drime: fix server-side copy over an existing file leaving a "name (1)" copy

When server-side copying to a destination which already existed, the
Drime server gave the copy the name "name (1)" and rclone only renamed
it if the source and destination leaf names differed. The existing file
was then deleted leaving the copy under the wrong name.

The server refuses to rename an entry to a name which is already in
use, so this removes the existing file straight after the copy, then
renames the copy whenever its name differs from the destination name.

(cherry picked from commit eb10c48a17)

backend/drime/drime.go

@@ -1040,17 +1040,28 @@ func (f *Fs) copy(ctx context.Context, id, newDirID string) (item *api.Item, err
 }
 
 // copy and rename a file or folder to directoryID with leaf
-func (f *Fs) copyTo(ctx context.Context, srcID, srcLeaf, dstLeaf, dstDirectoryID string) (info *api.Item, err error) {
-	// Can have duplicates so don't have to be careful here
-
+//
+// If existing is set it is removed once the copy has succeeded.
+func (f *Fs) copyTo(ctx context.Context, srcID, dstLeaf, dstDirectoryID string, existing fs.Object) (info *api.Item, err error) {
 	// Copy to dstDirectoryID first
 	info, err = f.copy(ctx, srcID, dstDirectoryID)
 	if err != nil {
 		return nil, err
 	}
 
+	// The server names the copy "name (1)" if the destination
+	// directory already has an entry called "name" and refuses to
+	// rename it to "name" until that entry is removed.
+	if existing != nil {
+		fs.Debugf(existing, "Server side copy: removing existing object after successful copy")
+		err = existing.Remove(ctx)
+		if err != nil {
+			return nil, err
+		}
+	}
+
 	// Rename if required
-	if srcLeaf != dstLeaf {
+	if info.Name != f.opt.Enc.FromStandardName(dstLeaf) {
 		info, err = f.rename(ctx, info.ID.String(), dstLeaf)
 		if err != nil {
 			return nil, err
@@ -1074,8 +1085,6 @@ func (f *Fs) Copy(ctx context.Context, src fs.Object, remote string) (dst fs.Obj
 		fs.Debugf(src, "Can't copy - not same remote type")
 		return nil, fs.ErrorCantCopy
 	}
-	srcLeaf := path.Base(srcObj.remote)
-
 	srcPath := srcObj.fs.rootSlash() + srcObj.remote
 	dstPath := f.rootSlash() + remote
 	if srcPath == dstPath {
@@ -1084,15 +1093,8 @@ func (f *Fs) Copy(ctx context.Context, src fs.Object, remote string) (dst fs.Obj
 
 	// Find existing object
 	existingObj, err := f.NewObject(ctx, remote)
-	if err == nil {
-		defer func() {
-			// Don't remove existing object if returning an error
-			if err != nil {
-				return
-			}
-			fs.Debugf(existingObj, "Server side copy: removing existing object after successful copy")
-			err = existingObj.Remove(ctx)
-		}()
+	if err != nil {
+		existingObj = nil
 	}
 
 	// Create temporary object
@@ -1102,7 +1104,7 @@ func (f *Fs) Copy(ctx context.Context, src fs.Object, remote string) (dst fs.Obj
 	}
 
 	// Copy the object
-	info, err := f.copyTo(ctx, srcObj.id, srcLeaf, dstLeaf, dstDirectoryID)
+	info, err := f.copyTo(ctx, srcObj.id, dstLeaf, dstDirectoryID, existingObj)
 	if err != nil {
 		return nil, err
 	}