onedrive: make --onedrive-delta quicker when not listing from the drive root

Rclone always asked for the delta listing of the whole drive and threw
away the items which weren't under the directory being listed.

The delta API now works on any folder, so ask for the delta listing of
the directory being listed instead, falling back to listing from the
root of the drive for drives which only support delta there.

backend/onedrive/onedrive.go

@@ -438,21 +438,12 @@ Setting this flag speeds up these things greatly:
     rclone size onedrive:
     rclone rc vfs/refresh recursive=true
 
-**However** the delta listing API **only** works at the root of the
-drive. If you use it not at the root then it recurses from the root
-and discards all the data that is not under the directory you asked
-for. So it will be correct but may not be very efficient.
-
-This is why this flag is not set as the default.
-
-As a rule of thumb if nearly all of your data is under rclone's root
-directory (the |root/directory| in |onedrive:root/directory|) then
-using this flag will be a big performance win. If your data is
-mostly not under the root then using this flag will be a big
-performance loss.
-
-It is recommended if you are mounting your onedrive at the root
-(or near the root when using crypt) and using rclone |rc vfs/refresh|.
+Rclone asks for the delta listing of the directory being listed. If
+the drive only supports delta listings at the root of the drive (as
+some older OneDrive for Business and SharePoint drives do) then
+rclone lists from the root and discards all the data that is not
+under the directory you asked for. So it will be correct but may not
+be very efficient.
 `, "|", "`"),
 			Advanced: true,
 		}, {
@@ -1511,10 +1502,6 @@ func (f *Fs) ListR(ctx context.Context, dir string, callback fs.ListRCallback) (
 		return err
 	}
 
-	// ListR only works at the root of a onedrive, not on a folder
-	// So we have to filter things outside of the root which is
-	// inefficient.
-
 	list := list.NewHelper(callback)
 
 	// list a folder conventionally - used for shared folders
@@ -1590,17 +1577,26 @@ func (f *Fs) ListR(ctx context.Context, dir string, callback fs.ListRCallback) (
 		return nil
 	}
 
-	opts := rest.Opts{
-		Method: "GET",
-		Path:   "/root/delta",
-		Parameters: map[string][]string{
-			// "token": {token},
+	listDelta := func(opts rest.Opts) error {
+		opts.Parameters = url.Values{
 			"$top": {fmt.Sprintf("%d", f.opt.ListChunk)},
-		},
+		}
+		var result api.DeltaResponse
+		return f._listAll(ctx, "", false, false, fn, &opts, &result, &result.Value, &result.NextLink)
 	}
 
-	var result api.DeltaResponse
-	err = f._listAll(ctx, "", false, false, fn, &opts, &result, &result.Value, &result.NextLink)
+	err = listDelta(f.newOptsCall(directoryID, "GET", "/delta"))
+	// Some drives only support delta listings at the root of the
+	// drive, in which case list the whole drive and filter out the
+	// items outside dir.
+	var apiErr *api.Error
+	if err != nil && len(seen) == 0 && errors.As(err, &apiErr) {
+		fs.Debugf(f, "Delta listing of directory failed, listing from the root of the drive instead: %v", err)
+		err = listDelta(rest.Opts{
+			Method: "GET",
+			Path:   "/root/delta",
+		})
+	}
 	if err != nil {
 		return err
 	}

docs/content/onedrive.md

@@ -326,10 +326,11 @@ This can be useful with `rclone mount` and [rclone rc vfs/refresh
 recursive=true](/rc/#vfs-refresh)) to very quickly fill the mount with
 information about all the files.
 
-The API used for the recursive listing (`ListR`) only supports listing
-from the root of the drive. This will become increasingly inefficient
-the further away you get from the root as rclone will have to discard
-files outside of the directory you are using.
+Rclone asks for the delta listing of the directory being listed. Some
+drives only support delta listings from the root of the drive, in
+which case rclone lists the whole drive and discards the files outside
+of the directory you are using, which is increasingly inefficient the
+further away from the root you get.
 
 Some commands (like `rclone lsf -R`) will use `ListR` by default - you
 can turn this off with `--disable ListR` if you need to.