New static configuration loading system.

Co-authored-by: Mathieu Lonjaret <mathieu.lonjaret@gmail.com>

pkg/cli/loader.go

@@ -0,0 +1,21 @@
+package cli
+
+// ResourceLoader is a configuration resource loader.
+type ResourceLoader interface {
+	// Load populates cmd.Configuration, optionally using args to do so.
+	Load(args []string, cmd *Command) (bool, error)
+}
+
+type filenameGetter interface {
+	GetFilename() string
+}
+
+// GetConfigFile returns the configuration file corresponding to the first configuration file loader found in ResourceLoader, if any.
+func GetConfigFile(loaders []ResourceLoader) string {
+	for _, loader := range loaders {
+		if v, ok := loader.(filenameGetter); ok {
+			return v.GetFilename()
+		}
+	}
+	return ""
+}