SVG are loosing classes when using `embed-resources`, impacting revealjs features (`class="slide-logo"`, `.absolute`)

[mcanouil]

Using Quarto 122b0f3093c560a6c24365fc9241bb83d4590ef4 It works as expected using v1.4.554

Expected behaviour

Quarto document	HTML
````qmd --- title: "Quarto Playground" format: revealjs: logo: https://raw.githubusercontent.com/mcanouil/hex-stickers/main/SVG/rlille.svg embed-resources: false --- ## Slide This is a playground for Quarto.  ````

Actual behaviour

Quarto document	HTML
````qmd --- title: "Quarto Playground" format: revealjs: logo: https://raw.githubusercontent.com/mcanouil/hex-stickers/main/SVG/rlille.svg embed-resources: true --- ## Slide This is a playground for Quarto.  ````

The class="slide-logo" is lost when embedding.

[cderv]

This is Pandoc issue IMO so if it was working before probably following an update of pandoc

Try

❯ quarto pandoc --to html --embed-resources -o embed.html
<img src="https://raw.githubusercontent.com/mcanouil/hex-stickers/main/SVG/rlille.svg" class="slide-logo">
^Z

And look in embed.html - the class is missing.

[cderv]

But doing the same with Quarto 1.4.554 works - so this is a change in Pandoc.

[cderv]

1.4.554 uses pandoc 3.1.11.1 and latest use pandoc 3.2

And we can determine that change happens in Pandoc 3.2

library(pandoc)

min <- "3.1.11"
max <- "3.2"

versions <- pandoc::pandoc_available_releases()
#> ℹ Fetching Pandoc releases info from github...
versions <- versions[seq.int(which(versions == min), which(versions == max))]

for(version in versions) {
  if (!pandoc::pandoc_is_installed(version)) {
    pandoc::pandoc_install(version)
  }
  embed <- pandoc::pandoc_convert(
    text = '<img src="https://raw.githubusercontent.com/mcanouil/hex-stickers/main/SVG/rlille.svg" class="slide-logo">',
    to = "html",
    args = "--embed-resources", 
    version = version)
  if (!any(grepl("slide-logo", embed))) {
    cat("pandoc version ", version, " does not keep classes")
    break
  }
}
#> pandoc version  3.2  does not keep classes

^{Created on 2024-05-31 with reprex v2.1.0}

[cderv]

Probably related to @cscheid PR in pandoc

• https://github.com/jgm/pandoc/issues/9652
• https://github.com/jgm/pandoc/pull/9653

so we may have broken ourself Quarto through Pandoc by trying to fix another issue 😅

Though I don't see how merging would mess this up, because we should have kept the class. So either if no class on the svg, it does not keep image class.

Or this is a side effect of this change somewhere else

[cderv]

Testing with another svg from pandoc repo

❯ quarto pandoc --to html --embed-resources -o embed.html
```{=html}
<img class="something" src="https://raw.githubusercontent.com/jgm/pandoc/7abfec3d2c0e6084b8029d38cd45912697822f3a/test/command/SVG_logo.svg" />

^Z

I don't get the class name either 
````html
<svg id="svg_7e8f68c20ccd090c0566" role="img" viewBox="-50 -50 100 100" width="100" height="100">
<title>SVG Logo</title>

So it seems when no class on the svg, the one from img tag is lost.

@cscheid I don't know Haskell enough to know if your change is supposed to handle this case.

[cscheid]

Hm - if this is a Pandoc regression (even one I introduced 🤦) we won't be able to fix it for 1.5.

[cderv]

What about doing a "hack" to at least restore behavior ? I have a branch working with the following

• wrap the logo image in a span of a class we know.
• Leverage revealjs plugin system to restore the class on the element in the span when it is missing.

This would not solve the underlying svg issue, but this would "hide" this issue until we have a proper fix. I can make a PR with the idea.

[cscheid]

I don't know. This would only fix it in logo and format: revealjs, right? The bug would still exist in other usages of embed-resources. I'm not sure it's worth the extra complexity in the code base, that would then need to be reverted once upstream is fixed.

[cderv]

This would only fix it in logo and format: revealjs, right?

Yes exactly.

I'm not sure it's worth the extra complexity in the code base, that would then need to be reverted once upstream is fixed.

That is the question. I'll share the idea in a PR and you'll be the judge of that.

[cderv]

Here is one use case where another class is lost: When using .absolute class for positioning on an svg element. See

• https://github.com/quarto-dev/quarto-cli/discussions/10613

---
title: test SVG
format: revealjs
embed-resources: true
---

## Slide 1

![](https://quarto.org/docs/presentations/revealjs/demo/mini/images/kitten-450-250.jpeg){.absolute top=50 right=50 width="450" height="250"}

![](https://dev.w3.org/SVG/tools/svgweb/samples/svg-files/410.svg){.absolute top=50 right=50 width="450" height="250"}