fix:(gatsby-plugin-mdx) Require a default export when needed (#21861)

* Require default export when needed

* Fix typo

Author: jlkiri

packages/gatsby-plugin-mdx/gatsby/source-nodes.js

@@ -14,6 +14,7 @@ const getTableOfContents = require(`../utils/get-table-of-content`)
 const defaultOptions = require(`../utils/default-options`)
 const genMDX = require(`../utils/gen-mdx`)
 const { mdxHTMLLoader: loader } = require(`../utils/render-html`)
+const { interopDefault } = require(`../utils/interop-default`)
 
 async function getCounts({ mdast }) {
   let counts = {}
@@ -96,7 +97,7 @@ module.exports = (
    */
   for (let plugin of options.gatsbyRemarkPlugins) {
     debug(`requiring`, plugin.resolve)
-    const requiredPlugin = require(plugin.resolve)
+    const requiredPlugin = interopDefault(require(plugin.resolve))
     debug(`required`, plugin)
     if (_.isFunction(requiredPlugin.setParserPlugins)) {
       for (let parserPlugin of requiredPlugin.setParserPlugins(

packages/gatsby-plugin-mdx/utils/get-source-plugins-as-remark-plugins.js

@@ -1,6 +1,7 @@
 const visit = require(`unist-util-visit`)
 const _ = require(`lodash`)
 const debug = require(`debug`)(`get-source-plugins-as-remark-plugins`)
+const { interopDefault } = require(`./interop-default`)
 
 let fileNodes
 
@@ -43,7 +44,7 @@ module.exports = async function getSourcePluginsAsRemarkPlugins({
   // return list of remarkPlugins
   const userPlugins = gatsbyRemarkPlugins
     .filter(plugin => {
-      if (_.isFunction(require(plugin.resolve))) {
+      if (_.isFunction(interopDefault(require(plugin.resolve)))) {
         return true
       } else {
         debug(`userPlugins: filtering out`, plugin)
@@ -52,7 +53,7 @@ module.exports = async function getSourcePluginsAsRemarkPlugins({
     })
     .map(plugin => {
       debug(`userPlugins: constructing remark plugin for `, plugin)
-      const requiredPlugin = require(plugin.resolve)
+      const requiredPlugin = interopDefault(require(plugin.resolve))
       const wrappedPlugin = () =>
         async function transformer(markdownAST) {
           await requiredPlugin(

packages/gatsby-plugin-mdx/utils/interop-default.js

@@ -0,0 +1,4 @@
+const interopDefault = exp =>
+  exp && typeof exp === `object` && `default` in exp ? exp[`default`] : exp
+
+exports.interopDefault = interopDefault