Circular metadata needs better error

[royfrancis]

Description

I had a situation where I defined a metadata in a qmd file like

---
title: Something
subtitle: "{{< meta subtitle >}}"
format: html
---

I expected this to be read from _metadata.yml where I had

subtitle: "Bla"

And I got this random garbage of a message which is hundreds of lines long.

Error running filter /opt/conda/share/quarto/filters/main.lua:
C stack overflow
stack traceback:
        [C]: in metamethod 'index'
        /opt/conda/share/quarto/filters/main.lua:498: in function 'is_custom_node'
        /opt/conda/share/quarto/filters/main.lua:685: in function </opt/conda/share/quarto/filters/main.lua:684>
        [C]: in ?
        [C]: in method 'walk'
        /opt/conda/share/quarto/pandoc/datadir/_utils.lua:607: in function '_utils.walk'
        /opt/conda/share/quarto/filters/main.lua:572: in function </opt/conda/share/quarto/filters/main.lua:550>
        (...tail calls...)
        /opt/conda/share/quarto/filters/main.lua:20618: in field 'Pandoc'
        /opt/conda/share/quarto/filters/main.lua:586: in function 'run_emulated_filter'
        /opt/conda/share/quarto/filters/main.lua:20585: in local 'filter_fn'
        ...     (skipping 766 levels)
        /opt/conda/share/quarto/filters/main.lua:20585: in local 'filter_fn'
        /opt/conda/share/quarto/filters/main.lua:653: in function </opt/conda/share/quarto/filters/main.lua:643>
        (...tail calls...)
        [C]: in ?
        [C]: in method 'walk'
        /opt/conda/share/quarto/pandoc/datadir/_utils.lua:607: in function '_utils.walk'
        /opt/conda/share/quarto/filters/main.lua:572: in function </opt/conda/share/quarto/filters/main.lua:550>
        (...tail calls...)
        /opt/conda/share/quarto/filters/main.lua:20638: in field 'Pandoc'
        /opt/conda/share/quarto/filters/main.lua:586: in function 'run_emulated_filter'
        /opt/conda/share/quarto/filters/main.lua:1318: in local 'callback'
        /opt/conda/share/quarto/filters/main.lua:1336: in upvalue 'run_emulated_filter_chain'
        ...

Eventually, I realized that it's probably because subtitle is already a metadata and I am defining it again. Changing the metadata from subtitle to something else fixes the issue. This error message could be more sensible.

▸ quarto --version
1.8.25

[mcanouil]

I don't disagree with the error issue, but why would you even do: subtitle: "{{< meta subtitle >}}"
_metadata.yml allows to define metadata that are going to be used as default for all documents next to the file, so your subtitle will get _metadata.yml subtitle without doing anything.
Maybe what you actually wanted is _variables.yml.

[cscheid]

This is really quite hard to solve in general, and there's not quick solution for it. (in the limit, this is as hard as the halting problem). In practice, we might be able to figure something out with linting, but don't hold your breath.