Feed generation warns: "Received true for a non-boolean attribute" when using {2,3} highlighting

[KELEN]

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 new version is 2.0.0-beta.14

```jsx {2,3}
const a = 123;

return {
  a: 1
}
```

Warning: Received `true` for a non-boolean attribute `{2,3}`.

If you want to write it to the DOM, pass a string instead: {2,3}="true" or {2,3}={value.toString()}.
    at code
    at D:\github\website\node_modules\@mdx-js\react\dist\cjs.js:153:30

Steps to reproduce

when use highlight code，eg: {2, 3}

npm run build，throw warning

Expected behavior

No warning show

Actual behavior

Warning: Received true for a non-boolean attribute {2,3}.

Your environment

• Public source code:
• Public site URL:
• Docusaurus version used:
• Environment name and version (e.g. Chrome 89, Node.js 16.4):
• Operating system and version (e.g. Ubuntu 20.04.2 LTS):

Reproducible demo

No response

Self-service

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

[Josh-Cena]

I do remember seeing the warning some time back in our production builds, but at some point they are gone. Could you delete node_modules and lock file, re-install, run clear, and build to see if the issue persists?

[slorber]

😅 never seen this warning before, weird

[Josh-Cena]

Just realized I saw it not on the Docusaurus site build, but on my site...

https://app.circleci.com/pipelines/github/Josh-Cena/Josh-Cena.github.io/30/workflows/b0668fe3-97ae-4ef1-8e8d-1f431c3cbda8/jobs/28

In the "Deploy to GitHub Pages" step, the build emits warning.

I know what's the issue: this is thrown from @mdx-js/runtime, and is only visible when you have line highlights in the blog. This is because the blog feeds do not go through the MDXComponentProvider and therefore these markups end up in the final React output. I think we should just recommend using comments for highlighting for a multitude of reasons.

[slorber]

Oh I see

Agree, I don't like too much the {2,3} notation, trying to emphasis the start/end comments more

[dsmmcken]

I get something similar, where I have a custom remark plugin preprocessing my code snippets to feed them to a testing framework. Some code blocks have an skip-testing annotation like:

```python skip-test
# untested example
```

and this warns with a similar error.

[Josh-Cena]

@dsmmcken This basically happens with any codeblock meta that's not foo="bar". It's a really common pattern, but if there's no remark plugin to consume it, it ends up in the final MDX output, which is the case for our blog feeds feature, which uses mdx/runtime