Which metadata extension is run first?

[andrewpbray]

Description

If I add two different metadata extensions to my Quarto project, each with a pre-render script, which one runs first?

This brings to my mind something that's been slowly maturing for me over the months/years. Lua Filters modify the way Quarto/pandoc compiles single docs. They're effectively Document Extensions. A document can call many document extensions and specify the order in which they're run.

Pre-and post-render scripts modify the way Quarto compiles multidoc projects. They're effectively Project Extensions. A project can call many such project extensions, but ... I don't know of a way to specify the order they're run (or make apparent in _quarto.yml that they're even being run).

The analog to filters appearing in document yaml seems like it'd be a _quarto.yml that read:

project:
  type: website
  extensions:
    - my-first-extension
    - my-second-extension

[cscheid]

I hear you.

Context: We designed the filter declarations purposefully expecting that they would interfere with one another and so the user needs to declare their order. We generally don't expect extensions to interfere with one another, and so we didn't want to burden users with the same verboseness that comes in filter declarations.

Technical answer: we specify that behavior (that is, you can't really currently control it, because we don't promise it'll be a defined order).

Honestly: I don't know, we'd have to look. I don't think I want users to be able to control it, because I'd like to encourage extensions to be written in a way that they are independent of each other.

[cscheid]

... nevermind - I read your proposed syntax and it infiltrated my mind! I guess this is an admission that we should have that :)

[fuhrmanator]

I have a similar question -- I'm using the fontawesome extension, and I wanted to write some lua filter to add some icons into certain styled blocks. I was hoping to just insert inline markdown {{< fa thumbs-up >}}

But in debugging my filter it seems that the {{< fa thumbs-up >}} (or similar) has already been converted to Span with __quarto_custom_type, etc. before my filter runs:

Span ("",[],[("__quarto_custom","true"),("__quarto_custom_type","Shortcode"),("__quarto_custom_context","Inline"),("__quarto_custom_id","1")]) []]

I tried putting a full path to the fontawesome.lua (filter?) from the extension at the bottom of my filters: list, but it changes nothing (and doesn't error out).

If I understand it, we can't control this order either? Anyway, maybe it's another use case.

[cscheid]

@fuhrmanator I think you're trying to manipulate the contents of a shortcode expression at runtime, or, equivalently, to create a new shortcode expression in Lua.

It takes a bit of trickery, but your filter can target the AST node for the Shortcode directly. We envisioned this to exist for people to replace the behavior of certain shortcodes; you want to, in addition, create a new shortcode from Lua, which is a bit harder. But this is a minimal example:

---
format: html
key1: value1
key2: value2
filters:
  - change_meta_shortcode.lua
---

{{< meta key1 >}}

The filter:

-- change_meta_shortcode.lua
function Shortcode(shortcode)
  local node = quarto._quarto.ast.create_custom_node_scaffold("Shortcode", "Inline")
  return quarto.Shortcode({
    __quarto_custom_node = node,
    name = "meta",
    params = {
      {
        type = "param",
        value = "key2"
      }
    }
  })
end

[cscheid]

For a bit more context: the Span you're seeing is the internal representation of a custom AST node for shortcodes in Quarto's AST. (We need it to be like that to avoid Pandoc interpreting shortcode parameter strings as Markdown: {{< eg this--should--not--have--en--dashes >}} otherwise behaves badly). Quarto actually "transforms" those raw shortcodes before Pandoc sees them. Then, our internal Lua representation converts that transformed input into a custom AST node, and from there, filters can target it.

This is not the first time someone asked for the ability to create shortcode invocations from inside a Lua filter. We should allow that: tracking the enhancement request here.

[fuhrmanator]

This is not the first time someone asked for the ability to create shortcode invocations from inside a Lua filter.

Thanks for the info and the enhancement request.

I finally used macros (\newcommand) in LaTeX, since it's possible to put them in the quarto source. Of course it only works in PDF format. It's the old way I used to do this before shortcodes and the fontawesome extension :)