Convert member to extension: preserve visibility

#KT-29248 Fixed

idea/src/org/jetbrains/kotlin/idea/intentions/declarations/ConvertMemberToExtensionIntention.kt

@@ -267,7 +267,12 @@ class ConvertMemberToExtensionIntention : SelfTargetingRangeIntention<KtCallable
             }
         }
 
-        return processSingleDeclaration(element, allowExpected)
+        val classVisibility = element.containingClass()?.visibilityModifierType()
+        val (extension, bodyToSelect) = processSingleDeclaration(element, allowExpected)
+        if (classVisibility != null && extension.visibilityModifier() == null) {
+            extension.addModifier(classVisibility)
+        }
+        return extension to bodyToSelect
     }
 
     private fun newTypeParameterList(member: KtCallableDeclaration): KtTypeParameterList? {

idea/testData/intentions/declarations/convertMemberToExtension/privateInInternalClass.kt

@@ -0,0 +1,3 @@
+internal class Foo {
+    private fun <caret>bar() {}
+}

idea/testData/intentions/declarations/convertMemberToExtension/privateInInternalClass.kt.after

@@ -0,0 +1,4 @@
+internal class Foo {
+}
+
+private fun Foo.bar() {}

idea/testData/intentions/declarations/convertMemberToExtension/publicInInternalClass.kt

@@ -0,0 +1,3 @@
+internal class Foo {
+    fun <caret>bar() {}
+}

idea/testData/intentions/declarations/convertMemberToExtension/publicInInternalClass.kt.after

@@ -0,0 +1,4 @@
+internal class Foo {
+}
+
+internal fun Foo.bar() {}

idea/testData/intentions/declarations/convertMemberToExtension/publicInPrivateClass.kt

@@ -0,0 +1,3 @@
+private class Foo {
+    fun <caret>bar() {}
+}

idea/testData/intentions/declarations/convertMemberToExtension/publicInPrivateClass.kt.after

@@ -0,0 +1,4 @@
+private class Foo {
+}
+
+private fun Foo.bar() {}

idea/tests/org/jetbrains/kotlin/idea/intentions/IntentionTestGenerated.java

@@ -8703,6 +8703,11 @@ public class IntentionTestGenerated extends AbstractIntentionTest {
                 runTest("idea/testData/intentions/declarations/convertMemberToExtension/private.kt");
             }
 
+            @TestMetadata("privateInInternalClass.kt")
+            public void testPrivateInInternalClass() throws Exception {
+                runTest("idea/testData/intentions/declarations/convertMemberToExtension/privateInInternalClass.kt");
+            }
+
             @TestMetadata("protected.kt")
             public void testProtected() throws Exception {
                 runTest("idea/testData/intentions/declarations/convertMemberToExtension/protected.kt");
@@ -8713,6 +8718,16 @@ public class IntentionTestGenerated extends AbstractIntentionTest {
                 runTest("idea/testData/intentions/declarations/convertMemberToExtension/public.kt");
             }
 
+            @TestMetadata("publicInInternalClass.kt")
+            public void testPublicInInternalClass() throws Exception {
+                runTest("idea/testData/intentions/declarations/convertMemberToExtension/publicInInternalClass.kt");
+            }
+
+            @TestMetadata("publicInPrivateClass.kt")
+            public void testPublicInPrivateClass() throws Exception {
+                runTest("idea/testData/intentions/declarations/convertMemberToExtension/publicInPrivateClass.kt");
+            }
+
             @TestMetadata("secondaryConstructor.kt")
             public void testSecondaryConstructor() throws Exception {
                 runTest("idea/testData/intentions/declarations/convertMemberToExtension/secondaryConstructor.kt");