Adding a protoc plugin option

You might already have an idea of how to add options to the plugin. If you remember, we created an instance of protogen.Options in our main plugin. This Options object can work with the flags package in the standard library. We simply need to define our flags and pass the Set function to the Options instance. This looks like this (cmd/protoc-gen-check/main.go):

import (
  "flags"
  //...
)
func main() {
  var flags flag.FlagSet
  phoneRegexp := flags.String("phone_regexp", "", "custom regex for 
  phone checking.")
  opts := protogen.Options{
    ParamFunc: flags.Set,
  }
  //...
}

If you are not familiar with the flags package from the standard library, we define a flag of type string, the name phone_regexp, and the default value of the empty string.

We can now pass the phoneRegexp variable to our generateFile...