Unexpected characters when applying to md file

[mattrunyon]

Initial checklist

• I read the support docs
• I read the contributing guide
• I agree to follow the code of conduct
• I searched issues and discussions and couldn’t find anything (or linked relevant results below)

Affected package

[email protected]

Steps to reproduce

1. Open a basic test.md file in VSCode w/ the MDX extension.
2. Put a word in the document.
3. Change the language mode (Click Markdown in the bottom right) to MDX

Actual behavior

The MDX plugin raises errors about unknown identifiers or other ts-plugin errors.

Expected behavior

The MDX plugin should work on the contents regardless of the file extension

Runtime

No response

Package manager

No response

Operating system

No response

Build and bundle tools

No response

[remcohaszing]

Why are you changing the language mode of a markdown file to MDX? This will break several tools.

[mattrunyon]

We have a Docusaurus project that mostly has .md extensions but might use some MDX. This is supported in Docusaurus and both just compile as MDX.

I don't think changing the file language in VSCode should break other tools. A file extension doesn't guarantee the actual contents of a file. It's just a hint.

Just something I noticed when trying to use the MDX extension on .md. I don't know why it would have parsing issues just because of the file extension. You can put JS code in a .py file and tell VSCode it's JS and everything works just fine.

Also, since MDX is (mostly) a superset of MD, it should work mostly fine.

[remcohaszing]

We have a Docusaurus project that mostly has .md extensions but might use some MDX. This is supported in Docusaurus and both just compile as MDX.

The MDX compiler can handle both markdown and MDX files into React components. It detects the format based on the file extension. If Docusaurus treats .md files as MDX instead of markdown, that’s a Docusaurus bug.

I don't think changing the file language in VSCode should break other tools. A file extension doesn't guarantee the actual contents of a file. It's just a hint.

Changing the language in an editor doesn’t change the build tool.

Just something I noticed when trying to use the MDX extension on .md. I don't know why it would have parsing issues just because of the file extension.

This is true to some extent. VSCode does treat a file based on the language ID. That’s why, if you change the language of a .md file to MDX, you see TypeScript errors coming from the MDX TypeScript plugin.

TypeScript however, doesn’t use these language IDs. TypeScript checking is based on file extensions. The MDX TypeScript plugin treats .mdx file in a special way. It has no knowledge of the .md file extension. So the .md file you see is being treated as if it is TypeScript.

You can put JS code in a .py file and tell VSCode it's JS and everything works just fine.

This is a good example. I created a file named test.py, changed the language to JavaScript, and added the following content:

/**
 * @returns {string}
 */
export function example() {
  return 42
}

Based on hover info and diagnostics, you can see that this is treated as TypeScript, not JavaScript. TypeScript uses the inferred return type instead of the explicit JSDoc return type, and suggests to use a TypeScript type annotation instead of a JSDoc annotation.