Filters not applied on labelled math formulas when rendering to PDF

[knuesel]

Lua filters can change the content of math fomulas, except for formulas with labels when rendering to PDF.

This can be worked around by running the Lua filter before the quarto filters, so maybe it's not a bug? But it's a bit confusing that the behavior changes depending on the format and label vs no label...

Here's an MWE, tested with quarto 0.9.58: create a.qmd with

---
filters:
  - filter.lua
---

$$x=1$$ {#eq-x}

and filter.lua with

function Math(el)
    el.text = 'y'
    return el
end

The filter simply replaces all math formulas with y.

Running quarto render a.qmd gives the expected HTML output: the formula is "y".

However quarto render a.qmd --to pdf makes a PDF with the original equation "x=1".

It does work if the label is removed, i.e. if the document contains $$x=1$$ instead of $$x=1$$ {#eq-x} then the PDF shows "y".

[jjallaire]

This is a consequence of the fact that Pandoc outputs display equations with \[ (rather than \begin{equation}, which is required for labels). So we need to generate the raw latex in order to include the label.

That said, there is certainly a way for us to do this using latex post-processing rather than lua filters. We have a few other equation related items we are planning on working on soon and we'll make sure to address this at that time.

[mcanouil]

I stumbled upon this and it does seem to work as expected under latest Quarto version:

[mcanouil]

I'm going ahead and close as resolved.