eslint-plugin-expect-type
ESLint plugin with `^?` Twoslash, `$ExpectError`, and `$ExpectType` type assertions. π§©
```ts
let value = 9001;
// ^? let value: number
// $ExpectError
value = "over nine thousand";
// $ExpectType number
9001;
```
## Installation
Make sure you have TypeScript and @typescript-eslint/parser installed, then install the plugin:
```sh
npm i -D eslint-plugin-expect-type
```
> See [typescript-eslint's Getting Started docs](https://typescript-eslint.io/docs) for how to run ESLint on TypeScript files.
## Usage
Add the following options to your [ESLint configuration file](https://eslint.org/docs/latest/user-guide/configuring/configuration-files-new):
```ts
import expectType from "eslint-plugin-expect-type/configs/recommended";
export default [
// your other ESLint configurations
expectType,
];
```
> For CommonJS, use `const expectType = require("eslint-plugin-expect-type/configs/recommended").default;`.
Then, you'll be able to use `^?`, `$ExpectError`, `$ExpectType`, and `$ExpectTypeSnapshot` comments in code assert on types.
### Usage (Legacy Config)
If you're still using the [legacy ESLint configuration file format](https://eslint.org/docs/latest/user-guide/configuring/configuration-files):
```json
{
"extends": ["plugin:expect-type/recommended"],
"plugins": ["expect-type"]
}
```
## Rules
πΌ Configurations enabled in.\
β
Set in the `recommended` configuration.\
π§ Automatically fixable by the [`--fix` CLI option](https://eslint.org/docs/user-guide/command-line-interface#--fix).\
π Requires [type information](https://typescript-eslint.io/linting/typed-linting).
| Name | Description | πΌ | π§ | π |
| :----------------------------- | :------------------------------------------ | :- | :- | :- |
| [expect](docs/rules/expect.md) | Expects type error, type snapshot, or type. | β
| π§ | π |
## References
You might consider using other popular libraries and tools that can run type assertions:
- **[expect-type](https://github.com/mmkal/expect-type)**: Provides functions that return assorted generic type assertion methods, such as `expectTypeOf('abc').toMatchTypeOf()`.
- **[ts-expect](https://github.com/TypeStrong/ts-expect)**: Provides generic type assertion function, used like `expectType('abc')()`.
- **[tsd](https://github.com/SamVerschueren/tsd)**: Allows writing tests specifically for `.d.ts` definition files.
- **[TSTyche](https://tstyche.org)**: A type testing tool that ships with `describe()` and `test()` helpers, `expect` style assertions and a mighty test runner which allows to use specified version of TypeScript.
- **[Vitest](https://vitest.dev/guide/testing-types.html)**: Includes `assertType` and `expectTypeOf` assertions.
## TypeScript Version Support
`eslint-plugin-expect-type` mirrors the [DefinitelyTyped TypeScript Support Window](https://github.com/DefinitelyTyped/DefinitelyTyped/#support-window).
Roughly, that's major versions of TypeScript less than 2 years old.
## Appreciation
Many thanks to [@ibezkrovnyi](https://github.com/ibezkrovnyi) for creating the initial version and core infrastructure of this package! π
## Contributors
> π This package was templated with [create-typescript-app](https://github.com/JoshuaKGoldberg/create-typescript-app).
