Resource annotation presence

This rule enforces that any field with a google.api.resource_reference annotation has a string type, as described in AIP-123.

Details

This rule scans all fields with a google.api.resource_reference annotation. If one is found, the type is checked, and the rule complains if the type is anything other than string.

It suggests the removal of the annotation rather than fixing the type, because what we have observed in real life is that the annotation is usually what is in error rather than the selected type.

Examples

Incorrect code for this rule:

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

  // This is not a resource reference; the annotation does not belong.
  Author author = 2 [(google.api.resource_reference) = {
    type: "library.googleapis.com/Author"
  }];
}

Correct code for this rule:

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

  Author author = 2;
}

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

  string author = 2 [(google.api.resource_reference) = {
    type: "library.googleapis.com/Author"
  }];
}

Disabling

Do not violate this rule; it will break several tools.