chore(v2): Define type for markdown right table of contents (#3306)

packages/docusaurus-mdx-loader/src/remark/rightToc/search.js

@@ -5,11 +5,29 @@
  * LICENSE file in the root directory of this source tree.
  */
 
+// @ts-check
+
 const toString = require('mdast-util-to-string');
 const visit = require('unist-util-visit');
 const escapeHtml = require('escape-html');
 
+/** @typedef {import('@docusaurus/types').MarkdownRightTableOfContents} TOC */
+/** @typedef {import('unist').Node} Node */
+
+/**
+ * @typedef {Object} StringValuedNode
+ * @property {string} type
+ * @property {string} value
+ * @property {number} depth
+ * @property {Object} data
+ * @property {StringValuedNode[]} children
+ */
+
 // https://github.com/syntax-tree/mdast#heading
+/**
+ * @param {StringValuedNode | undefined} node
+ * @returns {string}
+ */
 function toValue(node) {
   if (node && node.type) {
     switch (node.type) {
@@ -34,11 +52,22 @@ function toValue(node) {
 
 // Visit all headings. We `slug` all headings (to account for
 // duplicates), but only take h2 and h3 headings.
+/**
+ * @param {StringValuedNode} node
+ * @returns {TOC[]}
+ */
 function search(node) {
+  /** @type {TOC[]} */
   const headings = [];
   let current = -1;
   let currentDepth = 0;
 
+  /**
+   * @param {StringValuedNode} child
+   * @param {number} index
+   * @param {Node | undefined} parent
+   * @returns {void}
+   */
   const onHeading = (child, index, parent) => {
     const value = toString(child);