[Bug] ZIndex spacing issue

[Kyle-Ye]

GeometryReader { proxy in
    VStack {
        Color.yellow
            .frame(width: 100, height: 100, alignment: .center)
            .zIndex(1)
        Color.red
            .frame(width: 100, height: 100, alignment: .center)
   }
    .frame(width: 200, height: 200)
}
.ignoresSafeArea()

OSUI:

(display-list
  (item #:identity 2 #:version 1
    (frame (50.0 102.0; 100.0 100.0))
    (content-seed 3)
    (color #FF3B30FF))
  (item #:identity 1 #:version 2
    (frame (50.0 -2.0; 100.0 100.0))
    (content-seed 5)
    (color #FFCC00FF)))

SUI:

(display-list
  (item #:identity 2 #:version 1
    (frame (50.0 104.0; 100.0 100.0))
    (content-seed 3)
    (color #FF3B30FF))
  (item #:identity 1 #:version 2
    (frame (50.0 -4.0; 100.0 100.0))
    (content-seed 5)
    (color #FFCC00FF)))

Originally posted by @Kyle-Ye in #576 (comment)

[Kyle-Ye]

The root cause for this is VStack is using a wrong layout computer for its child in FrameLayoutCommon.commonPlacement. The child.dimensions(in: childProposal) is expected to call into FrameLayoutCommon.commonPlacement again this we also use frame for the child.

Stacking back, it is due to a wrong mapping of DynamicLayoutMap.attributes due the wrong order of map value.

[Kyle-Ye]

Partially fixed by #579, #580.

Now the DL is

(display-list
  (item #:identity 2 #:version 1
    (frame (50.0 104.0; 100.0 100.0))
    (content-seed 3)
    (color #FF3B30FF))
  (item #:identity 1 #:version 2
    (frame (50.0 0.0; 100.0 100.0))
    (content-seed 5)
    (color #FFCC00FF)))

[Kyle-Ye]

After #580 fix, DynamicLayoutMap.attributes first element is not AnyAttribute.nil but the second one is still AnyAttribute.nil

Update #580 with a new fix and the issue is now fully resolved.