Fixes #16173

## What

Restores handling of termination signals, `SIGTERM` and `SIGINT`, to allow graceful termination of next commands. Seems to have been removed during a child process refactor #6450, was this intentional?

## Why 

Currently the command processes have to be forcefully killed. This would help those using Next.js with custom servers and tools like Docker and Kubernetes that rely on termination signals to shutdown instances.

---

Where would be a good location to add some tests? [test/integration/cli/test/index.test.js](https://github.com/vercel/next.js/blob/fc98c13a2e6bc545073de0eedbe045352b387f6d/test/integration/cli/test/index.test.js)?

Leverage [execa](https://github.com/sindresorhus/execa) for writing to `stdin`.

Update for rebranding purposes

Fixes #19399

h/t to @prateekbh for noticing this test isn't cleaning up properly 

Closes: https://github.com/vercel/next.js/issues/19369

This updates the fallback locale for `locale: false` to be the `defaultLocale` instead of the currently active `locale` as it allows passing through URLs more seamlessly as a URL without the locale prefixed can be treated as the `defaultLocale` instead of having to worry if the locale matches the currently active locale. This also ensures `locale={false}` is tested in the i18n-support-catchall suite

Closes: https://github.com/vercel/next.js/issues/19048

* Exclude well known files when trailing slash: true

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

This adds additional test coverage and more handling for i18n + `trailingSlash: true`

Closes: https://github.com/vercel/next.js/issues/19069

This updates the export progress to make sure we log out the final progress update when less pages than number of progress updates (segments). This also adds tests to ensure we are logging the progress out as expected. 

Fixes: https://github.com/vercel/next.js/issues/19122
Closes: https://github.com/vercel/next.js/pull/19123

This ensures navigations to non-configured locales causes the 404 page to be shown, it also adds tests to ensure direct visits for non-configured locales 404s correctly. 

Fixes: https://github.com/vercel/next.js/issues/19214

This fixes the case where we were returning page data when rendering `/_error` in `serverless` mode with `next start`

Closes: https://github.com/vercel/next.js/issues/19068

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 ensures redirects are handled properly with i18n + `trailingSlash: true`, additional tests have also been added to ensure this is covered 

Fixes: https://github.com/vercel/next.js/issues/19069

This makes sure SSG data is correctly prefetched for the default locale and other locales on the same page. Tests for this behavior have been added for catch-all and normal pages. 

Closes: https://github.com/vercel/next.js/issues/19048

This fixes compatibility with React 17 and `styled-jsx`.

Fixes #19242

Co-authored-by: NJoe Haddad <joe.haddad@zeit.co>

We accidentally regressed back in 9.5 and dropped support for inline CSS comments. PostCSS always parses these as pass-through (and not a syntax error), which can cause problems when minifying.

Browsers do a similar thing and ignore the comments.

To ensure we generate valid CSS, this adds support for stripping the CSS comments from the build.

--- 

Fixes #15589
Closes #17130

This allows SSG pages that return `notFound` to be revalidated. 

Closes: https://github.com/vercel/next.js/issues/18651

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 #18557 

- Fixes #19120
- Closes #18413 
- Related to #19041 

Co-authored-by: NGerald Monaco <gbmonaco@google.com>

Fixes #18720

This removes image preloading. It doesn't work correctly on any browser other than Chrome (with Chrome's real engine). On all other browsers, it triggers 2x the bytes to be downloaded. The tradeoff isn't worth it here IMO.

Chrome itself should be smart enough to bump an `<img />` tag's priority over other preloads that are script type during the preparse phase.

We can reintroduce this when we don't hurt non-Chrome users.

Fixes #18415 by using the default config as fallback.

Users who wish to use their `next.config.js` values will still need the workaround from https://github.com/vercel/next.js/issues/18415#issuecomment-718180659

This ensures root optional-catch-all index routes with i18n are output to the correct location and are also loaded from the `prerender-manifest` correctly. 

Fixes: https://github.com/vercel/next.js/issues/19095

## Description

Fixes #18338 - Fixed an issue with `trailingSlash: true` adding a slash to the end of an external link.

After
```
<h1 class="Home_title__3DjR7">Welcome to <a href="https://nextjs.org">Without slash</a></h1>
<h1 class="Home_title__3DjR7">Welcome to <a href="https://nextjs.org">With slash?</a></h1>
```

Before
```
<h1 class="Home_title__3DjR7">Welcome to <a href="https://nextjs.org">Without slash</a></h1>
<h1 class="Home_title__3DjR7">Welcome to <a href="https://nextjs.org/">With slash?</a></h1>
```

This ensures the mixed `notFound`/`redirect` error is shown correctly and adds an err.sh for the error. 

Closes: https://github.com/vercel/next.js/issues/18727

This fixes a few things related to optional catch-all routes and i18n. The first thing is it ensures the correct data route is generated on the client so that the locale isn't duplicated for an optional catch-all route, the next is it ensures the browser history is updated correctly when only a locale change is occurring, and then it also ensures we handle the locales and normalizing for fallback optional catch-all pages correctly.

Tests have been added to ensure these cases are covered properly and we don't regress on them, these changes were also tested on Vercel [here](https://next-js-bug-i18n-root-params-nybg44l0b.vercel.app/)

Fixes: https://github.com/vercel/next.js/issues/18633 
Fixes: https://github.com/vercel/next.js/issues/19059

This pull request completely replaces our old page loader with a brand new route loader.

Our existing comprehensive test suite means I did not need to add a bunch of tests. I did add them where behavior was added or fixed.

Summary of the changes:

- Eagerly evaluates prefetched pages in browser idle time (speeds up transitions)
- Router is **no longer frozen** indefinitely if the Build Manifest never arrives
- Router is **no longer frozen** indefinitely if a page fails to bootstrap
- New `withFuture` utility instead of ad-hoc deduping per resource
- Prefetching is now delayed until browser idle time to not impact TTI
- Browsers without `prefetch` now fall back to eager evaluation instead of using `preload`
- We're now ready to serve non-static assets **with `no-store` without breaking prefetching**
- **Application can now hydrate without fetching CSS assets—this is a huge performance win that was previously blocking hydration**

---

The minor size increase here is unfortunate, but we have to incur it for correctness.

---

Fixes #18389
Fixes #18642

Fixes #18356 

This ensures we match the `basePath` handling for redirects in `next.config.js` with redirects from `getStaticProps` and `getServerSideProps` and also adds a separate test suite to ensure GS(S)P redirects with `basePath` work correctly

Fixes: https://github.com/vercel/next.js/issues/18984
Closes: https://github.com/vercel/next.js/pull/18892

This ensures we use the `defaultLocale` for a locale domain when rendering non-static pages. Static pages will initially contain the global `defaultLocale` and then be updated on the client since we don't currently prerender a version of the pages for each locale domain. 

Closes: https://github.com/vercel/next.js/issues/18970

Co-authored-by: NJoe Haddad <joe.haddad@zeit.co>

We fixed this in a previous PR but there were no tests for `.ico` so this PR adds a test for it to ensure we don't regress.

Similar to SVG, we bypass ICO because it typically contains multiple sizes in a single file.

Closes #18600 

Fixes #18563 by adding the etag header to the optimized image response.

This does _not_ change the expireAt (TTL) for cached files on the server, which still uses the max-age of the upstream response.

The new file format on disk for cached image files is the following:

```
.next/cache/images/<HASHED_QUERYSTRING>/<EXPIREAT>.<ETAG>.<EXT>
```

Prevent `catch` assertions in tests.

This allows to import the type `ImageProps` from `next/image` like `next/link`.

https://github.com/vercel/next.js/blob/a6660729ea82fbcb26cfe7c89637b1af37255c9f/packages/next/client/link.tsx#L21

## Usage

```tsx
import Image, { ImageProps } from 'next/image'

const CustomImage: React.FC<ImageProps> = (props) => (
  <Image {...props} unsized />
)
```