[css-color] Eager evaluation of calc() for specified value serialization of non-rgb() colors

[weinig]

The CSS Color 4 spec currently only requires eager evaluation of calc() for rgb colors:

For historical reasons, when calc() in sRGB colors resolves to a single value, the declared value serialises without the "calc(" ")" wrapper.

This leaves all the other color types without this behavior, but currently, WPT seems to contradict that. For example, in the test for specified value serialization of lab(), the following test has this expectation [input, expected serialization]:

    ["lab(calc(50 * 3) calc(0.5 - 1) calc(1.5) / calc(-0.5 + 1))", "lab(100 -0.5 1.5 / 0.5)"],

I think the spec makes sense, and is consistent with most other CSS properties, but before changing the tests, I wanted to verify my understanding was correct.

@svgeesus @LeaVerou

[svgeesus]

@tabatkins I recall we changed this (for legacy and modern rgb() and rgba(), only) based on input from you about calc evaluation. Do you recall any details of the web-compat story on this one? @emilio does this ring any bells?

[emilio]

@weinig is it really consistent with other properties? Specified values do generally preserve calc-ness (simplified):

document.body.style.zIndex = "calc(1 + 1)"
document.body.style.zIndex // calc(2)

[svgeesus]

The 'historical reasons' removing calc() was added here because of

• [css-color-4] Specified value for color when calc() is used #8318 (comment)

by css wg resolution

[weinig]

@weinig is it really consistent with other properties? Specified values do generally preserve calc-ness (simplified):

document.body.style.zIndex = "calc(1 + 1)"
document.body.style.zIndex // calc(2)

I’m not entirely sure what you are asking, because I agree, and think preserving calc() is the right thing to do.

The issue is that WPT currently assumes calc() is not preserved, and I want to fix the tests, and was just checking before I made the change.

[emilio]

Ahh, alright, I think I misread you as arguing for the opposite.

[svgeesus]

OK so we are all agreed that the non-rgb specified value WPT tests are wrong to eagerly eliminate calc() and need to be fixed. Great.

[weinig]

I'm working on a fix for them.

[weinig]

I have a PR to update the test here -> web-platform-tests/wpt#48075