feat(v2): support rightToc, emoji, slug for docs (#1382)

* add remark-slug and remark-emoji

* implement right TOC remark plugin

* use rehype-slug ecosystem instead of remark for perf

* first rough implementation for right toc

* nits

* remove unwanted changes

* fix left border styling

* remove depths

* inline snapshot

packages/docusaurus-mdx-loader/src/rightToc/index.js

@@ -0,0 +1,78 @@
+/**
+ * Copyright (c) 2017-present, Facebook, Inc.
+ *
+ * This source code is licensed under the MIT license found in the
+ * LICENSE file in the root directory of this source tree.
+ */
+const {parse} = require('@babel/parser');
+const traverse = require('@babel/traverse').default;
+const stringifyObject = require('stringify-object');
+const search = require('./search');
+
+const parseOptions = {
+  plugins: ['jsx'],
+  sourceType: 'module',
+};
+const isImport = child => child.type === 'import';
+const hasImports = index => index > -1;
+const isExport = child => child.type === 'export';
+
+const isTarget = (child, name) => {
+  let found = false;
+  const ast = parse(child.value, parseOptions);
+  traverse(ast, {
+    VariableDeclarator: path => {
+      if (path.node.id.name === name) {
+        found = true;
+      }
+    },
+  });
+
+  return found;
+};
+
+const getOrCreateExistingTargetIndex = (children, name) => {
+  let importsIndex = -1;
+  let targetIndex = -1;
+
+  children.forEach((child, index) => {
+    if (isImport(child)) {
+      importsIndex = index;
+    } else if (isExport(child) && isTarget(child, name)) {
+      targetIndex = index;
+    }
+  });
+
+  if (targetIndex === -1) {
+    const target = {
+      default: false,
+      type: 'export',
+      value: `export const ${name} = [];`,
+    };
+
+    targetIndex = hasImports(importsIndex) ? importsIndex + 1 : 0;
+    children.splice(targetIndex, 0, target);
+  }
+
+  return targetIndex;
+};
+
+const plugin = (options = {}) => {
+  const name = options.name || 'rightToc';
+
+  const transformer = node => {
+    const headings = search(node);
+    const {children} = node;
+    const targetIndex = getOrCreateExistingTargetIndex(children, name);
+
+    if (headings && headings.length) {
+      children[targetIndex].value = `export const ${name} = ${stringifyObject(
+        headings,
+      )};`;
+    }
+  };
+
+  return transformer;
+};
+
+module.exports = plugin;