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 />
)
```

This ensures dynamic routes are correctly generated for `next start` with i18n and adds tests to the i18n suite to ensure they are working correctly. 

Closes: https://github.com/vercel/next.js/issues/18397

This PR fixes two bugs causing HTML validators to complain.

- Error: Bad value data:image/svg+xml;charset=utf-8, for attribute src on element img: Illegal character in scheme data: < is not allowed.
  - Fixed by using base64 for svg during `layout=intrinsic` to avoid angle brackets
- Error: Element img is missing required attribute src.
  - Fixed by using base64 transparent gif for `loading=lazy` placeholder

Fixes #18850 

This PR adds additional security tests.

This makes sure to compile query values for rewrites/redirects as non-path items to prevent param like values e.g. `https://` from causing the destination to fail to compile. 

Fixes: https://github.com/vercel/next.js/issues/17440 
x-ref: https://github.com/vercel/next.js/issues/18670

This pull request fixes `<Image />` not updating when new props are passed by removing external DOM mutations and relying on React to do it instead.

As an added bonus, I've extracted the intersection observer from both the `<Image />` and `<Link />` component, as their instance can be shared!

The increase in size is minor (+3B), and actually a decrease for apps using both `<Image />` and `<Link />`.

---

Fixes #18698
Fixes #18369

While we were fixing how Next.js handled CSS, we added a complex prefetch, preload, fetch sequence to acquire the CSS asset.

This unnecessarily overcomplicated what could've been only a `fetch()` from the very start!

---

Fixes #16932

This corrects this test failing from an arrow function being used in ie11 which isn't supported natively

```
 ● Production Usage › Dynamic import › default behavior › should not remove css styles for same css file between page transitions

    JavascriptError: Error executing JavaScript

      at Object.throwDecodedError (../node_modules/selenium-webdriver/lib/error.js:550:15)
      at parseHttpResponse (../node_modules/selenium-webdriver/lib/http.js:565:13)
      at Executor.execute (../node_modules/selenium-webdriver/lib/http.js:491:26)
```

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.

* Ensure we prefetch on hover

* double because of hovering prefetch

* rerun workflow

* disable flaky test

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.

* Fix chromedriver set-up to test electron separately

* Update workflow

* Update compiled

Fixes #18794