experimental: css inlining

crates/next-api/src/app.rs

@@ -1190,6 +1190,7 @@ impl AppEndpoint {
                     ssr_chunking_context,
                     this.app_project.project().next_config(),
                     runtime,
+                    this.app_project.project().next_mode(),
                 )
                 .to_resolved()
                 .await?;

crates/next-core/src/next_config.rs

@@ -551,6 +551,7 @@ pub struct ExperimentalConfig {
     fully_specified: Option<bool>,
     gzip_size: Option<bool>,
 
+    pub inline_css: Option<bool>,
     instrumentation_hook: Option<bool>,
     client_trace_metadata: Option<Vec<String>>,
     large_page_data_bytes: Option<f64>,

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

@@ -4,7 +4,7 @@ use turbo_rcstr::RcStr;
 use turbo_tasks::{FxIndexSet, TryJoinIterExt, Value, ValueToString, Vc};
 use turbo_tasks_fs::{File, FileSystemPath};
 use turbopack_core::{
-    asset::AssetContent,
+    asset::{Asset, AssetContent},
     chunk::{
         availability_info::AvailabilityInfo, ChunkItem, ChunkItemExt, ChunkableModule,
         ChunkingContext, ModuleId as TurbopackModuleId,
@@ -14,8 +14,9 @@ use turbopack_core::{
 };
 use turbopack_ecmascript::utils::StringifyJs;
 
-use super::{ClientReferenceManifest, ManifestNode, ManifestNodeEntry, ModuleId};
+use super::{ClientReferenceManifest, CssResource, ManifestNode, ManifestNodeEntry, ModuleId};
 use crate::{
+    mode::NextMode,
     next_app::ClientReferencesChunks,
     next_client_reference::{ClientReferenceGraphResult, ClientReferenceType},
     next_config::NextConfig,
@@ -37,6 +38,7 @@ impl ClientReferenceManifest {
         ssr_chunking_context: Option<Vc<Box<dyn ChunkingContext>>>,
         next_config: Vc<NextConfig>,
         runtime: NextRuntime,
+        mode: Vc<NextMode>,
     ) -> Result<Vc<Box<dyn OutputAsset>>> {
         let mut entry_manifest: ClientReferenceManifest = Default::default();
         let mut references = FxIndexSet::default();
@@ -241,40 +243,66 @@ impl ClientReferenceManifest {
         for (server_component, client_chunks) in
             client_references_chunks.layout_segment_client_chunks.iter()
         {
-            let client_chunks = &client_chunks.await?;
-
-            let client_chunks_paths = client_chunks
-                .iter()
-                .map(|chunk| chunk.ident().path())
-                .try_join()
-                .await?;
-
             let server_component_name = server_component
                 .server_path()
                 .with_extension("".into())
                 .to_string()
                 .await?;
 
-            let entry_css_files = entry_manifest
-                .entry_css_files
-                .entry(server_component_name.clone_value())
-                .or_default();
-
+            let mut entry_css_files_with_chunk = Vec::new();
             let entry_js_files = entry_manifest
                 .entry_js_files
                 .entry(server_component_name.clone_value())
                 .or_default();
 
-            for chunk_path in client_chunks_paths {
+            let client_chunks = &client_chunks.await?;
+            let client_chunks_with_path = client_chunks
+                .iter()
+                .map(|chunk| async move { Ok((chunk, chunk.ident().path().await?)) })
+                .try_join()
+                .await?;
+
+            for (chunk, chunk_path) in client_chunks_with_path {
                 if let Some(path) = client_relative_path.get_path_to(&chunk_path) {
                     let path = path.into();
                     if chunk_path.extension_ref() == Some("css") {
-                        entry_css_files.insert(path);
+                        entry_css_files_with_chunk.push((path, chunk));
                     } else {
                         entry_js_files.insert(path);
                     }
                 }
             }
+
+            let inlined = next_config.await?.experimental.inline_css.unwrap_or(false)
+                && mode.await?.is_production();
+            let entry_css_files_vec = entry_css_files_with_chunk
+                .into_iter()
+                .map(|(path, chunk)| async {
+                    let content = if inlined {
+                        if let Some(content_file) =
+                            chunk.content().file_content().await?.as_content()
+                        {
+                            Some(content_file.content().to_str()?.into())
+                        } else {
+                            Some("".into())
+                        }
+                    } else {
+                        None
+                    };
+                    Ok(CssResource {
+                        path,
+                        inlined,
+                        content,
+                    })
+                })
+                .try_join()
+                .await?;
+
+            let entry_css_files = entry_manifest
+                .entry_css_files
+                .entry(server_component_name.clone_value())
+                .or_default();
+            entry_css_files.extend(entry_css_files_vec);
         }
 
         let client_reference_manifest_json = serde_json::to_string(&entry_manifest).unwrap();

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

@@ -355,12 +355,20 @@ pub struct ClientReferenceManifest {
     pub edge_rsc_module_mapping: HashMap<ModuleId, ManifestNode>,
     /// Mapping of server component path to required CSS client chunks.
     #[serde(rename = "entryCSSFiles")]
-    pub entry_css_files: HashMap<RcStr, FxIndexSet<RcStr>>,
+    pub entry_css_files: HashMap<RcStr, FxIndexSet<CssResource>>,
     /// Mapping of server component path to required JS client chunks.
     #[serde(rename = "entryJSFiles")]
     pub entry_js_files: HashMap<RcStr, FxIndexSet<RcStr>>,
 }
 
+#[derive(Serialize, Debug, Clone, Eq, Hash, PartialEq)]
+pub struct CssResource {
+    pub path: RcStr,
+    pub inlined: bool,
+    #[serde(skip_serializing_if = "Option::is_none")]
+    pub content: Option<RcStr>,
+}
+
 #[derive(Serialize, Default, Debug)]
 #[serde(rename_all = "camelCase")]
 pub struct ModuleLoading {

packages/next/src/build/webpack-config.ts

@@ -1895,6 +1895,7 @@ export default async function getBaseWebpackConfig(
           ? new ClientReferenceManifestPlugin({
               dev,
               appDir,
+              experimentalInlineCss: !!config.experimental.inlineCss,
             })
           : new FlightClientEntryPlugin({
               appDir,

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

@@ -32,6 +32,7 @@ import type { ModuleInfo } from './flight-client-entry-plugin'
 interface Options {
   dev: boolean
   appDir: string
+  experimentalInlineCss: boolean
 }
 
 /**
@@ -83,6 +84,19 @@ export interface ClientReferenceManifestForRsc {
   }
 }
 
+export type CssResource = InlinedCssFile | UninlinedCssFile
+
+interface InlinedCssFile {
+  path: string
+  inlined: true
+  content: string
+}
+
+interface UninlinedCssFile {
+  path: string
+  inlined: false
+}
+
 export interface ClientReferenceManifest extends ClientReferenceManifestForRsc {
   readonly moduleLoading: {
     prefix: string
@@ -95,7 +109,7 @@ export interface ClientReferenceManifest extends ClientReferenceManifestForRsc {
     [moduleId: string]: ManifestNode
   }
   entryCSSFiles: {
-    [entry: string]: string[]
+    [entry: string]: CssResource[]
   }
   entryJSFiles?: {
     [entry: string]: string[]
@@ -200,11 +214,13 @@ export class ClientReferenceManifestPlugin {
   dev: Options['dev'] = false
   appDir: Options['appDir']
   appDirBase: string
+  experimentalInlineCss: Options['experimentalInlineCss']
 
   constructor(options: Options) {
     this.dev = options.dev
     this.appDir = options.appDir
     this.appDirBase = path.dirname(this.appDir) + path.sep
+    this.experimentalInlineCss = options.experimentalInlineCss
   }
 
   apply(compiler: webpack.Compiler) {
@@ -296,9 +312,29 @@ export class ClientReferenceManifestPlugin {
         /[\\/]/g,
         path.sep
       )
+
       manifest.entryCSSFiles[chunkEntryName] = entrypoint
         .getFiles()
         .filter((f) => !f.startsWith('static/css/pages/') && f.endsWith('.css'))
+        .map((file) => {
+          const source = compilation.assets[file].source()
+          if (
+            this.experimentalInlineCss &&
+            // Inline CSS currently does not work properly with HMR, so we only
+            // inline CSS in production.
+            !this.dev
+          ) {
+            return {
+              inlined: true,
+              path: file,
+              content: typeof source === 'string' ? source : source.toString(),
+            }
+          }
+          return {
+            inlined: false,
+            path: file,
+          }
+        })
 
       const requiredChunks = getAppPathRequiredChunks(entrypoint, rootMainFiles)
       const recordModule = (modId: ModuleId, mod: webpack.NormalModule) => {

packages/next/src/export/index.ts

@@ -358,6 +358,7 @@ async function exportAppImpl(
       expireTime: nextConfig.expireTime,
       after: nextConfig.experimental.after ?? false,
       dynamicIO: nextConfig.experimental.dynamicIO ?? false,
+      inlineCss: nextConfig.experimental.inlineCss ?? false,
     },
     reactMaxHeadersLength: nextConfig.reactMaxHeadersLength,
   }

packages/next/src/server/app-render/create-component-styles-and-scripts.tsx

@@ -4,6 +4,7 @@ import { getLinkAndScriptTags } from './get-css-inlined-link-tags'
 import type { AppRenderContext } from './app-render'
 import { getAssetQueryString } from './get-asset-query-string'
 import { encodeURIPath } from '../../shared/lib/encode-uri-path'
+import { renderCssResource } from './render-css-resource'
 
 export async function createComponentStylesAndScripts({
   filePath,
@@ -18,40 +19,14 @@ export async function createComponentStylesAndScripts({
   injectedJS: Set<string>
   ctx: AppRenderContext
 }): Promise<[React.ComponentType<any>, React.ReactNode, React.ReactNode]> {
-  const { styles: cssHrefs, scripts: jsHrefs } = getLinkAndScriptTags(
+  const { styles: entryCssFiles, scripts: jsHrefs } = getLinkAndScriptTags(
     ctx.clientReferenceManifest,
     filePath,
     injectedCSS,
     injectedJS
   )
 
-  const styles = cssHrefs
-    ? cssHrefs.map((href, index) => {
-        const fullHref = `${ctx.assetPrefix}/_next/${encodeURIPath(
-          href
-        )}${getAssetQueryString(ctx, true)}`
-
-        // `Precedence` is an opt-in signal for React to handle resource
-        // loading and deduplication, etc. It's also used as the key to sort
-        // resources so they will be injected in the correct order.
-        // During HMR, it's critical to use different `precedence` values
-        // for different stylesheets, so their order will be kept.
-        // https://github.com/facebook/react/pull/25060
-        const precedence =
-          process.env.NODE_ENV === 'development' ? 'next_' + href : 'next'
-
-        return (
-          <link
-            rel="stylesheet"
-            href={fullHref}
-            // @ts-ignore
-            precedence={precedence}
-            crossOrigin={ctx.renderOpts.crossOrigin}
-            key={`style-${index}`}
-          />
-        )
-      })
-    : null
+  const styles = renderCssResource(entryCssFiles, ctx)
 
   const scripts = jsHrefs
     ? jsHrefs.map((href, index) => (

packages/next/src/server/app-render/get-css-inlined-link-tags.tsx

@@ -1,4 +1,7 @@
-import type { ClientReferenceManifest } from '../../build/webpack/plugins/flight-manifest-plugin'
+import type {
+  ClientReferenceManifest,
+  CssResource,
+} from '../../build/webpack/plugins/flight-manifest-plugin'
 import type { DeepReadonly } from '../../shared/lib/deep-readonly'
 
 /**
@@ -10,9 +13,9 @@ export function getLinkAndScriptTags(
   injectedCSS: Set<string>,
   injectedScripts: Set<string>,
   collectNewImports?: boolean
-): { styles: string[]; scripts: string[] } {
+): { styles: CssResource[]; scripts: string[] } {
   const filePathWithoutExt = filePath.replace(/\.[^.]+$/, '')
-  const cssChunks = new Set<string>()
+  const cssChunks = new Set<CssResource>()
   const jsChunks = new Set<string>()
 
   const entryCSSFiles =
@@ -21,12 +24,12 @@ export function getLinkAndScriptTags(
     clientReferenceManifest.entryJSFiles?.[filePathWithoutExt] ?? []
 
   if (entryCSSFiles) {
-    for (const file of entryCSSFiles) {
-      if (!injectedCSS.has(file)) {
+    for (const css of entryCSSFiles) {
+      if (!injectedCSS.has(css.path)) {
         if (collectNewImports) {
-          injectedCSS.add(file)
+          injectedCSS.add(css.path)
         }
-        cssChunks.add(file)
+        cssChunks.add(css)
       }
     }
   }

packages/next/src/server/app-render/get-layer-assets.tsx

@@ -5,6 +5,7 @@ import type { AppRenderContext } from './app-render'
 import { getAssetQueryString } from './get-asset-query-string'
 import { encodeURIPath } from '../../shared/lib/encode-uri-path'
 import type { PreloadCallbacks } from './types'
+import { renderCssResource } from './render-css-resource'
 
 export function getLayerAssets({
   ctx,
@@ -72,47 +73,7 @@ export function getLayerAssets({
     }
   }
 
-  const styles = styleTags
-    ? styleTags.map((href, index) => {
-        // In dev, Safari and Firefox will cache the resource during HMR:
-        // - https://github.com/vercel/next.js/issues/5860
-        // - https://bugs.webkit.org/show_bug.cgi?id=187726
-        // Because of this, we add a `?v=` query to bypass the cache during
-        // development. We need to also make sure that the number is always
-        // increasing.
-        const fullHref = `${ctx.assetPrefix}/_next/${encodeURIPath(
-          href
-        )}${getAssetQueryString(ctx, true)}`
-
-        // `Precedence` is an opt-in signal for React to handle resource
-        // loading and deduplication, etc. It's also used as the key to sort
-        // resources so they will be injected in the correct order.
-        // During HMR, it's critical to use different `precedence` values
-        // for different stylesheets, so their order will be kept.
-        // https://github.com/facebook/react/pull/25060
-        const precedence =
-          process.env.NODE_ENV === 'development' ? 'next_' + href : 'next'
-
-        preloadCallbacks.push(() => {
-          ctx.componentMod.preloadStyle(
-            fullHref,
-            ctx.renderOpts.crossOrigin,
-            ctx.nonce
-          )
-        })
-        return (
-          <link
-            rel="stylesheet"
-            href={fullHref}
-            // @ts-ignore
-            precedence={precedence}
-            crossOrigin={ctx.renderOpts.crossOrigin}
-            key={index}
-            nonce={ctx.nonce}
-          />
-        )
-      })
-    : []
+  const styles = renderCssResource(styleTags, ctx, preloadCallbacks)
 
   const scripts = scriptTags
     ? scriptTags.map((href, index) => {