feat($theme-default): allow 'auto' in defined sidebars (close: #1252) (#2380)

Author: bobheadxi

packages/@vuepress/theme-default/util/index.js

@@ -138,6 +138,9 @@ export function resolveSidebarItems (page, regularPath, site, localePath) {
     return []
   } else {
     const { base, config } = resolveMatchingConfig(regularPath, sidebarConfig)
+    if (config === 'auto') {
+      return resolveHeaders(page)
+    }
     return config
       ? config.map(item => resolveItem(item, pages, base))
       : []

packages/docs/docs/theme/default-theme-config.md

@@ -273,6 +273,8 @@ module.exports = {
         'four'   /* /bar/four.html */
       ],
 
+      '/baz/': 'auto', /* automatically generate single-page sidebars */
+
       // fallback
       '/': [
         '',        /* / */