[css-properties-values-api-1] Figure out what to do with font-relative lengths

[tabatkins]

Per #8169 (comment), there might be a remaining circularity issue if font-relative lengths are used in custom properties with <length> type.

[Loirooriol]

The problem isn't just for <length> type. w3c/css-houdini-drafts#1080

[fantasai]

Maybe you need two different <length> types: those that can be used in unit-influencing properties like font-size and line-height, and those that can't.

[lilles]

As @Loirooriol points out, this is not just limited to <length> values.

Assume --number is a registered custom property with the <number> syntax:

p {
  --number: calc(10 + 2 * sign(1em - 20px));
  font-size: calc(var(--number) * 2px);
}

[css-meeting-bot]

The CSS Working Group just discussed [css-properties-values-api-1] Figure out what to do with font-relative lengths.

The full IRC log of that discussion

<JoshT> TabAtkins: the deal here is that if you have registered custom properties. we resolve unit math.
<JoshT> ... if you have an em, this now depends on the font-size property
<JoshT> ... I have proposal to add constaints to length type custom properties
<fantasai> what constraints?
<JoshT> ... not yet complete. number typed ones could also get this from algebra
<JoshT> ... this doesn't require any resolutions
<JoshT> ... I need to a: extend this to apply to all typed custom properties
<JoshT> ... b: reqrite to use the new dependency mapping property that is in all the new CSS specs
<JoshT> ... will just be a mechanical transform, but I think there's a solution. just need to take care of it now
<JoshT> fantasai: I don't understand why it was brought up to the WG
<fantasai> s/WG/WG if not going to even explain what we're doing/
<JoshT> TabAtkins: was brought up by oriall. I'm just acknowledging that it is being worked on
<TabAtkins> s/oriall/oriol/
<oriol> I didn't remember adding this to agenda, happy to wait for Tab's edits
<fantasai> ok, that was a really long way to say "let's take this off the agenda until futher work"
<JoshT> astearns: so we'll take it off the agenda and keep the issue open. will bring it back when Tab has done some work