Move: Do not use existing file name when moving its top-level declaration(s)

#KT-7697 Fixed

idea/src/org/jetbrains/kotlin/idea/refactoring/move/moveTopLevelDeclarations/MoveKotlinTopLevelDeclarationsHandler.kt

@@ -51,8 +51,7 @@ public class MoveKotlinTopLevelDeclarationsHandler : MoveHandlerDelegate() {
             for (element in elements) {
                 if (element !is JetNamedDeclaration) continue
 
-                val fileName = element.getFileNameAfterMove()
-                if (fileName != null && !fileNames.add(fileName)) {
+                if (!fileNames.add(element.getFileNameAfterMove())) {
                     val message = RefactoringBundle.getCannotRefactorMessage(
                             RefactoringBundle.message("there.are.going.to.be.multiple.destination.files.with.the.same.name")
                     )

idea/src/org/jetbrains/kotlin/idea/refactoring/move/moveTopLevelDeclarations/MoveKotlinTopLevelDeclarationsProcessor.kt

@@ -241,8 +241,8 @@ public class MoveKotlinTopLevelDeclarationsProcessor(
             val targetPsi = moveTarget.getOrCreateTargetPsi(declaration)
             val targetFile =
                     if (targetPsi is PsiDirectory) {
-                        val existingFile = if (targetPsi != file!!.getContainingDirectory()) targetPsi.findFile(file.getName()) else null
-                        existingFile ?: declaration.getFileNameAfterMove()?.let {createKotlinFile(it, targetPsi)}
+                        val targetFileName = declaration.getFileNameAfterMove()
+                        targetPsi.findFile(targetFileName) ?: createKotlinFile(targetFileName, targetPsi)
                     }
                     else targetPsi
 

idea/src/org/jetbrains/kotlin/idea/refactoring/move/moveUtils.kt

@@ -156,11 +156,7 @@ fun createMoveUsageInfoIfPossible(
     return MoveRenameUsageInfo(element, reference, startOffset, endOffset, referencedElement, false)
 }
 
-public fun JetNamedDeclaration.getFileNameAfterMove(): String? {
-    return (getContainingFile() as? JetFile)?.let { file ->
-        if (file.getDeclarations().size() > 1) "${getName()}.${JetFileType.EXTENSION}" else file.getName()
-    }
-}
+public fun JetNamedDeclaration.getFileNameAfterMove(): String = "${getName()}.${JetFileType.EXTENSION}"
 
 // returns true if successful
 private fun updateJavaReference(reference: PsiReferenceExpression, oldElement: PsiElement, newElement: PsiElement): Boolean {