Incorrect Subcaption Numbering in Figures for PDF Output

[produnis]

Bug description

When plotting multiple figures in a single chunk with parameters such as layout-ncol: 3 and fig-subcap, the subcaption numbering is incorrect in the PDF output. All subcaptions start with "a)" instead of incrementing as expected ("a)", "b)", "c)", etc.).

Steps to reproduce

Create and render this document to PDF.

---
title: "Test subcaption"
author: "me"
format: 
  pdf:
    keep-tex: true
  html: default
---

::: {.callout-note appearance="default"}
test
:::

::: {.callout-important appearance="simple"}
here come some plots
:::

```{r}
#| layout-ncol: 3
#| fig-subcap: 
#|   - This
#|   - is a
#|   - test
x <- c(1:100)
y <- x+x+2
plot(x, y)
hist(y, breaks=5)
barplot(table(x,y))

Or use minimal example here https://github.com/produnis/minimal_examples/tree/subcaption

Expected behavior

The 3 figures are numbered "a)", "b)", "c)"

Actual behavior

The 3 figures are numbered as "a)" "a)" "a)".

Your environment

archlinux, quarto 1.6.32 and 1.5.57

Quarto check output

$ quarto check
Quarto 1.6.32
[✓] Checking environment information...
      Quarto cache location: /home/produnis/.cache/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: 1.6.32
      Path: /opt/quarto/bin

[✓] Checking tools....................OK
      Chromium: 869685
      TinyTeX: (not installed)

[✓] Checking LaTeX....................OK
      Using: Installation From Path
      Path: /sbin
      Version: undefined

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

[✓] Checking Python 3 installation....OK
      Version: 3.12.7
      Path: /sbin/python3
      Jupyter: (None)

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

[✓] Checking R installation...........OK
      Version: 4.4.2
      Path: /usr/lib64/R
      LibPaths:
        - /home/produnis/R/x86_64-pc-linux-gnu-library/4.4
        - /usr/lib/R/library
      knitr: 1.48
      rmarkdown: 2.27

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

[cderv]

This works for cross referencable figure when fig-cap is provided

---
title: "Test subcaption"
author: "me"
format: 
  pdf:
    keep-tex: true
  html: default
keep-md: true
---

```{r}
#| label: fig-test
#| layout-ncol: 3
#| fig-cap: main caption
#| fig-subcap: 
#|   - This
#|   - is a
#|   - test
x <- c(1:100)
y <- x+x+2
plot(x, y)
hist(y, breaks=5)
barplot(table(x,y))
```

I believe without fig-cap, and only fig-subcap, this will be considered as three figures, and fig-subcap will be passed as fig-cap, just using letters instead of numbers (because \subcaption{} is used instead if \caption{}).

I think this falls under both of this next work

• [EPIC] Differences on generated Markdown between knitr and jupyter engine #7670
• mini-epic: AST uniformization across engines for floats #7062

We need to document the canonical markdown produced for this case, and check knitr is doing the right thing.

Out of curiosity I looked in past version for this content

```{r}
#| layout-ncol: 3
#| fig-subcap: 
#|   - This
#|   - is a
#|   - test
x <- c(1:100)
y <- x+x+2
plot(x, y)
hist(y, breaks=5)
barplot(table(x,y))
```

• Quarto 1.4.555
  
• Quarto v1.3.450
  
• Quarto v1.2.475
  

So we have various behaviors over time.

Though our doc for subcaptions (https://quarto.org/docs/authoring/figures.html#subcaptions) uses optionnaly for the fig- label

You can create subcaptions for computational output by combining the fig-cap and fig-subcap options. When applying captions to computational output you can optionally include a label with a fig- prefix—if you do this then the figure will be numbered and cross-referenceable.

But label: fig- seems to be needed for this to work
Doing

```{r}
#| layout-ncol: 3
#| fig-cap: Main Caption
#| fig-subcap: 
#|   - This
#|   - is a
#|   - test
x <- c(1:100)
y <- x+x+2
plot(x, y)
hist(y, breaks=5)
barplot(table(x,y))
```

yields

which is not what is document 🤔

[cderv]

I think this falls under both of this next work

• [EPIC] Differences on generated Markdown between knitr and jupyter engine #7670
• mini-epic: AST uniformization across engines for floats #7062

Definitely related to Jupyter vs Knitr logic because too.

I check Jupyter behavior for this

---
title: "Test subcaption"
author: "me"
format: 
  pdf:
    keep-tex: true
  html: default
keep-md: true
---

```{python}
#| fig-subcap: 
#|   - "First"
#|   - "Second"
#| layout-ncol: 2

import matplotlib.pyplot as plt
plt.plot([1,23,2,4])
plt.show()

plt.plot([8,65,23,90])
plt.show()
```

fig-subcap is just ignored when no fig-cap. This is because fig-subcap is known by knitr historically before Quarto so it is supported as a way to pass fig cap to figure. Two behavior should be align

For fig-cap and fig-subcap, numbering problem is similar

---
title: "Test subcaption"
author: "me"
format: 
  pdf:
    keep-tex: true
  html: default
keep-md: true
---

```{python}
#| fig-cap: Main
#| fig-subcap: 
#|   - "First"
#|   - "Second"
#| layout-ncol: 2

import matplotlib.pyplot as plt
plt.plot([1,23,2,4])
plt.show()

plt.plot([8,65,23,90])
plt.show()
```

Adding label: fig-test fixes it

So for both Jupyter and Knitr, it does not behave like documented and fig-subcap requires label to work.

We need to decide which is expected behavior here, and if this is possible or not to correctly create the LaTeX code that allows fig-scap to work, when not a cross referenced figures. 🤔