Experimental swc external helpers options

[SukkaW]

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: Fixes Investigate using @swc/helpers #30806
• 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

cc @timneutkens

Make swc's externalHelpers available as an experimental option.

A memo list:

• Do we need a https://nextjs.org/message link for that? If we need it, what should we put in there?
• It is up to the Next.js team to decide if it should be added to the telemetry.
• swcExternalHelpers is disabled by default thus there is no reason to include @swc/helpers in next's package.json, which means users will have to install it manually and locally.
• The impact of next's built-in compiled module should be measured before enabling it in task thus should be another PR.

[ijjk]

Stats from current PR

Default Build (Decrease detected ✓)

General Overall increase ⚠️

	vercel/next.js canary	SukkaW/next.js swc-external-helpers	Change
buildDuration	17.1s	18s	⚠️ +904ms
buildDurationCached	7s	6.6s	-400ms
nodeModulesSize	372 MB	372 MB	⚠️ +978 B

Page Load Tests Overall decrease ⚠️

	vercel/next.js canary	SukkaW/next.js swc-external-helpers	Change
/ failed reqs	0	0	✓
/ total time (seconds)	3.145	3.535	⚠️ +0.39
/ avg req/sec	794.79	707.23	⚠️ -87.56
/error-in-render failed reqs	0	0	✓
/error-in-render total time (seconds)	1.392	1.566	⚠️ +0.17
/error-in-render avg req/sec	1796.49	1596.22	⚠️ -200.27

Client Bundles (main, webpack)

	vercel/next.js canary	SukkaW/next.js swc-external-helpers	Change
925.HASH.js gzip	179 B	179 B	✓
framework-HASH.js gzip	42 kB	42 kB	✓
main-HASH.js gzip	27.9 kB	27.9 kB	✓
webpack-HASH.js gzip	1.44 kB	1.44 kB	✓
Overall change	71.6 kB	71.6 kB	✓

Legacy Client Bundles (polyfills)

	vercel/next.js canary	SukkaW/next.js swc-external-helpers	Change
polyfills-HASH.js gzip	31 kB	31 kB	✓
Overall change	31 kB	31 kB	✓

Client Pages

	vercel/next.js canary	SukkaW/next.js swc-external-helpers	Change
_app-HASH.js gzip	1.36 kB	1.36 kB	✓
_error-HASH.js gzip	192 B	192 B	✓
amp-HASH.js gzip	309 B	309 B	✓
css-HASH.js gzip	327 B	327 B	✓
dynamic-HASH.js gzip	2.57 kB	2.57 kB	✓
head-HASH.js gzip	351 B	351 B	✓
hooks-HASH.js gzip	920 B	920 B	✓
image-HASH.js gzip	5.09 kB	5.09 kB	✓
index-HASH.js gzip	263 B	263 B	✓
link-HASH.js gzip	2.26 kB	2.26 kB	✓
routerDirect..HASH.js gzip	320 B	320 B	✓
script-HASH.js gzip	387 B	387 B	✓
withRouter-HASH.js gzip	319 B	319 B	✓
85e02e95b279..7e3.css gzip	107 B	107 B	✓
Overall change	14.8 kB	14.8 kB	✓

Client Build Manifests

	vercel/next.js canary	SukkaW/next.js swc-external-helpers	Change
_buildManifest.js gzip	460 B	460 B	✓
Overall change	460 B	460 B	✓

Rendered Page Sizes

	vercel/next.js canary	SukkaW/next.js swc-external-helpers	Change
index.html gzip	530 B	530 B	✓
link.html gzip	544 B	544 B	✓
withRouter.html gzip	524 B	524 B	✓
Overall change	1.6 kB	1.6 kB	✓

---

Default Build with SWC (Decrease detected ✓)

General Overall increase ⚠️

	vercel/next.js canary	SukkaW/next.js swc-external-helpers	Change
buildDuration	20.7s	21.4s	⚠️ +752ms
buildDurationCached	7s	7s	-35ms
nodeModulesSize	372 MB	372 MB	⚠️ +978 B

Page Load Tests Overall decrease ⚠️

	vercel/next.js canary	SukkaW/next.js swc-external-helpers	Change
/ failed reqs	0	0	✓
/ total time (seconds)	3.398	3.516	⚠️ +0.12
/ avg req/sec	735.67	711.06	⚠️ -24.61
/error-in-render failed reqs	0	0	✓
/error-in-render total time (seconds)	1.533	1.558	⚠️ +0.03
/error-in-render avg req/sec	1630.32	1604.13	⚠️ -26.19

Client Bundles (main, webpack)

	vercel/next.js canary	SukkaW/next.js swc-external-helpers	Change
925.HASH.js gzip	178 B	178 B	✓
framework-HASH.js gzip	42.3 kB	42.3 kB	✓
main-HASH.js gzip	28.2 kB	28.2 kB	✓
webpack-HASH.js gzip	1.45 kB	1.45 kB	✓
Overall change	72.2 kB	72.2 kB	✓

Legacy Client Bundles (polyfills)

	vercel/next.js canary	SukkaW/next.js swc-external-helpers	Change
polyfills-HASH.js gzip	31 kB	31 kB	✓
Overall change	31 kB	31 kB	✓

Client Pages

	vercel/next.js canary	SukkaW/next.js swc-external-helpers	Change
_app-HASH.js gzip	1.35 kB	1.35 kB	✓
_error-HASH.js gzip	179 B	179 B	✓
amp-HASH.js gzip	313 B	313 B	✓
css-HASH.js gzip	324 B	324 B	✓
dynamic-HASH.js gzip	2.56 kB	2.56 kB	✓
head-HASH.js gzip	351 B	351 B	✓
hooks-HASH.js gzip	921 B	921 B	✓
image-HASH.js gzip	5.23 kB	5.23 kB	✓
index-HASH.js gzip	261 B	261 B	✓
link-HASH.js gzip	2.33 kB	2.33 kB	✓
routerDirect..HASH.js gzip	322 B	322 B	✓
script-HASH.js gzip	388 B	388 B	✓
withRouter-HASH.js gzip	317 B	317 B	✓
85e02e95b279..7e3.css gzip	107 B	107 B	✓
Overall change	15 kB	15 kB	✓

Client Build Manifests

	vercel/next.js canary	SukkaW/next.js swc-external-helpers	Change
_buildManifest.js gzip	459 B	459 B	✓
Overall change	459 B	459 B	✓

Rendered Page Sizes

	vercel/next.js canary	SukkaW/next.js swc-external-helpers	Change
index.html gzip	531 B	531 B	✓
link.html gzip	545 B	545 B	✓
withRouter.html gzip	527 B	527 B	✓
Overall change	1.6 kB	1.6 kB	✓

Commit: 0d67101

[SukkaW]

The issue is superseded by #37150.