Lua filter error with gfm for a crossref figure

[cderv]

The following example throws an error on quarto 1.5.54

---
title: "Minimal example"
format: gfm
---

```{python}
#| label: fig-sin
import matplotlib.pyplot as plt
import numpy as np

x = np.linspace(0,1,10)
y = np.sin(x)

plt.plot(x,y)
```

The error is the following:

Error running filter /home/opt/quarto-1.5.54/share/filters/main.lua:
Block, list of Blocks, or compatible element expected, got table
        while retrieving function argument blocks
        while retrieving arguments for function Blocks
stack traceback:
        /home/opt/quarto-1.5.54/share/filters/main.lua:22460: in field 'render'
        /home/opt/quarto-1.5.54/share/filters/main.lua:1233: in local 'filter_fn'
        /home/opt/quarto-1.5.54/share/filters/main.lua:635: in function </home/opt/quarto-1.5.54/share/filters/main.lua:625>
        (...tail calls...)
        [C]: in ?
        [C]: in method 'walk'
        /home/opt/quarto-1.5.54/share/filters/main.lua:557: in function </home/opt/quarto-1.5.54/share/filters/main.lua:546>
        (...tail calls...)
        /home/opt/quarto-1.5.54/share/filters/main.lua:1334: in local 'callback'
        /home/opt/quarto-1.5.54/share/filters/main.lua:1352: in upvalue 'run_emulated_filter_chain'
        /home/opt/quarto-1.5.54/share/filters/main.lua:1388: in function </home/opt/quarto-1.5.54/share/filters/main.lua:1385>
stack traceback:
        /home/opt/quarto-1.5.54/share/filters/main.lua:557: in function </home/opt/quarto-1.5.54/share/filters/main.lua:546>
        (...tail calls...)
        /home/opt/quarto-1.5.54/share/filters/main.lua:1334: in local 'callback'
        /home/opt/quarto-1.5.54/share/filters/main.lua:1352: in upvalue 'run_emulated_filter_chain'
        /home/opt/quarto-1.5.54/share/filters/main.lua:1388: in function </home/opt/quarto-1.5.54/share/filters/main.lua:1385>

It sounds like it has something to do with the gfm output format, it works correctly if I render to html. The first time I encountered this bug I was rendering my project to both gfm and html, and changing that to just render html works as expected. I was using gfm because it gives a nice preview on GitHub.

Originally posted by @mbellitti in #9334 (comment)

[cderv]

@cscheid I think this is a required follow up on

• lua - protect against nil caption_long fields in floats #10198

quarto-cli/src/resources/filters/customnodes/floatreftarget.lua

Lines 1041 to 1057 in 0d87b08

	if caption_location == "top" then
	return pandoc.Blocks({
	open_block,
	float.caption_long,
	float.content,
	close_block
	})
	else
	return pandoc.Blocks({
	open_block,
	float.content,
	pandoc.RawBlock("markdown", "\n"),
	float.caption_long,
	close_block
	})
	end
	end)

We probably need to deal with float.caption_long the same way everywhere.

I see addition local to lightbox - should have a new helper to use everywhere ?

quarto-cli/src/resources/filters/layout/lightbox.lua

Lines 142 to 148 in 0d87b08

	local function get_caption_content(floatEl)
	if floatEl.caption_long then
	return floatEl.caption_long.content or floatEl.caption_long
	else
	return pandoc.Inlines({})
	end
	end

Also sometimes, it seems with use pandoc.Inlines({}) as default

quarto-cli/src/resources/filters/customnodes/floatreftarget.lua

Line 205 in 0d87b08

local caption_content = (float.caption_long and float.caption_long.content) or float.caption_long or pandoc.Inlines({})

And other time pandoc.Div({}), which then handle float.caption_long.content correctly. So not the same everywhere.

quarto-cli/src/resources/filters/quarto-post/latex.lua

Lines 322 to 324 in 0d87b08

	if float.caption_long == nil then
	float.caption_long = pandoc.Div({})
	end

and other place using already a helper as_blocks

quarto-cli/src/resources/extensions/quarto/docusaurus/docusaurus.lua

Line 168 in 0d87b08

pandoc.Div(quarto.utils.as_blocks(float.caption_long)),

Anyhow, handling a default works,

diff --git a/src/resources/filters/customnodes/floatreftarget.lua b/src/resources/filters/customnodes/floatreftarget.lua
index 913e7e5fc..6eb085535 100644
--- a/src/resources/filters/customnodes/floatreftarget.lua
+++ b/src/resources/filters/customnodes/floatreftarget.lua
@@ -1037,11 +1037,11 @@ end, function(float)
 
   local open_block = pandoc.RawBlock("markdown", "<div id=\"" .. float.identifier .. "\">\n")
   local close_block = pandoc.RawBlock("markdown", "\n</div>")

   if caption_location == "top" then
     return pandoc.Blocks({
       open_block,
-      float.caption_long,
+      float.caption_long or pandoc.Div({}),
       float.content,
       close_block
     })
@@ -1050,7 +1050,7 @@ end, function(float)
       open_block,
       float.content,
       pandoc.RawBlock("markdown", "\n"),
-      float.caption_long,
+      float.caption_long or pandoc.Div({}),
       close_block
     })
   end

but I am thinking maybe we should be sure to handle this everywhere needed. So assigning to you as you know better each part of FloatRefTarget

[cscheid]

The root cause of this is the upgrade to Pandoc where accessing the nodes no longer creates empty content. The fix is easy and I'll backport.