[css-sizing] height: stretch on a float shouldn't ignore margins #11905
Description
Follow-up from #11044. https://drafts.csswg.org/css-sizing-4/#stretch-fit-sizing
Behaves as 100%, except it sizes the margin box regardless of the value of box-sizing.
If this is a block axis size, and the element is in a Block Layout formatting context, and the parent element does not have a block-start border or padding and is not an independent formatting context, treat the element’s block-start margin as zero for the purpose of calculating this size. Do the same for the block-end margin.
<!DOCTYPE html>
<div style="width: 100px; height: 100px; outline: solid magenta">
<div style="float: left; width: stretch; height: stretch; background: cyan; margin: 25px"></div>
</div>- The float is participating in a BFC
- The parent has no border nor padding
- The parent doesn't establish an independent formatting context
Therefore, the spec implies the float should ignore margins and resolve height: stretch to 100px.
But of course that doesn't make sense, because the margins of a float don't collapse!
Blink has implemented the reasonable thing instead of the spec, I plan to do the same in Servo.
