feat(seo): add link tag to frontmatter allowed values

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

@@ -7,6 +7,7 @@
  <meta name="description" content="{{ description }}">
  {{{ userHeadTags }}}
  {{{ pageMeta }}}
+ {{{ pageLink }}}
  {{{ renderResourceHints() }}}
  {{{ renderStyles() }}}
  </head>

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

@@ -140,12 +140,15 @@ module.exports = class Build extends EventEmitter {
 
  // #565 Avoid duplicate description meta at SSR.
  const meta = (page.frontmatter && page.frontmatter.meta || []).filter(item => item.name !== 'description')
- const pageMeta = renderPageMeta(meta)
+ const link = page.frontmatter && page.frontmatter.link || []
+ const pageLink = renderPageEmptyTag('link', link)
+ const pageMeta = renderPageEmptyTag('meta', meta)
 
  const context = {
  url: page.path,
  userHeadTags: this.userHeadTags,
  pageMeta,
+ pageLink,
  title: 'VuePress',
  lang: 'en',
  description: ''
@@ -225,16 +228,17 @@ function renderAttrs (attrs = {}) {
 }
 
 /**
- * Render meta tags
+ * Render html empty tags
  *
- * @param {Array} meta
+ * @param {String} tagName
+ * @param {Array} tags
  * @returns {Array<string>}
  */
 
-function renderPageMeta (meta) {
- if (!meta) return ''
- return meta.map(m => {
- let res = `<meta`
+function renderPageEmptyTag (tagName, tags) {
+ if (!tags) return ''
+ return tags.map(m => {
+ let res = `<tag`
  Object.keys(m).forEach(key => {
  res += ` ${key}="${escape(m[key])}"`
  })

packages/docs/docs/guide/frontmatter.md

@@ -101,6 +101,21 @@ meta:
 ---
 ```
 
+### link
+
+- Type: `array`
+- Default: `undefined`
+
+Specify extra link tags to be injected:
+
+``` yaml
+---
+link:
+ - rel: canonical
+ content: https://my-canonical-url.com/article/1
+---
+```
+
 ## Predefined Variables Powered By Default Theme
 
 ### navbar