\boldsymbol rendered incorrectly to PDF default (using Lualatex) because unicode-math takes precedence

[Guest-1013]

Bug description

I was rendering a .qmd file into a PDF document when I found that \boldsymbol didn't work: the letters inside them are just ordinary, not bold.

However, rendering it to HTML would work perfectly; the \boldsymbols are rendered as bold characters.

I was using a separate install of TinyTeX (directly, without Quarto), whose path was manually added to Path.

---

A test of TinyTeX itself was done as follows: I write a separate .tex file:

\documentclass{article}
\usepackage{amsmath}

\begin{document}

$$
\boldsymbol{r} r
$$

\end{document}

and used xelatex test.tex AND lualatex test.tex to render it; the result is perfect, the first r is bold while the second is ordinary.

Also, directly using pandoc to convert to PDF file works perfect.

Steps to reproduce

---
title: "quarto boldsymbol test"
format:
    pdf:
        toc: false

latex-tinytex: true
---

# Title

$\boldsymbol{r} r$

$$
\boldsymbol{r} r
$$

---

I also tried using xelatex as PDF engine, which didn't work either.

I also tried latex-tinytex: false, which didn't work either.

I also tried manually adding amsmath by:

header-includes:
    - \usepackage{amsmath}

which didn't work.

Actual behavior

For example, in the .qmd file above, the rendered PDF file displays every r as ordinary letters, no bold.

Expected behavior

rs inside \boldsymbol should be bold.

Your environment

• OS: Windows 11
• Quarto: 1.9.37
• TinyTeX:
  • tlmgr: tlmgr revision 78616 (2026-04-06 15:48:59 +0200)
  • xelatex: XeTeX 3.141592653-2.6-0.999998 (TeX Live 2026)
  • lualatex: This is LuaHBTeX, Version 1.24.0 (TeX Live 2026) Development id: 7724

[cderv]

Thanks for the report.

The issue comes from the default PDF engine. Quarto defaults to lualatex, which causes unicode-math to be loaded. Under unicode-math, \boldsymbol silently produces non-bold output. The reason: \boldsymbol works internally by calling \mathversion{bold} (from amsbsy.sty, which amsmath loads), a traditional TeX font-switching mechanism that doesn't interact with unicode-math's Unicode character slot system.
In unicode-math, bare math letters like r are mapped to specific Unicode positions — regular italic r is U+1D45F (𝑟), bold italic r is U+1D493 (𝒓). Switching math version doesn't change which Unicode slot is used, so r stays non-bold. No error is raised, which makes this hard to diagnose.

amsmath is already loaded unconditionally in Quarto's template, so adding it in header-includes has no effect. The problem is not a missing package: \boldsymbol is defined (via amsbsy, which amsmath loads), but the font-switching mechanism it relies on is inoperative under unicode-math.

As this is lower level, I looked into Pandoc side too.
This reproduces at the Pandoc level, independent of Quarto. Given a file repro.md containing $\boldsymbol{r} r$:

cat > repro.md << 'MDEOF'
$\boldsymbol{r} r$
MDEOF

# Works — pdflatex does not load unicode-math
pandoc repro.md --pdf-engine=pdflatex -o repro-pdflatex.pdf

# Fails — lualatex loads unicode-math, \boldsymbol silently produces non-bold output
pandoc repro.md --pdf-engine=lualatex -o repro-lualatex.pdf

Pandoc defaults to pdflatex, so "direct pandoc" worked in your test. Quarto sets lualatex as its default:

quarto-cli/src/format/pdf/format-pdf.ts

Line 136 in 45ecb6e

[kPdfEngine]: "lualatex",

Workarounds

Switch to pdflatex — avoids unicode-math entirely, \boldsymbol works as expected:

format:
  pdf:
    pdf-engine: pdflatex

Or keep lualatex and redefine \boldsymbol to the unicode-math equivalent in header-includes:

header-includes:
  - \renewcommand{\boldsymbol}[1]{\symbfit{#1}}

\symbfit produces bold italic (U+1D493, 𝒓), which matches the traditional intent of \boldsymbol. If you want bold upright instead, use \symbf.

Or replace \boldsymbol in your source directly with \symbfit{r} (bold italic) or \symbf{r} (bold upright).

I don't exactly know is this is something we can improve at Quarto level, or if this is at Pandoc level to avoid unicode-math to override, unless amsmath and unicode-math are not really to be used together...