feat($core): infer page's date via directory name (#1553)

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

@@ -146,6 +146,17 @@ module.exports = class Page {
     this.buildPermalink()
   }
 
+  /**
+   * name of page's parent directory.
+   *
+   * @returns {string}
+   * @api public
+   */
+
+  get dirname () {
+    return path.basename(path.dirname(this._filePath || this.regularPath))
+  }
+
   /**
    * file name of page's source markdown file, or the last cut of regularPath.
    *
@@ -202,7 +213,7 @@ module.exports = class Page {
    */
 
   get date () {
-    return inferDate(this.frontmatter, this.filename)
+    return inferDate(this.frontmatter, this.filename, this.dirname)
   }
 
   /**

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

@@ -54,13 +54,16 @@ exports.applyUserWebpackConfig = function (userConfig, config, isServer) {
 const DATE_RE = /(\d{4}-\d{1,2}(-\d{1,2})?)-(.*)/
 exports.DATE_RE = DATE_RE
 
-exports.inferDate = function (frontmatter = {}, filename) {
+exports.inferDate = function (frontmatter = {}, filename, dirname) {
+  let matches
+
   if (frontmatter.date) {
     return frontmatter.date
+  } else if (filename && (matches = filename.match(DATE_RE))) {
+    return matches[1]
+  } else if (dirname && (matches = dirname.match(DATE_RE))) {
+    return matches[1]
+  } else {
+    return null
   }
-  const match = filename.match(DATE_RE)
-  if (match) {
-    return match[1]
-  }
-  return null
 }