There's currently two bugs with the font optimization, but we'd really like to ship a stable version.

To unblock the stable release, we're **temporarily** reflagging this. It'll be unflagged on canary again!

Makes https://www.npmjs.com/package/@zeit/next-source-maps a built-in feature so that it can be deprecated.

Solves some of the cache warnings when using webpack 5

Fixes #19939

Nitpicky change, but the version string contained a double `|`, implying that there might be an empty value between `process.env.__NEXT_VERSION` and the environment variables.

This ensures i81n custom routes are resolving correctly, it also corrects redirects for default locales when `locale: false` is not used, and this also simplifies the resolving for custom routes with i18n in `next-server` adding types for the i18n config. This also adds additional tests to prevent regression and starts leveraging a shared `NextConfig` type to allow us to share types for config values. 

Fixes: https://github.com/vercel/next.js/issues/19521
Fixes: https://github.com/vercel/next.js/issues/19403
Fixes: https://github.com/vercel/next.js/issues/19302
Fixes: https://github.com/vercel/next.js/issues/19227

- Making font optimizations as default
- Re-enabling tests
- Fixes #19159

* make the error message more clear if webpack config comes back undefined

* Update check and add test

* bump

* Update build-output test
Co-authored-by: NJJ Kasper <jj@jjsweb.site>

Co-authored-by: NJJ Kasper <jj@jjsweb.site>

This PR removes the modern mode experiment because:

- It does not yield meaningful bundle size wins when compared to other initiatives we've taken
- It's not compatible with webpack 5 (which we're upgrading to)
- It's currently broken and causes most apps to malfunction
- There's no champion currently owning the experiment

We can re-introduce this in the future when we'd like to make it a default for all Next.js apps.

Note: **Next.js still supports Differential Loading (`nomodule`) and does it by default.** This PR strictly removes the experimental modern _syntax_, and does not disable our existing modern/legacy polyfilling.

---

Fixes #19200
Fixes #18960
Fixes #14707
Fixes #14465

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 fixes the current regression with an ncc revert for now.

I will continue to follow up with the ncc upgrade in https://github.com/vercel/next.js/pull/18860.

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.

Co-authored-by: Nkodiakhq[bot] <49736102+kodiakhq[bot]@users.noreply.github.com>

This does two things:

- Rename `iconSizes` to `imageSizes`.
- Give priority to `imageSizes` regardless of `deviceSizes` as a means to opt-out of the srcset behavior.

This separates the `next.config.js` property `images.sizes` into to properties: `images.deviceSizes` and `images.iconSizes`.

The purpose is for images that are not intended to take up the majority of the viewport.


Related to #18122 

* Add next/image default loader errors

* Add domains check

* Apply suggestions from PR

* Update test

Co-authored-by: NTim Neutkens <timneutkens@me.com>

Co-authored-by: NTim Neutkens <timneutkens@me.com>

This makes sure that we detect the correct default locale for domain specific locales since a domain can have a different default locale residing at the root and we need to check this on the client for prerendered/auto-static pages. This also makes sure we disable the built-in redirect handling when on Vercel since it's handled already. 

Tests for this are tricky since we need to load the browser with a custom domain which requires editing the host file. Existing tests should ensure this doesn't break non-domain specific locale behavior though. This was also tested manually while testing https://github.com/vercel/vercel/pull/5298



x-ref: https://github.com/vercel/next.js/pull/17370

Co-authored-by: NLuis Alvarez D <luis@vercel.com>
Co-authored-by: NTim Neutkens <tim@timneutkens.nl>

Co-authored-by: NTim Neutkens <timneutkens@me.com>
Co-authored-by: NTim Neutkens <tim@timneutkens.nl>

This adds the initial changes outlined in the [i18n routing RFC](https://github.com/vercel/next.js/discussions/17078). This currently treats the locale prefix on routes similar to how the basePath is treated in that the config doesn't require any changes to your pages directory and is automatically stripped/added based on the detected locale that should be used. 

Currently redirecting occurs on the `/` route if a locale is detected regardless of if an optional catch-all route would match the `/` route or not we may want to investigate whether we want to disable this redirection automatically if an `/index.js` file isn't present at root of the pages directory. 

TODO: 

- [x] ensure locale detection/populating works in serverless mode correctly
- [x] add tests for locale handling in different modes, fallback/getStaticProps/getServerSideProps

To be continued in fall-up PRs

- [ ] add tests for revalidate, auto-export, basePath + i18n
- [ ] add mapping of domains with locales
- [ ] investigate detecting locale against non-index routes and populating the locale in a cookie

x-ref: https://github.com/vercel/next.js/issues/17110

On the latest beta of webpack 5 resolving fails with the below error and according to https://github.com/webpack/webpack/issues/11467 is due to the imports in this module not being fully specified. This adds the config mentioned in the thread to correct the resolving for this module. 

```sh
Failed to compile.
--
16:33:50.046 | ModuleNotFoundError: Module not found: Error: Can't resolve './assertThisInitialized' in '/vercel/f03cc85/node_modules/@babel/runtime/helpers/esm'
16:33:50.046 | > Build error occurred
16:33:50.047 | Error: > Build failed because of webpack errors
16:33:50.047 | at build (/vercel/f03cc85/node_modules/next/dist/build/index.js:15:918)
16:33:50.099 | error Command failed with exit code 1.
```
 

Earlier today #17038 was merged which I opened to fix a problem when using `webpack@5.0.0-beta.30` with Next.js using the new Webpack 5 support. In that PR, the only change was the renaming of a configuration key. I later discovered that the change on the Webpack side was different than I initially thought, and this meant that the fix I submittted to Next.js didn't work.

This PR intends to fix the remaining problems. Webpack 5 now accepts a `environment` key that can be used to configure the target output. Previously, this was known as `ecmaVersion` and accepted a number. Now, `environment` accepts a configuration object with individual options. I've configured this in such a way where it resembles an ES5 environment:
```js
environment: {
   arrowFunction: false,
   bigIntLiteral: false,
   const: false,
   destructuring: false,
   dynamicImport: false,
   forOf: false,
   module: false,
}
```

This PR fixes #17035. As described in the issue, there was a breaking change in `webpack@5.0.0-beta.30`: `output.ecmaVersion` was replaced by `output.environment`. This meant Next.js apps using this `webpack` version would break. This PR updates the relevant Webpack config.

I think this will break any apps that are still using `webpack@5.0.0-beta.29`, but I don't know whether that is a problem as this is a beta feature. If it is, I'd love it if someone could let me know how to detect beta versions in the code so I can make it backwards-compatible.

When the webpack 5 beta is used disk caching will be automatically enabled to improve incremental build performance.

Handles:

- Next.js version
- next.config.js `env` key
- `NEXT_PUBLIC_` prefixed environment variables
- next.config.js keys that affect performance

Ideally we don't invalidate the whole cache when `NEXT_PUBLIC_` / `env` key variables change, but this is just to initially make the caching reliable, this behavior is similar to the current webpack 4 behavior, so it can only be improved 👍 

Fixes #16259
Caused by #16022
Follow up issue: #16450

This PR skips polyfilling Node modules in webpack 4 which are ignored by the `browsers` key.

Don't use this yet as it's still being developed. This is a first iteration that enables the webpack cache. There's still more to do here, for example if css modules are used there's currently a bug where webpack does not save the cache for browser compilation (impacting build performance). @sokra is going to look into that issue.

Co-authored-by: NTim Neutkens <timneutkens@me.com>

Co-authored-by: NTim Neutkens <tim@timneutkens.nl>
Co-authored-by: NJoe Haddad <joe.haddad@zeit.co>

Co-authored-by: NKristoffer K. <merceyz@users.noreply.github.com>