From 700fad192edef1f5d4681d714d3eaebbd77eab95 Mon Sep 17 00:00:00 2001
From: Divyansh Singh <40380293+brc-dd@users.noreply.github.com>
Date: Sun, 16 Jul 2023 19:32:07 +0530
Subject: [PATCH] feat(build): add `metaChunk` option to extract metadata to
 separate chunk (#2626)

Co-authored-by: Bojan Rajh <b.rajh@shopware.com>
---
 src/node/build/build.ts  | 69 ++++++++++++++++++++++++++++++++--------
 src/node/build/render.ts | 30 +++++++----------
 src/node/config.ts       |  1 +
 src/node/siteConfig.ts   |  7 ++++
 4 files changed, 74 insertions(+), 33 deletions(-)

diff --git a/src/node/build/build.ts b/src/node/build/build.ts
index ed71ffc3..2d778b70 100644
--- a/src/node/build/build.ts
+++ b/src/node/build/build.ts
@@ -1,3 +1,4 @@
+import { createHash } from 'crypto'
 import fs from 'fs-extra'
 import { createRequire } from 'module'
 import ora from 'ora'
@@ -7,9 +8,9 @@ import { rimraf } from 'rimraf'
 import type { OutputAsset, OutputChunk } from 'rollup'
 import { pathToFileURL } from 'url'
 import type { BuildOptions } from 'vite'
-import { resolveConfig } from '../config'
-import type { HeadConfig } from '../shared'
-import { serializeFunctions } from '../utils/fnSerialize'
+import { resolveConfig, type SiteConfig } from '../config'
+import { slash, type HeadConfig } from '../shared'
+import { deserializeFunctions, serializeFunctions } from '../utils/fnSerialize'
 import { bundle, failMark, okMark } from './bundle'
 import { renderPage } from './render'
 
@@ -79,6 +80,8 @@ export async function build(
             chunk.moduleIds.some((id) => id.includes('client/theme-default'))
         )
 
+      const metadataScript = generateMetadataScript(pageToHashMap, siteConfig)
+
       if (isDefaultTheme) {
         const fontURL = assets.find((file) =>
           /inter-roman-latin\.\w+\.woff2/.test(file)
@@ -97,15 +100,6 @@ export async function build(
         }
       }
 
-      // We embed the hash map and site config strings into each page directly
-      // so that it doesn't alter the main chunk's hash on every build.
-      // It's also embedded as a string and JSON.parsed from the client because
-      // it's faster than embedding as JS object literal.
-      const hashMapString = JSON.stringify(JSON.stringify(pageToHashMap))
-      const siteDataString = JSON.stringify(
-        JSON.stringify(serializeFunctions({ ...siteConfig.site, head: [] }))
-      )
-
       await Promise.all(
         ['404.md', ...siteConfig.pages]
           .map((page) => siteConfig.rewrites.map[page] || page)
@@ -119,8 +113,7 @@ export async function build(
               cssChunk,
               assets,
               pageToHashMap,
-              hashMapString,
-              siteDataString,
+              metadataScript,
               additionalHeadTags
             )
           )
@@ -168,3 +161,51 @@ function linkVue() {
   }
   return () => {}
 }
+
+function generateMetadataScript(
+  pageToHashMap: Record<string, string>,
+  config: SiteConfig
+) {
+  if (config.mpa) {
+    return { html: '', inHead: false }
+  }
+
+  // We embed the hash map and site config strings into each page directly
+  // so that it doesn't alter the main chunk's hash on every build.
+  // It's also embedded as a string and JSON.parsed from the client because
+  // it's faster than embedding as JS object literal.
+  const hashMapString = JSON.stringify(JSON.stringify(pageToHashMap))
+  const siteDataString = JSON.stringify(
+    JSON.stringify(serializeFunctions({ ...config.site, head: [] }))
+  )
+
+  const metadataContent = `window.__VP_HASH_MAP__=JSON.parse(${hashMapString});${
+    siteDataString.includes('_vp-fn_')
+      ? `${deserializeFunctions.toString()};window.__VP_SITE_DATA__=deserializeFunctions(JSON.parse(${siteDataString}));`
+      : `window.__VP_SITE_DATA__=JSON.parse(${siteDataString});`
+  }`
+
+  if (!config.metaChunk) {
+    return { html: `<script>${metadataContent}</script>`, inHead: false }
+  }
+
+  const metadataFile = path.join(
+    config.assetsDir,
+    'chunks',
+    `metadata.${createHash('sha256')
+      .update(metadataContent)
+      .digest('hex')
+      .slice(0, 8)}.js`
+  )
+
+  const resolvedMetadataFile = path.join(config.outDir, metadataFile)
+  const metadataFileURL = slash(`${config.site.base}${metadataFile}`)
+
+  fs.ensureDirSync(path.dirname(resolvedMetadataFile))
+  fs.writeFileSync(resolvedMetadataFile, metadataContent)
+
+  return {
+    html: `<script type="module" src="${metadataFileURL}"></script>`,
+    inHead: true
+  }
+}
diff --git a/src/node/build/render.ts b/src/node/build/render.ts
index e391ed39..40675408 100644
--- a/src/node/build/render.ts
+++ b/src/node/build/render.ts
@@ -18,7 +18,6 @@ import {
   type PageData,
   type SSGContext
 } from '../shared'
-import { deserializeFunctions } from '../utils/fnSerialize'
 
 export async function renderPage(
   render: (path: string) => Promise<SSGContext>,
@@ -29,8 +28,7 @@ export async function renderPage(
   cssChunk: OutputAsset | null,
   assets: string[],
   pageToHashMap: Record<string, string>,
-  hashMapString: string,
-  siteDataString: string,
+  metadataScript: { html: string; inHead: boolean },
   additionalHeadTags: HeadConfig[]
 ) {
   const routePath = `/${page.replace(/\.md$/, '')}`
@@ -150,15 +148,7 @@ export async function renderPage(
     }
   }
 
-  let metadataScript = `__VP_HASH_MAP__ = JSON.parse(${hashMapString})\n`
-  if (siteDataString.includes('_vp-fn_')) {
-    metadataScript += `${deserializeFunctions.toString()}\n__VP_SITE_DATA__ = deserializeFunctions(JSON.parse(${siteDataString}))`
-  } else {
-    metadataScript += `__VP_SITE_DATA__ = JSON.parse(${siteDataString})`
-  }
-
-  const html = `
-<!DOCTYPE html>
+  const html = `<!DOCTYPE html>
 <html lang="${siteData.lang}" dir="${siteData.dir}">
   <head>
     <meta charset="utf-8">
@@ -166,21 +156,22 @@ export async function renderPage(
     <title>${title}</title>
     <meta name="description" content="${description}">
     ${stylesheetLink}
+    ${metadataScript.inHead ? metadataScript.html : ''}
     ${
       appChunk
         ? `<script type="module" src="${siteData.base}${appChunk.fileName}"></script>`
-        : ``
+        : ''
     }
     ${await renderHead(head)}
   </head>
   <body>${teleports?.body || ''}
     <div id="app">${content}</div>
-    ${config.mpa ? '' : `<script>${metadataScript}</script>`}
+    ${metadataScript.inHead ? '' : metadataScript.html}
     ${inlinedScript}
   </body>
-</html>`.trim()
-  const htmlFileName = path.join(config.outDir, page.replace(/\.md$/, '.html'))
+</html>`
 
+  const htmlFileName = path.join(config.outDir, page.replace(/\.md$/, '.html'))
   await fs.ensureDir(path.dirname(htmlFileName))
   const transformedHtml = await config.transformHtml?.(html, htmlFileName, {
     page,
@@ -224,8 +215,8 @@ function resolvePageImports(
   ]
 }
 
-function renderHead(head: HeadConfig[]): Promise<string> {
-  return Promise.all(
+async function renderHead(head: HeadConfig[]): Promise<string> {
+  const tags = await Promise.all(
     head.map(async ([tag, attrs = {}, innerHTML = '']) => {
       const openTag = `<${tag}${renderAttrs(attrs)}>`
       if (tag !== 'link' && tag !== 'meta') {
@@ -244,7 +235,8 @@ function renderHead(head: HeadConfig[]): Promise<string> {
         return openTag
       }
     })
-  ).then((tags) => tags.join('\n  '))
+  )
+  return tags.join('\n    ')
 }
 
 function renderAttrs(attrs: Record<string, string>): string {
diff --git a/src/node/config.ts b/src/node/config.ts
index bb187a9c..6144d876 100644
--- a/src/node/config.ts
+++ b/src/node/config.ts
@@ -115,6 +115,7 @@ export async function resolveConfig(
     vite: userConfig.vite,
     shouldPreload: userConfig.shouldPreload,
     mpa: !!userConfig.mpa,
+    metaChunk: !!userConfig.metaChunk,
     ignoreDeadLinks: userConfig.ignoreDeadLinks,
     cleanUrls: !!userConfig.cleanUrls,
     useWebFonts:
diff --git a/src/node/siteConfig.ts b/src/node/siteConfig.ts
index 152eca1e..6a1cea00 100644
--- a/src/node/siteConfig.ts
+++ b/src/node/siteConfig.ts
@@ -98,6 +98,12 @@ export interface UserConfig<ThemeConfig = any>
    */
   mpa?: boolean
 
+  /**
+   * Extracts metadata to a separate chunk.
+   * @experimental
+   */
+  metaChunk?: boolean
+
   /**
    * Don't fail builds due to dead links.
    *
@@ -176,6 +182,7 @@ export interface SiteConfig<ThemeConfig = any>
     | 'vite'
     | 'shouldPreload'
     | 'mpa'
+    | 'metaChunk'
     | 'lastUpdated'
     | 'ignoreDeadLinks'
     | 'cleanUrls'