fix: duplicate meta tags

packages/@vuepress/core/lib/client/index.ssr.html

@@ -4,7 +4,6 @@
     <meta charset="utf-8">
     <meta name="viewport" content="width=device-width,initial-scale=1">
     <title>{{ title }}</title>
-    <meta name="description" content="{{ description }}">
     <meta name="generator" content="VuePress {{ version }}">
     {{{ userHeadTags }}}
     {{{ pageMeta }}}

packages/@vuepress/core/lib/client/root-mixins/updateMeta.js

@@ -1,38 +1,53 @@
+import unionBy from 'lodash/unionBy'
+
 export default {
+  // created will be called on both client and ssr
   created () {
     if (this.$ssrContext) {
+      const siteMetaTags = this.$site.headTags
+        .filter(item => item[0] === 'meta')
+        .map(item => item[1])
+
+      const meta = this.getMergedMetaTags(siteMetaTags)
+
       this.$ssrContext.title = this.$title
       this.$ssrContext.lang = this.$lang
-      this.$ssrContext.description = this.$page.description || this.$description
+      this.$ssrContext.pageMeta = renderPageMeta(meta)
     }
   },
-
+  // Other life cycles will only be called at client
   mounted () {
+    // init currentMetaTags from DOM
+    this.currentMetaTags = [...document.querySelectorAll('meta')]
+
+    // indirectly init siteMetaTags from DOM
+    this.siteMetaTags = this.currentMetaTags.map(element => {
+      const siteMeta = {}
+      for (const attribute of element.attributes) {
+        siteMeta[attribute.name] = attribute.value
+      }
+      return siteMeta
+    })
+
     // update title / meta tags
-    this.currentMetaTags = new Set()
     this.updateMeta()
   },
 
   methods: {
     updateMeta () {
       document.title = this.$title
       document.documentElement.lang = this.$lang
-      const userMeta = this.$page.frontmatter.meta || []
-      const meta = userMeta.slice(0)
-      const useGlobalDescription = userMeta.filter(m => m.name === 'description').length === 0
-
-      // #665 Avoid duplicate description meta at runtime.
-      if (useGlobalDescription) {
-        meta.push({ name: 'description', content: this.$description })
-      }
 
-      // Including description meta coming from SSR.
-      const descriptionMetas = document.querySelectorAll('meta[name="description"]')
-      if (descriptionMetas.length) {
-        descriptionMetas.forEach(m => this.currentMetaTags.add(m))
-      }
+      const newMetaTags = this.getMergedMetaTags(this.siteMetaTags)
+      this.currentMetaTags = updateMetaTags(newMetaTags, this.currentMetaTags)
+    },
 
-      this.currentMetaTags = new Set(updateMetaTags(meta, this.currentMetaTags))
+    getMergedMetaTags (siteMeta) {
+      const pageMeta = (this.$page.frontmatter.meta || []).slice(0)
+      // pageMetaTags have higher priority than siteMetaTags
+      // description needs special attention for it has too many entries
+      return unionBy([{ name: 'description', content: this.$description }],
+        pageMeta, siteMeta, metaIdentifier)
     }
   },
 
@@ -47,14 +62,20 @@ export default {
   }
 }
 
-function updateMetaTags (meta, current) {
-  if (current) {
-    [...current].forEach(c => {
+/**
+ * Replace currentMetaTags with newMetaTags
+ * @param {Array<Object>} newMetaTags
+ * @param {Array<HTMLElement>} currentMetaTags
+ * @returns {Array<HTMLElement>}
+ */
+function updateMetaTags (newMetaTags, currentMetaTags) {
+  if (currentMetaTags) {
+    [...currentMetaTags].forEach(c => {
       document.head.removeChild(c)
     })
   }
-  if (meta) {
-    return meta.map(m => {
+  if (newMetaTags) {
+    return newMetaTags.map(m => {
       const tag = document.createElement('meta')
       Object.keys(m).forEach(key => {
         tag.setAttribute(key, m[key])
@@ -64,3 +85,35 @@ function updateMetaTags (meta, current) {
     })
   }
 }
+
+/**
+ * Try to identify a meta tag by name, property or itemprop
+ *
+ * Return a complete string if none provided
+ * @param {Object} tag from frontmatter or siteMetaTags
+ * @returns {String}
+ */
+function metaIdentifier (tag) {
+  for (const item of ['name', 'property', 'itemprop']) {
+    if (tag.hasOwnProperty(item)) return tag[item] + item
+  }
+  return JSON.stringify(tag)
+}
+
+/**
+ * Render meta tags
+ *
+ * @param {Array} meta
+ * @returns {Array<string>}
+ */
+
+function renderPageMeta (meta) {
+  if (!meta) return ''
+  return meta.map(m => {
+    let res = `<meta`
+    Object.keys(m).forEach(key => {
+      res += ` ${key}="${m[key]}"`
+    })
+    return res + `>`
+  }).join('\n    ')
+}

packages/@vuepress/core/lib/node/App.js

@@ -438,6 +438,7 @@ module.exports = class App {
       title: this.siteConfig.title || '',
       description: this.siteConfig.description || '',
       base: this.base,
+      headTags: this.siteConfig.head || [],
       pages: this.pages.map(page => page.toJson()),
       themeConfig: this.siteConfig.themeConfig || {},
       locales
@@ -499,4 +500,3 @@ module.exports = class App {
     return this
   }
 }
-

packages/@vuepress/core/lib/node/build/index.js

@@ -77,9 +77,11 @@ module.exports = class Build extends EventEmitter {
     })
 
     // pre-render head tags from user config
+    // filter out meta tags for they will be injected in updateMeta.js
     this.userHeadTags = (this.context.siteConfig.head || [])
+      .filter(item => item[0] !== 'meta')
       .map(renderHeadTag)
-      .join('\n  ')
+      .join('\n    ')
 
     // if the user does not have a custom 404.md, generate the theme's default
     if (!this.context.pages.some(p => p.path === '/404.html')) {
@@ -138,14 +140,10 @@ module.exports = class Build extends EventEmitter {
     readline.cursorTo(process.stdout, 0)
     process.stdout.write(`Rendering page: ${pagePath}`)
 
-    // #565 Avoid duplicate description meta at SSR.
-    const meta = (page.frontmatter && page.frontmatter.meta || []).filter(item => item.name !== 'description')
-    const pageMeta = renderPageMeta(meta)
-
     const context = {
       url: page.path,
       userHeadTags: this.userHeadTags,
-      pageMeta,
+      pageMeta: null,
       title: 'VuePress',
       lang: 'en',
       description: '',
@@ -225,24 +223,6 @@ function renderAttrs (attrs = {}) {
   }
 }
 
-/**
- * Render meta tags
- *
- * @param {Array} meta
- * @returns {Array<string>}
- */
-
-function renderPageMeta (meta) {
-  if (!meta) return ''
-  return meta.map(m => {
-    let res = `<meta`
-    Object.keys(m).forEach(key => {
-      res += ` ${key}="${escape(m[key])}"`
-    })
-    return res + `>`
-  }).join('')
-}
-
 /**
  * find and remove empty style chunk caused by
  * https://github.com/webpack-contrib/mini-css-extract-plugin/issues/85