KT-7704 Intention actions on visibility modifier for quick changing it

#KT-7704 Fixed

compiler/frontend/src/org/jetbrains/kotlin/psi/JetClass.java

@@ -22,6 +22,7 @@ import com.intellij.navigation.ItemPresentationProviders;
 import com.intellij.openapi.util.text.StringUtil;
 import com.intellij.psi.PsiElement;
 import com.intellij.psi.PsiFile;
+import com.intellij.psi.tree.TokenSet;
 import com.intellij.psi.util.PsiTreeUtil;
 import com.intellij.util.IncorrectOperationException;
 import org.jetbrains.annotations.NotNull;
@@ -255,4 +256,9 @@ public class JetClass extends JetTypeParameterListOwnerStub<KotlinClassStub> imp
         JetClassBody body = getBody();
         return body != null ? body.getSecondaryConstructors() : Collections.<JetSecondaryConstructor>emptyList();
     }
+
+    @Nullable
+    public PsiElement getClassOrTraitKeyword() {
+        return findChildByType(TokenSet.create(JetTokens.CLASS_KEYWORD, JetTokens.TRAIT_KEYWORD));
+    }
 }

compiler/frontend/src/org/jetbrains/kotlin/psi/JetNamedFunction.java

@@ -79,7 +79,7 @@ public class JetNamedFunction extends JetTypeParameterListOwnerStub<KotlinFuncti
     }
 
     @NotNull
-    public PsiElement getFunToken() {
+    public PsiElement getFunKeyword() {
         PsiElement element = findChildByType(JetTokens.FUN_KEYWORD);
         assert element != null : "'fun' must be present: " + PsiUtilPackage.getElementTextWithContext(this);
         return element;

compiler/frontend/src/org/jetbrains/kotlin/psi/addRemoveModifier.kt

@@ -52,9 +52,7 @@ internal fun addModifier(modifierList: JetModifierList, modifier: JetModifierKey
 
     if (modifier == defaultVisibilityModifier) { // do not insert explicit 'internal' keyword (or 'public' for primary constructor)
         //TODO: code style option
-        if (modifierToReplace != null) {
-            modifierToReplace.delete()
-        }
+        modifierToReplace?.delete()
         return
     }
 
@@ -72,8 +70,17 @@ internal fun addModifier(modifierList: JetModifierList, modifier: JetModifierKey
             return newModifierOrder > order
         }
 
-        val anchor = modifierList.getLastChild()?.siblings(forward = false)?.firstOrNull(::placeAfter)
+        val lastChild = modifierList.getLastChild()
+        val anchor = lastChild?.siblings(forward = false)?.firstOrNull(::placeAfter)
         modifierList.addAfter(newModifier, anchor)
+
+        if (anchor == lastChild) { // add line break if needed, otherwise visibility keyword may appear on previous line
+            val whiteSpace = modifierList.getNextSibling() as? PsiWhiteSpace
+            if (whiteSpace != null && whiteSpace.getText().contains('\n')) {
+                modifierList.addAfter(whiteSpace, anchor)
+                whiteSpace.delete()
+            }
+        }
     }
 }