Fixes: https://github.com/vercel/next.js/issues/16926

I do not know this is the right way.
Please review it.

This PR fixes webpack 5 compatibility with older betas.

This ensures the pages-manifest only includes forward slashes and not backslashes when adding i18n page references, this also adds tests ensuring we don't regress on this in the i18n-support test suite. 

Fixes: https://github.com/vercel/next.js/issues/20330

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!

Adds profiling for terser and css-minimizer. Will move the old profiler to this new system as well.

When using `getServerSideProps` with Typescript, it looks like it's expecting `req` to be a plain `IncomingMessage` from `http`, but Next middleware (?) is adding `cookies`:

![image](https://user-images.githubusercontent.com/22530815/100816292-680e8a00-340b-11eb-8c40-19ec4f9ea356.png)

Here's a reproduction showing the example:

https://codesandbox.io/s/nextjs-server-side-props-cookies-vr547?file=/pages/index.tsx

In the terminal, you can see that there is a value for cookies, but `IncomingMessage` doesn't include it by default.

I still need to get more familiar with all the Next.js internals, but I imagine there are a few other places where this type could be used if cookies are being included. Any help would be appreciated.

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

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

This PR is an implementation of RFC #13276 (more specifically @banerjeesouvik's [suggestion](https://github.com/vercel/next.js/discussions/13276#discussioncomment-17874)) which solves #3322 by adding an extra parameter to the router events that'll allow you to see whether or not the route is shallow.

This is a recreation of PR #13243.

This keeps track of required server files in a manifest file

Solves the following warning:

> (node:1484) [DEP_WEBPACK_MAIN_TEMPLATE_REQUIRE_FN] DeprecationWarning: MainTemplate.requireFn is deprecated (use "__webpack_require__")

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

Adds brief summary in Getting Started to explain the `pages/api` functionality. The intention here is reduce confusion to new users of Next.js as to what `pages/api` is and how it works.

Fixes  #17813 

Solves some of the cache warnings when using webpack 5

This makes sure the `locale` doesn't cause the wrong `href` to be resolved, this also ensures route specificity is correct when loading dynamic routes in production mode. 

Fixes: https://github.com/vercel/next.js/issues/19747

Currently if sizes is not defined, Next.js is setting sizes as:
```
(max-width: 640px) 640px, (max-width: 750px) 750px, (max-width: 828px) 828px, (max-width: 1080px) 1080px, (max-width: 1200px) 1200px, (max-width: 1920px) 1920px, (max-width: 2048px) 2048px, 3840px'
```

This pull request will make sizes be `100vw` by default, which will allow us to download "smaller" images than what's currently happening. 

In a demo app I have, the difference is between downloading 488KB vs 1.4MB (in images)

Fixes #18056

Closes https://github.com/vercel/next.js/issues/20046

Fixes #19923.

Before:
<img width="564" alt="Screen Shot 2020-12-08 at 3 07 11 PM" src="https://user-images.githubusercontent.com/5074763/101535738-1adc6c00-3967-11eb-8c80-c7f2e75f8de5.png">

After:
<img width="574" alt="Screen Shot 2020-12-08 at 3 07 18 PM" src="https://user-images.githubusercontent.com/5074763/101535742-1b750280-3967-11eb-828b-1ecac08c6511.png">

Adds an err.sh link to the production build missing message. Also clears up `valid` as `production`.

Also fixes an edge case where an unhelpful error would be thrown because we checked for `.next` instead of `.next/BUILD_ID`

Added the out directory location as the list line during export to make sure people know where the files are output. 

Fixes #19778
Fixes #19788

Noticed Azure tests have started failing after https://github.com/vercel/next.js/pull/19758 due to the middleware taking longer than the allotted threshold which adds unexpected logs to stderr. This attempts to resolve these test failures by increasing the allotted time for the middleware when running on Azure. 

x-ref: https://dev.azure.com/nextjs/next.js/_build/results?buildId=22617&view=logs&jobId=5ee44de4-e310-59d9-0ba5-4a271a649fb0&j=5ee44de4-e310-59d9-0ba5-4a271a649fb0&t=af3fb693-3771-5a1a-ec97-2ba4cc77f25c
x-ref: https://dev.azure.com/nextjs/next.js/_build/results?buildId=22619&view=logs&jobId=5ee44de4-e310-59d9-0ba5-4a271a649fb0&j=5ee44de4-e310-59d9-0ba5-4a271a649fb0&t=af3fb693-3771-5a1a-ec97-2ba4cc77f25c 

Fixes #19939

This ensures locales aren't applied for the trailing slash redirect un-necessarily

Fixes: https://github.com/vercel/next.js/issues/19784

## Why

Some users prefer to use a custom server implementation that handles body parsing. If they do this, they have no way to opt out of all body parsing in API Routes. Requests with bodies die if next's `bodyParser` is not disabled. Requests just hang forever.

Instead of adding [this config](https://nextjs.org/docs/api-routes/api-middlewares#custom-config) to every API Route, we do a simple check to avoid parsing the body twice.

Fixes #8315
Fixes #7960

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

This updates to the latest version of the `@ampproject/toolbox-optimizer` which contains updates for dependencies to remove the warnings on install from `npm`

x-ref: https://github.com/vercel/next.js/pull/18994
Closes: https://github.com/vercel/next.js/issues/17416