Callouts without text create fatal error when rendering to GFM

[azankl]

I have:

• searched the issue tracker for similar issues
• installed the latest version of Quarto CLI
• formatted my issue following the Bug Reports guide

Bug description

Quarto exits with a fatal error when trying to render a Callout with a Title but no text to GFM format.

Steps to reproduce

---
title: "Reproducible Quarto Document"
format: gfm
---

::: {.callout-tip}
## This will cause an error when rendering to gfm format.
:::

::: {.callout-tip}
## This will work
Because there is some text after the title.
:::

Actual behavior

I get this error:

FATAL (/Applications/quarto/share/filters/main.lua:21447) An error occurred:
This is an internal error. Please file a bug report at https://github.com/quarto-dev/quarto-cli/
Error running filter /Applications/quarto/share/filters/main.lua:
/Applications/quarto/share/filters/main.lua:1213: FATAL QUARTO ERROR
stack traceback:
        /Applications/quarto/share/filters/main.lua:2619: in function 'fatal'
        /Applications/quarto/share/filters/main.lua:2199: in function 'fail'
        /Applications/quarto/share/filters/main.lua:2204: in function 'internal_error'
        /Applications/quarto/share/filters/main.lua:21447: in field 'render'
        /Applications/quarto/share/filters/main.lua:1213: in local 'filter_fn'
        /Applications/quarto/share/filters/main.lua:653: in function </Applications/quarto/share/filters/main.lua:643>
        (...tail calls...)
        ...uarto/share/pandoc/datadir/../../filters/modules/jog.lua:34: in upvalue 'run_filter_function'
        ...uarto/share/pandoc/datadir/../../filters/modules/jog.lua:223: in function <...uarto/share/pandoc/datadir/../../filters/modules/jog.lua:202>
        (...tail calls...)
        [C]: in function 'pandoc.List.map'
        ...uarto/share/pandoc/datadir/../../filters/modules/jog.lua:125: in upvalue 'recurse'
        ...uarto/share/pandoc/datadir/../../filters/modules/jog.lua:222: in local 'jogger'
        ...uarto/share/pandoc/datadir/../../filters/modules/jog.lua:171: in upvalue 'recurse'
        ...uarto/share/pandoc/datadir/../../filters/modules/jog.lua:222: in function <...uarto/share/pandoc/datadir/../../filters/modules/jog.lua:202>
        (...tail calls...)
        /Applications/quarto/share/filters/main.lua:572: in function </Applications/quarto/share/filters/main.lua:550>
        (...tail calls...)
        /Applications/quarto/share/filters/main.lua:1314: in local 'callback'
        /Applications/quarto/share/filters/main.lua:1332: in upvalue 'run_emulated_filter_chain'
        /Applications/quarto/share/filters/main.lua:1368: in function </Applications/quarto/share/filters/main.lua:1365>
WARN: Error encountered when rendering files

Expected behavior

Quarto should render the document to GFM format.

Your environment

Positron Version: 2025.10.1 build 4
Code - OSS Version: 1.103.0
Commit: b13dd1ca4803bc04a4a9165395b589b8caf4ab58
Date: 2025-10-14T21:43:42.876Z
Electron: 37.2.3
Chromium: 138.0.7204.100
Node.js: 22.17.0
V8: 13.8.500258-electron.0
OS: Darwin arm64 25.0.0

MacOS 26.0.1

Quarto check output

Quarto 1.8.25
[✓] Checking environment information...
      Quarto cache location: /Users/azankl/Library/Caches/quarto
[✓] Checking versions of quarto binary dependencies...
      Pandoc version 3.6.3: OK
      Dart Sass version 1.87.0: OK
      Deno version 2.3.1: OK
      Typst version 0.13.0: OK
[✓] Checking versions of quarto dependencies......OK
[✓] Checking Quarto installation......OK
      Version: 1.8.25
      Path: /Applications/quarto/bin

[✓] Checking tools....................OK
      TinyTeX: v2025.06
      Chromium: (not installed)

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

[✓] Checking Chrome Headless....................OK
      Using: Chrome found on system
      Path: /Applications/Google Chrome.app/Contents/MacOS/Google Chrome
      Source: MacOS known location

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

[✓] Checking Python 3 installation....OK
      Version: 3.9.17
      Path: /Users/azankl/.pyenv/versions/3.9.17/bin/python
      Jupyter: (None)

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

[✓] Checking R installation...........OK
      Version: 4.5.1
      Path: /Library/Frameworks/R.framework/Resources
      LibPaths:
        - /Library/Frameworks/R.framework/Versions/4.5-arm64/Resources/library
      knitr: 1.50
      rmarkdown: 2.29

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

[mcanouil]

Could you properly format your post using code blocks for code and terminal outputs? Thanks.
If your code contains code blocks, you need to enclose it using more backticks, i.e., usually four ````.
See https://quarto.org/bug-reports.html#formatting-make-githubs-markdown-work-for-us.

[mcanouil]

I can reproduce on latest Quarto CLI development version and it seems specific to gfm format.

[cderv]

yeah this is specific to gfm it does not currently handle empty content callout

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

Lines 200 to 219 in 20c2761

	_quarto.ast.add_renderer("Callout", function(_)
	return _quarto.format.isGithubMarkdownOutput()
	end, function(callout)
	local result = pandoc.Blocks({})
	local header = "[!" .. callout.type:upper() .. "]"
	result:insert(pandoc.RawBlock("markdown", header))
	local tt = pandoc.utils.type(callout.title)
	if tt ~= "nil" then
	result:insert(pandoc.Header(3, quarto.utils.as_inlines(callout.title)))
	end
	local ct = pandoc.utils.type(callout.content)
	if ct == "Block" then
	result:insert(callout.content)
	elseif ct == "Blocks" then
	result:extend(callout.content)
	else
	internal_error()
	end
	return pandoc.BlockQuote(result)
	end)

I'll fix that for 1.9. Thanks for the report!