vfs: enable rename for nearly all remotes using server side Move or Copy

Before this change remotes without server side Move (eg swift, s3,
gcs) would not be able to rename files.

After it means nearly all remotes will be able to rename files on
rclone mount with the notable exceptions of b2 and yandex.

This changes checks to see if the remote can do Move or Copy then
calls `operations.Move` to do the actual move.  This will do a server
side Move or Copy but won't download and re-upload the file.

It also checks to see if the destination exists first which avoids
conflicts or duplicates.

Fixes #1965
Fixes #2569

fs/operations/operations.go

@@ -359,6 +359,11 @@ func Copy(f fs.Fs, dst fs.Object, remote string, src fs.Object) (newDst fs.Objec
 // Move src object to dst or fdst if nil.  If dst is nil then it uses
 // remote as the name of the new object.
 //
+// Note that you must check the destination does not exist before
+// calling this and pass it as dst.  If you pass dst=nil and the
+// destination does exist then this may create duplicates or return
+// errors.
+//
 // It returns the destination object if possible.  Note that this may
 // be nil.
 func Move(fdst fs.Fs, dst fs.Object, remote string, src fs.Object) (newDst fs.Object, err error) {

vfs/dir_test.go

@@ -423,6 +423,8 @@ func TestDirRename(t *testing.T) {
 	r := fstest.NewRun(t)
 	defer r.Finalise()
 	vfs, dir, file1 := dirCreate(t, r)
+	file3 := r.WriteObject("dir/file3", "file3 contents!", t1)
+	fstest.CheckListingWithPrecision(t, r.Fremote, []fstest.Item{file1, file3}, []string{"dir"}, r.Fremote.Precision())
 
 	root, err := vfs.Root()
 	require.NoError(t, err)
@@ -434,11 +436,12 @@ func TestDirRename(t *testing.T) {
 	err = root.Rename("dir", "dir2", root)
 	assert.NoError(t, err)
 	checkListing(t, root, []string{"dir2,0,true"})
-	checkListing(t, dir, []string{"file1,14,false"})
+	checkListing(t, dir, []string{"file1,14,false", "file3,15,false"})
 
 	// check the underlying r.Fremote
 	file1.Path = "dir2/file1"
-	fstest.CheckListingWithPrecision(t, r.Fremote, []fstest.Item{file1}, []string{"dir2"}, r.Fremote.Precision())
+	file3.Path = "dir2/file3"
+	fstest.CheckListingWithPrecision(t, r.Fremote, []fstest.Item{file1, file3}, []string{"dir2"}, r.Fremote.Precision())
 
 	// refetch dir
 	node, err := vfs.Stat("dir2")
@@ -449,10 +452,20 @@ func TestDirRename(t *testing.T) {
 	err = dir.Rename("file1", "file2", root)
 	assert.NoError(t, err)
 	checkListing(t, root, []string{"dir2,0,true", "file2,14,false"})
-	checkListing(t, dir, []string(nil))
+	checkListing(t, dir, []string{"file3,15,false"})
 
 	// check the underlying r.Fremote
 	file1.Path = "file2"
+	fstest.CheckListingWithPrecision(t, r.Fremote, []fstest.Item{file1, file3}, []string{"dir2"}, r.Fremote.Precision())
+
+	// Rename a file on top of another file
+	err = root.Rename("file2", "file3", dir)
+	assert.NoError(t, err)
+	checkListing(t, root, []string{"dir2,0,true"})
+	checkListing(t, dir, []string{"file3,14,false"})
+
+	// check the underlying r.Fremote
+	file1.Path = "dir2/file3"
 	fstest.CheckListingWithPrecision(t, r.Fremote, []fstest.Item{file1}, []string{"dir2"}, r.Fremote.Precision())
 
 	// read only check

vfs/file.go

@@ -9,6 +9,7 @@ import (
 
 	"github.com/ncw/rclone/fs"
 	"github.com/ncw/rclone/fs/log"
+	"github.com/ncw/rclone/fs/operations"
 	"github.com/pkg/errors"
 )
 
@@ -108,18 +109,16 @@ func (f *File) applyPendingRename() {
 // Otherwise it will queue the rename operation on the remote until no writers
 // remain.
 func (f *File) rename(destDir *Dir, newName string) error {
-	// FIXME: could Copy then Delete if Move not available
+	if features := f.d.f.Features(); features.Move == nil && features.Copy == nil {
-	// - though care needed if case insensitive...
+		err := errors.Errorf("Fs %q can't rename files (no server side Move or Copy)", f.d.f)
-	doMove := f.d.f.Features().Move
-	if doMove == nil {
-		err := errors.Errorf("Fs %q can't rename files (no Move)", f.d.f)
 		fs.Errorf(f.Path(), "Dir.Rename error: %v", err)
 		return err
 	}
 
 	renameCall := func() error {
 		newPath := path.Join(destDir.path, newName)
-		newObject, err := doMove(f.o, newPath)
+		dstOverwritten, _ := f.d.f.NewObject(newPath)
+		newObject, err := operations.Move(f.d.f, dstOverwritten, newPath, f.o)
 		if err != nil {
 			fs.Errorf(f.Path(), "File.Rename error: %v", err)
 			return err