Add support for custom validations

[Gictorbit]

Is there a way to add custom validation functions to generated protobuf messages in go?
for example, we can have another function to receive a validation function which receives a message struct and will be validated after calling validate or validateAll functions

message Person{
  string name=1;
  int age=2;
}

func main(){
  me := &pb.Person {
    Name: "viktor",
    Age: 23,
  }
  me.AddCustomValidation(func(person *pb.Person)error{
    if person.Age > 100 {
      return errAge
    }
      return nil
  })
  if err := me.Validate();err!=nil{
    panic(err)
  }
}

[elliotmjackson]

I'm not sure there is a place for this feature within protoc-gen-validate. Sure, we would achieve being able to execute anon funcs to a method on the base-type but I dont struggle to see why this is necessary. Given your example above, why not just name the anonymous function?

main() {
  me := &pb.Person {
    Name: "viktor",
    Age: 23,
  }
  if err := CustomValidation(me);err!=nil{
    panic(err)
  }
  if err := me.Validate();err!=nil{
    panic(err)
  }
} 
func CustomValidation(person *pb.Person)error{
    if person.Age > 100 {
      return errAge
    }
      return nil
}

I am nevertheless too conscious of my own idiocy that i simply may not grasp the true power of your feature request, if you think this is the case - please dont hesitate to call me out.

[mcgaw]

It would be nice to be able to add some custom validation code that is then "compiled in" to the standard Validate method. This is perhaps what @Gictorbit was alluding to.

[elliotmjackson]

We added custom validation expressions to protovalidate, go check it out! we likely won't add this sort of functionality as we want to make the constraints portable across any consumers of the protos.