Previously we special cased serverless builds and ran the client/server builds serially to allow the server build to load manifests produced in the client. To help with memory usage and for consistency this updates server mode to build in the same way.  

## Bug

- [ ] Related issues linked using `fixes #number`
- [ ] Integration tests added

## 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.

## Documentation / Examples

- [ ] Make sure the linting passes

This adds support for a `has` field to `rewrites`, `redirects`, and `headers` to allow matching against `header`, `cookie`, and `query` values. Documentation and additional tests for the feature is also added in this PR. 

Closes: https://github.com/vercel/next.js/issues/22345

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

## Bug

- [x] Related issues linked using `fixes #number`
- [ ] Integration tests added

## 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.

## Documentation / Examples

- [ ] Make sure the linting passes

Fixes #23240

This PR upgrades `jest-worker` and `jest-cli` to the latest pre-release version, also removed `jest-circus` which is included in Jest by default. `jest-worker@next` includes a fix for memory leak that we need (https://github.com/facebook/jest/pull/11187). 

Fixes #22925. This will also improve the OOM issue for `next dev` #15855.

This fixes index data route loading for i18n with `trailingSlash: true` enabled and also fixes prerendering `asPath` values not containing a trailingSlash when enabled. 


Fixes: https://github.com/vercel/next.js/issues/17813
Fixes: https://github.com/vercel/next.js/issues/22747

This makes sure we don't trigger the export step if we aren't exporting any static pages during a build. This also adds an invariant to ensure we don't attempt creating a progress with 0 items.

Fixes: https://github.com/vercel/next.js/issues/22994

A number of changes here.  I recommend viewing the diff with the <a href="?w=1">whitespace flag enabled</a>.

- OpenTelemetry is replaced with a custom and lightweight tracing solution.
- Three trace targets are currently supported: console, Zipkin, and NextJS.
- Tracing is now governed by environment variables rather than `--require instrument.js`.
  + `TRACE_TARGET`: one of `CONSOLE`, `ZIPKIN`, or `TELEMETRY`; defaults to `TELEMETRY` if unset or invalid.
  + `TRACE_ID`: an 8-byte hex-encoded value used as the Zipkin trace ID; if not provided, this value will be randomly generated and passed down to subprocesses.

Other sundry:

- I'm missing something, probably a setup step, with the Zipkin target.  Traces are captured successfully, but you have to manually enter the Trace ID in order to view the trace - it doesn't show up in queries.
- I'm generally unhappy with [this commit](https://github.com/vercel/next.js/pull/22713/commits/235cedcb3ead76b630b4c8aa695f904489da2831).  It is... untidy to provide a telemetry object via `setGlobal`, but I don't have a ready alternative.  Is `distDir` strictly required when creating a new Telemetry object?  I didn't dig too deep here.

As noted, there are a lot of changes, so it'd be great if a reviewer could:

- [ ] pull down the branch and try to break it
- [ ] check the Zipkin traces and identify possible regressions in the functionality

Closes #22570
Fixes #22574

This adds an `appDir` field to the `required-server-files` manifest signifying where the app source is located. 

x-ref: https://github.com/vercel/next.js/issues/22847

This updates to not automatically export `/500` from `_error` if a custom `getInitialProps` is used since logic may be used inside of this method that causes the export to fail. Users can still opt-in to the static `/500` by adding a `pages/500.js` file. 

This also refactors checking `_app` for custom `getInitialProps` to outside of the static check loop to prevent a potential race condition where we could run this check multiple times un-necessarily.  

Fixes: https://github.com/vercel/next.js/issues/22815

This ensures we load `_document` then `_app` and then the page's component in all cases which matches behavior between the serverless target and the default server target.  Additional tests to ensure this order is followed has been added to prevent regression. 

Fixes: https://github.com/vercel/next.js/issues/22732

Just the conversion of config loading from sync to async from https://github.com/vercel/next.js/pull/22153

cc @Timer 

This adds generating a static 500 status page when a `pages/500.js` file is added similar to how we handle generating static 404 pages when `pages/404.js` is present. This allows showing a customized error page when a 500 error occurs in an optimal way.  

This pull request removes the native `sharp` dependency (which doesn't work on some Linux variants, nor **M1 Mac**) and replaces it with a wasm equivalent.

It also reduces Next.js' installed size by 27.3 MB.

The code is adapted from the [Squoosh CLI](https://github.com/GoogleChromeLabs/squoosh).

This PR still supports:

- Rotation normalization
- Resizing
- PNG
- JPEG
- Webp

However, it (temporarily) removes support for:
- Resizing Gifs
- Resizing Tiff

(these formats still get served and rendered correctly by the image component)

---

Fixes #20456
Closes #20738
Closes #21762

This adds ncc'ing the AMP optimizer package to speed up install times and cache the runtime. 

Closes: https://github.com/vercel/next.js/issues/20404

This insures we add entries for each locale version of a non-dynamic SSG page since they can have unique revalidate values. This requires a version bump in the `prerender-manifest` since the static routes now contain additional values which need to be handled separately. 

Fixes: https://github.com/vercel/next.js/issues/21568 

Allows building without permission to write to the application directory, useful for containers and sandboxes.

This helps catch conflicting paths returned from `getStaticPaths` with a friendly error

<details>

<summary>
Preview of error
</summary>


<img width="962" alt="Screen Shot 2021-01-08 at 5 03 04 PM" src="https://user-images.githubusercontent.com/22380829/104074719-6e481100-51d6-11eb-9397-938aee3ae30b.png">
<img width="962" alt="Screen Shot 2021-01-08 at 5 03 41 PM" src="https://user-images.githubusercontent.com/22380829/104074722-6f793e00-51d6-11eb-90f6-7cdf9882bf00.png">

</details>




Closes: https://github.com/vercel/next.js/issues/19527

Fixes #20585
Closes #20406 as it duplicates Babel dependencies
Closes #18926 as it's outdated

This ensures we handle encoding/decoding for SSG prerendered/fallback pages correctly. Since we only encode path delimiters when outputting to the disk we need to match this encoding when building the `ssgCacheKey` to look-up the prerendered pages. This also fixes non-ascii prerendered paths (e.g. 商業日語) not matching correctly. 

This does not resolve 👉  https://github.com/vercel/next.js/issues/10084 and further investigation will be needed before addressing non-ascii paths for non-SSG pages. 

The encoding output was tested against https://tst-encoding-l7amu5b9c.vercel.app/ to ensure the values will match correctly on Vercel. 

Closes: https://github.com/vercel/next.js/issues/17582
Closes: https://github.com/vercel/next.js/issues/17642
x-ref: https://github.com/vercel/next.js/pull/14717

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.

This keeps track of required server files in a manifest file

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

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 mirrors the `basePath: false` behavior for custom-routes with `locale: false` to allow users to configure the locales manually (`locale: false`) or have the locales be handled automatically for custom-routes. 

Fixes: https://github.com/vercel/next.js/issues/18927
Fixes: https://github.com/vercel/next.js/issues/18795

Fixes #18356 

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 corrects additional fallback pages being generated without the fallback flag causing `getStaticProps` to be called without params with i18n. The revalidation aspect of the issue has been corrected separately in https://github.com/vercel/next.js/pull/18569

Fixes: https://github.com/vercel/next.js/issues/18404

This records new configs being leveraged

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 removes the `unstable_` prefix to prepare for stabilizing the feature

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