feat(v2): local plugin path resolve (#1294)

* feat(v2): plugin resolve

* nits

* Update README.md

v2/lib/load/config.js

@@ -25,8 +25,6 @@ const REQUIRED_FIELDS = [
 
 const OPTIONAL_FIELDS = [
   'algolia',
-  'chainWebpack',
-  'configureWebpack',
   'customDocsPath',
   'customFields',
   'defaultLanguage',

v2/lib/load/index.js

@@ -75,12 +75,26 @@ module.exports = async function load(siteDir) {
   const context = {env, siteDir, siteConfig};
 
   // Initialize plugins.
-  const plugins = pluginConfigs.map(({name, options}) => {
-    // TODO: Resolve using node_modules as well.
-    // eslint-disable-next-line
-    const Plugin = require(path.resolve(__dirname, '../../plugins', name));
-    return new Plugin(options, context);
-  });
+  const pluginDir = path.resolve(__dirname, '../../plugins');
+  const plugins = pluginConfigs.map(
+    ({name, path: pluginPath = path.join(pluginDir, name), options}) => {
+      let Plugin;
+      // If it exist in provided path or official plugin directory
+      if (pluginPath && fs.existsSync(pluginPath)) {
+        // eslint-disable-next-line
+        Plugin = require(pluginPath);
+      } else {
+        // Resolve using node_modules as well.
+        try {
+          // eslint-disable-next-line
+          Plugin = require(name);
+        } catch (e) {
+          throw new Error(`'${name}' plugin cannot be found.`);
+        }
+      }
+      return new Plugin(options, context);
+    },
+  );
 
   // Plugin lifecycle - loadContents().
   // Currently plugins run lifecycle in parallel and are not order-dependent. We could change

v2/plugins/README.md

@@ -0,0 +1,78 @@
+# Docusaurus Plugins
+
+Plugins are one of the best ways to add functionality to our Docusaurus. Plugins allow third-party developers to extend or modify the default functionality that Docusaurus provides.
+
+## Installing a Plugin
+
+A plugin is usually a dependency, so you install them like other packages in node using NPM. However, you don't need to install official plugin provided by Docusaurus team because it comes by default.
+
+```bash
+yarn add docusaurus-plugin-name
+```
+
+Then you add it in your site's `docusaurus.config.js` plugin arrays:
+
+```js
+module.exports = {
+  plugins: [
+    {
+      name: 'docusaurus-plugin-content-pages',
+    },
+    {
+      // Plugin with options
+      name: 'docusaurus-plugin-content-blog',
+      options: {
+        include: ['*.md', '*.mdx'],
+        path: '../v1/website/blog',
+      },
+    },
+  ],
+};
+```
+
+Docusaurus can also load plugins from your local folder, you can do something like below:
+
+```js
+module.exports = {
+  plugins: [
+    {
+      path: '/path/to/docusaurus-local-plugin',
+    },
+  ],
+}
+```
+
+## Basic Plugin Architecture
+
+For examples, please refer to several official plugins created.
+
+```js
+// A JavaScript class
+class DocusaurusPlugin {
+  constructor(options, context) {
+      
+    // options are the plugin options set on config file
+    this.options = {...options};
+    
+    // context are provided from docusaurus. Example: siteConfig can be accessed from context
+    this.context = context;
+  }
+
+  getName() {
+    // plugin name identifier
+  }
+
+  async loadContents() {
+    // Content loading hook that runs the first time plugin is loaded
+    // expect a content data structure to be returned
+  }
+
+  async generateRoutes({metadata, actions}) {
+    // This is routes generation hook
+  }
+
+  getPathsToWatch() {
+    // path to watch
+  }
+}
+```