config: make config file reads reload the config file if needed #4996

Before this change the config file needed to be explicitly reloaded.
This coupled the config file implementation with the backends
needlessly.

This change stats the config file to see if it needs to be reloaded on
every config file operation.

This allows us to remove calls to

- config.SaveConfig
- config.GetFresh

Which now makes the the only needed interface to the config file be
that provided by configmap.Map when rclone is not being configured.

This also adds tests for configfile

fs/config/config.go

@@ -230,7 +230,7 @@ func LoadConfig(ctx context.Context) {
 var ErrorConfigFileNotFound = errors.New("config file not found")
 
 // SaveConfig calling function which saves configuration file.
-// if saveConfig returns error trying again after sleep.
+// if SaveConfig returns error trying again after sleep.
 func SaveConfig() {
 	ctx := context.Background()
 	ci := fs.GetConfig(ctx)
@@ -253,19 +253,6 @@ func SaveConfig() {
 func SetValueAndSave(name, key, value string) error {
 	// Set the value in config in case we fail to reload it
 	Data.SetValue(name, key, value)
-
-	// Reload the config file
-	err := Data.Load()
-	if err == ErrorConfigFileNotFound {
-		// Config file not written yet so ignore reload
-		return nil
-	} else if err != nil {
-		return err
-	}
-	if !Data.HasSection(name) {
-		// Section doesn't exist yet so ignore reload
-		return nil
-	}
 	// Save it again
 	SaveConfig()
 	return nil
@@ -281,20 +268,6 @@ func getWithDefault(name, key, defaultValue string) string {
 	return value
 }
 
-// FileGetFresh reads the config key under section return the value or
-// an error if the config file was not found or that value couldn't be
-// read.
-func FileGetFresh(section, key string) (value string, err error) {
-	if err := Data.Load(); err != nil {
-		return "", err
-	}
-	value, found := Data.GetValue(section, key)
-	if !found {
-		return "", errors.New("value not found")
-	}
-	return value, nil
-}
-
 // UpdateRemote adds the keyValues passed in to the remote of name.
 // keyValues should be key, value pairs.
 func UpdateRemote(ctx context.Context, name string, keyValues rc.Params, doObscure, noObscure bool) error {
@@ -446,11 +419,6 @@ func FileDeleteKey(section, key string) bool {
 
 var matchEnv = regexp.MustCompile(`^RCLONE_CONFIG_(.*?)_TYPE=.*$`)
 
-// FileRefresh ensures the latest configFile is loaded from disk
-func FileRefresh() error {
-	return Data.Load()
-}
-
 // FileSections returns the sections in the config file
 // including any defined by environment variables.
 func FileSections() []string {