cache: Fix Server Side Copy with Temp Upload

When wrapping a backend that supports Server Side Copy (e.g. `b2`, `s3`)
and configuring the `tmp_upload_path` option, the `cache` backend would
erroneously report that Server Side Copy/Move was not supported, causing
operations such as file moves to fail. This change fixes this issue
under these circumstances such that Server Side Copy will now be used
when the wrapped backend supports it.

Fixes #3206

backend/cache/cache.go

@@ -520,9 +520,6 @@ func NewFs(name, rootPath string, m configmap.Mapper) (fs.Fs, error) {
 	// override only those features that use a temp fs and it doesn't support them
 	//f.features.ChangeNotify = f.ChangeNotify
 	if f.opt.TempWritePath != "" {
-		if f.tempFs.Features().Copy == nil {
-			f.features.Copy = nil
-		}
 		if f.tempFs.Features().Move == nil {
 			f.features.Move = nil
 		}
@@ -1533,6 +1530,9 @@ func (f *Fs) Copy(ctx context.Context, src fs.Object, remote string) (fs.Object,
 		fs.Errorf(src, "source remote (%v) doesn't support Copy", src.Fs())
 		return nil, fs.ErrorCantCopy
 	}
+	if f.opt.TempWritePath != "" && src.Fs() == f.tempFs {
+		return nil, fs.ErrorCantCopy
+	}
 	// the source must be a cached object or we abort
 	srcObj, ok := src.(*Object)
 	if !ok {

cmd/backend/backend.go

@@ -59,7 +59,7 @@ Note to run these commands on a running backend then see
 [backend/command](/rc/#backend/command) in the rc docs.
 `,
 	RunE: func(command *cobra.Command, args []string) error {
-		cmd.CheckArgs(2, 1E6, command, args)
+		cmd.CheckArgs(2, 1e6, command, args)
 		name, remote := args[0], args[1]
 		cmd.Run(false, false, command, func() error {
 			// show help if remote is a backend name