fs/cache: fix recreation of backends after they have expired

Before this change, on the first attempt to create a backend we used a
non-canonicalized string. When the backend expired the second attempt
to create it would use the canonicalized string (because it was in the
remap cache) which would fail because it was now `name{XXXX}:`

This change makes sure that whenever we create a backend we always use
the non-canonicalized string.

See: https://forum.rclone.org/t/connection-string-inconsistencies-on-beta/23171

fs/cache/cache.go

@@ -56,10 +56,10 @@ func addMapping(fsString, canonicalName string) {
 // it afresh with the create function
 func GetFn(ctx context.Context, fsString string, create func(ctx context.Context, fsString string) (fs.Fs, error)) (f fs.Fs, err error) {
 	createOnFirstUse()
-	fsString = Canonicalize(fsString)
+	canonicalFsString := Canonicalize(fsString)
 	created := false
-	value, err := c.Get(fsString, func(fsString string) (f interface{}, ok bool, err error) {
-		f, err = create(ctx, fsString)
+	value, err := c.Get(canonicalFsString, func(canonicalFsString string) (f interface{}, ok bool, err error) {
+		f, err = create(ctx, fsString) // always create the backend with the original non-canonicalised string
 		ok = err == nil || err == fs.ErrorIsFile
 		created = ok
 		return f, ok, err
@@ -71,19 +71,19 @@ func GetFn(ctx context.Context, fsString string, create func(ctx context.Context
 	// Check we stored the Fs at the canonical name
 	if created {
 		canonicalName := fs.ConfigString(f)
-		if canonicalName != fsString {
+		if canonicalName != canonicalFsString {
 			// Note that if err == fs.ErrorIsFile at this moment
 			// then we can't rename the remote as it will have the
 			// wrong error status, we need to add a new one.
 			if err == nil {
-				fs.Debugf(nil, "fs cache: renaming cache item %q to be canonical %q", fsString, canonicalName)
-				value, found := c.Rename(fsString, canonicalName)
+				fs.Debugf(nil, "fs cache: renaming cache item %q to be canonical %q", canonicalFsString, canonicalName)
+				value, found := c.Rename(canonicalFsString, canonicalName)
 				if found {
 					f = value.(fs.Fs)
 				}
-				addMapping(fsString, canonicalName)
+				addMapping(canonicalFsString, canonicalName)
 			} else {
-				fs.Debugf(nil, "fs cache: adding new entry for parent of %q, %q", fsString, canonicalName)
+				fs.Debugf(nil, "fs cache: adding new entry for parent of %q, %q", canonicalFsString, canonicalName)
 				Put(canonicalName, f)
 			}
 		}