show-whitespace is wrong for tabs in markdown because of a GitHub bug

[fregante]

Please ensure:

• The bug is caused by Refined GitHub. It doesn't happen if I disable the extension.
• The bug happens after clearing extension cache. The "Clear cache" button below can also be found at the bottom of the options page.

Example URLs

• Testing show-whitespace sandbox#18
• https://github.com/fregante/content-scripts-register-polyfill
• this issue

Extension version

22.5.22

Browser(s) used

Safari

Description

Custom tab size is broken for me: https://github.com/settings/appearance

Tabs are rendered as 8 spaces even my setting is for 2:

This is because GitHub isn't adding any data-tab-size attributes in comments for me, even without RGH. I'm only seeing them on embedded code.

And for some reason we default to "4" instead of "8" in our code:

refined-github/source/features/show-whitespace.css

Line 39 in 50c6faf

background-size: calc(var(--tab-size, 4) * 1ch) 1.25em;

Demo

Live:

 1 space
	1 tab

Screenshot:

Solution

We have 2 options:

• set a global default of 4 via non-specific selector: :where(:root) {--tab-size: 4; tab-size: 4}
• change that default to 8

We should probably do both. The latter can be hotfixed.

Include in this issue:

• Screenshots/video/gif demonstrating the bug, if it’s visual
• Console errors, if any