Optional fields

This rule enforces that fields that are explicitly documented as optional also have a machine-readable annotation, as mandated by AIP-203.

Details

This rule looks at any field with “optional” (or similar forms) in the comment, and complains if it does not have a google.api.field_behavior annotation.

Note: It is generally recommended not to document “optional” at all.

Examples

Incorrect code for this rule:

// Incorrect.
message Book {
  string name = 1;

  // @Optional
  // The foreword for the book.
  string foreword = 2;
}

// Incorrect.
message Book {
  string name = 1;

  // Optional. The foreword for the book.
  string foreword = 2;
}

Correct code for this rule:

// Correct.
message Book {
  string name = 1;

  // The foreword for the book.
  string foreword = 2 [(google.api.field_behavior) = OPTIONAL];
}

Disabling

If you need to violate this rule, use a leading comment above the field. Remember to also include an aip.dev/not-precedent comment explaining why.

message Book {
  string name = 1;

  // Optional. The foreword for the book.
  // (-- api-linter: core::0203::optional=disabled
  //     aip.dev/not-precedent: We need to do this because reasons. --)
  string foreword = 2;
}

If you need to violate this rule for an entire file, place the comment at the top of the file.