feat: add "unlisted" front matter option for blog posts (#1396)

* Add `unlisted` header option for blog posts, fixes #1393.

Previously, the blog sidebar listed the most recent blog posts sorted by
their publish date. This commit adds the ability to hide a specific blog
post from the sidebar and the feed of all blog posts by adding the
`unlisted: true` header option.

```md
title: My Draft Post
unlisted: true # Hide from blog sidebar and main blog page feed.
---
```

* Rename "unlisted" into "draft".

packages/docusaurus-1.x/lib/core/BlogPageLayout.js

@@ -10,6 +10,8 @@ const BlogPost = require('./BlogPost.js');
 const BlogSidebar = require('./BlogSidebar.js');
 const Container = require('./Container.js');
 const MetadataBlog = require('./MetadataBlog.js');
+
+const MetadataPublicBlog = MetadataBlog.filter(item => !item.draft);
 const Site = require('./Site.js');
 const utils = require('./utils.js');
 
@@ -40,8 +42,10 @@ class BlogPageLayout extends React.Component {
           />
           <Container className="mainContainer postContainer blogContainer">
             <div className="posts">
-              {MetadataBlog.slice(page * perPage, (page + 1) * perPage).map(
-                post => (
+              {MetadataPublicBlog.slice(
+                page * perPage,
+                (page + 1) * perPage,
+              ).map(post => (
                 <BlogPost
                   post={post}
                   content={post.content}
@@ -52,15 +56,14 @@ class BlogPageLayout extends React.Component {
                   }
                   config={this.props.config}
                 />
-                ),
-              )}
+              ))}
               <div className="docs-prevnext">
                 {page > 0 && (
                   <a className="docs-prev" href={this.getPageURL(page - 1)}>
                     ← Prev
                   </a>
                 )}
-                {MetadataBlog.length > (page + 1) * perPage && (
+                {MetadataPublicBlog.length > (page + 1) * perPage && (
                   <a className="docs-next" href={this.getPageURL(page + 1)}>
                     Next →
                   </a>

packages/docusaurus-1.x/lib/core/BlogSidebar.js

@@ -10,6 +10,8 @@ const SideNav = require('./nav/SideNav.js');
 
 const MetadataBlog = require('./MetadataBlog.js');
 
+const MetadataPublicBlog = MetadataBlog.filter(item => !item.draft);
+
 class BlogSidebar extends React.Component {
   render() {
     let blogSidebarCount = 5;
@@ -17,7 +19,7 @@ class BlogSidebar extends React.Component {
     let blogSidebarTitle = blogSidebarTitleConfig.default || 'Recent Posts';
     if (this.props.config.blogSidebarCount) {
       if (this.props.config.blogSidebarCount === 'ALL') {
-        blogSidebarCount = MetadataBlog.length;
+        blogSidebarCount = MetadataPublicBlog.length;
         blogSidebarTitle = blogSidebarTitleConfig.all || 'All Blog Posts';
       } else {
         blogSidebarCount = this.props.config.blogSidebarCount;
@@ -28,7 +30,7 @@ class BlogSidebar extends React.Component {
       {
         type: 'CATEGORY',
         title: blogSidebarTitle,
-        children: MetadataBlog.slice(0, blogSidebarCount).map(item => ({
+        children: MetadataPublicBlog.slice(0, blogSidebarCount).map(item => ({
           type: 'LINK',
           item,
         })),

packages/docusaurus-1.x/lib/core/__tests__/__fixtures__/blog-post-with-draft.md

@@ -0,0 +1,5 @@
+---
+title: Draft Example
+draft: true
+---
+This blog post should not appear in the sidebar or the blog feed because it is a draft.

packages/docusaurus-1.x/lib/server/feed.js

@@ -28,6 +28,7 @@ module.exports = function(type) {
 
   readMetadata.generateMetadataBlog(siteConfig);
   const MetadataBlog = require('../core/MetadataBlog.js');
+  const MetadataPublicBlog = MetadataBlog.filter(item => !item.draft);
 
   const feed = new Feed({
     title: `${siteConfig.title} Blog`,
@@ -38,10 +39,10 @@ module.exports = function(type) {
     link: blogRootURL,
     image: siteImageURL,
     copyright: siteConfig.copyright,
-    updated: new Date(MetadataBlog[0].date),
+    updated: new Date(MetadataPublicBlog[0].date),
   });
 
-  MetadataBlog.forEach(post => {
+  MetadataPublicBlog.forEach(post => {
     const url = `${blogRootURL}/${post.path}`;
     const description = utils.blogPostHasTruncateMarker(post.content)
       ? renderMarkdown(utils.extractBlogPostBeforeTruncate(post.content))