Remove webpack 4 support

[timneutkens]

This is the minimal version of #26915 which only removes the webpack 4 bundle and updates the webpack config. It does not touch existing plugins so that this PR is easier to land. We'll follow up with updating the individual webpack plugins.

Bug

• Related issues linked using fixes #number
• Integration tests added
• Errors have helpful link attached, see contributing.md

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.
• Errors have helpful link attached, see contributing.md

Documentation / Examples

• Make sure the linting passes

[sokra]

Could we put this on a Next.js 12 TODOs list?

[sokra]

Can we drop schema-utils2 and webpack-sources1 too or is this still used by something else?

[timneutkens]

webpack-sources1 is being used in mini-css-extract-plugin. schema-utils2 is being used in file-loader

[ijjk]

Stats from current PR

Default Build (Decrease detected ✓)

General Overall decrease ✓

	vercel/next.js canary	timneutkens/next.js add/remove-webpack-4	Change
buildDuration	14.9s	15.3s	⚠️ +355ms
buildDurationCached	3.9s	3.7s	-199ms
nodeModulesSize	193 MB	190 MB	-3.04 MB

Page Load Tests Overall decrease ⚠️

	vercel/next.js canary	timneutkens/next.js add/remove-webpack-4	Change
/ failed reqs	0	0	✓
/ total time (seconds)	3.215	3.336	⚠️ +0.12
/ avg req/sec	777.65	749.37	⚠️ -28.28
/error-in-render failed reqs	0	0	✓
/error-in-render total time (seconds)	1.554	1.545	-0.01
/error-in-render avg req/sec	1608.87	1617.61	+8.74

Client Bundles (main, webpack, commons)

	vercel/next.js canary	timneutkens/next.js add/remove-webpack-4	Change
779.HASH.js gzip	179 B	179 B	✓
framework-HASH.js gzip	42.2 kB	42.2 kB	✓
main-HASH.js gzip	26.9 kB	26.9 kB	✓
webpack-HASH.js gzip	1.45 kB	1.45 kB	✓
Overall change	70.8 kB	70.8 kB	✓

Legacy Client Bundles (polyfills)

	vercel/next.js canary	timneutkens/next.js add/remove-webpack-4	Change
polyfills-a4..dd70.js gzip	31 kB	31 kB	✓
Overall change	31 kB	31 kB	✓

Client Pages

	vercel/next.js canary	timneutkens/next.js add/remove-webpack-4	Change
_app-HASH.js gzip	977 B	977 B	✓
_error-HASH.js gzip	194 B	194 B	✓
amp-HASH.js gzip	311 B	311 B	✓
css-HASH.js gzip	328 B	328 B	✓
dynamic-HASH.js gzip	2.67 kB	2.67 kB	✓
head-HASH.js gzip	351 B	351 B	✓
hooks-HASH.js gzip	918 B	918 B	✓
image-HASH.js gzip	4.15 kB	4.15 kB	✓
index-HASH.js gzip	260 B	260 B	✓
link-HASH.js gzip	1.66 kB	1.66 kB	✓
routerDirect..HASH.js gzip	320 B	320 B	✓
script-HASH.js gzip	386 B	386 B	✓
withRouter-HASH.js gzip	319 B	319 B	✓
bb14e60e810b..30f.css gzip	125 B	125 B	✓
Overall change	13 kB	13 kB	✓

Client Build Manifests

	vercel/next.js canary	timneutkens/next.js add/remove-webpack-4	Change
_buildManifest.js gzip	494 B	494 B	✓
Overall change	494 B	494 B	✓

Rendered Page Sizes

	vercel/next.js canary	timneutkens/next.js add/remove-webpack-4	Change
index.html gzip	539 B	539 B	✓
link.html gzip	552 B	552 B	✓
withRouter.html gzip	534 B	534 B	✓
Overall change	1.63 kB	1.63 kB	✓

---

Default Build with SWC (Increase detected ⚠️)

General Overall decrease ✓

	vercel/next.js canary	timneutkens/next.js add/remove-webpack-4	Change
buildDuration	7.8s	7.4s	-395ms
buildDurationCached	3.9s	3.5s	-416ms
nodeModulesSize	193 MB	190 MB	-3.04 MB

Page Load Tests Overall increase ✓

	vercel/next.js canary	timneutkens/next.js add/remove-webpack-4	Change
/ failed reqs	0	0	✓
/ total time (seconds)	3.296	3.274	-0.02
/ avg req/sec	758.55	763.5	+4.95
/error-in-render failed reqs	0	0	✓
/error-in-render total time (seconds)	1.594	1.553	-0.04
/error-in-render avg req/sec	1568.26	1610.02	+41.76

Client Bundles (main, webpack, commons)

	vercel/next.js canary	timneutkens/next.js add/remove-webpack-4	Change
675-HASH.js gzip	13.8 kB	13.8 kB	✓
770.HASH.js gzip	178 B	178 B	✓
framework-HASH.js gzip	50.7 kB	50.7 kB	✓
main-HASH.js gzip	34.9 kB	34.9 kB	✓
webpack-HASH.js gzip	1.64 kB	1.64 kB	✓
Overall change	101 kB	101 kB	✓

Legacy Client Bundles (polyfills)

	vercel/next.js canary	timneutkens/next.js add/remove-webpack-4	Change
polyfills-a4..dd70.js gzip	31 kB	31 kB	✓
Overall change	31 kB	31 kB	✓

Client Pages

	vercel/next.js canary	timneutkens/next.js add/remove-webpack-4	Change
_app-HASH.js gzip	1.33 kB	1.33 kB	✓
_error-HASH.js gzip	180 B	180 B	✓
amp-HASH.js gzip	315 B	315 B	✓
css-HASH.js gzip	331 B	331 B	✓
dynamic-HASH.js gzip	2.79 kB	2.79 kB	✓
head-HASH.js gzip	356 B	356 B	✓
hooks-HASH.js gzip	637 B	637 B	✓
image-HASH.js gzip	573 B	573 B	✓
index-HASH.js gzip	262 B	262 B	✓
link-HASH.js gzip	2.2 kB	2.2 kB	✓
routerDirect..HASH.js gzip	326 B	326 B	✓
script-HASH.js gzip	393 B	393 B	✓
withRouter-HASH.js gzip	322 B	322 B	✓
bb14e60e810b..30f.css gzip	125 B	125 B	✓
Overall change	10.1 kB	10.1 kB	✓

Client Build Manifests

	vercel/next.js canary	timneutkens/next.js add/remove-webpack-4	Change
_buildManifest.js gzip	511 B	511 B	✓
Overall change	511 B	511 B	✓

Rendered Page Sizes

	vercel/next.js canary	timneutkens/next.js add/remove-webpack-4	Change
index.html gzip	538 B	538 B	✓
link.html gzip	550 B	550 B	✓
withRouter.html gzip	532 B	532 B	✓
Overall change	1.62 kB	1.62 kB	✓

Commit: d164dbc