allow to provide postcss plugin options as a string

[sokra]

fixes #35117

@balazsorban44 this needs a test case

Bug

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

[nicolas-cusan]

Is there anything that I can do to speed this up? Would be great to see this merged as it is currently a blocker for a project I am working on.

[ijjk]

Stats from current PR

Default Build (Increase detected ⚠️)

General Overall increase ⚠️

	vercel/next.js canary	vercel/next.js bugfix/postcss-options-as-string	Change
buildDuration	18.1s	18.6s	⚠️ +414ms
buildDurationCached	7.3s	7.2s	-61ms
nodeModulesSize	478 MB	478 MB	⚠️ +72 B

Page Load Tests Overall increase ✓

	vercel/next.js canary	vercel/next.js bugfix/postcss-options-as-string	Change
/ failed reqs	0	0	✓
/ total time (seconds)	3.745	3.753	⚠️ +0.01
/ avg req/sec	667.56	666.08	⚠️ -1.48
/error-in-render failed reqs	0	0	✓
/error-in-render total time (seconds)	1.585	1.558	-0.03
/error-in-render avg req/sec	1577.58	1604.29	+26.71

Client Bundles (main, webpack)

	vercel/next.js canary	vercel/next.js bugfix/postcss-options-as-string	Change
925.HASH.js gzip	179 B	179 B	✓
framework-HASH.js gzip	42 kB	42 kB	✓
main-HASH.js gzip	28 kB	28 kB	✓
webpack-HASH.js gzip	1.44 kB	1.44 kB	✓
Overall change	71.7 kB	71.7 kB	✓

Legacy Client Bundles (polyfills)

	vercel/next.js canary	vercel/next.js bugfix/postcss-options-as-string	Change
polyfills-HASH.js gzip	31 kB	31 kB	✓
Overall change	31 kB	31 kB	✓

Client Pages

	vercel/next.js canary	vercel/next.js bugfix/postcss-options-as-string	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	3.05 kB	3.05 kB	✓
head-HASH.js gzip	351 B	351 B	✓
hooks-HASH.js gzip	920 B	920 B	✓
image-HASH.js gzip	5.64 kB	5.64 kB	✓
index-HASH.js gzip	263 B	263 B	✓
link-HASH.js gzip	2.32 kB	2.32 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	15.9 kB	15.9 kB	✓

Client Build Manifests

	vercel/next.js canary	vercel/next.js bugfix/postcss-options-as-string	Change
_buildManifest.js gzip	459 B	459 B	✓
Overall change	459 B	459 B	✓

Rendered Page Sizes

	vercel/next.js canary	vercel/next.js bugfix/postcss-options-as-string	Change
index.html gzip	531 B	531 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 (Increase detected ⚠️)

General Overall increase ⚠️

	vercel/next.js canary	vercel/next.js bugfix/postcss-options-as-string	Change
buildDuration	21.4s	20.9s	-523ms
buildDurationCached	7.2s	7.3s	⚠️ +32ms
nodeModulesSize	478 MB	478 MB	⚠️ +72 B

Page Load Tests Overall increase ✓

	vercel/next.js canary	vercel/next.js bugfix/postcss-options-as-string	Change
/ failed reqs	0	0	✓
/ total time (seconds)	3.798	3.799	0
/ avg req/sec	658.26	658.13	⚠️ -0.13
/error-in-render failed reqs	0	0	✓
/error-in-render total time (seconds)	1.637	1.62	-0.02
/error-in-render avg req/sec	1527.53	1543.51	+15.98

Client Bundles (main, webpack)

	vercel/next.js canary	vercel/next.js bugfix/postcss-options-as-string	Change
925.HASH.js gzip	178 B	178 B	✓
framework-HASH.js gzip	42.3 kB	42.3 kB	✓
main-HASH.js gzip	28.3 kB	28.3 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	vercel/next.js bugfix/postcss-options-as-string	Change
polyfills-HASH.js gzip	31 kB	31 kB	✓
Overall change	31 kB	31 kB	✓

Client Pages

	vercel/next.js canary	vercel/next.js bugfix/postcss-options-as-string	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	325 B	325 B	✓
dynamic-HASH.js gzip	3.03 kB	3.03 kB	✓
head-HASH.js gzip	351 B	351 B	✓
hooks-HASH.js gzip	921 B	921 B	✓
image-HASH.js gzip	5.7 kB	5.7 kB	✓
index-HASH.js gzip	261 B	261 B	✓
link-HASH.js gzip	2.38 kB	2.38 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	15.9 kB	15.9 kB	✓

Client Build Manifests

	vercel/next.js canary	vercel/next.js bugfix/postcss-options-as-string	Change
_buildManifest.js gzip	459 B	459 B	✓
Overall change	459 B	459 B	✓

Rendered Page Sizes

	vercel/next.js canary	vercel/next.js bugfix/postcss-options-as-string	Change
index.html gzip	531 B	531 B	✓
link.html gzip	544 B	544 B	✓
withRouter.html gzip	527 B	527 B	✓
Overall change	1.6 kB	1.6 kB	✓

Commit: 684e58d