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CSS Working Group Editor Drafts
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[css-sizing] Does indefinite `stretch` behave as automatic size or as initial value? #11006

Open Loirooriol opened 1 month ago

Loirooriol commented 1 month ago

First, consider

<!DOCTYPE html>
<div style="min-height: max-content; height: 0; width: 200px; border: solid">lorem ipsum</div>
Spec, Blink Gecko, WebKit

@bfgeek told me that Blink had to deal with some breakage when they adopted this behavior, but that it's the correct thing to do. But what about stretch?

<!DOCTYPE html>
<div style="min-height: -moz-available; min-height: -webkit-fill-available; min-height: stretch; 
            height: 0; width: 200px; border: solid">lorem ipsum</div>
Spec Gecko, Blink WebKit

(WebKit seems to stretch elements with an indefinite height that contain some -webkit-fill-available, so it's always definite)

From https://drafts.csswg.org/css-sizing-4/#stretch-fit-sizing

Formally, its behavior is the same as specifying an automatic size together with a self-alignment property value of stretch

But here Blink is not implementing this, not sure if due to an oversight.

And then the situation is that browsers are implementing stretch, but nobody follows the spec here. It may be too late for *-content, but I would like to have an agreement for stretch before it ships. So Agenda+.

Loirooriol commented 1 month ago

For Servo following the spec seems a bit simpler than aligning with Blink, so I guess I will go with that for now.

bfgeek commented 1 month ago

Formally, its behavior is the same as specifying an automatic size together with a self-alignment property value of stretch

So I think this was intended just to be applicable to main sizes, (e.g. not min/max-sizes).

IMO this should be consistent with min-height: 100%, e.g. if a percentage is indefinite it behaves as zero for min-height, and Infinity for max-height.

(e.g. The Blink/Gecko behaviour).

For example it'd be pretty weird if:

<!DOCTYPE html>
<div style="max-height: stretch; height: 200px; width: 200px; border: solid">lorem ipsum</div>

got clamped by the intrinsic size (when stretch is an extrinsic constraint).

cc/ @tabatkins

Loirooriol commented 1 month ago

I'm not convinced we should treat it like a percentage. For example, with a min/max-content of 100px, fit-content is basically clamp(100px, stretch, 100px), and in Blink max-height: fit-content behaves as 100px but max-height: clamp(100px, 100%, 100px) behaves as none. And doing this like Blink seems more annoying to implement in Servo.

So I think we should either:

bfgeek commented 1 month ago

I'm not convinced we should treat it like a percentage. For example, with a min/max-content of 100px, fit-content is basically clamp(100px, stretch, 100px)

This isn't correct - we recently did a change to follow Firefox in this regard. See: https://github.com/w3c/csswg-drafts/issues/10721 When the stretch is indefinite - min-size: fit-content resolves to min-size: min-content, and max-size: fit-content to max-size: max-content respectively.

And doing this like Blink seems more annoying to implement in Servo.

I'm curious why this is difficult in Servo? This might result in difficulty when attempting to implement calc-size() for example.

I'm pretty convinced that we should just be consistent with 100% here, (again see the max-height:stretch example above, it'd be super weird if we coerce an explicitly extrinsic constraint to be intrinsic).

Loirooriol commented 1 month ago

we recently did a change to follow Firefox in this regard. See: https://github.com/w3c/csswg-drafts/issues/10721

Not sure if that is the best behavior, I have commented there.

I'm curious why this is difficult in Servo?

I misunderstood what you were doing for fit-content, I thought it was trickier. Resolving keywords in different ways depending on the property and having a potentially indefinite stretch size during layout still adds some complexity. But not a big deal I guess.

it'd be super weird if we coerce an explicitly extrinsic constraint to be intrinsic

Maybe a bit weird indeed.

Loirooriol commented 1 month ago

It's worth noting that there is a difference among major browsers:

<!DOCTYPE html>
<div style="display: flex; flex-direction: column; border: solid cyan; min-height: 100px; width: 200px;">
  <div style="min-height: -moz-available; min-height: -webkit-fill-available; min-height: stretch;
              flex-basis: 0; border: solid">lorem ipsum</div>
</div>
Gecko Blink, WebKit

Interestingly, they all treat min-height: 0% as 0px.

bfgeek commented 1 month ago

I wouldn't read too much into the block direction behaviour with FF (support was lacking last time I checked).

dholbert commented 1 month ago

Indeed, the FF behavior is just because I haven't implemented stretch behavior in the block axis yet (keep getting distracted by other tasks, but made a little local progress this week, hope to be done soonish).

Loirooriol commented 1 month ago

Sure, but if the spec changes, we need to decide whether min-height: stretch should behave as auto or as 0px or whatever 100% would do (the spec says that 100% should behave as 0px, but browsers don't follow the spec in general).