Code blocks (```) inside HTML tags lack syntax highlighting

[gnidan]

Is this a hackmd.io issue?

• [x] Yes, the bug happens on https://hackmd.io
• [ ] No. If it's a self-hosted CodiMD instance, please fire up the issue in the repo of CodiMD: https://github.com/hackmdio/codimd

What's the problem

Code blocks that specify language normally get syntax highlighting according to that language. This breaks when using a code block inside a literal HTML tag, even though the rendering works fine.

Current behaviour

Reproduce with the following content:

## Example

<details><summary>Component diagram</summary>

```javascript
console.log("hello");
```
</details>

Compare with screenshot:

Expected behaviour

The code block should be highlighted, like how Github does in the example above.

Environment

I use HackMD on:

Desktop

• OS: macOS
• Browser: Chromium-like
• Browser Version: 91.0.4472.106