Enum unspecified value

This rule enforces that all enums have a default unspecified value, as mandated in AIP-126.

Because our APIs create automatically-generated client libraries, we need to consider languages that have varying behavior around default values. To avoid any ambiguity or confusion across languages, all enumerations should use an “unspecified” value beginning with the name of the enum itself as the first (0) value.

Details

This rule finds all enumerations and ensures that the first one is named after the enum itself with an _UNSPECIFIED suffix appended.

Examples

Incorrect code for this rule:

// Incorrect.
enum Format {
  HARDCOVER = 0;  // Should have "FORMAT_UNSPECIFIED" first.
}

// Incorrect.
enum Format {
  UNSPECIFIED = 0;  // Should be "FORMAT_UNSPECIFIED".
  HARDCOVER = 1;
}

Correct code for this rule:

// Correct.
enum Format {
  FORMAT_UNSPECIFIED = 0;
  HARDCOVER = 1;
}

Disabling

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

enum Format {
  // (-- api-linter: core::0126::unspecified=disabled
  //     aip.dev/not-precedent: We need to do this because reasons. --)
  HARDCOVER = 0;
}

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