I have a spacer in a row that is meant to be a separator line. If I define it as:

Spacer(
   modifier = Modifier
      .width(1.dp)
      .height(IntrinsicSize.Max)
      .background(MaterialTheme.colorScheme.outline)
)

it doesn't show up at all. If I change it to

Spacer(
   modifier = Modifier
      .width(1.dp)
      .fillMaxHeight()
      .background(MaterialTheme.colorScheme.outline)
)

Then it shows up, but makes the row be as tall as the screen nearly. How does one achieve the middle ground? I want it to vertically fill the whole row's height, but I don't want it to contribute to how tall the row is, other labels and buttons in the row are doing that already? I have a hunch it's some variation of .layout modifier. But it's not clear how the child node communicates "you can measure my height as big as you're going to be, but really no preference here"

I believe there is a matchParentHigh modifier or sort of name. With this exact purpose

there's a

matchParentSize

in BoxScope, but that's the only match* thing I see

Humm, only for box? I thought it had this specific purpose. Not sure why is not implemented in row/column, to me is a bit more intuitive than the intrinsic height/width thing. It is like telling the parent, don't measure me, measure other siblings and give me whatever height is determined. But well intrinsic seems to work that way, so is a matter of naming

I just discovered though that if you have a Row in Column, and you've set the weight of the row to 1f (for the column), and then also add the intrinsic height minimum, your app crashes 😄 So it's not a trick you use ubiquituously apparently

Dang, you break it man, congrats lol

if you try implementing something like

Row { Modifier.matchParentHeight() }

yourself, you'll find that it's doable - if you don't support

Modifier.weight()

. if you do, then measurement can't be done single-pass

Humm, 🤔. You mean the same child request for a weight and also matching parent size. Or you mean if another sibling request weight? If is the case of the same child I would say is intuitive if matchParent overrides weight

they apply in different directions but you can't measure on one axis only

Ahh right, both axes have to be measured I guess. But it is still under one layout pass. Didn't run your code but it seems to work.

The problem is,

weight

requires all the other children been measured, and

matchParentCrossAxisSize

also requires that, but they're on the different axes, so if there were a child with

weight

and another with

matchParentCrossAxisSize

, it's a deadlock.

the code I posted only supports

Row { Modifier.matchParentHeight() }

, but not

Modifier.weight()

. I think you'd need separate scope types, and it would be kind of difficult to disambiguate by overload so you'd want separate layout names as well, but haven't thought through it

I'm just brainstorming 😄

Selecting one modifier over the other could be an alternative but that would bring another concept, 'modifier priority' which people already get bothered because the applying order matters

it is not a matter of which modifier has priority

Got you

it's broken even if there are other children

Ahhh, even if at least one specifies a desired height, well 🤷🏻. Yeah complicated to measure everything in one pass.