feature: configuration for css inlining behavior (#6659)

* feature(inline stylesheets): implement as experimental

* test: rename css-inline -> css-import-as-inline

* test(content collections): add de-duplication of css

* test: add new suite for inlineStylesheets configuration

* fix(inline stylesheets): did not act on propagated styles

* hack(inline stylesheets testing): duplicate fixtures

Content collections reuses build data across multiple fixture.builds, even though a configuration change may have changed it.
Duplicating fixtures avoids usage of the stale cache.
https://cdn.discordapp.com/attachments/1039830843440504872/1097795182340092024/Screenshot_87_colored.png

* refactor(css plugin): reduce nesting

* optimization(css rendering): merge <style> tags

Chrome, but not Safari or Firefox, is slower to match rules when they are split across multiple files or style tags.
https://nolanlawson.com/2022/06/22/style-scoping-versus-shadow-dom-which-is-fastest/

Having the abiility to inline stylesheets opens us up to this optimization.
Ideally, it would extend to propagated styles, but that ended up being a rabbit hole.

* typedocs(inlineStylesheets config): ensure consistency

Co-authored-by: Sarah Rainsberger <sarah@rainsberger.ca>

* chore(build internals): update comment

* correct minor mistake in test

* test(inline stylesheets): unique package names for duplicate fixtures

* refactor(css build plugin): maps -> records

* refactor(css build plugin): remove use of spread operator

---------

Co-authored-by: Sarah Rainsberger <sarah@rainsberger.ca>

.changeset/friendly-fishes-sing.md

@@ -0,0 +1,5 @@
+---
+'astro': minor
+---
+
+Implement Inline Stylesheets RFC as experimental

packages/astro/src/@types/astro.ts

@@ -1036,6 +1036,26 @@ export interface AstroUserConfig {
 		 */
 		assets?: boolean;
 
+		/**
+		 * @docs
+		 * @name experimental.inlineStylesheets
+		 * @type {('always' | 'auto' | 'never')}
+		 * @default `never`
+		 * @description
+		 * Control whether styles are sent to the browser in a separate css file or inlined into <style> tags. Choose from the following options:
+		 *  - `'always'` - all styles are inlined into <style> tags
+		 *  - `'auto'` - only stylesheets smaller than `ViteConfig.build.assetsInlineLimit` (default: 4kb) are inlined. Otherwise, styles are sent in external stylesheets.
+		 *  - `'never'` - all styles are sent in external stylesheets
+		 *
+		 * ```js
+		 * {
+		 * 	experimental: {
+		 *		inlineStylesheets: `auto`,
+		 * 	},
+		 * }
+		 */
+		inlineStylesheets?: 'always' | 'auto' | 'never';
+
 		/**
 		 * @docs
 		 * @name experimental.middleware

packages/astro/src/content/runtime.ts

@@ -6,7 +6,6 @@ import {
 	createHeadAndContent,
 	renderComponent,
 	renderScriptElement,
-	renderStyleElement,
 	renderTemplate,
 	renderUniqueStylesheet,
 	unescapeHTML,
@@ -152,13 +151,21 @@ async function render({
 				links = '',
 				scripts = '';
 			if (Array.isArray(collectedStyles)) {
-				styles = collectedStyles.map((style: any) => renderStyleElement(style)).join('');
+				styles = collectedStyles
+					.map((style: any) => {
+						return renderUniqueStylesheet(result, {
+							type: 'inline',
+							content: style,
+						});
+					})
+					.join('');
 			}
 			if (Array.isArray(collectedLinks)) {
 				links = collectedLinks
 					.map((link: any) => {
 						return renderUniqueStylesheet(result, {
-							href: prependForwardSlash(link),
+							type: 'external',
+							src: prependForwardSlash(link),
 						});
 					})
 					.join('');

packages/astro/src/content/vite-plugin-content-assets.ts

@@ -123,7 +123,8 @@ export function astroConfigBuildPlugin(
 						chunk.type === 'chunk' &&
 						(chunk.code.includes(LINKS_PLACEHOLDER) || chunk.code.includes(SCRIPTS_PLACEHOLDER))
 					) {
-						let entryCSS = new Set<string>();
+						let entryStyles = new Set<string>();
+						let entryLinks = new Set<string>();
 						let entryScripts = new Set<string>();
 
 						for (const id of Object.keys(chunk.modules)) {
@@ -137,7 +138,8 @@ export function astroConfigBuildPlugin(
 									const _entryScripts = pageData.propagatedScripts?.get(id);
 									if (_entryCss) {
 										for (const value of _entryCss) {
-											entryCSS.add(value);
+											if (value.type === 'inline') entryStyles.add(value.content);
+											if (value.type === 'external') entryLinks.add(value.src);
 										}
 									}
 									if (_entryScripts) {
@@ -150,10 +152,16 @@ export function astroConfigBuildPlugin(
 						}
 
 						let newCode = chunk.code;
-						if (entryCSS.size) {
+						if (entryStyles.size) {
+							newCode = newCode.replace(
+								JSON.stringify(STYLES_PLACEHOLDER),
+								JSON.stringify(Array.from(entryStyles))
+							);
+						}
+						if (entryLinks.size) {
 							newCode = newCode.replace(
 								JSON.stringify(LINKS_PLACEHOLDER),
-								JSON.stringify(Array.from(entryCSS).map(prependBase))
+								JSON.stringify(Array.from(entryLinks).map(prependBase))
 							);
 						}
 						if (entryScripts.size) {

packages/astro/src/core/app/index.ts

@@ -24,7 +24,7 @@ import {
 import { RouteCache } from '../render/route-cache.js';
 import {
 	createAssetLink,
-	createLinkStylesheetElementSet,
+	createStylesheetElementSet,
 	createModuleScriptElement,
 } from '../render/ssr-element.js';
 import { matchRoute } from '../routing/match.js';
@@ -180,7 +180,9 @@ export class App {
 		const url = new URL(request.url);
 		const pathname = '/' + this.removeBase(url.pathname);
 		const info = this.#routeDataToRouteInfo.get(routeData!)!;
-		const links = createLinkStylesheetElementSet(info.links);
+		// may be used in the future for handling rel=modulepreload, rel=icon, rel=manifest etc.
+		const links = new Set<never>();
+		const styles = createStylesheetElementSet(info.styles);
 
 		let scripts = new Set<SSRElement>();
 		for (const script of info.scripts) {
@@ -203,6 +205,7 @@ export class App {
 				pathname,
 				componentMetadata: this.#manifest.componentMetadata,
 				scripts,
+				styles,
 				links,
 				route: routeData,
 				status,

packages/astro/src/core/app/types.ts

@@ -11,6 +11,10 @@ import type {
 
 export type ComponentPath = string;
 
+export type StylesheetAsset =
+	| { type: 'inline'; content: string }
+	| { type: 'external'; src: string };
+
 export interface RouteInfo {
 	routeData: RouteData;
 	file: string;
@@ -21,6 +25,7 @@ export interface RouteInfo {
 		// Hoisted
 		| { type: 'inline' | 'external'; value: string }
 	)[];
+	styles: StylesheetAsset[];
 }
 
 export type SerializedRouteInfo = Omit<RouteInfo, 'routeData'> & {

packages/astro/src/core/build/generate.ts

@@ -40,15 +40,25 @@ import { createEnvironment, createRenderContext, renderPage } from '../render/in
 import { callGetStaticPaths } from '../render/route-cache.js';
 import {
 	createAssetLink,
-	createLinkStylesheetElementSet,
+	createStylesheetElementSet,
 	createModuleScriptsSet,
 } from '../render/ssr-element.js';
 import { createRequest } from '../request.js';
 import { matchRoute } from '../routing/match.js';
 import { getOutputFilename } from '../util.js';
 import { getOutDirWithinCwd, getOutFile, getOutFolder } from './common.js';
-import { eachPageData, getPageDataByComponent, sortedCSS } from './internal.js';
-import type { PageBuildData, SingleFileBuiltModule, StaticBuildOptions } from './types';
+import {
+	eachPageData,
+	getPageDataByComponent,
+	cssOrder,
+	mergeInlineCss,
+} from './internal.js';
+import type {
+	PageBuildData,
+	SingleFileBuiltModule,
+	StaticBuildOptions,
+	StylesheetAsset,
+} from './types';
 import { getTimeStat } from './util.js';
 
 function shouldSkipDraft(pageModule: ComponentInstance, settings: AstroSettings): boolean {
@@ -161,8 +171,14 @@ async function generatePage(
 	const renderers = ssrEntry.renderers;
 
 	const pageInfo = getPageDataByComponent(internals, pageData.route.component);
-	const linkIds: string[] = sortedCSS(pageData);
+
+	// may be used in the future for handling rel=modulepreload, rel=icon, rel=manifest etc.
+	const linkIds: [] = [];
 	const scripts = pageInfo?.hoistedScript ?? null;
+	const styles = pageData.styles
+		.sort(cssOrder)
+		.map(({ sheet }) => sheet)
+		.reduce(mergeInlineCss, []);
 
 	const pageModule = ssrEntry.pageMap?.get(pageData.component);
 	const middleware = ssrEntry.middleware;
@@ -183,6 +199,7 @@ async function generatePage(
 		internals,
 		linkIds,
 		scripts,
+		styles,
 		mod: pageModule,
 		renderers,
 	};
@@ -273,6 +290,7 @@ interface GeneratePathOptions {
 	internals: BuildInternals;
 	linkIds: string[];
 	scripts: { type: 'inline' | 'external'; value: string } | null;
+	styles: StylesheetAsset[];
 	mod: ComponentInstance;
 	renderers: SSRLoadedRenderer[];
 }
@@ -341,7 +359,15 @@ async function generatePath(
 	middleware?: AstroMiddlewareInstance<unknown>
 ) {
 	const { settings, logging, origin, routeCache } = opts;
-	const { mod, internals, linkIds, scripts: hoistedScripts, pageData, renderers } = gopts;
+	const {
+		mod,
+		internals,
+		linkIds,
+		scripts: hoistedScripts,
+		styles: _styles,
+		pageData,
+		renderers,
+	} = gopts;
 
 	// This adds the page name to the array so it can be shown as part of stats.
 	if (pageData.route.type === 'page') {
@@ -350,13 +376,15 @@ async function generatePath(
 
 	debug('build', `Generating: ${pathname}`);
 
-	const links = createLinkStylesheetElementSet(
-		linkIds,
+	// may be used in the future for handling rel=modulepreload, rel=icon, rel=manifest etc.
+	const links = new Set<never>();
+	const scripts = createModuleScriptsSet(
+		hoistedScripts ? [hoistedScripts] : [],
 		settings.config.base,
 		settings.config.build.assetsPrefix
 	);
-	const scripts = createModuleScriptsSet(
-		hoistedScripts ? [hoistedScripts] : [],
+	const styles = createStylesheetElementSet(
+		_styles,
 		settings.config.base,
 		settings.config.build.assetsPrefix
 	);
@@ -431,6 +459,7 @@ async function generatePath(
 		request: createRequest({ url, headers: new Headers(), logging, ssr }),
 		componentMetadata: internals.componentMetadata,
 		scripts,
+		styles,
 		links,
 		route: pageData.route,
 		env,

packages/astro/src/core/build/internal.ts

@@ -1,5 +1,5 @@
 import type { Rollup } from 'vite';
-import type { PageBuildData, ViteID } from './types';
+import type { PageBuildData, StylesheetAsset, ViteID } from './types';
 
 import type { SSRResult } from '../../@types/astro';
 import type { PageOptions } from '../../vite-plugin-astro/types';
@@ -224,39 +224,56 @@ export function hasPrerenderedPages(internals: BuildInternals) {
 	return false;
 }
 
+interface OrderInfo {
+	depth: number;
+	order: number;
+}
+
 /**
  * Sort a page's CSS by depth. A higher depth means that the CSS comes from shared subcomponents.
  * A lower depth means it comes directly from the top-level page.
- * The return of this function is an array of CSS paths, with shared CSS on top
- * and page-level CSS on bottom.
+ * Can be used to sort stylesheets so that shared rules come first
+ * and page-specific rules come after.
  */
-export function sortedCSS(pageData: PageBuildData) {
-	return Array.from(pageData.css)
-		.sort((a, b) => {
-			let depthA = a[1].depth,
-				depthB = b[1].depth,
-				orderA = a[1].order,
-				orderB = b[1].order;
-
-			if (orderA === -1 && orderB >= 0) {
-				return 1;
-			} else if (orderB === -1 && orderA >= 0) {
-				return -1;
-			} else if (orderA > orderB) {
-				return 1;
-			} else if (orderA < orderB) {
-				return -1;
-			} else {
-				if (depthA === -1) {
-					return -1;
-				} else if (depthB === -1) {
-					return 1;
-				} else {
-					return depthA > depthB ? -1 : 1;
-				}
-			}
-		})
-		.map(([id]) => id);
+export function cssOrder(a: OrderInfo, b: OrderInfo) {
+	let depthA = a.depth,
+		depthB = b.depth,
+		orderA = a.order,
+		orderB = b.order;
+
+	if (orderA === -1 && orderB >= 0) {
+		return 1;
+	} else if (orderB === -1 && orderA >= 0) {
+		return -1;
+	} else if (orderA > orderB) {
+		return 1;
+	} else if (orderA < orderB) {
+		return -1;
+	} else {
+		if (depthA === -1) {
+			return -1;
+		} else if (depthB === -1) {
+			return 1;
+		} else {
+			return depthA > depthB ? -1 : 1;
+		}
+	}
+}
+
+export function mergeInlineCss(
+	acc: Array<StylesheetAsset>,
+	current: StylesheetAsset
+): Array<StylesheetAsset> {
+	const lastAdded = acc.at(acc.length - 1);
+	const lastWasInline = lastAdded?.type === 'inline';
+	const currentIsInline = current?.type === 'inline';
+	if (lastWasInline && currentIsInline) {
+		const merged = { type: 'inline' as const, content: lastAdded.content + current.content };
+		acc[acc.length - 1] = merged;
+		return acc;
+	}
+	acc.push(current)
+	return acc;
 }
 
 export function isHoistedScript(internals: BuildInternals, id: string): boolean {

packages/astro/src/core/build/page-data.ts

@@ -53,7 +53,7 @@ export async function collectPagesData(
 				component: route.component,
 				route,
 				moduleSpecifier: '',
-				css: new Map(),
+				styles: [],
 				propagatedStyles: new Map(),
 				propagatedScripts: new Map(),
 				hoistedScript: undefined,
@@ -76,7 +76,7 @@ export async function collectPagesData(
 			component: route.component,
 			route,
 			moduleSpecifier: '',
-			css: new Map(),
+			styles: [],
 			propagatedStyles: new Map(),
 			propagatedScripts: new Map(),
 			hoistedScript: undefined,