cmd/providers: add DefaultStr, ValueStr and Type fields

These fields are auto generated:
- DefaultStr - a string rendering of Default
- ValueStr - a string rendering of Value
- Type - the type of the option

fs/fs.go

@@ -2,6 +2,7 @@
 package fs
 
 import (
+	"encoding/json"
 	"fmt"
 	"io"
 	"io/ioutil"
@@ -132,6 +133,29 @@ type Option struct {
 	Advanced   bool             // set if this is an advanced config option
 }
 
+// BaseOption is an alias for Option used internally
+type BaseOption Option
+
+// MarshalJSON turns an Option into JSON
+//
+// It adds some generated fields for ease of use
+// - DefaultStr - a string rendering of Default
+// - ValueStr - a string rendering of Value
+// - Type - the type of the option
+func (o *Option) MarshalJSON() ([]byte, error) {
+	return json.Marshal(struct {
+		BaseOption
+		DefaultStr string
+		ValueStr   string
+		Type       string
+	}{
+		BaseOption: BaseOption(*o),
+		DefaultStr: fmt.Sprint(o.Default),
+		ValueStr:   o.String(),
+		Type:       o.Type(),
+	})
+}
+
 // GetValue gets the current current value which is the default if not set
 func (o *Option) GetValue() interface{} {
 	val := o.Value