Add support for `--output-file` on ESLint cli, based on this discussion https://github.com/vercel/next.js/discussions/26179, and this closed PR https://github.com/vercel/next.js/pull/35154. With this flag, it is possible to save the output in a file and use it for any purpose.
## Feature
- [ ] Implements an existing feature request or RFC. Make sure the feature request has been accepted for implementation before opening a PR.
- [ ] Related issues linked using `fixes #number`
- [ ] Integration tests added
- [ ] Documentation added
- [ ] Telemetry added. In case of a feature if it's used or not.
- [ ] Errors have helpful link attached, see `contributing.md`
## Documentation / Examples
- [x] Make sure the linting passes by running `yarn lint`
Co-authored-by: JJ Kasper <22380829+ijjk@users.noreply.github.com>
This PR introduces an improved developer experience when `next lint` is run for the first time.
### Current behavior
`eslint-config-next` is a required package that must be installed before proceeding with `next lint` or `next build`:
Although this has helped many developers start using the new ESLint config, this has also resulted in a few issues:
- Users are required to install the full config (`eslint-config-next`) even if they do not use it or use the Next.js plugin directly (`eslint-plugin-next`).
- #26348
- There's some confusion on why `eslint-config-next` needs to be installed or how it should be used instead of `eslint-plugin-next`.
- #26574
- #26475
- #26438
### New behavior
Instead of enforcing `eslint-config-next` as a required package, this PR prompts the user by asking what config they would like to start. This happens when `next lint` is run for the first time **and** if no ESLint configuration is detected in the application.
<img src="https://user-images.githubusercontent.com/12476932/124331177-e1668a80-db5c-11eb-8915-38d3dc20f5d4.gif" width="800" />
- The CLI will take care of installing `eslint` or `eslint-config-next` if either is not already installed
- Users now have the option to choose between a strict configuration (`next/core-web-vitals`) or just the base configuration (`next`)
- For users that decide to create their own ESLint configuration, or already have an existing one, **installing `eslint-config-next` will not be a requirement for `next lint` or `next build` to run**. A warning message will just show if the Next.js ESLint plugin is not detected in an ESLint config.
<img width="682" alt="Screen Shot 2021-06-25 at 3 02 12 PM" src="https://user-images.githubusercontent.com/12476932/123473329-6cc4a680-d5c6-11eb-9a57-d5c0b89a2732.png">
---
In addition, this PR also:
- Fixes#26348
- Updates documentation to make it more clear what approach to take for new and existing ESLint configurations
This PR re-includes ESLint with some notable changes, namely a guided setup similar to how TypeScript is instantiated in a Next.js application.
To add ESLint to a project, developers will have to create an `.eslintrc` file in the root of their project or add an empty `eslintConfig` object to their `package.json` file.
```js
touch .eslintrc
```
Then running `next build` will show instructions to install the required packages needed:
<img width="862" alt="Screen Shot 2021-04-19 at 7 38 27 PM" src="https://user-images.githubusercontent.com/12476932/115316182-dfd51b00-a146-11eb-830c-90bad20ed151.png">
Once installed and `next build` is run again, `.eslintrc` will be automatically configured to include the default config:
```json
{
"extends": "next"
}
```
In addition to this change:
- The feature is now under the experimental flag and requires opt-in. After testing and feedback, it will be switched to the top-level namespace and turned on by default.
- A new ESLint shareable configuration package is included that can be extended in any application with `{ extends: 'next' }`
- This default config extends recommended rule sets from [`eslint-plugin-react`](https://www.npmjs.com/package/eslint-plugin-react), [`eslint-plugin-react-hooks`](https://www.npmjs.com/package/eslint-plugin-react-hooks), and [`eslint-plugin-next`](https://www.npmjs.com/package/@next/eslint-plugin-next)
- All rules in [`eslint-plugin-next`](https://www.npmjs.com/package/@next/eslint-plugin-next) have been modified to include actionable links that show more information to help resolve each issue
This pull request **temporarily** removes ESLint, as it was not landed in accordance with our standard experimental policies. We are fully committed to landing this change again.
This is being reverted because:
- Next.js has very strict goals for its install size. This feature resulted in adding over 17MB, or a 43.6% increase.
- The feature was not first landed under the `experimental` key in `next.config.js`, rather, it was added under the stable namespace (top-level)
- Using the feature doesn't do a "guided setup" like TypeScript, it should ask you to "bring your own" dependencies for ESLint
- It uses a undesirable ESLint plugin name: `plugin:@next/next/recommended`. This should read out as strictly `next`, or as short as we can get it.
- Does not provide actionable warnings (missing link to resolve issue)
- Does not follow appropriate console output styling. We need to revisit how these are presented.
To re-land this, we need to ensure the following minimums are met:
- Very minor change in install size
- Fully experimental (i.e. flagged) with warnings
- Finalized package name and configuration shape, preferably so we can do ` { extends: 'next' } `.
For #22228
This PR:
- Adds ESLint to toolchain
- Included by default for builds (`next build`)
- Can be enabled for development (`next dev`)
- Custom formatter built for output
- Adds appropriate tests
- Adds two documentation pages
