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Oct 8, 2023
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docs(website): mention how rule options should be handled #7713

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52 changes: 52 additions & 0 deletions docs/developers/Custom_Rules.mdx
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Expand Up @@ -121,6 +121,58 @@ export const rule = ESLintUtils.RuleCreator.withoutDocs({
We recommend any custom ESLint rule include a descriptive error message and link to informative documentation.
:::

## Handling rule options

ESLint rules can take options. When handling options, you will need to add information in at most three places:

- The `Options` generic type argument to `RuleCreator`, where you declare the type of the options
- The `meta.schema` property, where you add a JSON schema describing the options shape
- The `defaultOptions` property, where you add the default options value

```ts
type MessageIds = 'lowercase' | 'uppercase';

type Options = [
{
preferredCase: 'lower' | 'upper';
},
];

export const rule = createRule<Options, MessageIds>({
meta: {
// ...
schema: [
{
type: 'object',
properties: {
preferredCase: {
type: 'string',
enum: ['lower', 'upper'],
},
},
additionalProperties: false,
},
],
},
defaultOptions: [
{
preferredCase: 'lower',
},
],
create(context, options) {
if (options[0].preferredCase === 'lower') {
// ...
}
},
});
```

:::warning

When reading the options, use the second parameter of the `create` function, not `context.options` from the first parameter. The first is created by ESLint and does not have the default options applied.

:::

## AST Extensions

`@typescript-eslint/estree` creates AST nodes for TypeScript syntax with names that begin with `TS`, such as `TSInterfaceDeclaration` and `TSTypeAnnotation`.
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