feat(fieldbehavior): Support optional keyword when validating REQUIRED fields

[felipeparaujo]

https://google.aip.dev/149 says the following on the optional keyword and the REQUIRED annotation:

The field behavior annotation and optional label are not mutually exclusive, because they address different problems. The former, google.api.field_behavior, focuses on communicating the server's perception of a field within the API e.g. if it is required or not, if it is immutable, etc. The latter, proto3's optional, is a wire format and code generation option that is strictly for toggling field presence tracking. While it might be confusing for a field to be simultaneously annotated with google.api.field_behavior = REQUIRED and labeled as optional, they are unrelated in practice and can reasonably be used together.

This is useful for distinguishing setting the field to its default value (0, false, or empty string) and not setting it at all.

This PR enables validating for this combination.

[alethenorio]

Thank you for your contribution.

Please make sure that your commit message follows the conventional commit standard

It also looks like you have not explicitly enabled optinal support.

You should be able to do this in the main file, something like

plugin.SupportedFeatures = uint64(pluginpb.CodeGeneratorResponse_FEATURE_PROTO3_OPTIONAL)

[felipeparaujo]

hi @alethenorio, thanks for the quick feedback. I've made the changes requested

[alethenorio]

I am running this test without the above changes (other than enabling optional support) and it seems to pass for me.
Can you describe what kind of problem you ran into that prompted this PR? Is there a way to reproduce the issue in a test?

[felipeparaujo]

My bad, that test wasn't enough. I've added a happy path test that hopefully clears things up a bit.

The gist of the problem is that if a field is annotated with REQUIRED it can't be set to its default value, 0 in the case of an int64. The optional keyword allows for that by differentiating unset from default values. This is reflected in the generated code by making the fields pointers:

int64 personnel_count = 7;

generates

PersonnelCount int64 `protobuf:"varint,7,opt,name=personnel_count,json=personnelCount,proto3,oneof" json:"personnel_count,omitempty"`

whereas

optional int64 personnel_count = 7;

generates

PersonnelCount *int64 `protobuf:"varint,7,opt,name=personnel_count,json=personnelCount,proto3,oneof" json:"personnel_count,omitempty"`

Therefore, if a field uses the proto3 keyword optional but has a REQUIRED annotation, it needs to be validated as != nil, which allows for an int64 to be 0 in a request.

The use case I want to cover, specifically, is validating the following message:

message ExtentOrBoundingBox {
  // The position of a corner
  message Position {
    // X axis
    // We use optional on a required field to differentiate between 0 and unset.
    // For more info see: https://aip.dev/149#field-behavior-and-optional
    optional double x = 1 [(google.api.field_behavior) = REQUIRED];

    // Y axis
    // We use optional on a required field to differentiate between 0 and unset.
    // For more info see: https://aip.dev/149#field-behavior-and-optional
    optional double y = 2 [(google.api.field_behavior) = REQUIRED];

    // Z axis. Not required because this message could be used for a 2D representation too.
    optional double z = 3 [(google.api.field_behavior) = OPTIONAL];
  }

  // lower corner
  Position min = 1 [(google.api.field_behavior) = REQUIRED];

  // upper corner
  Position max = 2 [(google.api.field_behavior) = REQUIRED];
}

Here, x and y are required values that can be 0.0, the default value.

[felipeparaujo]

@alethenorio @odsod PTAL

[github-actions]

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[felipeparaujo]

@alethenorio @odsod PTAL