- Reduce jest retries to 2 for a total of 3 attempts
- Disable retries in `invalid-href` test. I noticed jest retries don't help when this test fails (see log output of https://github.com/vercel/next.js/runs/904147534).

Forces all Next.js users to have this patch installed: https://twitter.com/timneutkens/status/1282129714627448832

Huge thanks to @paulmillr and @sokra 🙏

* Add with-sitemap Example

* Update README

* Update examples/with-sitemap/scripts/generate-sitemap.js
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* Update examples/with-sitemap/package.json
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* Update examples/with-sitemap/public/sitemap.xml
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* Update README

* Add .env Info to README

* Update examples/with-sitemap/README.md
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* Update examples/with-sitemap/README.md
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* More helpful README

Updated to include more details about Next.js, link to the interactive tutorial, showcase, etc. Content mostly based on the official Next.js site.

* create-next-app readme

An updated readme with more details on options, benefits, etc.

* Apply edits from code review
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* Remove redundant intro

* Update packages/create-next-app/README.md

* Remove introduction and list in showcase

* Apply suggestions from code review

* Update packages/next/README.md
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* Update Sentry example for use with Sentry/Vercel integration

* update linting

* Update link in readme

* Update readme, add comment

* Add step about commit SHA

* Updated readme

* Use if

* dont call sentry webpack plugin w/o a commit sha present

* Update examples/with-sentry/README.md
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* update release value

* prettier readme

* Updated note
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* MongoDB Example

* Apply suggestions from code review

* Add changes based on feedback.

* clean up code with more descriptive props

* Use MongoDB in ServerSideProps instead of separate API route

* Update examples/with-mongodb/README.md
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* Update examples/with-mongodb/README.md
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* Update examples/with-mongodb/README.md
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* Update examples/with-mongodb/README.md
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* Update examples/with-mongodb/README.md
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* Update examples/with-mongodb/README.md
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Fixes #15342

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The statement is not true, we provide mocks for `req` and `res`.

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Closes #15330

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

Low hanging fruit 🍎 
Resolves: #15321

`https://react-md.mlaursen.com/` -> `https://react-md.dev/`

This particular variable was not being read correctly. Added a test for the behavior.

Fixes #15261

Fixes https://github.com/vercel/next.js/issues/12046
Fixes https://github.com/vercel/next.js/issues/11992
Closes https://github.com/vercel/next.js/pull/13456

* Do not duplicate compilation errors

* Add tests

* Attempt to fix test

* Fix test

For reference: https://en.wikipedia.org/wiki/Wikipedia:Lists_of_common_misspellings/For_machines

Fixes https://github.com/vercel/next.js/issues/15188

`parseRelativeUrl` was used on urls that weren't always relative. It was used to generate a cache key, but we actually don't need these cache keys to be relative if the urls aren't relative.

Also took a look at the overall static data fetching logic and found a few things:

- [x] cache key is unnecessarily transformed through `prepareRoute`, we can just cache by resolved `dataHref` and remove that function. Pretty sure that `prepareRoute` was also introducing edge cases with `assetPath` and `delBasePath`
- [x] there is [a bug in the caching logic](https://github.com/vercel/next.js/blob/ebdfa2e7a3f8e22e03b94dfb5f00481bf06254b6/packages/next/next-server/lib/router/router.ts#L898) that made it fail on the second visit: it should be `Promise.resolve(this.sdc[pathname])` instead of `Promise.resolve(this.sdc[dataHref])`. Also added a test for this
- [x] ~converted to async await to improve stacktraces and readability.~ I assumed this was fine since I saw some async/awaits in that file already but it seems to just blow up the size of the non-modern bundle.
- [x] extracted nested `getResponse` function and define it top level. this should improve runtime performance
- [x] convert `_getStaticData` and `_getServerData` to class methods instead of properties. Not sure why they were defined as properties but I think they belong on the prototype instead.
- [x] remove `cb` property from `fetchNextData`, it's unnecessary and makes the async flow hard to understand.  The exact same logic can go in the `.then` instead.
- [ ] data fetching logic [retries on 5xx errors](https://github.com/vercel/next.js/blob/ebdfa2e7a3f8e22e03b94dfb5f00481bf06254b6/packages/next/next-server/lib/router/router.ts#L157), but not on network level errors. It should also retry on those. It should also not retry on every 5xx, probably only makes sense on 502, 503 and 504. (e.g. 500 is a server error that I wouldn't expect to succeed on a retry)

The overall result also is a few bytes smaller in size

- Introduces a lint rule which points towards the unwanted polyfill.io features.
- Aim here is to make the user aware that which of the requested features are actually required vs which are already covered under `next-polyfills`

Next step: If the remaining required polyfills amounts to a only a few KBs then its better to include them in 1P javascript and remove the third party render blocking script tag.

Makes the difference between optional catch all routes and catch all routes clearer.

Closes #15229