Merge pull request #1086 from akramarenkov/fix-altsrc-nil-source-flag

Fix bug 'Unable to load file' in altsrc

altsrc/default_input_source.go

@@ -0,0 +1,6 @@
+package altsrc
+
+// defaultInputSource creates a default InputSourceContext.
+func defaultInputSource() (InputSourceContext, error) {
+	return &MapInputSource{file: "", valueMap: map[interface{}]interface{}{}}, nil
+}

altsrc/json_source_context.go

@@ -17,8 +17,12 @@ import (
 // by the given flag.
 func NewJSONSourceFromFlagFunc(flag string) func(c *cli.Context) (InputSourceContext, error) {
 	return func(context *cli.Context) (InputSourceContext, error) {
+		if context.IsSet(flag) {
 			return NewJSONSourceFromFile(context.String(flag))
 		}
+
+		return defaultInputSource()
+	}
 }
 
 // NewJSONSourceFromFile returns an InputSourceContext suitable for

altsrc/toml_file_loader.go

@@ -87,9 +87,13 @@ func NewTomlSourceFromFile(file string) (InputSourceContext, error) {
 // NewTomlSourceFromFlagFunc creates a new TOML InputSourceContext from a provided flag name and source context.
 func NewTomlSourceFromFlagFunc(flagFileName string) func(context *cli.Context) (InputSourceContext, error) {
 	return func(context *cli.Context) (InputSourceContext, error) {
+		if context.IsSet(flagFileName) {
 			filePath := context.String(flagFileName)
 			return NewTomlSourceFromFile(filePath)
 		}
+
+		return defaultInputSource()
+	}
 }
 
 func readCommandToml(filePath string, container interface{}) (err error) {

altsrc/yaml_file_loader.go

@@ -33,9 +33,13 @@ func NewYamlSourceFromFile(file string) (InputSourceContext, error) {
 // NewYamlSourceFromFlagFunc creates a new Yaml InputSourceContext from a provided flag name and source context.
 func NewYamlSourceFromFlagFunc(flagFileName string) func(context *cli.Context) (InputSourceContext, error) {
 	return func(context *cli.Context) (InputSourceContext, error) {
+		if context.IsSet(flagFileName) {
 			filePath := context.String(flagFileName)
 			return NewYamlSourceFromFile(filePath)
 		}
+
+		return defaultInputSource()
+	}
 }
 
 func readCommandYaml(filePath string, container interface{}) (err error) {