Specifying URL links as variables, works in HTML but not in latex output

[SereDef]

Description

Repex

https://github.com/SereDef/Quarto_repex [Note: this is a quarto book because that is my use case]

The problem

I would like to specify some URLs in the yml header of my quarto documents so I can then use the links multiple times inside the document. These links should be rendered correctly in both HTML (which is fine) and PDF (which is giving me problems).

What I have tried

I first tried to use variables, as described in the documentation. So for example:

---
title: "Chapter 1"
repo_url: https://github.com/SereDef/Quarto_repex
---

Check the [repex]({{< meta repo_url >}}) 

which did not work very well and was only recognised correctly in the HTML output.

So then I tried to write an ad-hoc lua filter to replace the variable names in the document with the associated value form meta.
I would specify the header as before and use the following kind of arbitrary syntax in the document [repex](__repo_url__). I register the filter at the top level of the _quarto.yml (because I am writing a book and I want this applied to all chapters) and I checked that the filter does run during rendering of both outputs. This is what the filter looks like:

local meta = {}

-- Extract the metadata from the document
function Meta(m)
  for k, v in pairs(m) do
    local t = pandoc.utils.type(v)
    if type(v) == "table" and t == "Inlines" then
      meta[k] = pandoc.utils.stringify(v)
    end
  end
end

-- Replace the __var name__ with its value
function Link(el)
  local url = el.target
  local key = url:match("^__([%w_]+)__$")

  if key and meta[key] then
    el.target = meta[key]
    return el
  end
  return nil
end

-- Return two filter tables: Meta first, then Link
return {
    { Meta = Meta },
    { Link = Link }
  }

Now this again works for HTML output but (for the love of me) not in the PDF. When I check the intermediate tex file I see \href{__repo_url__}{repex}, so __repo_url__ is not being replaced (despite the filter running). I think it has something to do with the order with which Pandoc applies Lua filters (that is different for the HTML and the PDF output...?). I need Meta to run before Link but I cannot make it happen for latex. Help?

My quarto check output

Quarto 1.4.549
[✓] Checking versions of quarto binary dependencies...
      Pandoc version 3.1.11: OK
      Dart Sass version 1.69.5: OK
      Deno version 1.37.2: OK
[✓] Checking versions of quarto dependencies......OK
[✓] Checking Quarto installation......OK
      Version: 1.4.549
      Path: /Applications/quarto/bin

[✓] Checking tools....................OK
      TinyTeX: v2025.03.10
      Chromium: (not installed)

[✓] Checking LaTeX....................OK
      Using: TinyTex
      Path: /Users/Serena/Library/TinyTeX/bin/universal-darwin
      Version: 2025

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

[✓] Checking Python 3 installation....OK
      Version: 3.9.1
      Path: /Users/Serena/.pyenv/versions/3.9.1/bin/python3
      Jupyter: (None)

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

[✓] Checking R installation...........OK
      Version: 4.4.1
      Path: /Library/Frameworks/R.framework/Resources
      LibPaths:
        - /Library/Frameworks/R.framework/Versions/4.4-x86_64/Resources/library
      knitr: 1.48
      rmarkdown: 2.28

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

[mcanouil]

You should upgrade your version of Quarto CLI before going further in your trials.
You are using a version more than one year old.

[mcanouil]

@SereDef Again as stated before, I cannot reproduce your issue.
Note that I'm on the latest version.

[SereDef]

@mcanouil thanks for trying to help. I have the same problem with the Quarto current release (1.7.29). Could you please share your env then maybe? besides the Pandoc version (3.6.3) I have no idea what else could be the source of the problem

[mcanouil]

I've tried on multiple environments and got the exact same and correct output.
For example using https://github.com/mcanouil/quarto-codespaces + TinyTex

[SereDef]

Thanks again for trying to help. I tried to execute the same example inside your quarto codespace (latest version, thanks for that) but I am still getting the the same problem in the pdf output. I am confused, are you also testing this book, right? could it maybe have something to do with document class (though I have tried a couple without success)?

Just checking, you are using xelatex as pdf-engine, or something else?

@SereDef ➜ /workspaces/quarto-codespaces/repex (main) $ quarto check 
Quarto 1.8.1
[✓] Checking environment information...
      Quarto cache location: /home/vscode/.cache/quarto
[✓] Checking versions of quarto binary dependencies...
      Pandoc version 3.6.3: OK
      NOTE: Dart Sass version 1.87.0 does not strictly match 1.85.1 and strict checking is enabled. Please use 1.85.1.
      Deno version 1.46.3: OK
      Typst version 0.13.0: OK
[✓] Checking versions of quarto dependencies......OK
[✓] Checking Quarto installation......OK
      Version: 1.8.1
      Path: /opt/quarto/bin

[✓] Checking tools....................OK
      TinyTeX: v2025.05
      Chromium: (not installed)

[✓] Checking LaTeX....................OK
      Using: TinyTex
      Path: /home/vscode/.TinyTeX/bin/x86_64-linux
      Version: 2025

[✓] Checking Chrome Headless....................OK
      Chrome:  (not detected)

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

[✓] Checking Python 3 installation....OK
      Version: 3.13.3
      Path: /usr/local/python/current/bin/python3
      Jupyter: 5.7.2
      Kernels: julia-1.11, python3

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

[✓] Checking R installation...........OK
      Version: 4.5.0
      Path: /opt/R/4.5.0/lib/R
      LibPaths:
        - /home/vscode/R/x86_64-pc-linux-gnu-library/4.5
        - /opt/R/4.5.0/lib/R/library
      knitr: 1.50
      rmarkdown: 2.29

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

[mcanouil]

Sorry, I missed the "book project" part from #12626 (reply in thread)

The issue is that you set your variable inside the document, but in book project, for LaTeX PDF, there isn't multiple documents, there is in fact only one.
Meaning metadata at document level are not supported for Book PDF format it seems as metadata would need to be merged for PDF. (cc @cscheid @cderv )

As a workaround, you have two options:

• set the metadata in _quarto.yml
• use variables _variables.yml to store your variables instead of storing them as meta. https://quarto.org/docs/authoring/variables.html