Cannot pass an R vector to `fig-subcap` with YAML validation, but works without

[jack-davison]

Bug description

When YAML validation is on, I can't pass an R vector to fig-subcap:. I get the below error.

Watching files for changes
In file qmd.qmd
(line 20, columns 16--29) Field "fig-subcap" has value !expr 'yaxes', which must instead be 'true'

When I set validate-yaml: false it progresses and produces the desired output:

Clearly fig-subcap doesn't want/need a value true.

Steps to reproduce

This fails:

---
title: "Quarto Playground"
format: html
engine: knitr
execute:
  echo: false
---

```{r}
library(ggplot2)

dat <- mtcars

yaxes <- names(mtcars)[names(mtcars) != "mpg"]
```

```{r}
#| label: fig-polarplots
#| fig-cap: !expr 'paste("Air", "Quality")'
#| fig-subcap: !expr 'yaxes'
#| layout-ncol: 2

purrr::map(yaxes, \(x) plot(mtcars[["mpg"]], mtcars[[x]]))
```

This works:

---
title: "Quarto Playground"
format: html
engine: knitr
validate-yaml: false
execute:
  echo: false
---

```{r}
library(ggplot2)

dat <- mtcars

yaxes <- names(mtcars)[names(mtcars) != "mpg"]
```

```{r}
#| label: fig-polarplots
#| fig-cap: !expr 'paste("Air", "Quality")'
#| fig-subcap: !expr 'yaxes'
#| layout-ncol: 2

purrr::map(yaxes, \(x) plot(mtcars[["mpg"]], mtcars[[x]]))
```

Expected behavior

Either:

• Yaml validation shouldn't complain being given a R vector via !expr.

• Passing an R vector to fig-subcap should never work (note: I'd much rather this wasn't the case unless there was some alternative to dynamically setting fig subcaps!)

Actual behavior

See bug description - errors w/ yaml validation.

Your environment

• IDE: RStudio 2024.12.0.467
• OS: Windows 11

Quarto check output

[>] Checking environment information...
      Quarto cache location: C:\Users\JD38\AppData\Local\quarto
[>] Checking versions of quarto binary dependencies...
      Pandoc version 3.4.0: OK
      Dart Sass version 1.70.0: OK
      Deno version 1.46.3: OK
      Typst version 0.11.0: OK
[>] Checking versions of quarto dependencies......OK
[>] Checking Quarto installation......OK
      Version: 1.6.39
      Path: C:\Users\JD38\AppData\Local\Programs\Quarto\bin
      CodePage: 1252

[>] Checking tools....................OK
      TinyTeX: (external install)
      Chromium: (not installed)

[>] Checking LaTeX....................OK
      Using: TinyTex
      Path: C:\Users\JD38\AppData\Roaming\TinyTeX\bin\windows\
      Version: 2024

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

[>] Checking Python 3 installation....(None)

      Unable to locate an installed version of Python 3.
      Install Python 3 from https://www.python.org/downloads/

[>] Checking R installation...........OK
      Version: 4.4.2
      Path: C:/PROGRA~1/R/R-44~1.2
      LibPaths:
        - C:/Users/JD38/AppData/Local/R/win-library/4.4
        - C:/Program Files/R/R-4.4.2/library
      knitr: 1.49
      rmarkdown: 2.29

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

[cderv]

Is this happening in RStudio IDE context ?

I see the linting problem

But it does not prevent rendering for me.

Anyhow, this is another case where !expr should be allowed in knitr engine context for the YAML validation

purrr::map(yaxes, (x) plot(mtcars[["mpg"]], mtcars[[x]]))

BTW I change this to purrr::walk() to avoid NULL being printed in output

[cderv]

Our schema does support string or array of string

quarto-cli/src/resources/schema/cell-figure.yml

Lines 18 to 23 in b822c3f

	- name: fig-subcap
	schema:
	anyOf:
	- enum: [true]
	- maybeArrayOf: string
	description: Figure subcaptions

So not sure why the first value only is seen 🤔

it does not prevent rendering for me.

Same in Positron BTW I can render with error

[cderv]

@cscheid do we have specific treatment somewhere for which fields could support !expr in knitr cell ?

I am interested to have a discussion on this at our next meeting so that I can know what to look for on my own for those type of enhancement.

[jack-davison]

Is this happening in RStudio IDE context ?

I see the linting problem

But it does not prevent rendering for me.

It is preventing rendering for me - I don't know if its my specific version of RStudio/Quarto (in original post) or something I/our IT has done to configure it, but it very much stops rendering when the YAML fails.

[cderv]

I am running 2025.04.0-daily+281 version of RStudio. I'll try with the same as you.
For Quarto, I tried with 1.6.40.

I think it is expected to get rendering error on YAML validation failure, so not sure why I don't have it.

Anyhow, thanks for the report. We'll try to fix the validation for this specific !expr usage. This is knitr specific support and not cross engine, so it makes it harder to support.