From 8f36afac891789cad38b2a1e31b98de97af66df8 Mon Sep 17 00:00:00 2001
From: Nick Craig-Wood <nick@craig-wood.com>
Date: Wed, 22 Jul 2020 13:10:16 +0100
Subject: [PATCH] vfs: check destination on rename and delete if it exists
 first FIXME needs tests

Some backends (eg onedrive) will throw an error if we rename over an
existing file and some (drive) will create a duplicate.

This patch checks to see if the destination exists and removes it or
returns an error as appropriate.

Fixes #4293
---
 vfs/dir.go | 29 +++++++++++++++++++++++++++++
 1 file changed, 29 insertions(+)

diff --git a/vfs/dir.go b/vfs/dir.go
index 972f75b23..7e3664663 100644
--- a/vfs/dir.go
+++ b/vfs/dir.go
@@ -781,6 +781,9 @@ func (d *Dir) Rename(oldName, newName string, destDir *Dir) error {
 		fs.Errorf(oldPath, "Dir.Rename error: %v", err)
 		return err
 	}
+	// Check to see if destination exists
+	newNode, _ := destDir.stat(newName)
+	destinationExists := newNode != nil
 	switch x := oldNode.DirEntry().(type) {
 	case nil:
 		if oldFile, ok := oldNode.(*File); ok {
@@ -793,6 +796,19 @@ func (d *Dir) Rename(oldName, newName string, destDir *Dir) error {
 			return EPERM
 		}
 	case fs.Object:
+		if destinationExists {
+			// Can't overwrite dir with file
+			if newNode.IsDir() {
+				return EEXIST // EISDIR is POSIX
+			}
+			// Try to delete the file
+			fs.Debugf(newPath, "Dir.Rename removing existing file")
+			err = newNode.Remove()
+			if err != nil {
+				fs.Errorf(newPath, "Dir.Rename error: couldn't delete existing file: %v", err)
+				return err
+			}
+		}
 		if oldFile, ok := oldNode.(*File); ok {
 			if err = oldFile.rename(context.TODO(), destDir, newName); err != nil {
 				fs.Errorf(oldPath, "Dir.Rename error: %v", err)
@@ -804,6 +820,19 @@ func (d *Dir) Rename(oldName, newName string, destDir *Dir) error {
 			return err
 		}
 	case fs.Directory:
+		if destinationExists {
+			// Can't overwrite file with dir
+			if newNode.IsFile() {
+				return EEXIST // ENOTDIR is POSIX
+			}
+			// Try to delete the existing directory - will succeed only if empty
+			fs.Debugf(newPath, "Dir.Rename removing existing dir")
+			err = newNode.Remove()
+			if err != nil {
+				fs.Errorf(newPath, "Dir.Rename error: couldn't rmdir existing dir: %v", err)
+				return err
+			}
+		}
 		features := d.f.Features()
 		if features.DirMove == nil && features.Move == nil && features.Copy == nil {
 			err := errors.Errorf("Fs %q can't rename directories (no DirMove, Move or Copy)", d.f)