Font change on beamer slides when building with pandoc 3.5

[pck1980]

I just realized my freshly built beamer slides look different than they used to. The only thing I changed (as far as I remember) was updating pandoc from 3.4 to 3.5
I use the Metropolis theme which used to look like in the first screenshot, but now it looks as shown in the second screenshot.

The font change does not only affect the title, but all slides.

My markdown header looks like this:

---
title: blah
author: blah
date: blah
institute: blah 
theme: metropolis
keywords: [blah]
---

Forgot to mention: I built the slides with the command pandoc -s -t beamer --pdf-engine=lualatex -o slides.pdf slides.md -V theme:metropolis -V themeoptions:subsectionpage=progressbar -V lang=de

The changelog mentions several changes to Beamer output, but I have no idea what I have to do to get back to the old appearance.
Thanks in advance for any help.

[jgm]

Which of these matches the appearance metropolis is supposed to have?

[jgm]

I think that to diagnose this, you can do:

• use pandoc 3.5: pandoc test.md -t beamer -s -o test-3.5.tex -V theme:metropolis
• use pandoc 3.4: pandoc test.md -t beamer -s -o test-3.4.tex -V theme:metropolis
• diff -u test-3.4.tex test-3.5.tex

This should give us a full accounting of what has changed, and we can then test changes to test-3.5.tex that would restore the old behavior (assuming it is the proper one).

[pck1980]

I think the „old“ look is the correct one.

Can I simply install 3.4 again on macOS to go back to that version?

[pck1980]

I tried building a test document with both pandoc 3.4 and 3.5 as you suggested. Here's the output of diff:

diff.txt

And the test file I used:

test.md

Going back to 3.4 also confirmed that it was indeed the update to 3.5 that changed the appearance of my slides. With 3.4, I get the old (correct) look again.

[pck1980]

I just realized that both tex files result in a "wrong looking" pdf when processing them with pdflatex, whereas lualatex creates a correct-looking pdf from test-3.4.tex, but a wrong looking from test-3.5.tex

[pck1980]

It seems that moving the line \usetheme[]{metropolis} down to where it was with version 3.4 solves the issue.

[twsh]

I can confirm that trying it on a system without Fira Sans deliberately added, I see what you saw. I don't know how lualatex manages to find it. I do have a full texlive installation (on both systems) and that includes the Fira fonts.

[jgm]

OK, @badumont has clarified this.

So, I guess it looks like we should re-split the fonts partial. Originally instead of fonts I had two partials, fonts and font-settings. We could go back to that, but for backwards compatibility it might be wiser to create two new partials and include them from fonts. Then custom templates based on pandoc 3.5 would not need to be modified. The cost, though, would be an uglier and more indirect system. @tarleb do you have thougths on this?

[tarleb]

I can't really comment on possible alternatives, but fonts and font-settings seems clean enough IMHO. My only thought was that a name like fonts-override could help to clarify the intend for that partial, but I'm not sure.

[jgm]

My question wasn't really about the names, but about whether we should adopt a suboptimal plan (making the fonts partial include two new partials, as opposed to using the two partials directly in default.latex) in order to retain backwards compatibility with custom templates based on pandoc 3.5.

[tarleb]

Ah. I'd rather break backwards compatibility then. Projects like Quarto expect a certain instability and maturation period for new features, so I'd say it's fine to change it now.

[badumont]

I wonder why this would work with your xelatex setup but not mine? Note: I don't have "Fira Sans" installed on my system, but this doesn't seem to prevent lualatex from finding it (perhaps in the metropolis style files)?

LuaLaTeX probably finds it in your TeXLive directory (or whatever TeX distribution you use). But, as the fontspec manual says: “In XeTeX, fonts fond in the TEXMF tree can be loaded in Windows and Linux, but not on MacOS.”

[jgm]

I have pushed a fix that splits the fonts partial into two parts.