Fixes #9284

* Polyfilling fetch and object-assign

* Polyfilling corejs object-assign

* Adding object-assign in polyfills.js. IE11 does not support Object.assign

* Fixing failing test

* Updating object.assign polyfill to fix aliasing

* Updating test case value to match new build stats

* Increasing the size of default build to 225kb

* Fixing defer-script test case to not include polyfill.js

* Revert README.md

* Re-design the polyfill approach based on PR feedback

* Adding comment and fixing test case

* Rename polyfills chunk

* Extract aliases into helper

* Remove extra new line

* Fix TypeScript typings

* Adding _internal_fetch alias

* Adjust build manifest plugin

* Build manifest plugin changes - adding a separate entry for polyfills

* Rename polyfills entry in build-manifest.json

* Remove old comment

* Fix TS

* Set key

* Polyfills already added

* Filtring polyfill.module.js

* Fix test

* Add __internal_fetch to alias rule

* Adjust name

* bump size

* ignore polyfills

* sigh

* Disallow iSSG revalidation period of zero

* Fix revalidation period in test

* Add initial bit for plugins

* Add checks for needed metadata values

* Add test

* Initial plugins changes

* Add handling for _app middleware

* Add loading of _document middleware and
handling of multiple default export syntaxes

* Fix insert order for middleware member expression

* Remove early return from middleware plugin from testing

* Add tests for current plugin middlewares

* Update test plugin package.json

* Update handling for class default export

* Update to use webpack loader instead of babel
plugin, remove redundant middleware naming, and add field for required env for plugins

* Add middleware to support material-ui use case
and example material-ui plugin

* Update tests and remove tests stuff from google analytics plugin

* Remove old plugin suite

* Add init-server middleware

* Exit hard without stack trace when error in collecting plugins

* Add on-error-client and on-error-server and update
to run init-server with next-start in serverless mode

* Update init-client for google analytics plugin

* Add example Sentry plugin and update with-sentry-simple

* Remove middleware field/folder and use src dir for plugins

* Add post-hydration middleware and update
material-ui plugin

* Put plugins code behind flag

* Update chromedriver

* Revert "Update chromedriver"

This reverts commit 1461e978e677f7da05e29e0415ec614a04bf65f9.

* Update lock file

* Remove un-needed _app for sentry example

* Add auto loading of scoped packages, add plugins
config for manually listing plugins, and update
to only collect plugins once

* Update example plugins

* Expose plugins' config

* Rename plugin lifecycles and add babel-preset-build

* Rename other methods with unstable

* Update log when plugin config overrides auto-detecting

* Add handling for exportTrailingSlash for iSSG pages

* Update index.test.js

* Don't rely on page-config plugin to detect iSSG usage

* Make sure to only update sprStatus if page file

* Remove dead-code elimination for iSSG code

* Revert next-page-config.ts

* Update index.js

* Update index.test.js

* Update _app documentation to reflect no longer needing next/app

* Remove lint-staged

* Start the modern Child Compiler earlier during builds

* fix child compiler errors not bubbling

* closes #8989

fix

closes #8989

* test

* Update next.config.js

* Revert page1.js

* Revert page2.js

* Delete page4.js

* Delete page3.js

* Update index.test.js

* Revert index.test.js

* Revert next.config.js

* Add experimental config for React Mode

* Use latest types

* Use latest types

* Throw Error for next.config.ts

Ref: https://github.com/zeit/next-plugins/issues/555

* Check for .js else .ts

* Update Error Message
Co-Authored-By: NAlexander Kachkaev <alexander@kachkaev.ru>

* Add test case when both next.config.js and next.config.ts exist.

* Remove extra constant CONFIG_FILE_TS and Add check for ts/tsx/json

* Rename test config parameter and add tsx and json files

* Change messege

* change value

* Update next.config.json

* Update next.config.json

* Change message  and add jsx filter

* Adjust

* Simplify test

* adjust

* Apply format to webpack config

* hit all files

* Improve serverless build performance

Next's serverless build uses a custom resolver, injected the via Webpack's `externals` option that delegates out to `resolve-request` to more aggressively pull node modules into the serverless bundles.

When profiling a large Next.js application, I noticed an excessive number of filesystem calls near the end of the build. I narrowed this down to the serverless compiler pass, and eventually the custom resolver function that is the subject of this PR.  As it turns out, around half of the calls to the `externals` custom resolver function are for a `request` path that is a relative import. Next doesn't have any specific logic to apply to relative imports - it only needs to special-case bare module resolution.

Adding a simple bypass for relative module resolution reduces the number of blocking filesystem-bound `resolveRequest()` calls by 50% on a certain well-known Next.js website. This also results in a 30% reduction in production build times for incremental builds.

* Explain more in the comment

Usage of this option was removed in
61b8b732 but the cli was not updated.

* Update to use a historyId to track invalid popstates

* Remove log from debugging

* Use Math.random instead of Date.getTime to avoid mocks

* Enable granular chunks config for all chunk types

Adding comment

Bug fix

* Update index.test.js

* Update index.test.js

* Fix test cases. Adding next/link to not trigger a different bug

* Removing obsolete comment

* Split TypeScript Flag Docs

* reword

* Pass config.experimental.cpus to export during build

Currently, there is no way of specifying the number of worker threads of
`next export` when run as part of `next build`.

I suggest a sane default should be to just use the same amount of
workers that were used during the build process which currently seems to
be configured through `config.experimental.cpus`.

This setting is already respected in the two other places where
jest-workers are in use: The TerserPlugin and the staticCheckWorkers in
`next build`.

* Only enable worker threads if there is more than 1 worker

Multiple worker threads can cause problems when certain dependencies are
being used, see e.g. https://github.com/zeit/next.js/issues/7894

This patch allows disabling of worker threads by setting
`config.experimental.cpus = 1`.

The benefit of spawning 1 worker thread, if there is any at all, should
very limited anyways, so the workload can just as well be processed in
the main thread.

* Disable parallel build for firebase authentication example

* Add integration test to cover #7894

* Rename test suite and add worker_threads config

* Disable worker_threads by default

* Update index.test.js

* Use workerThreads config for TerserPlugin

* Update to use workerThreads config in
TerserPlugin for consistency

* Disable node 12 specific test

* Add a configuration flag to disable integrated type checker

* Add tests for typescript-transpileonly

* Restore removed argument

* Make output more coherent

* Split transpileOnly into ignoreDevErrors and ignoreBuildErrors

* Minor stylistic change

* Add warning for getStaticParams without getStaticProps

* Throw error instead of logging to make sure it's noticed

* Lower default concurrency for tests

* Take multiple values into account

* make typescript happy

* allow NextScript to optionally defer javascript

* move defer options to experimental feature

* combine defer flags into a single option

* Update deferScripts to work with serverless target

* Add test for defer and async property

* Read the async property

* Check versions of chrome and chromedriver

* Update to chromedriver 76

* Fix test

* Update Babel dependencies

* Update sizes

Before this patch users would see the following warning during initial
compilation:

```
Warning: Each child in a list should have a unique "key" prop. See https://fb.me/react-warning-keys for more information.
    in link
    in Head
    in html
    in Html
    in Document
    in Context.Provider
    in Context.Provider
```

* Add StrictMode toggle

* Rename option to reactStrictMode

* Default to false initially

* Ensure directory before flushing cache iSSG file

* Add test for prerender cache flush

* Nest the dynamic route test one more level

* update fetch for test

* Update error check

The correct option to use with `micro-cors` package is `allowMethods` instead `allowedMethods`. This PR fixes the example.