Expand variables in config paths.

kong.go

@@ -338,9 +338,14 @@ func (k *Kong) FatalIfErrorf(err error, args ...interface{}) {
 
 // LoadConfig from path using the loader configured via Configuration(loader).
 //
-// "path" will have ~/ expanded.
+// "path" will have ~ and any variables expanded.
 func (k *Kong) LoadConfig(path string) (Resolver, error) {
+	var err error
 	path = ExpandPath(path)
+	path, err = interpolate(path, k.vars)
+	if err != nil {
+		return nil, err
+	}
 	r, err := os.Open(path) // nolint: gas
 	if err != nil {
 		return nil, err

options.go

@@ -235,7 +235,7 @@ type ConfigurationLoader func(r io.Reader) (Resolver, error)
 //
 // Note: The JSON function is a ConfigurationLoader.
 //
-// ~ expansion will occur on the provided paths.
+// ~ and variable expansion will occur on the provided paths.
 func Configuration(loader ConfigurationLoader, paths ...string) Option {
 	return OptionFunc(func(k *Kong) error {
 		k.loader = loader