Go: avoid interface calls for zero-cost validation of messages without rules

[CAFxX]

Currently the go generator generates something like this for embedded messages:

func (m *Foo) Validate() error {
	if m == nil {
		return nil
	}

	if v, ok := interface{}(m.GetBar()).(interface{ Validate() error }); ok {
		if err := v.Validate(); err != nil {
			return FooValidationError{
				field:  "Bar",
				reason: "embedded message failed validation",
				cause:  err,
			}
		}
	}

	// ...

	return nil
}

The problem is that, if Bar has no validation rules, all this code is pointless.

It would be ideal if instead we generated, at least in the case of messages that we know are in the same package, and that therefore are being generated together:

func (m *Foo) Validate() error {
	if m == nil {
		return nil
	}

	if err := m.GetBar().Validate(); err != nil {
		return FooValidationError{
			field:  "Bar",
			reason: "embedded message failed validation",
			cause:  err,
		}
	}

	// ...

	return nil
}

This way if (*Bar).Validate() is just return nil (i.e. there are no validation rules), the compiler can completely remove the whole if (or it can potentially inline the call, if there's a single rule).

[stale]

This issue has been automatically marked as stale because it has not had recent activity. It will be closed if no further activity occurs. Thank you for your contributions.

[CAFxX]

Just pinging to signal that this issue is not stale, as it still applies.

[chrispine]

As explained in the README, this project is in maintenance mode. We recommend upgrading to protovalidate.

I'm going to go ahead and close this issue, but feel free to open one against protovalidate if needed. Thanks!