180,7 +188,7 @@ class AddFunctionToSupertypeFix private constructor(
         private fun generateFunctionSignatureForType(functionDescriptor: FunctionDescriptor, typeDescriptor: ClassDescriptor): FunctionDescriptor {
             // TODO: support for generics.
 
-            val modality = if (typeDescriptor.kind == ClassKind.INTERFACE) Modality.OPEN else typeDescriptor.modality
+            val modality = if (typeDescriptor.kind == ClassKind.INTERFACE) Modality.ABSTRACT else typeDescriptor.modality
 
             return functionDescriptor.copy(
                     typeDescriptor,

idea/testData/quickfix/override/nothingToOverride/addFunctionNoBody.kt

@@ -1,4 +1,4 @@
-// "Add 'open fun f()' to 'A'" "true"
+// "Add 'abstract fun f()' to 'A'" "true"
 interface A
 class B : A {
     <caret>override fun f() {}

idea/testData/quickfix/override/nothingToOverride/addFunctionNoBody.kt.after

@@ -1,6 +1,6 @@
-// "Add 'open fun f()' to 'A'" "true"
+// "Add 'abstract fun f()' to 'A'" "true"
 interface A {
-    open fun f()
+    fun f()
 }
 
 class B : A {

idea/testData/quickfix/override/nothingToOverride/addFunctionTrait.kt

@@ -1,4 +1,4 @@
-// "Add 'open fun f()' to 'A'" "true"
+// "Add 'abstract fun f()' to 'A'" "true"
 interface A {
 }
 class B : A {

idea/testData/quickfix/override/nothingToOverride/addFunctionTrait.kt.after

@@ -1,6 +1,6 @@
-// "Add 'open fun f()' to 'A'" "true"
+// "Add 'abstract fun f()' to 'A'" "true"
 interface A {
-    open fun f()
+    fun f()
 }
 class B : A {
     <caret>override fun f() {}

idea/testData/quickfix/override/nothingToOverride/addFunctionTwoTraits.kt.after

@@ -1,6 +1,6 @@
 // "Add function to supertype..." "true"
 interface A {
-    open fun foo()
+    fun foo()
 }
 interface B {}
 class C: A, B {