Breaking change in v2.2.0 of MDX Loader

Have you read the Contributing Guidelines on issues?

• I have read the Contributing Guidelines on issues.

Prerequisites

• I’m using the latest version of Docusaurus.
• I have tried the npm run clear or yarn clear command.
• I have tried rm -rf node_modules yarn.lock package-lock.json and re-installing packages.
• I have tried creating a repro with https://new.docusaurus.io.
• I have read the console error message carefully (if applicable).

Description

The 2.2.0 release for Mermaid introduced a breaking change to the type for Options in @docusaurus/mdx-loader.

This commit/line: https://github.com/facebook/docusaurus/commit/9c92a79d23533a61f3ad1bf3ea4d0889f0e2710f#diff-545a046200b390be351720ea1e83af42ec7ed096a4351213383e1550467d8cdcR66

markdownConfig should be an optional type or have a default value assigned, to align with semver.

Reproducible demo

No response

Steps to reproduce

1. Use @docusaurus/mdx-loader in a plugin/app pre 2.2.0
2. Upgrade to 2.2.0
3. Observe: Build breaks with error:

[ERROR] TypeError: Cannot read properties of undefined (reading 'mermaid')
    at Object.mdxLoader (/Users/ben/flagsmith/docs/node_modules/@docusaurus/mdx-loader/lib/loader.js:115:43)
    at LOADER_EXECUTION (/Users/ben/flagsmith/docs/node_modules/loader-runner/lib/LoaderRunner.js:132:14)
    at runSyncOrAsync (/Users/ben/flagsmith/docs/node_modules/loader-runner/lib/LoaderRunner.js:133:4)
    at iterateNormalLoaders (/Users/ben/flagsmith/docs/node_modules/loader-runner/lib/LoaderRunner.js:250:2)
    at /Users/ben/flagsmith/docs/node_modules/loader-runner/lib/LoaderRunner.js:223:4
    at /Users/ben/flagsmith/docs/node_modules/webpack/lib/NormalModule.js:834:15
    at eval (eval at create (/Users/ben/flagsmith/docs/node_modules/tapable/lib/HookCodeFactory.js:33:10), <anonymous>:12:1)
    at processTicksAndRejections (node:internal/process/task_queues:83:21)
    at runNextTicks (node:internal/process/task_queues:65:3)
    at processImmediate (node:internal/timers:437:9)

Can be seen here: https://github.com/cloud-annotations/docusaurus-openapi/issues/222

Expected behavior

Breaking changes should be reserved for major release cycles. markdownConfig should either be optional or have a default value assigned as its value.

Actual behavior

Build process breaks when upgrading to 2.2.0.

Your environment

• Docusaurus version used: v2.2.0
• Environment name and version (e.g. Chrome 89, Node.js 16.4): Chrome Version 107.0.5304.87 (Official Build) (arm64), Node.js v18.11.0
• Operating system and version (e.g. Ubuntu 20.04.2 LTS): Mac OS 13.0

Self-service

• I’d be willing to fix this bug myself.

[sean-perkins]

Ok cool. I think we can close out this issue then 👍 I have a viable change to the plugin and others that run into a similar issue can come across this issue as a reference.

Thanks for the quick follow-up!

[slorber]

handled in https://github.com/facebook/docusaurus/pull/8419

note this retro compatible change will be reverted in v3 (part of https://github.com/facebook/docusaurus/pull/8288) so make sure to upgrade your plugin code. In the future we want the loader to receive the global site markdown config so we do want an error if it’s not provided.