# `known-fragment-names`

✅ The `"extends": "plugin:@graphql-eslint/operations-recommended"` property in a configuration file enables this rule.

- Category: `Operations`
- Rule name: `@graphql-eslint/known-fragment-names`
- Requires GraphQL Schema: `true` [ℹ️](../../README.md#extended-linting-rules-with-graphql-schema)
- Requires GraphQL Operations: `false` [ℹ️](../../README.md#extended-linting-rules-with-siblings-operations)

A GraphQL document is only valid if all `...Fragment` fragment spreads refer to fragments defined in the same document.

> This rule is a wrapper around a `graphql-js` validation function. [You can find its source code here](https://github.com/graphql/graphql-js/blob/main/src/validation/rules/KnownFragmentNamesRule.ts).

## Usage Examples

### Incorrect (fragment not defined in the document)

```graphql
# eslint @graphql-eslint/known-fragment-names: 'error'

query {
  user {
    id
    ...UserFields
  }
}
```

### Correct

```graphql
# eslint @graphql-eslint/known-fragment-names: 'error'

fragment UserFields on User {
  firstName
  lastName
}

query {
  user {
    id
    ...UserFields
  }
}
```

### Correct (existing import to UserFields fragment)

```graphql
# eslint @graphql-eslint/known-fragment-names: 'error'

#import '../UserFields.gql'

query {
  user {
    id
    ...UserFields
  }
}
```

### False positive case

For extracting documents from code under the hood we use [graphql-tag-pluck](https://graphql-tools.com/docs/graphql-tag-pluck) that [don't support string interpolation](https://stackoverflow.com/questions/62749847/graphql-codegen-dynamic-fields-with-interpolation/62751311#62751311) for this moment.

```js
const USER_FIELDS = gql`
  fragment UserFields on User {
    id
  }
`

const GET_USER = /* GraphQL */ `
  # eslint @graphql-eslint/known-fragment-names: 'error'

  query User {
    user {
      ...UserFields
    }
  }

  # Will give false positive error 'Unknown fragment "UserFields"'
  ${USER_FIELDS}
`
```

## Resources

- [Rule source](https://github.com/graphql/graphql-js/blob/main/src/validation/rules/KnownFragmentNamesRule.ts)
- [Test source](https://github.com/graphql/graphql-js/tree/main/src/validation/__tests__/KnownFragmentNamesRule-test.ts)