avoid retaining webpack config too long

[sokra]

avoids keeping the webpack compiler during after webpack build build steps like SSG etc.

(review with ignore whitespace)

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 by running yarn lint

[ijjk]

Stats from current PR

Default Build (Increase detected ⚠️)

General Overall increase ⚠️

	vercel/next.js canary	vercel/next.js pref/memory-retain-compiler	Change
buildDuration	17.5s	17.8s	⚠️ +354ms
buildDurationCached	3.2s	3.3s	⚠️ +43ms
nodeModulesSize	347 MB	347 MB	⚠️ +591 B

Page Load Tests Overall increase ✓

	vercel/next.js canary	vercel/next.js pref/memory-retain-compiler	Change
/ failed reqs	0	0	✓
/ total time (seconds)	2.867	2.879	⚠️ +0.01
/ avg req/sec	872.14	868.39	⚠️ -3.75
/error-in-render failed reqs	0	0	✓
/error-in-render total time (seconds)	1.331	1.306	-0.02
/error-in-render avg req/sec	1877.7	1913.85	+36.15

Client Bundles (main, webpack, commons)

	vercel/next.js canary	vercel/next.js pref/memory-retain-compiler	Change
450.HASH.js gzip	179 B	179 B	✓
framework-HASH.js gzip	42.2 kB	42.2 kB	✓
main-HASH.js gzip	28.4 kB	28.4 kB	✓
webpack-HASH.js gzip	1.45 kB	1.45 kB	✓
Overall change	72.3 kB	72.3 kB	✓

Legacy Client Bundles (polyfills)

	vercel/next.js canary	vercel/next.js pref/memory-retain-compiler	Change
polyfills-HASH.js gzip	31 kB	31 kB	✓
Overall change	31 kB	31 kB	✓

Client Pages

	vercel/next.js canary	vercel/next.js pref/memory-retain-compiler	Change
_app-HASH.js gzip	1.37 kB	1.37 kB	✓
_error-HASH.js gzip	194 B	194 B	✓
amp-HASH.js gzip	312 B	312 B	✓
css-HASH.js gzip	326 B	326 B	✓
dynamic-HASH.js gzip	2.38 kB	2.38 kB	✓
head-HASH.js gzip	350 B	350 B	✓
hooks-HASH.js gzip	635 B	635 B	✓
image-HASH.js gzip	4.49 kB	4.49 kB	✓
index-HASH.js gzip	263 B	263 B	✓
link-HASH.js gzip	1.87 kB	1.87 kB	✓
routerDirect..HASH.js gzip	321 B	321 B	✓
script-HASH.js gzip	383 B	383 B	✓
withRouter-HASH.js gzip	318 B	318 B	✓
85e02e95b279..7e3.css gzip	107 B	107 B	✓
Overall change	13.3 kB	13.3 kB	✓

Client Build Manifests

	vercel/next.js canary	vercel/next.js pref/memory-retain-compiler	Change
_buildManifest.js gzip	460 B	460 B	✓
Overall change	460 B	460 B	✓

Rendered Page Sizes

	vercel/next.js canary	vercel/next.js pref/memory-retain-compiler	Change
index.html gzip	533 B	533 B	✓
link.html gzip	546 B	546 B	✓
withRouter.html gzip	527 B	527 B	✓
Overall change	1.61 kB	1.61 kB	✓

---

Default Build with SWC (Decrease detected ✓)

General Overall increase ⚠️

	vercel/next.js canary	vercel/next.js pref/memory-retain-compiler	Change
buildDuration	19.3s	19.2s	-85ms
buildDurationCached	3.3s	3.2s	-66ms
nodeModulesSize	347 MB	347 MB	⚠️ +591 B

Page Load Tests Overall decrease ⚠️

	vercel/next.js canary	vercel/next.js pref/memory-retain-compiler	Change
/ failed reqs	0	0	✓
/ total time (seconds)	2.874	2.89	⚠️ +0.02
/ avg req/sec	869.84	865.14	⚠️ -4.7
/error-in-render failed reqs	0	0	✓
/error-in-render total time (seconds)	1.324	1.327	0
/error-in-render avg req/sec	1887.74	1884.42	⚠️ -3.32

Client Bundles (main, webpack, commons)

	vercel/next.js canary	vercel/next.js pref/memory-retain-compiler	Change
450.HASH.js gzip	179 B	179 B	✓
framework-HASH.js gzip	42.3 kB	42.3 kB	✓
main-HASH.js gzip	28.6 kB	28.6 kB	✓
webpack-HASH.js gzip	1.44 kB	1.44 kB	✓
Overall change	72.5 kB	72.5 kB	✓

Legacy Client Bundles (polyfills)

	vercel/next.js canary	vercel/next.js pref/memory-retain-compiler	Change
polyfills-HASH.js gzip	31 kB	31 kB	✓
Overall change	31 kB	31 kB	✓

Client Pages

	vercel/next.js canary	vercel/next.js pref/memory-retain-compiler	Change
_app-HASH.js gzip	1.35 kB	1.35 kB	✓
_error-HASH.js gzip	180 B	180 B	✓
amp-HASH.js gzip	305 B	305 B	✓
css-HASH.js gzip	321 B	321 B	✓
dynamic-HASH.js gzip	2.37 kB	2.37 kB	✓
head-HASH.js gzip	342 B	342 B	✓
hooks-HASH.js gzip	622 B	622 B	✓
image-HASH.js gzip	4.53 kB	4.53 kB	✓
index-HASH.js gzip	256 B	256 B	✓
link-HASH.js gzip	1.9 kB	1.9 kB	✓
routerDirect..HASH.js gzip	314 B	314 B	✓
script-HASH.js gzip	375 B	375 B	✓
withRouter-HASH.js gzip	309 B	309 B	✓
85e02e95b279..7e3.css gzip	107 B	107 B	✓
Overall change	13.3 kB	13.3 kB	✓

Client Build Manifests

	vercel/next.js canary	vercel/next.js pref/memory-retain-compiler	Change
_buildManifest.js gzip	458 B	458 B	✓
Overall change	458 B	458 B	✓

Rendered Page Sizes

	vercel/next.js canary	vercel/next.js pref/memory-retain-compiler	Change
index.html gzip	533 B	533 B	✓
link.html gzip	546 B	546 B	✓
withRouter.html gzip	528 B	528 B	✓
Overall change	1.61 kB	1.61 kB	✓

Commit: 704a6cd