# enum-zero-value-suffix

Source: https://apigenie.pl/docs/linter/protobuf/rules/enum-zero-value-suffix

This rule checks whether the zero value of every enum ends with a suffix, `_UNSPECIFIED` by
default.

## Rule Details

In proto3, the zero value is the default of every enum field: a field that was never set reads
as zero. A name like `PET_KIND_UNSPECIFIED` makes it clear that the zero value means "not set",
rather than a real value such as `PET_KIND_DOG` that clients would then receive by accident.

The `enum-zero-value-suffix` rule checks every enum value whose number is `0`, and reports
`Enum zero value '<value>' should end with '<suffix>'` when its name does not end with the
suffix. When an enum allows aliases, every value numbered `0` is checked.

## Configuration

The configuration block can be a string or an object.

If it is a string, its value is the suffix.

If it is an object, it must contain only the `suffix` property, whose value is the suffix.

The suffix cannot be empty.

**Configuration Example**. The following two examples are equivalent. They specify that the zero
values must end with `_UNKNOWN`.

```yaml
version: "1.0"
commands:
  lint:
    protobuf:
      rules:
        enum-zero-value-suffix: [warning, _UNKNOWN]
```

```yaml
version: "1.0"
commands:
  lint:
    protobuf:
      rules:
        enum-zero-value-suffix:
          - warning
          - suffix: _UNKNOWN
```

## Examples

**Good**. With the default configuration.

```proto
syntax = "proto3";

package acme.pets.v1;

enum PetKind {
  PET_KIND_UNSPECIFIED = 0;
  PET_KIND_DOG = 1;
}
```

**Bad**. With the default configuration, the linter reports
`Enum zero value 'PET_KIND_UNKNOWN' should end with '_UNSPECIFIED'`.

```proto
syntax = "proto3";

package acme.pets.v1;

enum PetKind {
  PET_KIND_UNKNOWN = 0;
  PET_KIND_DOG = 1;
}
```

## When Not to Use It

You may disable this rule if the zero value of some enums is a meaningful value, for example in
enums mirroring an external standard. To allow a single enum, add an
`// apigenie-lint-disable enum-zero-value-suffix` comment to the enum.

## Compatibility

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