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
@timneutkens it'd be great to get your input.
These changes introduce a new Babel loader that eliminates much of the existing overhead, resulting in better HMR speeds.
Multithreading is still in flight, and may be omitted if speed improvements end up being negligible. For now, the new loader is hidden behind an `experimental` flag.
Items to be completed before this PR is ready to merge:
- [x] reconfigure `ncc` to precompile the parts of `@babel/core` and `@babel/traverse` that we're accessing directly
- [x] change `@babel/core/...` imports to `ncc`ed version
- [x] ~~measure multithreading (not currently pushed) functionality, and include the functionality depending on the results~~ I'll open a separate PR for this
- [x] ensure TypeScript is happy with all imports as final step (`--no-verify` was used to bypass)
There will be two follow-up PRs:
- loader support for projects with custom `.babelrc`
- multithreaded loader (should the change we warranted after measurement)
This picks up on the inlining work in https://github.com/vercel/next.js/pull/20598 to also include webpack loader inlining optimizations.
This includes:
* The dependencies of sass-loader
* resolve-url-loader
And for added benefit:
* babel-plugin-transform-define
* babel-plugin-transform-react-remove-prop-types
style-loader and css-loader didn't inline easily. Perhaps we can come back to these ones.
This upgrades to ncc@0.25.0 and fixes the previous bugs including:
* ncc not referenced correctly in build
* Babel type errors
* node-fetch, etag, chalk and raw-body dependencies not building with ncc - these have been "un-ncc'd" for now. As they are relatively small dependencies, this doesn't seem too much of an issue and we can follow up in the tracking ncc issue at https://github.com/vercel/ncc/issues/612.
* `yarn dev` issues
Took a lot of bisecting, but the overall diff isn't too bad here in the end.
This adds inlining for Babel and the Babel plugins used in next.
This is based to the PR at https://github.com/vercel/next.js/pull/18823.
The approach is to make one large bundle and then separate out the individual packages from that in order to avoid duplications.
In the first attempt the Babel bundle size was 10MB... using "resolutions" in the Yarn workspace to reduce the duplicated packages this was brought down to a 2.8MB bundle for Babel and all the used plugins which is exactly the expected file size here.
This will thus add a 2.8MB download size to the next package, but save downloading any babel dependencies separately, removing a large number of package dependencies from the overall install.
