feat($plugin-blog): add postsDir option (#998)

packages/@vuepress/plugin-blog/index.js

@@ -4,6 +4,7 @@ module.exports = (options, ctx) => {
   const { layoutComponentMap } = ctx
   const {
     pageEnhancers = [],
+    postsDir = '_posts',
     categoryIndexPageUrl = '/category/',
     tagIndexPageUrl = '/tag/',
     permalink = '/:year/:month/:day/:slug'
@@ -40,7 +41,7 @@ module.exports = (options, ctx) => {
       frontmatter: { layout: getLayout('Layout') }
     },
     {
-      when: ({ regularPath }) => regularPath.startsWith('/_posts/'),
+      when: ({ regularPath }) => regularPath.startsWith(`/${postsDir}/`),
       frontmatter: {
         layout: getLayout('Post', 'Page'),
         permalink: permalink

packages/docs/docs/plugin/official/plugin-blog.md

@@ -23,6 +23,11 @@ module.exports = {
 
 ## Options
 
+### postsDir
+
+- Type: `string`
+- Default: `_posts`
+
 ### categoryIndexPageUrl
 
 - Type: `string`

packages/docs/docs/zh/plugin/official/plugin-blog.md

@@ -23,6 +23,11 @@ module.exports = {
 
 ## 选项
 
+### postsDir
+
+- 类型: `string`
+- 默认值: `_posts`
+
 ### categoryIndexPageUrl
 
 - 类型: `string`
@@ -33,3 +38,9 @@ module.exports = {
 - 类型: `string`
 - 默认值: `/tag/`
 
+### permalink
+
+- 类型: `string`
+- 默认值: `/:year/:month/:day/:slug`
+
+为博客文章设置永久链接。详情参考 [Permalinks](/zh/guide/permalinks.html#模板变量)。