Allow enabling worker threads on dev server

[afbarbaro]

See this issue for context on use case. /node-clinic/issues/260.

There's already an experimental config option to turn on worker threads but it's not being passed to the worker instantiated on the dev server.

[afbarbaro]

clinicjs/node-clinic#260

[timneutkens]

This one intentionally does not use worker threads because of incompatibility with some Node.js libraries, maybe that's fine though as it's opt-in

[ijjk]

Stats from current PR

Default Build (Increase detected ⚠️)

General Overall increase ⚠️

	vercel/next.js canary	afbarbaro/next.js enable-worker-threads-dev-server	Change
buildDuration	11.9s	12.2s	⚠️ +321ms
buildDurationCached	3s	2.7s	-289ms
nodeModulesSize	49.5 MB	49.5 MB	⚠️ +194 B

Page Load Tests Overall increase ✓

	vercel/next.js canary	afbarbaro/next.js enable-worker-threads-dev-server	Change
/ failed reqs	0	0	✓
/ total time (seconds)	2.076	2.028	-0.05
/ avg req/sec	1204.21	1232.72	+28.51
/error-in-render failed reqs	0	0	✓
/error-in-render total time (seconds)	1.111	1.117	⚠️ +0.01
/error-in-render avg req/sec	2250.34	2238.38	⚠️ -11.96

Client Bundles (main, webpack, commons)

	vercel/next.js canary	afbarbaro/next.js enable-worker-threads-dev-server	Change
359.HASH.js gzip	2.96 kB	2.96 kB	✓
745.HASH.js gzip	180 B	180 B	✓
framework-HASH.js gzip	42.2 kB	42.2 kB	✓
main-HASH.js gzip	20.9 kB	20.9 kB	✓
webpack-HASH.js gzip	1.53 kB	1.53 kB	✓
Overall change	67.8 kB	67.8 kB	✓

Legacy Client Bundles (polyfills)

	vercel/next.js canary	afbarbaro/next.js enable-worker-threads-dev-server	Change
polyfills-HASH.js gzip	31.1 kB	31.1 kB	✓
Overall change	31.1 kB	31.1 kB	✓

Client Pages

	vercel/next.js canary	afbarbaro/next.js enable-worker-threads-dev-server	Change
_app-HASH.js gzip	803 B	803 B	✓
_error-HASH.js gzip	3.06 kB	3.06 kB	✓
amp-HASH.js gzip	554 B	554 B	✓
css-HASH.js gzip	329 B	329 B	✓
dynamic-HASH.js gzip	2.52 kB	2.52 kB	✓
head-HASH.js gzip	2.28 kB	2.28 kB	✓
hooks-HASH.js gzip	903 B	903 B	✓
image-HASH.js gzip	5.61 kB	5.61 kB	✓
index-HASH.js gzip	261 B	261 B	✓
link-HASH.js gzip	1.66 kB	1.66 kB	✓
routerDirect..HASH.js gzip	319 B	319 B	✓
script-HASH.js gzip	387 B	387 B	✓
withRouter-HASH.js gzip	320 B	320 B	✓
bb14e60e810b..30f.css gzip	125 B	125 B	✓
Overall change	19.1 kB	19.1 kB	✓

Client Build Manifests

	vercel/next.js canary	afbarbaro/next.js enable-worker-threads-dev-server	Change
_buildManifest.js gzip	490 B	490 B	✓
Overall change	490 B	490 B	✓

Rendered Page Sizes

	vercel/next.js canary	afbarbaro/next.js enable-worker-threads-dev-server	Change
index.html gzip	531 B	531 B	✓
link.html gzip	544 B	544 B	✓
withRouter.html gzip	525 B	525 B	✓
Overall change	1.6 kB	1.6 kB	✓

---

Webpack 4 Mode (Increase detected ⚠️)

General Overall increase ⚠️

	vercel/next.js canary	afbarbaro/next.js enable-worker-threads-dev-server	Change
buildDuration	9.9s	9.7s	-178ms
buildDurationCached	3.7s	4s	⚠️ +317ms
nodeModulesSize	49.5 MB	49.5 MB	⚠️ +194 B

Page Load Tests Overall increase ✓

	vercel/next.js canary	afbarbaro/next.js enable-worker-threads-dev-server	Change
/ failed reqs	0	0	✓
/ total time (seconds)	2.082	2.119	⚠️ +0.04
/ avg req/sec	1200.84	1179.54	⚠️ -21.3
/error-in-render failed reqs	0	0	✓
/error-in-render total time (seconds)	1.112	1.078	-0.03
/error-in-render avg req/sec	2248.38	2319.82	+71.44

Client Bundles (main, webpack, commons)

	vercel/next.js canary	afbarbaro/next.js enable-worker-threads-dev-server	Change
17.HASH.js gzip	2.98 kB	2.98 kB	✓
18.HASH.js gzip	185 B	185 B	✓
677f882d2ed8..HASH.js gzip	13.7 kB	13.7 kB	✓
framework.HASH.js gzip	41.9 kB	41.9 kB	✓
main-HASH.js gzip	8.4 kB	8.4 kB	✓
webpack-HASH.js gzip	1.22 kB	1.22 kB	✓
Overall change	68.4 kB	68.4 kB	✓

Legacy Client Bundles (polyfills)

	vercel/next.js canary	afbarbaro/next.js enable-worker-threads-dev-server	Change
polyfills-HASH.js gzip	31.3 kB	31.3 kB	✓
Overall change	31.3 kB	31.3 kB	✓

Client Pages

	vercel/next.js canary	afbarbaro/next.js enable-worker-threads-dev-server	Change
_app-HASH.js gzip	791 B	791 B	✓
_error-HASH.js gzip	3.76 kB	3.76 kB	✓
amp-HASH.js gzip	552 B	552 B	✓
css-HASH.js gzip	333 B	333 B	✓
dynamic-HASH.js gzip	2.71 kB	2.71 kB	✓
head-HASH.js gzip	2.97 kB	2.97 kB	✓
hooks-HASH.js gzip	911 B	911 B	✓
index-HASH.js gzip	231 B	231 B	✓
link-HASH.js gzip	1.64 kB	1.64 kB	✓
routerDirect..HASH.js gzip	298 B	298 B	✓
script-HASH.js gzip	3.02 kB	3.02 kB	✓
withRouter-HASH.js gzip	294 B	294 B	✓
e025d2764813..52f.css gzip	125 B	125 B	✓
Overall change	17.6 kB	17.6 kB	✓

Client Build Manifests

	vercel/next.js canary	afbarbaro/next.js enable-worker-threads-dev-server	Change
_buildManifest.js gzip	500 B	500 B	✓
Overall change	500 B	500 B	✓

Rendered Page Sizes

	vercel/next.js canary	afbarbaro/next.js enable-worker-threads-dev-server	Change
index.html gzip	577 B	577 B	✓
link.html gzip	587 B	587 B	✓
withRouter.html gzip	569 B	569 B	✓
Overall change	1.73 kB	1.73 kB	✓

Commit: 5f112c7

[ijjk]

This change looks good as it matches our other Worker usage during build and is opt-in as mentioned by Tim, thanks for the PR!