# oneof-comment-defined

Source: https://apigenie.pl/docs/linter/protobuf/rules/oneof-comment-defined

This rule checks whether every oneof of a Protobuf file has a leading comment.

## Rule Details

Comments are the documentation of a Protobuf API: `protoc` passes them to the code generators,
which copy them to the generated code, and documentation generators render them.

The `oneof-comment-defined` rule checks every oneof, and reports `Oneof '<name>' has no leading
comment` when there is no leading comment, or when it contains only whitespace. A leading
comment is the comment right before the declaration, as `protoc` attaches it: a comment
separated from the declaration by a blank line is a detached comment, and a comment after the
declaration on the same line is a trailing comment; neither counts. Both `//` and `/* */`
comments count.

The rule is only part of the `all` ruleset.

## Configuration

This rule has no options.

## Examples

**Good**.

```proto
syntax = "proto3";

package acme.pets.v1;

// A pet that lives in the shelter.
message Pet {
  string name = 1;
  // How the shelter can reach the owner.
  oneof contact {
    string email = 2;
    string phone = 3;
  }
}
```

**Bad**. The linter reports `Oneof 'contact' has no leading comment`.

```proto
syntax = "proto3";

package acme.pets.v1;

// A pet that lives in the shelter.
message Pet {
  string name = 1;
  oneof contact {
    string email = 2;
    string phone = 3;
  }
}
```

## When Not to Use It

You may disable this rule if the oneofs of your files are documented elsewhere, or if their
names are descriptive enough. To exempt the oneofs of a single message, add an
`// apigenie-lint-disable oneof-comment-defined` comment to the message.

## Compatibility

This rule is compatible with proto3 files. proto2 and editions files are rejected by the reader
and are not linted.