[css-values] calc()'s divisions should support numeric expressions

[nox]

https://drafts.csswg.org/css-values/#calc-syntax

The spec says calc() supports only numbers after /, thus excluding things like (1 + 1). Both Firefox and WebKit support the latter, so the spec should be changed.

Cc @dbaron @SimonSapin

[dbaron]

I believe the spec used to allow for dividing by numerical-only expressions; I'm not sure why that changed. (We also want to expand to allowing more in the future, so I don't see the harm in allowing the implemented thing now.)

[FremyCompany]

Works in Edge too. If it works everywhere, I agree we should update the spec.

[FremyCompany]

The grammar also doesn't allow the calc( calc(...) ) we resolved to accept, so it should be updated to include that option as well. Depending on how we decide to fix this issue, it might depend on previous PR so I'll refrain from making the change now.

[tabatkins]

The OP's bug is invalid; the grammar in https://drafts.csswg.org/css-values/#calc-syntax definitely allows numeric expressions in the denominator, and the type-checking in https://drafts.csswg.org/css-values/#calc-type-checking is referring to "resolved types". Expressions like (1 + 1) have a "resolved type" of <number>.

François's issue is also invalid - a calc() will always resolve to either a <number>, <percentage>, or <dimension>, so nested calc()s are definitely allowed per the grammar.

[FremyCompany]

@tabatkins Oh, yes, you are right about my second issue!

The first issue was valid before the spec changed. The spec seems to have been accidentally changed by my pull request, I don't know why... I made the commit in a branch. Did someone merge it?

[FremyCompany]

Here is what I see in the spec now:

The syntax of a calc() function is:
<calc()> = calc( <calc-sum> )
<calc-sum> = <calc-product> [ [ '+' | '-' ] <calc-product> ]*
<calc-product> = <calc-value> [ '*' <calc-value> | '/' <calc-number-value> ]*
<calc-value> = <number> | <dimension> | <percentage> | ( <calc-sum> )
<calc-number-sum> = <calc-number-product> [ [ '+' | '-' ] <calc-number-product> ]*
<calc-number-product> = <calc-number-value> [ '*' <calc-number-value> | '/' <calc-number-value> *
<calc-number-value> = <number> | ( <calc-number-sum> )

which is what my pull request was adding. I am fairly confused I must say.

[FremyCompany]

I think the bikeshed watcher screwed up. The spec was just updated to include my PR but the last commit in master is still 6 days old. Next time the watcher will regenerate the spec, my PR will disappear.

https://github.com/w3c/csswg-drafts/blob/master/css-values/Overview.bs

[tabatkins]

Sigh, yes, this confused me too. According to @plinss this is due to a bug in Mercurial's bridging. Okay, nm, let's just merge the PR.

(@plinss suggests not doing PRs from the main repo, as it causes this. Do it in your fork like normal.)

[FremyCompany]

Thanks for investigating! Good to know, too...

The downside is that it means I can't use the edit button on github to fix the specs. That seems mildly annoying. On my work PC it's a no-brainer but at home I find it easier.

[plinss]

@FremyCompany you can hit the "Fork" button on GitHub to fork the repo into your own account, then you can use the "Edit" button in that repo

[fantasai]

Agenda+ to confirm with the WG that this goes in L3. Since L4 is going to have unit algebra in the denominator, it seems to me that this edit was intended for L3).

[tabatkins]

Yes, this is just a mistake in the L3 spec (my fault, I think). It matches current impls.

[css-meeting-bot]

The CSS Working Group just discussed CSS Values and Units: numeric expression denominators, and agreed to the following resolutions:

• RESOLVED: Numeric expressions are explicitly allowed in denominators of calc() expressions

The full IRC log of that discussion

<fantasai> Topic: CSS Values and Units: numeric expression denominators
<fantasai> github topic: https://github.com//issues/1241
<myles> fantasai: we originally intended the denominator of calc() to have a numeric expression
<myles> fantasai: like calc(13 / (5 + 3))
<myles> fantasai: we don't like units because unit math is hard
<myles> fantasai: numeric math is ok though
<myles> fantasai: that isn't in the spec but we do have implementations. so we should add this to level 3
<myles> fantasai: level 4 doesn't make sense because level 4 will include all the unit math and everything which would be a superset of this
<myles> fantasai: but we need a resolution if we want to add it to level 3
<myles> Rossen: yes please
<myles> Rossen: <expresses support>
<myles> Rossen: any objections?
<myles> RESOLVED: Numeric expressions are explicitly allowed in denominators of calc() expressions

[FremyCompany]

I think edits were already made, closing the issue.