experimental: css inlining #72195

gaojude · 2024-11-01T21:12:48Z

Introducing experimental flag inlineCSS. This supports both Webpack and Turbopack on App Router.

When the flag is enabled, all the places where we originally generate the <link> tag will instead be generating a <style> tag. The CSS precedence/deduping is maintained by React 19 automatically.

Note that this flag will apply to all CSS assets for now.

This is an optimization of LCP/FCP for websites that

have CSS size being constant as a function of interaction
fresh visits are common

This flag is experimental now, so please do not use at production.

ijjk · 2024-11-01T21:56:35Z

Tests Passed

ijjk · 2024-11-01T22:01:11Z

Stats from current PR

Default Build (Increase detected ⚠️)

General Overall increase ⚠️

	vercel/next.js canary	vercel/next.js jude/experimental-css-inline	Change
buildDuration	19.5s	15.8s	N/A
buildDurationCached	15s	14.2s	N/A
nodeModulesSize	404 MB	404 MB	⚠️ +22.9 kB
nextStartRea..uration (ms)	470ms	477ms	N/A

Client Bundles (main, webpack)

	vercel/next.js canary	vercel/next.js jude/experimental-css-inline	Change
0b69cffb-HASH.js gzip	52.6 kB	52.6 kB	N/A
1924.HASH.js gzip	169 B	169 B	✓
195-HASH.js gzip	46.5 kB	46.5 kB	N/A
8589-HASH.js gzip	5.27 kB	5.28 kB	N/A
framework-HASH.js gzip	57.4 kB	57.4 kB	N/A
main-app-HASH.js gzip	232 B	230 B	N/A
main-HASH.js gzip	33.1 kB	33.1 kB	N/A
webpack-HASH.js gzip	1.71 kB	1.71 kB	N/A
Overall change	169 B	169 B	✓

Legacy Client Bundles (polyfills)

	vercel/next.js canary	vercel/next.js jude/experimental-css-inline	Change
polyfills-HASH.js gzip	39.4 kB	39.4 kB	✓
Overall change	39.4 kB	39.4 kB	✓

Client Pages

	vercel/next.js canary	vercel/next.js jude/experimental-css-inline	Change
_app-HASH.js gzip	193 B	193 B	✓
_error-HASH.js gzip	192 B	190 B	N/A
amp-HASH.js gzip	510 B	510 B	✓
css-HASH.js gzip	341 B	343 B	N/A
dynamic-HASH.js gzip	1.84 kB	1.84 kB	N/A
edge-ssr-HASH.js gzip	266 B	266 B	✓
head-HASH.js gzip	362 B	364 B	N/A
hooks-HASH.js gzip	393 B	392 B	N/A
image-HASH.js gzip	4.42 kB	4.42 kB	N/A
index-HASH.js gzip	268 B	268 B	✓
link-HASH.js gzip	2.77 kB	2.77 kB	N/A
routerDirect..HASH.js gzip	328 B	327 B	N/A
script-HASH.js gzip	398 B	396 B	N/A
withRouter-HASH.js gzip	325 B	322 B	N/A
1afbb74e6ecf..834.css gzip	106 B	106 B	✓
Overall change	1.34 kB	1.34 kB	✓

Client Build Manifests

	vercel/next.js canary	vercel/next.js jude/experimental-css-inline	Change
_buildManifest.js gzip	746 B	749 B	N/A
Overall change	0 B	0 B	✓

Rendered Page Sizes

	vercel/next.js canary	vercel/next.js jude/experimental-css-inline	Change
index.html gzip	522 B	523 B	N/A
link.html gzip	538 B	537 B	N/A
withRouter.html gzip	520 B	519 B	N/A
Overall change	0 B	0 B	✓

Edge SSR bundle Size

	vercel/next.js canary	vercel/next.js jude/experimental-css-inline	Change
edge-ssr.js gzip	128 kB	128 kB	N/A
page.js gzip	199 kB	199 kB	N/A
Overall change	0 B	0 B	✓

Middleware size

	vercel/next.js canary	vercel/next.js jude/experimental-css-inline	Change
middleware-b..fest.js gzip	673 B	668 B	N/A
middleware-r..fest.js gzip	156 B	155 B	N/A
middleware.js gzip	30.9 kB	31 kB	N/A
edge-runtime..pack.js gzip	844 B	844 B	✓
Overall change	844 B	844 B	✓

Next Runtimes

	vercel/next.js canary	vercel/next.js jude/experimental-css-inline	Change
732-experime...dev.js gzip	322 B	322 B	✓
732.runtime.dev.js gzip	314 B	314 B	✓
app-page-exp...dev.js gzip	320 kB	320 kB	N/A
app-page-exp..prod.js gzip	123 kB	123 kB	N/A
app-page-tur..prod.js gzip	136 kB	136 kB	N/A
app-page-tur..prod.js gzip	131 kB	131 kB	N/A
app-page.run...dev.js gzip	310 kB	311 kB	N/A
app-page.run..prod.js gzip	119 kB	119 kB	N/A
app-route-ex...dev.js gzip	36 kB	36 kB	✓
app-route-ex..prod.js gzip	24.4 kB	24.4 kB	✓
app-route-tu..prod.js gzip	24.4 kB	24.4 kB	✓
app-route-tu..prod.js gzip	24.2 kB	24.2 kB	✓
app-route.ru...dev.js gzip	37.6 kB	37.6 kB	✓
app-route.ru..prod.js gzip	24.2 kB	24.2 kB	✓
pages-api-tu..prod.js gzip	9.57 kB	9.57 kB	✓
pages-api.ru...dev.js gzip	11.4 kB	11.4 kB	✓
pages-api.ru..prod.js gzip	9.56 kB	9.56 kB	✓
pages-turbo...prod.js gzip	21 kB	21 kB	✓
pages.runtim...dev.js gzip	26.6 kB	26.6 kB	✓
pages.runtim..prod.js gzip	21 kB	21 kB	✓
server.runti..prod.js gzip	916 kB	916 kB	N/A
Overall change	271 kB	271 kB	✓

build cache Overall increase ⚠️

	vercel/next.js canary	vercel/next.js jude/experimental-css-inline	Change
0.pack gzip	2.02 MB	2.02 MB	N/A
index.pack gzip	146 kB	148 kB	⚠️ +1.58 kB
Overall change	146 kB	148 kB	⚠️ +1.58 kB

Diff details

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Diff for image-HASH.js

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-      const _routercontextsharedruntime = __webpack_require__(5575);
+      const _getimgprops = __webpack_require__(8821);
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@@ -1024,12 +1024,12 @@
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Commit: 3ec0b7c

gaojude · 2024-11-20T01:31:57Z

crates/next-core/src/next_manifests/client_reference_manifest.rs

h/t to @bgw for authoring the Rust change

feedthejim · 2024-11-20T04:55:46Z

I think it'd be preferable to also introduce an opt in option to be able to only inline particular stylesheets rather than all of them

unstubbable

Great work! 🚀

Things I noticed while testing this:

HMR does not work with Turbopack (throws runtime error Error: No link element found for chunk static/chunks/app_global_aef7b9.css)
HMR works with Webpack, but a new style element is added for every edit, without removing the old ones. This means you can only add/overwrite styles; deleted styles will be preserved. It might also be a memory concern.
Source-mapping (apparently a Turbopack-only feature?) is broken. I guess we would need to add a prefix to the sourceMappingURL, now that it can't be resolved relative to the css file.

Maybe worth considering shipping this as a build-only feature first. Then you can tackle the dev issues in a follow-up.

packages/next/src/server/app-render/render-css-resource.tsx

packages/next/src/build/webpack/plugins/flight-manifest-plugin.ts

vercel · 2024-11-20T17:42:05Z

Notifying the following users due to files changed in this PR based on this repo's notify modifiers:

@timneutkens, @ijjk, @shuding, @huozhi:

packages/next/src/server/config.ts

gaojude · 2024-11-20T18:45:55Z

I think it'd be preferable to also introduce an opt in option to be able to only inline particular stylesheets rather than all of them

Per discussion: This is intended to be a niche use case. We’ll consider supporting selective inlining if we see significant demand for it. For now, this is limited to canary only, so it’s not something that should be adopted at scale.

gaojude · 2024-11-20T18:46:58Z

Great work! 🚀

Things I noticed while testing this:

HMR does not work with Turbopack (throws runtime error Error: No link element found for chunk static/chunks/app_global_aef7b9.css)

HMR works with Webpack, but a new style element is added for every edit, without removing the old ones. This means you can only add/overwrite styles; deleted styles will be preserved. It might also be a memory concern.

Source-mapping (apparently a Turbopack-only feature?) is broken. I guess we would need to add a prefix to the sourceMappingURL, now that it can't be resolved relative to the css file.

Maybe worth considering shipping this as a build-only feature first. Then you can tackle the dev issues in a follow-up.

Thank you for testing. I've taken your advice and narrowed the scope to "production-only". Agreed that we should revisit the dev experience of CSS inlining.

packages/next/src/build/webpack/plugins/flight-manifest-plugin.ts

Co-authored-by: Hendrik Liebau <mail@hendrik-liebau.de>

## Why? Add documentation for experimental `inlineCss`. ``` import type { NextConfig } from 'next' const nextConfig: NextConfig = { experimental: { inlineCss: true, }, } ``` - x-ref: #72195

philwolstenholme · 2024-11-22T12:52:30Z

I think it'd be preferable to also introduce an opt in option to be able to only inline particular stylesheets rather than all of them

Per discussion: This is intended to be a niche use case. We’ll consider supporting selective inlining if we see significant demand for it. For now, this is limited to canary only, so it’s not something that should be adopted at scale.

Having it all-or-nothing helps the 'improve FCP by removing all render-blocking CSS links' use case, because if a user selectively inlined some CSS files but not others there would still be a render-blocking pause while the browser fetched any non-inlined CSS. This way the user can't forget to inline a file accidentally, or someone on their team forgets to opt into inlining a new file and the benefits are lost.

In an ideal world what you'd want is an option where the non-inlined CSS is loaded asyncronously to avoid render-blocking, but then you're into critical CSS and FOUC (flash of unstyled content) territory and things get much more fiddly, especially with dynamic/CMS content affecting what content is shown and therefore what the critical CSS needs to cover.

It's +1 from me for keeping it all-or-nothing for now at least

## Why? Add documentation for experimental `inlineCss`. ``` import type { NextConfig } from 'next' const nextConfig: NextConfig = { experimental: { inlineCss: true, }, } ``` - x-ref: #72195

ijjk added created-by: Next.js team PRs by the Next.js team. type: next labels Nov 1, 2024

gaojude force-pushed the jude/experimental-css-inline branch 2 times, most recently from 7bac059 to e6cfb50 Compare November 1, 2024 21:43

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gaojude force-pushed the jude/experimental-css-inline branch from 28574e9 to 64cdf3c Compare November 1, 2024 21:53

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gaojude force-pushed the jude/experimental-css-inline branch 4 times, most recently from 6e77d34 to 4020192 Compare November 12, 2024 21:49

gaojude force-pushed the jude/experimental-css-inline branch 3 times, most recently from 4de36bd to 0c21888 Compare November 19, 2024 22:20

gaojude and others added 3 commits November 19, 2024 20:23

v1

3ac4dd3

polish

aeb7bc0

turbopack inline css

ccabae7

gaojude force-pushed the jude/experimental-css-inline branch from 0c21888 to ccabae7 Compare November 20, 2024 01:23

ijjk added the Turbopack Related to Turbopack with Next.js. label Nov 20, 2024

gaojude commented Nov 20, 2024

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h/t to @bgw for authoring the Rust change

polish

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gaojude force-pushed the jude/experimental-css-inline branch from f40768d to 32a1710 Compare November 20, 2024 01:32

gaojude marked this pull request as ready for review November 20, 2024 01:35

fix dedup

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gaojude requested review from bgw and huozhi November 20, 2024 04:42

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limit to production only, limit to canary only

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neat

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disable inline at source

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Update flight-manifest-plugin.ts

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Co-authored-by: Hendrik Liebau <mail@hendrik-liebau.de>

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gaojude merged commit 4d76f98 into canary Nov 20, 2024
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gaojude deleted the jude/experimental-css-inline branch November 20, 2024 22:03

samcx mentioned this pull request Nov 21, 2024

docs(next-config): add experimental inline css docs #73070

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experimental: css inlining (vercel#72195)

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experimental: css inlining (#72195)

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