[rustdoc] Add sans-serif font setting

[GuillaumeGomez]

Fixes #52449.

This PR adds a new setting introducing the possibility to switch to a sans-serif font (Fira Sans) for the text.

Can be tested here.

cc @rust-lang/rustdoc-frontend
r? @notriddle

[rustbot]

Some changes occurred in HTML/CSS/JS.

cc @GuillaumeGomez, @jsha

[notriddle]

If you want Fira Sans for the main body type, then Fira Mono should be used for code. That way they have consistent point sizes, x-height, and other features.

[GuillaumeGomez]

Sounds good to me!

[notriddle]

The other problem I have with this change is that it was discussed before and rejected. I'm not sure why, though, so I'm not sure how to avoid hitting the same problems as back then:

#16207 #16173

[GuillaumeGomez]

Checking what studies say about it.

• https://dergipark.org.tr/en/download/article-file/252226 : this one seems to say that sans serif fonts are more adapted for computers and improve readability (although they only seemed to compare Verdana and Times New Roman)
• https://eric.ed.gov/?id=EJ1067757 : this one says that there is no significant difference between both
• https://www.researchgate.net/profile/Ricardo-Baeza-Yates/publication/262320823_Good_fonts_for_dyslexia/links/628133b3107cae2919a8b26d/Good-fonts-for-dyslexia.pdf: this one seems to say that sans serif are better
• https://library.oapen.org/bitstream/handle/20.500.12657/53344/978-3-030-90984-0.pdf : no difference
• https://peerj.com/articles/cs-1139.pdf : no difference
• https://www.researchgate.net/profile/Filiz-Cicek/publication/304358587_How_Serif_and_Sans_Serif_Typefaces_Influence_Reading_on_Screen_An_Eye_Tracking_Study/links/5783769608ae37d3af6bedaf/How-Serif-and-Sans-Serif-Typefaces-Influence-Reading-on-Screen-An-Eye-Tracking-Study.pdf : sans serif is a bit better

So seems like there is no difference or it's a bit better in favour of sans serif. In any case I want to ensure the team is on board with this as it's a big UI change. Better take our time to ensure that we're not missing something before approving the change.

[notriddle]

I realized I was kind of terse. Here's a slightly more detailed opinion, along with the reason why I hold it:

1. If you choose a body font, you need to choose a code font that goes with it, because Rustdoc mixes them freely in layouts like this one:

   before	after

   If you're not sure why I think "before" looks better, focus on the phrase "or target".

2. If we change something, we need to address the reasons why it was done that way originally. It's fine if the reason seems to be "nobody thought of it," but the choice of a serif font here was definitely deliberate.

   As a user with bad enough vision that they won't let me drive a car, Fira Sans doesn't seem significantly more readable than Source Serif. This adds up, since, even though it's a serif font, Source Serif is supposed to be usable as a screen font. On the other hand, cataracts, astigmatism, and amblyopia are all "bad eyesight," but they have totally different effects. Just because it WorksForMe(tm) doesn't mean it works for anybody else.

I think this is why even relatively un-customizable apps like Apple Books have multiple font packs built in. It's few enough that they can make sure every one of them looks good, but diverse enough to satisfy the most common problems someone might have with extended reading.

I think we should add an option to the Settings panel to change the font, just like Pocket and Firefox's Reader Mode. This is because, when you consider the "bikeshedding effect," there really aren't that many people complaining about Source Serif.

Now that CSS Variables are being used, implementing this shouldn't actually be that hard.

[GuillaumeGomez]

I realized I was kind of terse. Here's a slightly more detailed opinion, along with the reason why I hold it:

No I actually agreed with your point. I should have looked into it beforehand.

If you choose a body font, you need to choose a code font that goes with it, because Rustdoc mixes them freely in layouts like this one:

Starting the moment you mentioned it, I was planning to change it. I didn't because I don't want to invest more time into it unless I'm sure the team is onboard.

I think we should add an option to the Settings panel to change the font, just like Pocket and Firefox's Reader Mode.

I think as a first step (and eventually as final step too) it might be better. Like that people can pick serif or sans serif and everyone is happy.

[bors]

☔ The latest upstream changes (presumably #133634) made this pull request unmergeable. Please resolve the merge conflicts.

[GuillaumeGomez]

I added a new setting to use "sans serif font":

I updated online demo as well.

[GuillaumeGomez]

Rebased just in case but again, when running ./x.py test collect-license-metadata, no changes...

[GuillaumeGomez]

Yeah ok, I officially have no idea what's wrong with this script.

[notriddle]

I assume it's because you've got your config.toml set up to avoid building the embedded book and gcc, so they don't wind up included in this file even though they should be.

To fix this, would either do a truly complete rust build, or I would just hand-patch in the few lines that are added in your PR.

[GuillaumeGomez]

Ok, that makes more sense now. Thanks a lot!

[notriddle]

The PR description and title don't describe what it does any more. That should probably be changed, then it can be more easily FCP-ed.

[rfcbot]

🔔 This is now entering its final comment period, as per the review above. 🔔

[rfcbot]

The final comment period, with a disposition to merge, as per the review above, is now complete.

As the automated representative of the governance process, I would like to thank the author for their work and everyone else who contributed.

This will be merged soon.

[GuillaumeGomez]

CI fixed, let's go. :)

@bors r=rustdoc

[bors]

📌 Commit 2511faf has been approved by rustdoc

It is now in the queue for this repository.