Extraction Engine: Assume internal visibility for trait members

idea/src/org/jetbrains/kotlin/idea/refactoring/introduce/extractionEngine/extractableAnalysisUtil.kt

@@ -736,6 +736,15 @@ fun ExtractionData.isVisibilityApplicable(): Boolean {
     }
 }
 
+fun ExtractionData.getDefaultVisibility(): String {
+    if (!isVisibilityApplicable()) return ""
+
+    val parent = targetSibling.getStrictParentOfType<JetDeclaration>()
+    if (parent is JetClass && parent.isTrait()) return ""
+
+    return "private"
+}
+
 fun ExtractionData.performAnalysis(): AnalysisResult {
     if (originalElements.isEmpty()) {
         return AnalysisResult(null, Status.CRITICAL_ERROR, listOf(ErrorMessage.NO_EXPRESSION))
@@ -824,7 +833,7 @@ fun ExtractionData.performAnalysis(): AnalysisResult {
                     this,
                     bindingContext,
                     functionNames,
-                    if (isVisibilityApplicable()) "private" else "",
+                    getDefaultVisibility(),
                     adjustedParameters.sortBy { it.name },
                     receiverParameter,
                     paramsInfo.typeParameters.sortBy { it.originalDeclaration.getName()!! },

idea/testData/refactoring/extractFunction/basic/traitFunction.kt

@@ -0,0 +1,5 @@
+trait T{
+    fun foo(): Int {
+        return <selection>1</selection>
+    }
+}

idea/testData/refactoring/extractFunction/basic/traitFunction.kt.after

@@ -0,0 +1,9 @@
+trait T{
+    fun foo(): Int {
+        return i()
+    }
+
+    fun i(): Int {
+        return 1
+    }
+}

idea/testData/refactoring/introduceProperty/extractWithGetterToTrait.kt.after

@@ -1,6 +1,6 @@
 // EXTRACTION_TARGET: property with getter
 trait T {
-    private val i: Int
+    val i: Int
         get() {
             return 1
         }

idea/tests/org/jetbrains/kotlin/idea/refactoring/introduce/JetExtractionTestGenerated.java

@@ -483,6 +483,12 @@ public class JetExtractionTestGenerated extends AbstractJetExtractionTest {
                 String fileName = JetTestUtils.navigationMetadata("idea/testData/refactoring/extractFunction/basic/refInReturn.kt");
                 doExtractFunctionTest(fileName);
             }
+
+            @TestMetadata("traitFunction.kt")
+            public void testTraitFunction() throws Exception {
+                String fileName = JetTestUtils.navigationMetadata("idea/testData/refactoring/extractFunction/basic/traitFunction.kt");
+                doExtractFunctionTest(fileName);
+            }
         }
 
         @TestMetadata("idea/testData/refactoring/extractFunction/controlFlow")