Weird Bug: mermaid config option breaks OJS

[dasayan05]

Bug description

Just stumbled upon a weird bug. Maybe I'm missing something. Found this while working on a larger project. Managed to narrow down to a minimal example. I am just reporting my observation -- I didn't investigate further.

When I have config: ... option for mermaid code block, the OJS breaks.

Steps to reproduce

Run this simple test.qmd file

---
title: "Test"
date: "2026-08-10"
format: html
---

```{mermaid}
graph LR
    A --> B
```

```{ojs}
//| echo: true
x = 2
x ** 5
```

with quarto preview test.qmd.

Now run it with a config option in the mermaid block (everything else stays same)

---
title: "Test"
date: "2026-08-10"
format: html
---

```{mermaid}
---
config:
    look: handDrawn
---
graph LR
    A --> B
```

```{ojs}
//| echo: true
x = 2
x ** 5
```

In the second case, the ojs block stops executing -- it becomes just code.

Actual behavior

Left: Without, Right: With the mermaid option
(OJS breaks; although the mermaid option takes correct effect)

There's no error whatsoever.

Expected behavior

The OJS block shouldn't be affected by mermaid's option.

Your environment

Quarto 1.9.38
[✓] Checking environment information...
      Quarto cache location: /Users/k2692978/Library/Caches/quarto
[✓] Checking versions of quarto binary dependencies...
      Pandoc version 3.8.3: OK
      Dart Sass version 1.87.0: OK
      Deno version 2.4.5: OK
      Typst version 0.14.2: OK
[✓] Checking versions of quarto dependencies......OK
[✓] Checking Quarto installation......OK
      Version: 1.9.38
      Path: /Users/k2692978/Applications/quarto/bin

[✓] Checking tools....................OK
      TinyTeX: (not installed)
      Chromium: (not installed)
      Chrome Headless Shell: (not installed)
      VeraPDF: (not installed)

[✓] Checking LaTeX....................OK
      Tex:  (not detected)

[✓] Checking Chrome Headless....................OK
      Using: Chrome found on system
      Path: /Applications/Google Chrome.app/Contents/MacOS/Google Chrome
      Source: MacOS known location

[✓] Checking basic markdown render....OK

[✓] Checking R installation...........OK
      Version: 4.6.1
      Path: /Library/Frameworks/R.framework/Resources
      LibPaths:
        - /Users/k2692978/Library/R/arm64/4.6/library
        - /Library/Frameworks/R.framework/Versions/4.6/Resources/library
      knitr: 1.51
      rmarkdown: 2.31

[✓] Checking Knitr engine render......OK

[✓] Checking Python 3 installation....OK
      Version: 3.9.6
      Path: /Library/Developer/CommandLineTools/usr/bin/python3
      Jupyter: (None)

      Jupyter is not available in this Python installation.
      Install with python3 -m pip install jupyter

[✓] Checking Julia installation...

[mcanouil]

That's basically a parsing issue of the mermaid block related to the use of ---.
Meanwhile, the workaround is to use inline syntax from mermaid %%{init: ...}.

The issue is unrelated to OJS, whatever comes after is broken.

Adding keep-md: true show the bare and alone --- with no empty lines around.

---
title: "Test"
format: html
keep-md: true
---


::::::{.cell layout-align="default"}

:::::{.cell-output-display}

::::{}
`<figure class=''>`{=html}

:::{}

<pre class="mermaid mermaid-js">---
config:
    look: handDrawn
---
graph LR
    A --&gt; B
</pre>
:::
`</figure>`{=html}
::::
:::::
::::::

::::::{.cell}

```{.js .cell-code startFrom="20" source-offset="-0"}
x = 2
x ** 5
```

:::::{.cell-output .cell-output-display}

::::{}

:::{#ojs-cell-1-1 nodetype="declaration"}
:::
::::
:::::

:::::{.cell-output .cell-output-display}

::::{}

:::{#ojs-cell-1-2 nodetype="expression"}
:::
::::
:::::
::::::

[mcanouil]

@dasayan05

Important

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[mcanouil]

PR is up for the team to review, i.e., enclose mermaid code inside raw HTML block so --- are not treated as markdown.

[dasayan05]

ah, I had the same feeling that it was the ---.

thanks for the fix.