Document outline broken for title-less Quarto slides with slide-level attribute

[mine-cetinkaya-rundel]

System details

RStudio Edition : Desktop
RStudio Version : RStudio 2024.04.0-daily+689 "Chocolate Cosmos" Daily (9ee2b6131e42e36e31cec48a4eb88d2e700e272c, 2024-04-10) for macOS Mozilla/5.0 (Macintosh; Intel Mac OS X 10_15_7) AppleWebKit/537.36 (KHTML, like Gecko) RStudio/2024.04.0-daily+689 Chrome/120.0.6099.291 Electron/28.2.6 Safari/537.36, Quarto 1.4.553 (/Applications/quarto/bin/quarto)
OS Version      : Mac OS Ventura 13.5 (22G74)
R Version       : R version 4.3.3 (2024-02-29) -- "Angel Food Cake"

Steps to reproduce the problem

Create a Quarto slide deck with format: revealjs and include a mix of slides with and without titles:

---
format: revealjs
---

# Section with title

## Slide with title

Some content.

##

Slide without title

# Another section with title

## Another slide with title

What the document outline shows is not ideal (it completely ignores the title-less slide) but has the right indentation for sections and slides, in both the visual and source editors.

Now add a slide-level attribute to the title-less slide (e.g., {.smaller}). The document outline indentation is broken in the source editor, still look ok (even if not ideal) in the visual editor.

Describe the problem in detail

Title-less slides break document outline indentation in the source editor if they have an attribute at the slide level.

Describe the behavior you expected

I expected

1. Title-less slides to show up in the document outline
2. The behavior of the document outline to match between source and visual editors when title-less slide has a slide-level attribute.

• I have read the guide for submitting good bug reports.
• I have installed the latest version of RStudio, and confirmed that the issue still persists.
• If I am reporting an RStudio crash, I have included a diagnostics report.
• I have done my best to include a minimal, self-contained set of instructions for consistently reproducing the issue.

[ronblum]

Reproducible in both RStudio Desktop 2023.12.1+402 and 2024.04.0-daily+693 on Windows 11.