Fix nil pointer on watch function (#568)

It was exported in previous commit, but we have GetConfigFileUsed -- so use that.

viper.go

@@ -268,7 +268,7 @@ func (v *Viper) WatchConfig() {
 		defer watcher.Close()
 
 		// we have to watch the entire directory to pick up renames/atomic saves in a cross-platform way
-		filename, err := v.GetConfigFile()
+		filename, err := v.getConfigFile()
 		if err != nil {
 			log.Println("error:", err)
 			return
@@ -289,7 +289,9 @@ func (v *Viper) WatchConfig() {
 							if err != nil {
 								log.Println("error:", err)
 							}
-							v.onConfigChange(event)
+							if v.onConfigChange != nil {
+								v.onConfigChange(event)
+							}
 						}
 					}
 				case err := <-watcher.Errors:
@@ -1131,7 +1133,7 @@ func (v *Viper) Set(key string, value interface{}) {
 func ReadInConfig() error { return v.ReadInConfig() }
 func (v *Viper) ReadInConfig() error {
 	jww.INFO.Println("Attempting to read in config file")
-	filename, err := v.GetConfigFile()
+	filename, err := v.getConfigFile()
 	if err != nil {
 		return err
 	}
@@ -1161,7 +1163,7 @@ func (v *Viper) ReadInConfig() error {
 func MergeInConfig() error { return v.MergeInConfig() }
 func (v *Viper) MergeInConfig() error {
 	jww.INFO.Println("Attempting to merge in config file")
-	filename, err := v.GetConfigFile()
+	filename, err := v.getConfigFile()
 	if err != nil {
 		return err
 	}
@@ -1203,7 +1205,7 @@ func (v *Viper) MergeConfig(in io.Reader) error {
 // WriteConfig writes the current configuration to a file.
 func WriteConfig() error { return v.WriteConfig() }
 func (v *Viper) WriteConfig() error {
-	filename, err := v.GetConfigFile()
+	filename, err := v.getConfigFile()
 	if err != nil {
 		return err
 	}
@@ -1213,7 +1215,7 @@ func (v *Viper) WriteConfig() error {
 // SafeWriteConfig writes current configuration to file only if the file does not exist.
 func SafeWriteConfig() error { return v.SafeWriteConfig() }
 func (v *Viper) SafeWriteConfig() error {
-	filename, err := v.GetConfigFile()
+	filename, err := v.getConfigFile()
 	if err != nil {
 		return err
 	}
@@ -1705,7 +1707,7 @@ func (v *Viper) getConfigType() string {
 		return v.configType
 	}
 
-	cf, err := v.GetConfigFile()
+	cf, err := v.getConfigFile()
 	if err != nil {
 		return ""
 	}
@@ -1719,7 +1721,7 @@ func (v *Viper) getConfigType() string {
 	return ""
 }
 
-func (v *Viper) GetConfigFile() (string, error) {
+func (v *Viper) getConfigFile() (string, error) {
 	if v.configFile == "" {
 		cf, err := v.findConfigFile()
 		if err != nil {

viper_test.go

@@ -244,7 +244,7 @@ func (s *stringValue) String() string {
 
 func TestBasics(t *testing.T) {
 	SetConfigFile("/tmp/config.yaml")
-	filename, err := v.GetConfigFile()
+	filename, err := v.getConfigFile()
 	assert.Equal(t, "/tmp/config.yaml", filename)
 	assert.NoError(t, err)
 }
@@ -1177,7 +1177,7 @@ func TestUnmarshalingWithAliases(t *testing.T) {
 func TestSetConfigNameClearsFileCache(t *testing.T) {
 	SetConfigFile("/tmp/config.yaml")
 	SetConfigName("default")
-	f, err := v.GetConfigFile()
+	f, err := v.getConfigFile()
 	if err == nil {
 		t.Fatalf("config file cache should have been cleared")
 	}